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D A T - H E A D S
F R E Q U E N T L Y A S K E D Q U E S T I O N S
* M I C R O P H O N E E D I T I O N *
10 March 93 -- First Release
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I N T R O D U C T I O N
This is a collection of information of potential interest to users of
microphones, especially those who use them to record live musical
performances. The information was contributed by the users of the
DAT-Heads mailing list. The questions are listed below. You might find it
convenient to search on a question number in parenthesis to find a specific
answer.
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N O T I C E
Copyright 1993 by Jeff Maggard on behalf of all of the contributors. All
rights reserved.
This report may be copied by any means, as long as the following
requirements are met: <1> The report is always copied in whole, unchanged,
and with this notice; <2> The report is not sold commercially or used for
financial gain in any way.
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D I S C L A I M E R S
(1) The contributors are not responsible in any way for their
contributions. (2) The contributors' employers have nothing to do with the
contributions. In particular, the contributors and their employers are not
liable for any consequences arising from use or misuse of the information
contained herein. The contributors make no guarantee that the information
contained herein is correct. (3) Vendor names and prices are included here
for reference only. This is done without the vendor's permission. Prices
are approximate, actual price must be established by the vendor.
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F E E D B A C K
Each answer is followed by the author's initials in square brackets.
Authors are listed at the end of this report. If you would like to comment
on a contribution, email to the contributor or to DAT-Heads mailing list.
If you have a question, email it to DAT-Heads mailing list. If you would
like to contribute a question *AND* answer, email it to
(maggard@subpac.enet.dec.com).
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Q U E S T I O N S
General:
{1} What are some of the techniques for stereo microphone placement?
What is "MS," "XY," "AB," "concident pair," "ORTF," etc.?
{2} What's all the hubbub over MS mic-ing?
{3} What are the differences between microphone transducer types
(stereo, binaural, electret, condenser, dynamic)?
{4} What are the differences between microphone response patterns
(cardioid, hypercardioid, super-cardioid, shotgun, omni, figure 8)?
{5} What factors, other than microphone selection, will affect the
end result?
{6} Is there any advice you can give a beginner who's unfamiliar with
using microphones?
Live Recording:
{7} When should I use a shotgun/hypercardioid mic instead of an
omni/cardioid and vice versa?
{8} What types of mics should I consider for use in small venues (bars
and clubs)?
{9} What types of mics should I consider for use in medium-sized venues
(between 500 to 5,000 seats)?
{10} What types of mics should I consider for use in large venues
(>5,000 seats)?
{11} What mics are good for 'up front' (FOB) recording?
{12} What kind of mics are good for live recording with a DAT?
{13} What microphones are good for unobtrusive ("stealth") recording?
{14} What mics are good for radio reportage, radio drama, and film and
tv location work?
Choosing and Purchasing:
{15} What types power sources should I consider when buyuing a pair of
mics?
{16} What types of cables are good for keeping noise to a minimum?
{17} What is "phantom power"? Why would I want/not want mics that need
it?
{18} I'm interesed in getting into taping live shows, but I don't have a
deck or microphones. What are some things I need to consider?
{19} Where can I go to rent microphones? How much does it cost?
{20} How often to microphone manufacturers come out with new models --
Do I need to worry about blowing my money on an obsolete pair?
{21} How much better is a newer line of microphones than an older line?
Can I save a ton of money and not lose a lot in sound quality by
getting an older set of mics?
{22} What is a vocal mic and why should/shouldn't I use it for recording
at a Dead show?
{23} What are the advantages/disadvantages of buying mics that have a
selectable pattern?
{24} What are the advantages/disadvantages of buying mics that have
interchangeable capsules?
{25} What kinds of mic stands are there? Where do I go to get the
really tall ones that are good for use at a Grateful Dead concert?
{26} Where can I buy mics to use with a DAT?
{27} What are some other sources for hard to find mics?
{28} What are some popular models (and prices, freq resp, sensitivity,
max SPL, etc...) for each of the basic types of mics.
{29} What's the best mic for under $100?
{30} Are there any good microphones for under $200 per pair?
{31} What kinds of mics does Radio Shack make?
Using microphones:
{32} My DAT deck has an unbalanced mini-headphone jack for an analog
input. How do I get the best sound through that tiny jack -- what
types of adapters would give me the best results?
{33} My DAT deck has unbalanced RCA analog inputs -- how do I maximize
sound quality?
{34} What are the sources of mic noise?
{35} How do I keep mic noise to a minimum so I can have a decent S/N
ratio on quiet recordings?
{36} What's the difference between the capsules in a Neuman TLM-170 and
a Neuman KMi86?
{37} What is a PZM and how do I modify one?
{38} What kind of capicators should be used with a mic pre-amp? How
does choice of capacitor affect the sound?
{39} What kinds of capsules are typically used in 'stealth' microphones?
What's good/not good about them and why?
{40} Why do some shotgun mics have poor bass response?
{41} Which brands/models of shotguns have good bass response?
{42} What causes some mics to sound tinny or 'canned' in some
situations? How can I avoid it?
{43} How critial is it to aim a shotgun mic directly at the source?
What happens if I'm off by 5 degrees? 10 degrees?
{44} Why do recordings made with shotgun mics lack the 'presence' that
other mics have? (it sounds like there's a hole in the center of
the sound coming from my stereo system) What can I do to improve
the 'presence' in my recordings?
{45} What is "binaural recording?"
{46} What microphones are available to do binaural recordings?
{47} I've heard that binaural recording are supposed to be listened
to over headphones. How do they sound over speakers?
{48} Do you have to hold your head perfectly still while making a
binaural recording?
{49} Can I use headphones as microphones?
========================================================================
A N S W E R S
 
{1} What are some of the techniques for stereo microphone placement?
What is "MS," "XY," "AB," "concident pair," "ORTF," etc.?
Many different mic setups exist for location stereo recording. Refer to
_The New Stereo Soundbook_ by Alton Everest and Ron Streicher, Tab Books
1992, for more.
 
Coincident Pair - Two mics arranged (typically) one above the other, so
that sound waves reach both capsules at the same time. The following three
techniques are coincident pair techniques:
 
XY - Coincident cardioids at 90 degrees
 
MS - Mid/Side. Use a single mic, which may be anything from omni to
hypercardioid, facing forward (mid) and a figure-eight facing to the
left. Remember that the back lobe of a figure-eight is _out of phase
by 180 degrees_ from the front. When you add mid plus side, you get a
left-pointing pickup. When you subtract mid from side (mid plus
inverted side), you get a right-pointing pickup. If the mid mic is
cardioid, the resulting left and right signals are cardioid at 90
degrees. Theoretically the result is the same as XY.
 
Blumlein - Coincident figure-eight mics at 90 degrees
 
Semi-coincident - Two mics angled to encompass the sound stage but also
spaced between 6 and about 48 inches apart to add time-of-arrival/phase
differences to the amplitude differences caused by the directional pattern.
The following techniques are semi-coincident:
 
ORTF - Office de Radio-Television Francaise - two cardioids angled 110
degrees, spaced 170 mm.
 
NOS - Nederlandsche Omroep Stichting - two cardioids angled 90 degrees,
spaced 300 mm apart.
 
AB - Generally two spaced cardioids facing forward to slightly angled
apart
[dj]
===============
{2} What's all the hubbub over MS mic-ing?
MS is nothing but a different mathematical representation of the polar
patterns inherent in coincident AB recording. In theory there should be no
difference between an MS mic and an AB mic when positioned identically. In
practice, the greatest difference is due to the fact that sounds in the
centre of the stage hit the M mic bang on axis; such sounds arriving at a
coincident AB pair with a 90 degree angle are therefore 45 degrees off
axis, and it is a very good mic indeed whose frequency response is anything
like as good at 45 degrees as it is at 0 degrees. Therefore centre sounds
are likely to be better when MS mics are used. The biggest disadvantage of
the technique is that by definition, two non-identical mics are used. At
the very least you could use the same type of mic body in each case,
equipped with a cardioid capsule for the M, and a figure-eight for the S.
Purpose built single body stereo condenser mics are often capable of either
AB or MS working, but they are expensive.
Apart from the significance of MS mic techniques, remember that you can
convert a stereo signal to MS at any time; altering the relative amounts of
S will change the width of the stereo (the obvious reductio ad absurdum is
no S at all - you are merely left with the output of the single mono mic
fed to both speakers). Likewise you can achieve some increase in apparent
width by increasing the relative S level beyond the norm. The reductio ad
absurdum here relates to complete removal of the M signal - the output of
the S mic appears in anti-phase on each of the speakers and the resultant
signal when reduced to mono - zilch! So you have a convenient way of
controlling width on a single fader, with the possibility of going slightly
"super-wide" but beware; super-wide results in greater than normal
out-of-phase content which some listeners find disturbing, and mono
compatibility is always compromised. Apart from the super-wide .phpect, the
control of width available to you is really no different to that which you
achieve by closing up the panpots on an AB signal.
MS mic-ing offers no magic solutions. Assuming you are using coincident
techniques you are merely using a different model of the same signal. To
sum up: central sounds will probably be cleaner as they are on the M mic's
axis, but the fact that the two mics are non-identical may bring its own
problems. Whether the signals are handled as AB or MS further down the
chain is unlikely to make any sonic difference - AB is certainly more
convenient. [po]
 
[dj] refutes [po]'s comments:
>In practice, the greatest difference is due to the fact that sounds in the
>centre of the stage hit the M mic bang on axis; such sounds arriving at a
>coincident AB pair with a 90 degree angle are therefore 45 degrees off
>axis, and it is a very good mic indeed whose frequency response is
>anything like as good at 45 degrees as it is at 0 degrees.
 
Not quite. Nearly all cardioids show in fact identical response over a 90
degree cone (+/- 45 from center). It's the zone from 45 to 90 that's the
problem, where the left mic is picking up right signals (by definition, a
cardioid is only -6dB at 90 degrees!).
 
>The biggest disadvantage of the technique is that by definition, two
>non-identical mics are used. At the very least you could use the same type
>of mic body in each case, equipped with a cardioid capsule for the M, and
>a figure-eight for the S.
 
I don't think so. The two output channels left and right are produced with
the same virtual microphone, which is the sum of the two real microphones
used. My early MS work was done with a ribbon mic for S (an RCA 44BX, which
is flat to 20 Hz, something very few condenser figure-eights can claim) and
a cardioid condenser for M. This worked just fine. Remember you are
measuring very different things: the S mic is sampling particle velocity
while the M mic is sampling vector pressure. Each of the outputs L, R
contains equal amounts of the two microphones. The big problem with using
the same type of mic body is that this assumes, in all currently available
interchangeable capsule systems, a 19 to 21 mm maximum diameter. This works
OK for a cardioid or omni, but I have yet to hear a figure-eight that small
that sounds right, which is the reason I no longer make the KA800 capsule.
Schoeps tries to fix this problem with extensive baffling and damping; AKG
and Neumann don't attempt it anymore (AKG had a large diaphragm
figure-eight capsule in a wire mesh ball which would screw onto the end of
a C451 but does no longer); the Sennheiser small figure- eight uses fairly
radical electrical EQ in the (non-interchangeable) mic body to make the
capsule measure flat. Neumann made a small capsule dual-diaphragm mic that
synthesizes figure-eight by combining two cardioids back-to-back and out of
phase. This is found in their KM56, SM2 stereo mic and the KM88, and is
probably the best compromise for a small figure-eight but the frequency
response is not wonderful (-6 dB at 50 Hz, +6 at 6 kHz, -6 at 14 kHz).
 
> Assuming you are using coincident techniques you are merely using a
> different model of the same signal. To sum up: central sounds will
> probably be cleaner as they are on the M mic's axis
Given ideal microphones, they are the same signal. With practical
microphones central sounds will be very similar between the two techniques,
it's the edge sounds that will be most compromised by using XY. Another
minor problem with XY is that you can't get the two mics in the same place.
With MS, the mics are automatically in the same place and the physical
obstruction that one mic makes in the other's sound field is symmetrical
for the left and right channels. This is also the case for XY when you put
the mics in the same plane, but now you get reflections off one mic's
diaphragm grille right into the other mic, which makes for some nasty comb
filtering at high frequencies. If the mics are one on top of the other,
there is a vertical time of arrival difference of opposite sign between the
two channels that can cause odd shifts in the reverberent pickup. There's
no free lunch.
 
> Whether the signals are handled as AB or MS further down the chain is
> unlikely to make any sonic difference - AB is certainly more convenient.
Yes... which is why many people recording in MS will in fact matrix at the
recording site, putting down left and right tracks on tape rather than M
and S.
Note I left out of my earlier post on MS, there are two excellent sources
for info comparing the various stereo mic-ing techniques. One is the
compendium volume "Stereophonic Techniques" which is articles excerpted
from the Journal of the AES, and published by the AES. The other is the
"New Stereo Soundbook" by Alton Everest and Ron Streicher, published last
year by Tab Books.
[dj]
================
{3} What are the differences between microphone transducer types
(stereo, binaural, electret, condenser, dynamic)?
There are two principal types of transducers used in mics: dynamic and
condensor. Dynamics are often favored for miking individual instruments
because they add a favorable color to the sound. Condensor mics are
generally more accurate than dynamic and are preferable for audience
recording. Modern condensors use an "electret" design which enables the
mic to operate from a low voltage which can be supplied by an internal
battery or by an external power supply or by certain mic preamps. By
contrast dynamic mics need no power source.
[rg]
================
{4} What are the differences between microphone response patterns?
This is a type of question which is sure to get many "religious" responses,
but I will try to stick solely to the facts. I will also try to keep the
discussion in the context of audience recording, since this is probably the
most common application amongst DAT-Heads.
a) Omnidirectional
This type of microphone will pick up sound evenly from all
directions, hence the omni- prefix (they are sometimes called
non-directional). For this reason, omnis should be used only when
recording very close to the source. It is generally felt that
omnis offer the best sound as compared to directional mics, and top
omnis are often less expensive than top directional mics. For an
audience application, omnis are generally only used for fob
(upfront) recordings, since they tend to pick up too much audience
noise when used at too great a distance. Another common audience
application is to use an omni/shotgun mix from further back in the
hall. The shotguns are used to pick up the direct sound from the
sound system while the omnis provide ambient information. The
reasoning behind this method is to give "presence" to the mix,
which would be lacking in a shotgun-only recording.
When using a spaced omni setup (several inches to several feet
between mics) in quiet venues, distance is less important a factor;
quality recordings can be made even far from the source. For
binaural recordings (with the omnidirectional microphones mounted
near your ears and the recording played back over headphones),
closeness to the source is only a minor factor in achieving a
quality recording.
b) Cardioid
This type of microphone is slightly more directional than omnis.
Much of the sound coming from behind the microphone is not picked
up. There is also a small amount of side rejection as well.
Cardioids are often used as vocal mics since they will not pick up
most of the other noise onstage coming from the amps, monitors,
etc. For a Dead-show-type application, proximity to the sound
source is important, though not quite as critical as with omnis.
Like omnis, you will get the best results when used upfront. Some
people use cardioids from further back, but audience noise becomes
more of a problem the farther back you go. If you plan to use
cardioids from a large distance (i.e. the tapers' section at
Grateful Dead shows), the best results are usually obtained when
the mics are elevated as far as possible above the audience in
order to minimize crowd noise on the recording. Cardioids usually
work well in a small club setting and also outdoor amphi- theatres,
where the crowd noise tends to be more attenuated than on indoor
audience recordings due to the lack of reflective surfaces (i.e.
side walls and ceilings). A cardioid which has a 20-20000 Hz
frequency resonse will generally be less expensive than a
comparable hypercardioid or shotgun.
c) Hypercardioid
This type of microphone is more directional than standard cardioids
but less directional than shotguns. Hypercardioids are *not*
shotguns. They can be thought of as "short shotguns." They have
more side rejection than cardioids but not as much as shotguns. I
find the hypercardioid to be the most flexible of the four polar
patterns discussed here (in the context of audience recording).
Excellent results can be obtained from far back as well as upfront.
They also work quite well in small clubs. Hypercardioids are
generally the least common of the polar patterns and you can expect
to pay a tidy sum for a good pair.
d) Shotgun
This type of microphone is the most directional of the four.
Shotguns have the most side rejection and thus are well suited for
recording at a large distance. Shotguns are the microphone of
choice in the tapers' section at Grateful Dead shows. Shotguns
tend to have a number of drawbacks, however. The less expensive
shotguns will not have very good frequency response, especially in
the lower octaves. For this reason, lower-end shotguns are often
described as "tinny" or "hollow" sounding. Also, the drastic side
rejection of a shotgun often results in recordings with a lack of
"presence." Expect to pay a fairly large sum to get a shotgun with
20-20000 Hz perfromance. Because of their large size, shotguns are
not usually used upfront. Directionality is useful for increasing
the ratio of direct sound (from the stage and P.A. system) to
reverberant and ambient sound (from the rest of the room). This
becomes more critical as the distance from mic to stage is
increased. Generally, one must pay more money for a shotgun in
order to get as good sonic characteristics versus a less
directional mic.
In contrast to omni's and cardiods, microphone placement is very
critical with shotgun capsules, which some believe is more often
the reason behind the "tinny, hollow" sound than the technical
qualities of the microphones themselves. These mics are very
directional, and you really have to consider the fact that they are
recording where you point them -- unlike omnis which record the
sound where they are located. After some years of experimentation
with Nakamichi CM-100 bodies with the CP-4 shotgun capsules, I [sj]
have found that the amount of bass in the recording is highly
dependent on the position of the mic with respect to the PA. My
current alignment results in a very clear bass, almost to the point
of considering the use of the "Lo-Cut" switch. It is my opinion
that the "traditional Dead Taper" placement does not adequately
take these effects into account, hence the resulting "tinny,
hollow" recordings that people dislike.
 
[dj,jv,lm,sj]
DAT-head recording techniques are generally divided into stealth and
non-stealth projects. For the former, generally the technique of choice is
to wear a pair of mics more or less near the ears (binaural). This works
far better than it has any right to, given that commercial or
semi-commercial stereo mic systems can be had for less than $250, or you
can also build your own for less than $10 using the Panasonic WM063
capsules that seem to work best.
For non-stealth techniques (including overt on-stage taping when they want
you to be there) it's mostly a choice of directional pattern and tone
color. Less directional microphones generally sound better than more
directional ones, but often you need to record from a long way away, and
the only simple way to do this is with highly directional mics.
Omni mics are absolute pressure transducers and inherently would have
response down to DC but for a small air leak built in to allow them to be
shipped by air, not explode in tornados, etc.
 
While omni mics, being pressure transducers, almost always produce a
cleaner sound, many times the recordist finds that some directionality is
required. The practical way to achieve this is with a mic that combines
absolute pressure and pressure gradient responses. All of these mics have a
directional pattern that follows the equation x + y*(cos of angle) where
x+y=1 and the angle begins with 0 being on-axis to the microphone. The
standard cardioid is x=y=0.5, hypercardioid is x=0.3, y=0.7.
There are two families of directional mics in common use: phase shift
pressure gradient, and interference tube. Phase shift pressure gradient
mics are available in a continuum of patterns which can all be expressed
with the relation x + y*cos(theta) where theta is the angle from the mic to
the sound source. For x=0, the pattern is bidirectional with the implied
phase reversal toward the rear and sharp nulls at 90, 270 degrees. For y=0,
the pattern is omni. For x=y, the pattern is called "cardioid" (for
heart-shaped, not "cardiod", please) and the response at 90 degrees is 0.5
of (or -6dB from) the on-axis response. For x around 1, y around 2, the
pattern is called "supercardioid" or "hypercardioid" and there is a small
rear lobe out of phase with the front pickup, but sharp nulls at 135, 225
degrees.
Since the pressure gradient is sensed by leaving the mic diaphragm open on
both sides, the inherent frequency response is inversely proportional to
wavelength... the longer the wavelength, the less response, because there's
less pressure gradient at any instant between the front and the back of the
mic. This makes a frequency response curve that, left to its own devices,
would be very un-flat; rising 6dB per octave. Most unidirectional mics use
a lot of damping to flatten out the response at some point, above which it
doesn't rise anymore. But below this frequency (typically 100-400 Hz) you
have in effect a bass rolloff. Which is another reason that directional
mics are often used in concert recording, because all of the low frequency
energy is rolled off even before it gets to the first FET in the mic body.
Variable pattern mics are available (AKG C414, Neumann U87, U89, TLM170,
Milab, etc) that are either two cardioid capsules back-to-back (each one of
0.5 + 0.5 cos theta, you can work out the patterns that result when they're
added in phase and out of phase with each other), or are (Schoeps MK5) a
phase shift pressure gradient type with mechanically variable phase shift
parts to make different patterns.
Inteference tube mics use a perforated tube in front of a phase shift
pressure gradient type of microphone, that gives more directionality at
frequencies where the tube is more than a quarter wave long. Most
interference tube mics, even expensive ones, have a sort of strange hollow
sound which may be more than overcome by the fact that the performer sounds
closer than it would otherwise be possible to get, and as you point out
there is a lot less crowd noise.
[dj]
 
================
{5} What factors, other than microphone selection, will affect the end
result?
The general idea is to place microphone selection in perspective. If the
microphone is great, but the factors listed below are not considered, the
results can be disappointing. If the microphone is great, but the factors
listed below are not considered, the results can be disappointing.
Your actual results will depend on: the spiritual, emotional, and
intellectual content of the music; the skill and level of preparation of
the composer, musician, and recording engineer; the amount of ambient
noise; the musical instruments; the room acoustics; microphone
placement; the quality of the recording equipment (including the preamp);
the quality of the playback equipment; the environment in which the
playback takes place; and the ability of the listener to appreciate music.
[pd]
================
{6} Is there any advice you can give a beginner who's unfamiliar with
using microphones?
[td] writes:
> My conclusions ?
> I prefer using the Schoeps, Neumann's or B&K's.
> Why? I like the sound. Many other who hear them like the sound as well.
> However, they are not without problems.
> If the 4011's are used off center, they sound like shit.
> The KMi84's outdoors are a bit boomy (maybe that was just foxboro)
> The Schopes are a little tinny, etc...
>
> Each of these mics has its use and its place.
That perhaps is some of the most valuable experience a recordist can gain
about his or her art. The only way to know is by experimentation and LOTS
of listening. However, if you can only afford one set of microphones and
you rarely get a chance to compare them with any other, then you'll
probably be happy with whatever you have.
Someone once asked me, "...what's the best placement of a microphone to
record a piano?" I replied with, "...what's the best place to put a camera
to photograph a mountain?" [ss]
===============
{7} When should I use a shotgun/hypercardioid mic instead of an
omni/cardioid and vice versa?
Think about the pattern of the _null_ of the mic, rather than the pattern
of the main lobe. The on-axis performance of all of these mics can be quite
similar. The differences are in the off-axis response. Think about pointing
the null at the sound you don't want, rather than pointing the front at the
sound you do want. Use a tighter pattern when the reverberation or overall
room noise overpowers the desired sound.
Note that besides the design-center directionality pattern, there are a
host of other compromises the mic manufacturer must accept in order to have
a produceable model. While their specs may be identical, omnis, cardioids,
and hypercardioids all sound _very_ different. The main specifications that
are almost never reported include capsule-generated distortion, phase or
impulse response, off-axis frequency response, and frequency distribution
of mic-generated noise including capsule-generated noise.
[dj]
================
{8} What types of mics should I consider for use in small venues (bars
and clubs)?
{9} What types of mics should I consider for use in medium-sized venues
(between 500 to 5,000 seats)?
{10} What types of mics should I consider for use in large venues
(>5,000 seats)?
Very broad questions. Depends on the room acoustics. Start with one of
the pair techniques in {1}. Listen to how the room sounds and listen to
the sounds you want to get rid of. If you need more room isolation, think
about ways to orient the mics so that the nulls are pointed at the noises
you want to lose. [dj]
================
{11} What mics are good for 'up front' (FOB) recording?
In general, you can get away with using omnis/cardioids or other
less-directional mics up front, mostly because you are closer to the source
and the music is generally much louder than venue acoustics and crowd
noise. Using highly directional mics like shotguns up front might not
allow you to capture the entire sound. [jm]
================
{12} What kind of mics are good for live recording with a DAT?
Mic selection is generally driven by budget, personal taste, and
pattern requirements (which are in turn driven by recording location
and venue layout), and stereo recording technique. There is no such
thing as the perfect microphone, even for a single type of recording
situation. [rg]
Some of the most popular mics for live taping, along with miscellaneous
comments from users. In general, high cost means >$1000 per mic; mid is
~$1000 per mic, and low is $500 per mic or less.
model cost notes
===== ==== =====
AKG 414 high a very versatile microphone
AKG C460B + CK8X high shotgun, preferable over C460B + CK8
AKG C460B + CK8 high shotgun
AKG C451 + CK9 high shotgun, not recommended
B&K 4011 $2600/pr + pwr supply
Neumann TLM170 $3400/pr + pwr supply
5 position switch selectable, includes
subcard and hypercard. Nice bass response,
even on hypercard because of the very
large diaphram. A very large mic.
Perhaps the best multifunctional mic out
there.
Neumann KMi84 high Cardioid - Compact
 
Neumann KMi86 high Omni/Cardioid/Figure-8 - Switch selectable
pattern. Large. Nice sound. Older
model, around $2000 each or more. 2
84-series capsules back to back for each
mic.
Neumann KM1xx
(100 series) high mic body, with different replaceable
patterns (screw on) KM140 is a card. It
is compact, and with an optional remote
active cable (SKM140) just the capsule
need be exposed making it good for
stealth.
Schoeps CMC34 high cardioid, $1900/pr + pwr supply
(CMC3 + MK4)
Sennheiser MKH815 high shotgun
 
AKG C568 $700/pr shotgun, hypercardioid at low frequencies
 
Audio-Technica 4071 mid/lo
Audio-Technica 813 $300/pr cardioid, electret condensor
Core Sound Binaurals mid/lo quasi-binaural
Crown mid/lo pzm
Nakamichi CM100 + CP4 mid/lo shotgun
Nakamichi CM300 + CP4 mid/lo shotgun
Shure SM94 $500/pr cardioid
Sonic Studios $300/pr quasi-binaural
================
{13} What microphones are good for unobtrusive ("stealth") recording?
There are many microphones out there that are small yet provide good sound.
During the 80's, two of the more popular larger "stealth" microphones were
Nakamichi's 300 and 700, modified to use a short barrel. These are roughly
the size of a man's index finger and are sometimes built into hats.
Considerably smaller and stealthier than the Naks are the electret
condensor microphones that are designed to attach onto the temple pieces of
your eyeglasses, clip onto your jacket's shoulders or lapels, or clip to
any handy object (light grid, chair, curtain). At least two manufacturers
(Core Sound and Sonic Studios) offer these. These microphones are roughly
the size of jelly beans. Despite their small size, they typically have
very wide and flat frequency responses. A few models can record over very
large dynamic ranges with little distortion. This makes them ideal for a
compact, stealthy concert recording setup. Their main drawback compared to
larger, more expensive microphones is a relatively high self-noise (roughly
30 to 40 dBa) but the self-noise is normally swamped by the ambient noise
level at a concert. The microphone elements are typically omnidirectional
and can be used to make binaural or spaced-omni stereo recordings. Prices
under $500. Combine these microphones with a portable DAT recorder and you
have a stealthy, good sounding, reasonably priced and simple recording
setup. [lm]
================
{14} What mics are good for radio reportage, radio drama, and film and
tv location work? Mechanical durability, resistance to handling
noise, and cost need to be considered.
The all-time favorite mic for reportage, at least in the US, is the
Electro-Voice 635A series. This is an omni dynamic, available also in a
heavily padded and screened version called the RE50. They are nearly
indestructible, and older ones are covered by a lifetime warranty; if it
isn't mangled, they will fix it for free, forever. Used 635A's typically
bring $50. If I only had $100 for mics, that would be it.
================
{15} What types of power sources should I consider when buyuing a pair
of mics?
There are three: internal power, phantom and parallel. Trouble with
internal power is that you're always worrying about whether the mic battery
will die during your gig. Phantom is pretty much universal in the pro
world, and when done correctly will work fine. Parallel (also called AB or
Tonader powering) is used almost only in the film industry. It can work as
well as phantom but very little of the available equipment offers parallel
power. [dj]
A simple stereo phantom that runs for ~4 hrs on 1 9 volt is the Neumann
BS48i2. It is compact and the price is right (about $375 to $400). Other
people manufacture supplies, but they are frequently very expensive ($1100)
and bulky. [td]
================
{16} What types of cables are good for keeping noise to a minimum?
For electrostatic shielding, you need full coverage of the cable pair(s).
Multiple layers of shield braid are good. For electromagnetic shielding,
you want the pairs themselves to be twisted tightly. Four conductor "star
quad" cable from Mogami, Canare and others helps electromagnetic shielding
too. [dj]
================
{17} What is "phantom power"? Why would I want/not want mics that need
it?
See {15}. All electret and condenser mics require power for the impedance
converter stage, if nothing else. You can use a battery inside or the
mixer/ preamp etc. can supply the power using phantom. [dj]
================
{18} I'm interesed in getting into taping live shows, but I don't have a
deck or microphones. What are some things I need to consider?
Frequency response, both on and off axis. (Ideally, the response off-axis
should be as linear as on-axis, just attenuated in the desired direction).
Self-generated noise level. Maximum output level without overloading.
Subjective judgement about sound quality. Ruggedness. Price. Availability
of service. Matching of a stereo pair. [dj]
================
{19} Where can I go to rent microphones? How much does it cost?
Very few places. Try the pro sound places in NY and LA that cater to film
sound. Expect to pay 5-15% of the new price _per week_. [dj]
See also {27}.
================
{20} How often to microphone manufacturers come out with new models --
Do I need to worry about blowing my money on an obsolete pair?
 
Very seldom, actually. A mic product line, like the AKG 451 or the Neumann
KM83/84/85, is typically in production for 20 years or more. You don't
need to worry about buying an 'obsolete' microphone. [dj]
I'm not sure about the introduction rate of new models, but some older mics
are 'classic' now and are still in use. This comes to mind with some
Neumann models. For example, the KMi86 was the predecesor to the U87 and
TLM170 mics, and all are still in use. Old Neumann tube mics are still
used as wel. I don't think there is an obselescence as with other products
(computers, etc). [td]
================
{21} How much better is a newer line of microphones than an older line?
Can I save a ton of money and not lose a lot in sound quality by
getting an older set of mics?
By itself there is no correlation between age and quality. Most of the
older German and Austrian mics, even the ordinary ones, are worth far more
now than they were when new.
Sometimes. I bought a KM-84 at a flea market for $10. Unless you know the
type offered, stick to the well known brands: Neumann, AKG, Schoeps,
Sanken, MB, Bruel & Kjaer. The problem is to find out whether the mics are
in good shape. A good test is to see if two sound the same, because it's
unlikely that the same fault would appear in both mics. Another check is to
mix the two mics out of phase so that they null. Whatever sound is left, is
the difference between them. [dj]
 
================
{22} What is a vocal mic and why should/shouldn't I use it for recording
at a Dead show?
Vocal mics, such as the ubiquitous Shure SM58, typically have a rolled off
low frequency response (to compensate for the bass boost when used up
close) and a 6 to 12 dB boost in the 4-7 kHz range for "presence" and
punchiness. These are not attributes you want for recording at a distance.
[dj]
================
{23} What are the advantages/disadvantages of buying mics that have a
selectable pattern?
 
You can tailor your mic patern to suit the situation you are recording in.
It is a more flexible system, but it is more expensive.
[td]
================
{24} What are the advantages/disadvantages of buying mics that have
interchangeable capsules?
Again, you can tailor your mics to the situation, this time by changing the
capsule. This requires the purchase of a pair of capsules for each pattern
to be used. The patern change is not accomplished with electronics as the
swicth selectable mics do.
[td]
 
Selectable Pattern Interchangeable Capsule
 
Operating Usually back-to-back cardioids, Made to suit pattern:
Principle either discrete capsules or omnis are pure pressure
Braunmuehl-Weber type mics rather than two
cardioids added together
Cost Higher at first Cheaper at first
Flexibility All or most patterns available Must buy new capsule for
new patterns, no really
good figure-8 available
Sonics Subjectively warmer Subjectively cleaner
Flash Factor High Low
Obtrusiveness High Low
 
[dj]
================
{25} What kinds of mic stands are there? Where do I go to get the
really tall ones that are good for use at a Grateful Dead concert?
Two kinds: too small and too heavy. The tallest stock kind is the Shure
SA15 which is 15 feet tall, aluminum and about $150. These work OK if you
weight them down with a bag of lead shot or sand. The really tall ones come
from Matthews in LA and other people who make light stands for movie
production. [dj]
Get a LIGHTING stand, one made by BOGEN. They are more stable than a mic
stand. You can get adapters to get the proper fittings on them for mics.
[td]
================
{26} Where can I buy mics to use with a DAT?
For Schoeps:
 
Posthorn Recordings
New York, NY
(212)242-3737
For Core Sound Binaurals:
 
Len Moskowitz
bendix!moskowit@uunet.uu.net
 
or
 
Core Sound
839 River Road
Teaneck, NJ 07666
 
For Sonic Studios:
Sonic Studios
(503)599-2217
For Josephson:
Josephson Engineering
David Josephson
JOSEPHSON@AppleLink.Apple.COM
================
{27} What are some other sources for hard to find mics?
I went on a mic foraging expedition, and have come up with the following
list of music stores that seem to be willing to get mics of all
descriptions. I've only had dealings with a few of them, so use the usual
precautions when dealing with someone you don't know. If anyone has
additions, corrections, warnings, or recommendations about a particular
store, please let us know!
The first thing you need to decide is whether you want to purchase a
mic in a new or used state. I'm rather partial to saving money, and
used mics (with the possible exception of delicate ribbon designs) are
pretty likely to sound just as good as new ones. Depending on how
popular a given mic is, what type of people want it, and its condition,
savings can be from 20 to 50 percent for a used item. Make sure a used
item comes with all the accessories that a new one does before agreeing
to a price (the windscreen on a 414B costs $30, for example, and the
clip doesn't look cheap either!)
I learned the hard way that for used items you're much better off if
you start trying to find a mic well before you need it. I called over
40 stores and responded to 3 classified ads in my quest for a used
AKG414B/ULS, with no luck. This mic is so in demand that they are
usually gone within a day of their arrival -- several salesmen admitted
to scoffing them up themselves without even putting them up for sale!
If you want a mic that's this popular, start looking early, and
convince several stores that you're serious and would like to be
notified if one shows up -- but still check on things regularly. It's
also worth keeping an eye on the "forsale" and music-related newsgroups
on Usenet, as well as any local want-ad sources.
Here's the list of the stores I contacted that seemed reasonable and
will deal through the mail. I define places as "serious" if they have
things like the Neumann U-87 in stock, will sell you a Neve console or
a Sony 48-track digital, etc. With business like it is, most of these
people will talk with mere mortals anyway.
Adam's Pro Audio Rentals(617)773-8385 (rentals)
Akron Music (216)376-6189 or (800)962-3152 (new/some used)
American Pro Audio (800)333-2172
Audio Pro (617)926-8020 (repairs, used)
Audio Studio (617)277-0111
Audio Services Corp (818)980-9891 (new/used/rental, biggest dealerin
CA, specialize in film sound but
knowledgeable about all else)
Audio Video Research (617)924-0666 (big used, semi-seriious)
Anything Audio (617)426-2875 (New/Used, semi-serious-but-weird-
hole-in-the-wall)
Boynton Studio Supply (607)263-5695 (will send catalog, new/used/closeout)
Caruso Music (203)442-9600 (used/some new -- good place)
Dan Alexander Audio (415)986-8267 (serious used, tube mics)
DB Engineering (617)969-0585 (used/some new, *major serious*)
EAR Pro Audio/Video (602)267-0600 (used/new, serious)
Eight Street Music (800)878-8882 (new/some used)
Full-Compass (608)271-1100 or (800)356-5844
Goodman Music (800)842-4777
Grandma's (800)444-5252
Mercenary Audio (617)784-7610 (big used/some new, very serious)
Musicmakers (800)395-1005
Parson's Audio (617)431-8708 (helpful, cheap new)
Rhythm City (404)237-9552
Rock Street Music (717)655-6076
Sounds Incredible, Inc (214)238-9393 (new, boiler shop operation?)
Summit Audio (408)395-2448
Washington Professional Systems
(301)942-6800
[tb]
================
{28} What are some popular models (and prices, freq resp, sensitivity,
max SPL, etc...) for each of the basic types of mics.
[Coming soon. -jm]
================
{29} What's the best mic for under $100?
There is little correlation between mic quality and price, except that mics
that are cheaper to build cost less and are generally more fragile. The
large diaphragm mics like AKG C414, Neumann U87, U89, TLM170, etc. cost a
lot to make. Electret condenser mics may be more modern than traditional
DC-polarized condenser types, but few of them sound as good as the
traditional type. There are a lot of reasons for this, starting with the
type of geometry that's practical to do with a DC condenser mic (that isn't
with an electret mic). The DC polarized mics are made in much lower
quantities than the electret types, so they are a lot more expensive to
make.
There is a big gap between the inexpensive electrets ($100-200) and 'real'
condenser mics ($600-1200 each). One good possibility in this range is the
Shure SM81 which has a street price under $300 (Manny's Music $276). You
could also look around for used AKG 451's, Neumann KM84's etc. which
sometimes show up for less than $200. [dj]
================
{30} Are there any good microphones for under $200 per pair?
There's no comparison in sound quality between the professional microphones
made by Bruel & Kjaer, Schoeps, AKG, Neumann, and others, and the
microphones available for under $200. But not all of us can afford between
$1500 and $3000 for a pair of microphones. Just because you're not able to
spend that kind of money doesn't mean you can't make good quality,
satisfying recordings. There are some amazingly good microphones in the
under-$200 price range that offer high fidelity, ease of use (small size,
no need for bulky phantom power supplies), and durability. In some cases,
you won't perceive an appreciable improvement over the performance these
low-priced microphones offer until you spend more than $800 per pair.
There's Radio Shack's PZM (modified using Phil Rastoczny's instructions),
the Core Sound Binaural "standard" and battery box" models, Sonic Studio's
low end model, and a slew of so-called vocal microphones (Shure, EV,
Audio-Technica) commonly used by performers. [lm]
================
{31} What kinds of mics does Radio Shack make?
Here follow 3 catalog entries of Radio Shack (tandy) mics which have proven
to be of interest. One of the mics is no longer being made. Imho, it would
be of no difficulty for Tandy to bring this high-performer back into
production. In my opinion, this is one of the best values for the money
were it still in production. As of 1990, these mics were still available.
However, for several years, now, the 33-2011 has been out of manufacture,
and no longer available. I had it from a BBC sound technitian that they
were as good a value as any in the microphone field. I only wish I had
bought more of them. I use 2 on a regular bassis. Ok, here follow the
listings from the 1987 catalog with notes on current observations. Slim
Electret Microphone $20.95 3oz Cat. #33/2011 wide-range 20-13000hz 600 ohms
impedence comes supplied with 1/4inch plug on a 6-foot cable requires AAA
cell.
Personal observations. Although this microphone is no longer manufactured,
nevertheless, it is one of the best mics I have had occassion to use. In
appearance, it is slim, in a metal-clad hexagonically shaped body. Because
of its slimness, it can be placed in a wind-screen with good affect. The
mic has especially good handling characteristics. I have mounted it,
clipped to the side of a railway vehicle with no appreciable vibration
conducted through the shell. At one time, the elements could be replaced
assuming you could find the replacements. This is an omni-dirrectional mic
which may limmit its application. But, I haven't found any leval that was
enough to over-load the electret pre-amps.
Electret condenser omni directional microphones 1060. 20-13000hz comes
supplied with 1/8inch plug as well as switching lead sub-mini. Both of
these plugs terminate at the end of a 6-foot cable. Mic comes supplied
with stand, wind-screen and tripple/a battery. $16.95
Personal Observations. This microphone is still readily available. On the
face of it, seems a better deal than the 2030. It is available, and it is
cheaper. But the mic comes in a plastic housing, and in my experience, the
supplied wind-screen is less than useless. Also, the mic doesn't perform
well under high-noise levals. When I started using this mic, I thought it
had a better low-end than the 2011. However, during some high-sound tests,
I found that this microphone was wanting in the area of faithful
reproduction. My view is, it would be useful if members of the DATHEADs
community were to individually, and together put pressure on Tandy to bring
back the 2011.
Super Omni 30-18000 7/8 inch long. Catalog #33/1063 800 ohms 6 foot cord
comes with mini plug, and quarter-inch adapter. As well as clip, and
tie-pin. The system also comes with LR44 battery.
Personal Observations. This mic is still available. I think the price has
dropped somewhat, and for what it is, it is an excelent performer.
Although the specs imply a giant in mouse-clothing, this mic has its
limitations as one would expect with regards to its size. Like its bigger
brother the 1060, it is somewhat prone to fall down in high-leval
situations. I.E. an aircraft departing with after-burner in opperation.
Nevertheless, it is a good performer in average noise environments, and
highly reccomended for experiments with binaural sound. I have had
reliable results using these mics buried in a head-band, just above the
ears. there is an excelent 2-dimentional side-to-side panorama achievable
with this combination.
Other mic reccomendations that I have used with good results.
ECM-979 This mic is a single-point stereo microphone. I don't have the
specs handy, but something like 20-18000hz. This mic has a complicated
system of 3 elements. One on either side of the capsule, and one facing
outward. There is a pot on the front which controls the leval of the
forward-facing capsule. When this is in opperation, the affect on the
sound field is to fill-in the front. there is a detent on the pot, half-way
through its travel. I leave the mic set to this detent. I find the mic is
an excelent performer, but difficult to use in the out-doors due to wind.
Even with a sock, and extensive use of reticulated foam, the wind breaks
through with little difficulty. But, the sound is good. Last priced, this
mic sold for #179.00 in the U.K.
ECM-959. This mic has much the same characters as its more expensive
brother, but lacks the forward-facing element. according to the specs, it
goes down to only 50hz. But I never felt that this was a problem. What I
did feel to be significant was the amount of noise you got from handling
the mic. Seemed the body of the mic was coupled directly to the capsule,
giving it extremely sensetive handling characteristics. Now, just a word
on cheap, and dirty mic placement.
One solution is the co-incident placement. Both mics are placed 90 degrees
apart one above the other. Immagine they are connedted together with a nail
through the center of their bodies, and they can be rotated on this nail.
the mics form a triangle which is pointed with its base towards the
sound-source. what I use are a set of umbrella clips available from a
photographer suply house. These umbrella clips were original designed to
hold lamps, but will do nicely for mics. You can get a nice coincident
setup using these clips on a slim-line mic. Another way is place both mics
180 degrees apart, and in the case of omni-directionals, use a piece of
perspecs, or other reflective material in the middle of the array.
================
{32} My DAT deck has an unbalanced mini-headphone jack for an analog
input. How do I get the best sound through that tiny jack -- what
types of adapters would give me the best results?
The size of the jack has nothing to do with sound quality so long as it
makes good contact. But they wear out soon, so avoid lots of plug-in,
plug-out cycles. Make adapter cables with flexible cable rather than solid
adapters that put a lot of sideways load on the little jacks. [dj]
 
 
================
{33} My DAT deck has unbalanced RCA analog inputs -- how do I maximize
sound quality?
Same answer as {32}. Plus, use a good external mic preamp. [dj]
================
{34} What are the sources of mic noise?
I assume you mean hiss rather than hum or extraneous pickup caused by poor
wiring. In a typical recording setup, exclusive of the A-to-D or tape, in
order of decreasing loudness, the sources are mic preamp noise from its
circuitry, mic noise typically from the front end FET, Brownian motion
noise of the air inside the mic capsule, and thermal noise from the wire
and other resistance between the mic and the preamp. [dj]
Tony Berke reports on experiments he's done with various mics re noise
level, and comes to the conclusion that large capsules and omnis are
quieter, but that there's no really conclusive explanation why this might
be so, and why there seems to be such a disparity in specs from the various
mic makers. (Sorry if I have paraphrased too crudely, Tony!)
 
This is a big problem, and one that until recently the mic makers have not
addressed exactly openly. Like most.phpects of mic design, it's also very
sparsely covered in the literature. The only really cogent treatment of the
subject, and this is still incomplete, is an article by Dick Burwen in the
May 1977 Journal of the AES, which fortunately is reprinted in the AES
anthology of microphone articles. I have seen two other relevant articles,
"Microphone Thermal Agitation Noise" by Harry Olson in the Journal of the
ASA, Vol. 51, No. 2; however, like most Olson work, this deals with the
measured effects on a ribbon (pressure gradient) microphone rather than a
condenser (predominantly pressure) mic. There is also a useful paper in the
December 1970 AES Journal by Herman Wilms on the vagaries of noise
measurement, "Subjective or Psophometric Audio Noise Measurement: A Review
of Standards."
 
Noise is typically referred to in microphones in terms of equivalent sound
pressure level. But there's a major catch here. The measure used is
typically dBA: decibels above the hearing threshhold of 0.0002 microbar,
A-weighted. But A weighting is designed to measure the annoyance factor of
sounds in the normal background noise floor level -- 40 to 80 dB SPL more
or less -- not things that are below the ambient noise floor in theory but
are still audible and objectonable, as nearly all mic noise is. Usually,
the A-weighted curve is used because the number looks the best, but,
quoting from the CCIR working group, "...the A-weighting network curve...is
not considered suitable for the measurement of audio-frequency noise in
broadcasting and sound recording systems, as in this case it is the effect
of the noise on the program rather than the loudness of the noise itself
which is important." The standards by which microhone noise are measured
are also not shared among the various makers. Neumann tries to cover the
bases by referring to both the DIN/IEC 651 standard and the DIN 45405/CCIR
468-1 standard. But both standards ignore the effect of the capsule --
these are both just weighting curves for the equivalent SPL of the noise
generated by the electronics with a replacement capacitance connected in
place of the capsule. There is a DIN spec 45590 for measurement of
self-noise of the entire mic, but few mic makers use this spec; it's
difficult to do and the result looks too bad.
 
Over the last ten years, I have bought every microphone book in every
European language I could find, and they all fall way short of anything
really thorough on any of the important topics of mic design and
comparison. The most useful is probably _Acoustics_ by Leo Beranek, now
back in print as an ASA paperback. Of the popular books, the Lou Burroughs
book _Microphones_ is probably the best, but long out of print (and the
^*&^$# who borrowed my copy didn't bring it back!). Careful reading of the
articles in the AES anthology volume on mics taught me more than either of
those, however.
 
The electronics of the microphone can easily be modeled, measured and
improved. Nearly all condenser mics use an FET operating as a source
follower, or a low gain common source stage. The FET and its source and
drain resistors are typically the major noise sources. The noise current
from the high value gate bias and polarization resistors is delivered into
the capacitance of the capsule; the resultant RC pole results in a lowpass
filter that, with any reasonable value of resistance, puts most of the
noise in the infrasonic range, where it's blocked by coupling caps, servos,
etc later in the chain. Earlier mics used lower value resistors - 150 to
250 megohms - while modern mics use 1 to 3 gigohm resistors, and Burwen
uses a 20 gigohm resistor in his design. The cheapest electret capsules use
no resistor, just a reverse-biased diode whose leakage current biases the
FET (no polarization resistor is required in an electret).
 
The noise from the electronics is generally white above the 1/f corner of
the FET used. In modern design this is usually below 100 Hz and seldom a
problem, and the resulting A-weighted noise is around 1 microvolt RMS, or
-120 dBV. Unlike most mic and console makers, I don't use dBm. dBm refers
to noise _power_ (it is dB ref 1 milliwatt into 600 ohms) and is only
relevant when a matched transfer of power is taking place. The output
impedance of a microphone is seldom, if ever, matched these days into the
load impedance of the preamp which would make a power measurement
meaningful. If you ask the manufacturers about this, they will shuffle
their feet and say, "oh yes, we mean dB referenced to the voltage level
(0.775V) that 1 milliwatt from a 600 ohm source makes across a matched 600
ohm load." Arrgh.
 
The bigger problem, now that we have good quiet FET's, is the noise from
the capsule. Of course smaller capsules will have lower output, and the
electronic noise will predominate in relative terms. But the output level
at the capsule of a 1/2 inch omni and a 1.25 inch dual-cardioid like the
C414 is fairly close, around 12 mV/Pa. This is so because the size of the
diaphragm isn't the only contributing factor; larger diaphragms need to be
stretched more tightly and are often spaced away from the backplate further
than the small ones.
 
I have not yet seen a good explanation of the noise generation mechanism of
the air behind a backplate. One of the best engineers at AKG in years past
told me of an article in the Journal of the ASA about turbulent behavior of
the air between the diaphragm and the backplate but I have been unable to
find it. The Burwen paper notes without comment that his omni capsule was
some 10 dB quieter midband than the cardioid, and the bare electronics were
10 dB quieter than the omni. This was using a Schoeps MKT45 capsule, which
is a switchable omni/cardioid. The response is switched by opening or
closing vents in the capsule backplate, so diaphragm thickness, tension and
spacing are unchanged.
 
What does change between the various capsules, and what seems to cause the
major difference in _perceived_ noise floor, is the damping impedance
presented to the diaphragm by the air behind it. In theory, the "thermal
acoustic" noise is caused by Brownian motion of the air molecules; this is
modeled as a voltage which appears across the mechanical impedance of the
diaphragm. A capsule spaced very close to the backplate will be more
constrained by the air cushion behind it than if you were to open the
backplate up to sound arriving from the rear (as is done in cardioid mics).
Close spacing also boosts the output (better for noise) but requires lower
polarizing voltage or higher diaphragm tension (worse). This damping
impedance is also usually reactive -- therefore the tonal color of the
noise changes with capsule type. You can have two noise sources, one white
and one red, measured to have identical dBA equivalent loudness, and sound
very different.
 
What all of this comes down to is that different mics will sound noisier or
quieter in use, with little direct relation to their specs which can almost
be pulled out of the air. Someday, mic makers will publish noise spectral
curves just like transistor and IC makers do, so that this can all be
compared sensibly. Making an isolated chamber thats _really_ quiet is on my
list of things to do so that I can do this. So far only B&K has published
anything relevant in this field, and then only for their measurement
microphones. [dj]
================
{35} How do I keep mic noise to a minimum so I can have a decent S/N
ratio on quiet recordings?
Use mics that have a low self-noise, and use a quiet mic preamp.
[dj]
================
{36} What's the difference between the capsules in a Neuman TLM-170 and
a Neuman KMi86?
Ooo, why did you choose this particular pair of mics?! The capsule in a
TLM170 is essentially identical to that in the U89. It is about an inch in
outside diameter, and follows the Braunmuehl-Weber design which has two
diaphragms sharing a common backplate/resonator/phase shift assembly. The
two diaphragms produce two cardioid signals which are added together
electrically in phase or out of phase to produce the desired pattern.
Sometimes this is done by taking the audio output off the common backplate
and varying the polarizing voltage, sometimes it's done by mixing the two
separate audio signals. The other Neumann Braunmuehl-Weber capsules are the
KK67 family, found in the U67, U87, SM69, and the like, and the KK47
family, used in the U47 and M49. These types all have a center point
contact, where the diaphragm is attached to a post coming out of the
backplate. The TLM170/U89 capsule has no center point, it is attached only
at the circumference (like the Braunmuehl-Weber capsules made by AKG).
There was also a KK56/KK88 capsule which is center-point-less like the
TLM170 but smaller. The KM86 and KM86i use a back-to-back pair of KK84
capsules, which are also found in the KM84 front-address mic.
[dj]
The KMi86 (a short production run several years ago) consists of two KMi84
capsules mounted back to back, with the primary pickup direction being
perpendicular to the axis of the mic body. It contains internal electronics
to allow for pattern switching between omni/cardioid/figure-8.
The TLM170 is a shorter, stouter mic, with a larger diameter capsule, which
is also oriented perpendicular to the mic body. The 170 is also switch
selectable for omni/subcardioid/cardioid/hypercardioid/figure-8/
user-defineable. The user-defineable patern feature will be offered as an
electronics upgrade some time in the next year. A special power supply
(phantom/pattern controler) will be required.
Having used KMi84's, KMi86's and TLM170's to master with, I think that I
prefer the 86's. The 170's are nice, but the 86's have a warmer sound.
That may be because the 86's I use have been pro 'tweaked' to be the best
mic that they can be.
[td]
================
{37} What is a PZM? How do I modify one?
The following mod is affectionately referred to the ``Rastocny'' mod. I'm
still using this modified mic in a lot of situations, but I have a few
others that I use when conditions are right. The problem is finding the
right place and a big enough surface to use them properly.
[dv]
RECORDING TIPS WITH THE PZM
About recording pianos, Crown recommends that you tape two of them inside
of the lid. I place the mics in various positions depending upon the room.
When recording in a large hall, I place them on the floor about five feet
apart and 12' from the bend in the sound board (it's an unconventional
approach; I've never seen anyone else use it). When recording in a small
room, I tape them to the lid in various positions, depending upon the type
of piano.
Crown has several published tips on using the PZMs. If you can find a
dealer near you, they may have these articles in stock.
PZMs are wishful-sinful mics: they sound pretty good but they need to be
placed against a large surface to work properly. Sometimes this is just
not possible and you have to try other mics or go to extremes to find a
surface. And unfortunately, PZMs have a rising top octave response :-(
But they are seldom seen by the audience!
 
INTRODUCTION
The RS PZM microphone is an omnidirectional electret microphone patterned
after a principal invented by Crown International called the pressure zone
microphone (hence, PZM). The output impedance of the stock microphone is
about 600 ohms (unbalanced) and it requires a phantom supply voltage from
-1.5V to -12V DC for operation. The stock microphone has a supply module
and built-in line-matching transformer to convert 600 ohms unbalanced to
about 10K ohms unbalanced. The problem with this stock PZM is twofold:
1) you cannot use long cable runs on the mic since the line is unbalanced
2) the matching transformer used in the module is terrible
So the mods outlined below address these two problems by describing a
method of using a standard balanced microphone cable in conjunction with an
unbalanced (single-ended) microphone input configuration common to most
consumer tape recorders. There are compromises made when using this
approach, but the benefits in the case of this PZM far outway the
compromises.
 
 
MODIFYING THE RADIO SHACK PZM MICROPHONE
The stock assembly consists of a mic, a coax cable, a supply module, a
twinax (2-wire shielded) cable and a 1/4" phono plug as shown next.
===== ==============
|mic|---coax cable-----|power supply|----twinax cable---1/4" phono plug
===== ==============
1. Cut off the 2-wire shielded cable between the 1/4" plug and the power
supply. Toss the phono plug.
2. Take the mic apart (screws on the bottom). Unsolder the coax cable
from the mic element and replace with the 2-wire cable from step #1
above. This is a somewhat static sensative device so work with a
grounded soldering station and appropriate clothing. Connect the
low side to the dark color wire and high side to the light color
wire. DO NOT CONNECT THE SHIELD TO THE LOW SIDE!
3. Connect the other end of the 2-wire cable to an in-line male XLR
connector. You should now have something that looks like this:
male XLR
mic n/c --------------------------------------- shield (pin 1)
electret high -------light wire---------------------- pin 2
element low -------dark wire----------------------- pin 3
 
4. Make some long mic cables from some twinax or 2-wire microphone cable.
I made three 75' and three 25' cables for my setup. Shields are
connected on each end to pin 1 and the case on one side (I think it's
the female side) as shown next.
female XLR male XLR
case------shield --------------------------------------- shield (pin 1)
high --------------------------------------- pin 2
low --------------------------------------- pin 3
 
The next step is to build an in-line supply that also adapts the XLR
connectors to the 1/4" phono mic input of most consumer tape recorders
as shown next. There should be one of these supply boxes built for each
mic used.
-----------------------
female XLR-------|supply/adapter module|-------------1/4" phono plug
-----------------------
 
5. Cut a 24" piece of 2-wire mic cable and connect an in-line female XLR
to it as you did in step 3 above.
6. Cut a 24" piece of coax and connect an in-line 1/4" male phono plug to
it.
7. Cut holes large enough in a small steel project box to run the cables
through. Add chaffing and strain relief to these two cables.
8. Connect the shields from the two cables AND the low side of the 2-wire
mic cable to the same point (single point) on the project box. (If you
prefer to use chassis mounted XLR and phono connectors, instulate these
connectors from chassis ground and wire the cases internally to this
same single-point ground.)
9. Connect the "+" side of a 9V transistor radio battery jack to this
single point ground.
10. Connect the "-" side of this battery jack to a 2.2K ohm 1/4 watt
resistor.
11. Connect the other end of the resistor above to the high side of the
2-wire cable.
12. Connect a 10 uF mylar or metalized polypropylene capacitor from the
high side of the 2-wire mic cable to the center conductor of the coax
cable.
You should now have something that looks like this:
female
XLR 1/4" phono plug
1 ---shield-----+---+---- single-point ground ---------------shield-----
3 ---low--------| | ------hot--------
2 ---high----- ----- "+" "-" --- 2.2K ohm ----- |
| 9 volt | |
| battery | |
+--------------------------------------- |
| |
--------------||---------------------------
10 uF
input
cap.
When the mics are not connected, there is no drain on the battery so there
is no need for a switch.
Close up the project box and plug in the microphones and the tape recorder.
I think you'll be surprised by the improvement in these otherwise
inexpensive and ho-hum mics.
 
 
ONE LAST THOUGHT
If you are *ABSOLUTELY POSITIVE* that the input stage of your tape recorder
or mixer has an input capacitor (of adequate voltage) and then a load
resistor, you can replace the 10 uF cap with a piece of wire. (See below.)
REPLACE THE INPUT STAGE CAP DO NOT REPLACE THE INPUT STAGE CAP
WITH WIRE IF THE TAPE DECK WITH WIRE IF THE TAPE DECK INPUT
INPUT LOOKS LIKE THIS: LOOKS LIKE LIKE THIS:
input input
mic stage cap mic stage cap
jack----||--------input stage jack----------||--------input stage
| |
load load
resistor resistor
| |
ground ground
 
If you decide not to or cannot replace the input stage cap with wire,
you should replace the input stage caps of the tape deck or mixer with
an equivalent value of equal or higher voltage mylar or metalized
polypropylene capacitor to obtain the best performance.
 
 
VARIATIONS
You can eliminate any or all of the XLR connectors if you wish to make
a custom length, dedicated mic setup. The reason that I suggest the
XLRs is that as soon as you get serious about recording, you instantly
find out that you need about 10' more of cable than what the custom
lengths are to do what you want. With the XLRs, you can add or remove
cable for each situation.
For permanent installations in a mixer or tape deck, you could build
a phantom supply similar to what is shown next.
========== =========== ==========
|12V c.t.| |full wave| |-12 volt| 2.2K 2.2K 2.2K
|xformer |--| Bridge |-----| reg. IC|-----\/\/-----\/\/----\/\/--> -12V out
========== =========== | ========== | | |
--- | --- --- ---
--- 220uF| --- 220uF--- 220uF--- 220uF
| | | | |
---------------------------------------------> gnd
You can gang the passive RC components together to run several channels
from the same bridge. You could also put all of this inside of a "Bud"
box. I recommend using all similar value components since parts are
cheaper by the dozen.
This concept provides more than adequate ripple rejection and if you want a
bit improved high frequency clarity, shunt all 220uF caps with 0.1uF
polypro.
I've also done this for budget portable systems. I use one per channel:
2.2K 2.2K
9V battery--\/\/----------\/\/-----> -9V out
| | |
| --- ---
| 0.1 uF--- --- 220uF
| | |
-------------------------------> gnd
I drag a pair of these supplies with hard-wired 20' cables, a Sony Walkman
Pro, and a light weight pair of earphones out with me backpacking and get
some wonderful wildlife and wilderness recordings on batteries!
You can also replace the massive square metal plate with a piece of
plexiglass with tapered edges. The edges do influence the response of the
microphone, but in some situations, what you place the mics on or near will
equally degrade the response, so what the heck. My portable rig uses the
plexiglass plates; I usually pack in about 45 pounds worth of stuff and
shaving off every ounce that you can helps.
 
 
QUESTIONS FROM PREVIOUS POSTINGS
One person asked ``Why such a big capacitor?'' Well, it has to do
with the uncertainty of the input impedance of your tape recorder or
mixer. If you have a low input impedance (say 1,000 ohms or less)
you need this big of a capacitor to get the low frequency response
available with this microphone. If you have a high input impedance
(say 10,000 ohms or more), you can get away with a smaller capacitor.
If you use a lot of different tape recorders and mixers or if you
don't know what the input impedance will be, it's better to use the
big cap (and that's why I recommend it).
Some folks have asked why I don't shunt the mylar with a small exotic
cap. The answer is simple: the PZM has a rising top octave response.
The mylar tames a little of the peak; a shunt cap would only exagerate it.
 
 
SOURCES OF CAPACITORS
Some sources for 10uF esoteric capacitors are:
Manufacturer Type Part Number L x W (mm) DCV
ChateauRoux m-pprop ? 64 x 22 ? 250
El. Concepts m-pprop 5MP12D106K 38 x 20 100
El. Concepts m-pprop 5MP12F106K 57 x 23 200
El. Concepts m-pprop 5MP12J106K 57 x 39 400
IAR "Wonder" m-pprop X series 10uF 57 x 29 310
Illinois m-pest 106MWR063K 32 x 14 63
Illinois m-pest 106MWR100K 32 x 19 100
Illinois m-pest 106MWR250K 44 x 20 250
Illinois m-pprop 106MPW160K ? 160
Illinois m-pprop 106MPW250K ? 250
Illinois m-pprop 106MPW630K ? 630
?(Meniscus) mylar ? ? 100
Panasonic m-pest E1106 31 x 16 100
Paxton mylar 8uF 38 x 19 ? 100
Seacor m-pprop PMWAF100KG ? 100
Seacor m-pprop PMWFF100KG ? 100
Sidereal m-pprop ? 49 x 19 100
Sidereal m-pprop ? 57 x 27 200
Sprague m-pprop 735P106X9100USL 38 x 23 100
Sprague m-pprop 735P106X9200WVL 57 x 26 200
Sprague m-pprop 735P106X9400ZVL 57 x 42 400
 
I haven't had time to research all of the sources. I'd appreciate it
if you could contact me if you have other sources to contribute or
corrections/updates to this list. Addresses and telephone numbers
for the above capacitors are:
* Digi-Key, 701 Brooks Ave S, PO Box 677, Thief River Falls, MN 56701
Panasonic
(800) 344-4539
* Electronic Concepts, PO Box 627, Eatontown, NJ 07724
(201) 542-7880
* Gateway Electronics, 5115 N. Federal Blvd., Denver, CO 80221
Paxton
(303) 458-5444
* Illinois Capacitor, 3757 W Touhy Ave., Lincolnwood, IL 60645
(312) 675-1760
* Meniscus Systems, 3275 Gladiola SW, Wyoming, MI 49509-3224
Mylar; best prices on ChateauxRoux
(606) 534-9121
* Seacor Inc., 123 Woodland Ave, PO Box 541, Westwood, NJ 07675
(201) 666-5600
* Sidereal Akustic, 1969 Outrigger Way, Oceanside, CA 92054
SiderealKap, ChateauxRoux
(619) 722-7707
* Sprague Electric Co. There's probably a sales office in or near your
town. Ask for Engineering Bulletins #2092 and #2752, and catalogs
.php-420K and #C-567A.
* TRT, Box 4271, Berkeley, CA 94704
IAR "Wonder Caps"
no telephone number published
===============
{38} What kind of capicators should be used with a mic pre-amp? How
does choice of cap. affect the sound?
Len Moskowitz writes in DAT-Heads digest #300 that the CSB mics use 2 uF
polypropylene caps between the capsule and the output. Indeed polyprop (or
polystyrene, which are impossibly large in this sort of value) would be the
type of choice, with polyester or polycarbonate next on the list. Matching
within 1% is probably not necessary but it can't hurt (the input impedance
of the decks probably varies by 5% or more, negating any extra care taken
in cap matching). The input impedance of the deck (assuming it's resistive,
we'll call it R) and the cap in series produce a low cut filter with the 3
dB down point set by
 
f=1/(2*pi*R*C) with f, r and c in Hz, ohms and farads.
 
This means that with the typical (?) 2K input Z of a dat mic pre, the -3dB
point with a 2 uF cap is 40 Hz. To change this to 200 Hz, you would use .4
uF caps. For lower input impedances the frequencies go up because R goes
down, hence Guenther's comment that the capacitors sometimes need to be
larger for proper bass response.
 
Normally, f is set way lower than you would ever need, to be sure that no
part of the rolloff gets in the way of the music. 40 Hz sounds a little
high to me, so 2K is probably not the right value for a typical mic pre
input. But in the case of swamping the DAT input with low frequency signal,
what we're trying to do is roll off some of the LF information so it isn't
overpowering.
 
Good luck...
[dj]
===============
{39} What kinds of capsules are typically used in 'stealth' microphones?
What's good/not good about them and why?
Several DAT-Heads have written or posted on the problems with the small
electret capsules used in stealth mics. The capsule almost universally
preferred for these is the Panasonic WM-063, or the WM-060, which is
theoretically the same but with a phenolic circuit board rather than epoxy.
They sound different, though. The capsules are available from Digi-Key
(1-800-344-4539) for about $2. You have to buy a bunch and sort them,
because there are major differences in sound. There are several problems
with this capsule; some are endemic and some can be fixed.
 
Some complain that the output is too low; this can easily be fixed with a
gain stage. Using a higher voltage and larger load resistor (7-9 volts and
10K, for instance) rather than the 1.4 volt that's normally found in
tie-clip mics will also help and raise the maximum output level before
clipping. The output cap can be changed to a bigger and better kind. A
200-300 uF elcap bypassed with 0.5 of 1 uF of mylar or polypropylene makes
a difference.
 
The more difficult problems are noise and harshness. Because the active
area of the diaphragm is so small, the output is low, so the FET
contributes a lot of noise. You can fix this by opening the capsule,
discarding the FET and reassembling the mic in a new housing. Then you can
use a good FET and a 2-10 gigohm resistor for bias (which can cost more
than the whole mic capsule), instead of the diode leakage current that is
used in the "FET-IC" to bias the FET. You can also make the new housing
with an opening to the front that is as big as the active area of the
diaphragm, rather than the 2 mm hole covered with fuzz that's there now (a
Helmholtz resonator is formed by the hole, the fuzz and the space behind
it, which pushes up the HF response, but creates a pole that makes phase
problems, thus harshness).
 
There are better capsules around, but they are hand-made and not cheap. You
can use metal diaphragm instrumentation mic capsules, for instance the
standard 1/2" from B&K, ACO Pacific, or Larson-Davis. But these cost $580
(ACO) to $777 (B&K). There are other electret capsules (Sennheiser,
Lectret), normally available only to manufacturers, that aren't much
better. I have made a study of all the other available electret capsules
(Primo, NMB, Hosiden, Bo Sung, Pan, and others) but keep coming back to the
Panasonic.
 
There are some other mods that can be done to improve the Panasonic
capsule. They are generally the result of extensive experiment and are
considered proprietary by those who developed them. The critical issues
include: stabilizing the aging of the diaphragm and the back-electret
film, getting the front of the diaphragm out into the air as much as
possible, keeping the back of the diaphragm/backplate structure sealed from
the air as much as possible, keeping the mic housing still while only the
diaphragm moves, and operating the FET stage in the middle of a wide linear
transfer function. Okay, I haven't given away any secrets, but inquiring
minds ought to be able to work good solutions based on this list of
problems. [dj]
===============
{40} Why do some shotgun mics have poor bass response?
Most shotgun mics are phase shift hypercardioids at the bass end and line
interference types at higher frequencies. Hypercardioid capsules with good
LF response are difficult to make, and often it is desirable for their main
application (dialog pickup) to roll off the bass, so there won't be so much
(a) room rumble and (b) handling noise as the mic is panned around. [dj]
================
{41} Which brands/models of shotguns have good bass response?
Neumann, Sennheiser and AKG all make shotgun mics that are used a lot. They
all have rolled off bass. The Neumann long shotgun (KMR82) looks like the
best, at -3 dB at 60 Hz. Others have the -3 dB point as high as 150 Hz.
[dj]
================
{42} What causes some mics to sound tinny or 'canned' in some
situations? How can I avoid it?
Biggest problem is putting the mic where the sound is already tinny. Plug
one ear and listen to the sound with the other ear, where the mic is,
devoid of the psychoacoustic reinforcement you get when listening with two
ears. Move the mic to where it sounds better. [dj]
================
{43} How critial is it to aim a shotgun mic directly at the source?
What happens if I'm off by 5 degrees? 10 degrees?
 
Look at the polar plot of the mic. With most, plus-minus 10 degrees makes
little or no difference. [dj]
================
{44} Why do recordings made with shotgun mics lack the 'presence' that
other mics have? (it sounds like there's a hole in the center of
the sound coming from my stereo system) What can I do to improve
the 'presence' in my recordings?
By this definition of presence, you probably set the mics at too great an
angle apart. Narrow it. Some of the presence also comes from the
reverberant environment, which the shotgun mic is trying to get rid of for
you. So use something else, like a good hypercardioid. [dj]
================
{45} What is "binaural recording?"
Binaural recording actually predates stereo recording. In binaural
recording two microphones are placed near or in a listener's ears (or
alternately, an acoustically accurate dummy head's ears). The sounds that
the two microphones record are exactly what the listener hears, including
the effects of the outer ear (the pinna), the acoustic shadow of the head,
and inter-ear phase and frequency response differences that provide
localization cues (the information that lets you determine where a sound is
coming from).
When the binaural recording is played back over headphones, the ambient
sound field of the recording location is reproduced more-or-less exactly.
The sense of being there is amazing and you can pick out voices in the
surrounding crowd and the placement of instruments to an unparalleled
degree. Until you've heard a binaural recording played back over a good
set of headphones, you haven't heard how realistic a sound recording can
be.
(Stax sells a series of binaurally recorded CDs, including a demonstration
disk, whose realism will literally make your hair stand up on end.)
[lm]
================
{46} What microphones are available to do binaural recordings?
Both Core Sound and Sonic Studios offer a range of miniature microphones
that mount near your ears and are suitable for binaural recordings.
For binaural recording purists, Core Sound offer a set of in-ear
microphones that mount in your ear canals using custom made ear molds.
[lm]
================
{47} I've heard that binaural recording are supposed to be listened
to over headphones. How do they sound over speakers?
They sound good but different. Because binaural microphones have nominally
omnidirectional pickup patterns, you get roughly the same effect as a
spaced-omni microphone setup. But because the microphone spacing is a bit
narrow (7 to 9 inches instead of the more typical 24 to 36 inches) the
stereo image may sound a bit compressed.
Some binaural microphones can be conveniently used with wider spacings.
These provide the usual spaced-omni performance. [lm]
================
{48} Do you have to hold your head perfectly still while making a
binaural recording?
No. Slow movements or movements over a small range during recording are
normally unnoticeable during playback. Fast, large movements can be
perceived as a shift or rotation in soundstage.
[lm]
================
{49} Can I use headphones as microphones?
Ah yes. The old use-the-headphones-as-a-mic trick. I've tried this
with some Sony headphones and it worked but not extremely well. Those
Sennheiser HD 414's are a good choice because they come with wind screens.
Alot of people probably don't realize this, but you can also use mics as
headphones. Be sure to use dynamic mics! Take a pair of Sennheiser MD
421's and duct tape them to your head. You'll need some female-female XLR
adapters. This setup even gives you built-in tone controls! The mics will
conveniently attach to mic stands (or in this case headphone stands), which
might keep you from nodding off if you get tired. For safety's sake, be
sure not to use any mic that is more pointy than your elbow as headphones.
Shotguns are definately out.
Also, omnidirectional mics may make excellent point-source speaker
systems.
[rg]
========================================================================
A U T H O R S
[tb] tonyb@juliet.ll.mit.edu (Tony Berke)
[pd] peterd@hpwars.wal.hp.com (Peter Dabos)
[td] dalton@mtl.mit.edu (Tim Dalton)
[rg] gilde@jaco.ds.boeing.com (Rob Gilde)
[dj] david@josephson.com (David Josephson)
[jm] maggard@subpac.enet.dec.com (Jeff Maggard)
[lm] moskowit@Panix.Com (Len Moskowitz)
[po] pluto@cix.compulink.co.uk (Paul Ostwind)
[pr] (Phil Rastocny)
[ss] SteveSgt@torrent.sj.ca.us (Steve Sergeant)
[jv] varanelli@cs.virginia.edu (Jim Varanelli)
[dv] cptvideo@cbnewsc.att.com (David Vlack)
========================================================================
------------------------------
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