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Andy
 
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Default Gefell measurement mics for classical recording?

Hello everyone,
does anyone know if the Gefell mk102 omni capsule with the mv102 body would
be good for music recording? Maybe a couple of those could be use as spaced
pair omnis for recording classical music? I heard that they're very quiet
and I suppose the frequency response is pretty flat.

Thanks,
Andy



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Scott Dorsey
 
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Default Gefell measurement mics for classical recording?

Andy wrote:
Hello everyone,
does anyone know if the Gefell mk102 omni capsule with the mv102 body would
be good for music recording? Maybe a couple of those could be use as spaced
pair omnis for recording classical music? I heard that they're very quiet
and I suppose the frequency response is pretty flat.


I have always liked the IEC measurement mikes for orchestral recording.

But, I'll say first of all that using conventional measurement amplifiers
is a pain in the neck.

Secondly I will say that I like the 1" mikes more than the 1/2" ones,
because they get a little beamy at high frequencies. Work great in a
Jecklin disc.

Both ACO and Josephson make some amplifier modules that allow you to use
200V externally polarized measurement capsules but have a standard XLR
connector and standard phantom powering. I have not used the ACO one but
the Josephson one sounds excellent and is much more convenient than
fooling around with B&K 2115s and the like. Josephson will even sell
you the unit, pre-bundled with a Gefell capsule.

There have been a couple of recordings I've submitted to various RAP CD
compilations recorded with measurement mikes.
--scott


--
"C'est un Nagra. C'est suisse, et tres, tres precis."
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gunnar
 
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Default Gefell measurement mics for classical recording?

I get the impression that the companies making measurement mics elect
to make special versions for musical recordings. I would guess that one
reason might be to optimize for the sound instead of for a ruler flat
frequency response. I am not really into microphone design but I have
sort of gleaned that sometimes measurement mics are made accepting
large phase changes that the ear finds disturbing, but from a pure
measurement point of view has absolutely no influence.

Anyway, if you are planning on buying the mics Microtech Gefell does
make some versions intended for music, M296 is one exampel. And Bruel
and Kjaer (B&K) is the father for DPA mics, say the DPA4003 where the
mic capsule is still made by B&K (and marked with the B&K name).

If you are looking at getting them used, or already have them around,
please go ahead and tell the rest of us about your results.

Gunnar

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Scott Dorsey
 
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Default Gefell measurement mics for classical recording?

gunnar wrote:
I get the impression that the companies making measurement mics elect
to make special versions for musical recordings. I would guess that one
reason might be to optimize for the sound instead of for a ruler flat
frequency response.


Okay, we're talking about IEC Type I capsules, not the cheap electret
ones. For the most part, the reason B&K made "recording" versions of
their measurement microphones was cost. People didn't want to spend
$12,000 for a pair of recording mikes.

I am not really into microphone design but I have
sort of gleaned that sometimes measurement mics are made accepting
large phase changes that the ear finds disturbing, but from a pure
measurement point of view has absolutely no influence.


This is not the case at all for IEC Type I measurement mikes. They
are designed to have VERY tight phase response across the passband,
much better than you'd find from omnis made for recording work.

There are some bargain basement electret-based measurement mikes
out there from guys like Crown and Behringer and BSWA. Some of
these mikes to have wonky phase response and some of them are noisy,
because they are basically designed only to have a flat frequency
response, not anything else. This makes them unusable for a lot
of measurement work (like anything involving impulse responses).
These mikes are very inexpensive but they are sort of on the bare
border of being considered "measurement" mikes and they WILL NOT
meet IEC Type I measurement mike specs.

The conventional IEC Type I measurement mikes are all derivatives
of the Western Electric 640AA design, basically pressure response
microphones that have a nickel diaphragm and a very flat frequency
response due to the actual capsule physics. Do not confuse them
with the electret cheapies.
--scott
--
"C'est un Nagra. C'est suisse, et tres, tres precis."
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gunnar
 
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Default Gefell measurement mics for classical recording?

Okay, we're talking about IEC Type I capsules, not the cheap electret
ones. For the most part, the reason B&K made "recording" versions of
their measurement microphones was cost. People didn't want to spend
$12,000 for a pair of recording mikes.


Well, obviously you know more about this than I do. I remember having
read though that B&K did a rather extensive redesign of their capsule
to optimize the sound for recording. Maybe my memory is wrong there.

Regardless I really like the DPA 4003 sound and I think the newer
4006TL is coming close (the 4003 and 4006 have the same capsule but
different electronics). They are nothing like low-priced though but do
keep their value on the used market. An added benefit is the selection
of acoustical grids that can be used to tailor the frequency response.

I have also used the Microtech Gefell M296 which to my eyes looks
derived from their line of measurment mics (but as stated, I am no
expert). This is also a lovely mic, but it is more specialized than the
smaller DPA-s in my experience. While the 4003 always sounds good, the
M296 may not be the right tool every time.

Gunnar

GUnnar



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Andy
 
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Default Gefell measurement mics for classical recording?

Hello Scott and Gunnar and thanks for your responses. The reason I'm asking
about measurement mics is also because I found a couple of the Gefell mics I
mentioned (mk102 omni capsule with the mv102 body) for something like USD
300. I couldn't find specs for this combination.

Andy


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Scott Dorsey
 
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Default Gefell measurement mics for classical recording?

gunnar wrote:
Okay, we're talking about IEC Type I capsules, not the cheap electret
ones. For the most part, the reason B&K made "recording" versions of
their measurement microphones was cost. People didn't want to spend
$12,000 for a pair of recording mikes.


Well, obviously you know more about this than I do. I remember having
read though that B&K did a rather extensive redesign of their capsule
to optimize the sound for recording. Maybe my memory is wrong there.


Yes, they did. That optimization was to lower cost. There are a lot
of carefully-controlled characteristics in the IEC Type I capsules that
you don't need in a recording mike. Also, of course, the recording mikes
are available with cardioid designs as well.

Regardless I really like the DPA 4003 sound and I think the newer
4006TL is coming close (the 4003 and 4006 have the same capsule but
different electronics). They are nothing like low-priced though but do
keep their value on the used market. An added benefit is the selection
of acoustical grids that can be used to tailor the frequency response.


They are good mikes and I like them a lot. They don't have anything
like the flat response and careful phase response of the measurement
mikes, but they are a whole lot cheaper than the measurement mikes.

I have also used the Microtech Gefell M296 which to my eyes looks
derived from their line of measurment mics (but as stated, I am no
expert). This is also a lovely mic, but it is more specialized than the
smaller DPA-s in my experience. While the 4003 always sounds good, the
M296 may not be the right tool every time.


All of the nickel-diaphragm Gefell capsules are built with the same
basic procedure pioneered with the Western Electric 640AA measurement
capsule, as slightly modified by Schoeps in the fifties (the Schoeps 221b
is another example of a nickel-diaphragm capsule). But the overall
construction is quite diferent.
--scott

--
"C'est un Nagra. C'est suisse, et tres, tres precis."
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Bob Cain
 
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Default Gefell measurement mics for classical recording?

Scott Dorsey wrote:

There are some bargain basement electret-based measurement mikes
out there from guys like Crown and Behringer and BSWA. Some of
these mikes to have wonky phase response and some of them are noisy,
because they are basically designed only to have a flat frequency
response, not anything else. This makes them unusable for a lot
of measurement work (like anything involving impulse responses).


Unless correlated sweep methods are used. A mic has to be incredibly
noisy to much affect such a measurement. You can get highly repeatable
speaker impulse response measurement results with a busy highway 100 ft
away using this method (different noise source but same principle.)

But since he wants to use them to record, that quibble is moot.


Bob
--

"Things should be described as simply as possible, but no simpler."

A. Einstein
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Scott Dorsey
 
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Default Gefell measurement mics for classical recording?

In article ,
Bob Cain wrote:
Scott Dorsey wrote:

There are some bargain basement electret-based measurement mikes
out there from guys like Crown and Behringer and BSWA. Some of
these mikes to have wonky phase response and some of them are noisy,
because they are basically designed only to have a flat frequency
response, not anything else. This makes them unusable for a lot
of measurement work (like anything involving impulse responses).


Unless correlated sweep methods are used. A mic has to be incredibly
noisy to much affect such a measurement. You can get highly repeatable
speaker impulse response measurement results with a busy highway 100 ft
away using this method (different noise source but same principle.)


It's not the noise that is the problem in that case, so much as the wonky
phase response.

A lot of those mikes either use Panasonic electret capsules, or some
cheaper clones of the classic Panasonic design. These mikes have a
diaphragm resonance of around 18 Khz. To get the response out flat
to 20 KHz, they put a Helmholtz resonator tuned to around 20 KHz or so
in front of the diaphragm. the thing is, although the frequency responses
sum to zero, the system isn't minimum phase, so the phase responses do not.

But since he wants to use them to record, that quibble is moot.


I dunno. Those Panasonic capsules also tend to have gritty top end.
Whether this is due to the group delay or not, I don't know. But
I'd suggest avoiding them for impulse measurement and for recording.
They are cheap, though, and just fine for swept sine measurements.
--scott

--
"C'est un Nagra. C'est suisse, et tres, tres precis."
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Andy
 
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Default Gefell measurement mics for classical recording?


Scott Dorsey wrote:

Does it come with the power supply?


I don't know yet. I'm trying to find out.

Andy




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Scott Dorsey
 
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Default Gefell measurement mics for classical recording?

Andy wrote:
Scott Dorsey wrote:

Does it come with the power supply?


I don't know yet. I'm trying to find out.


The comparable B&K stuff would be, I think, a 4145 capsule, a 2627 body,
and a 2804 power supply.

I don't know if Gefell made a battery-powered supply as well as a battery
one, and I don't know if they used the 9-pin B&K plug or a LEMO plug like
ACO or something nonstandard. I don't know if you can mix and match the
B&K power supplies with Gefell preamps the way you can use the Gefell capsules
on B&K bodies.

Output will almost certainly be unbalanced, possibly on a shielded banana
plug.
--scott
--
"C'est un Nagra. C'est suisse, et tres, tres precis."
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Bob Cain
 
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Default Gefell measurement mics for classical recording?

Scott Dorsey wrote:

It's not the noise that is the problem in that case, so much as the wonky
phase response.

A lot of those mikes either use Panasonic electret capsules, or some
cheaper clones of the classic Panasonic design. These mikes have a
diaphragm resonance of around 18 Khz. To get the response out flat
to 20 KHz, they put a Helmholtz resonator tuned to around 20 KHz or so
in front of the diaphragm.


Scott, do you have a reference that derives that from the physical
parameters? I've heard it claimed and I've heard it intelligently
disputed that the volume in front of the diaphragm could be a resonator
tuned that low.

the thing is, although the frequency responses
sum to zero, the system isn't minimum phase, so the phase responses do not.


Why wouldn't the system be linear phase? It can all be modeled by
lumped reactive and resistive components and such models are minimum
phase. Regardless, I think your conclusion is correct that flat
response need not imply constant group delay.

I dunno. Those Panasonic capsules also tend to have gritty top end.
Whether this is due to the group delay or not, I don't know.


I don't even know what gritty means. It's one of those things like
"warmth" and "space." Can you put any kind of parameters to it?

Distortion products from the top half of the spectrum aren't audible
even if they could make it through the anti-alias filter at the front of
converters. Could be that you are hearing upper half distortion
products from the lower half and if a source follower is not used to
buffer the capsule (many circuits for those capsules are common source)
then the front end (highly non-linear) FET could be responsible.

But
I'd suggest avoiding them for impulse measurement and for recording.
They are cheap, though, and just fine for swept sine measurements.


My only reservation would be with respect to noise. The capsules in the
Earthworks TC30K (and others of their models) are Panasonics, btw. I'm
pretty sure that they employ source follower FET buffers. Have you
heard them and do you consider them gritty?


Bob
--

"Things should be described as simply as possible, but no simpler."

A. Einstein
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anahata
 
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Default Gefell measurement mics for classical recording?

Bob Cain wrote:

Distortion products from the top half of the spectrum aren't audible
even if they could make it through the anti-alias filter at the front of
converters.


Intermodulation products could be all over the audio spectrum.

--
Anahata
-+- http://www.treewind.co.uk
Home: 01638 720444 Mob: 07976 263827
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Scott Dorsey
 
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Default Gefell measurement mics for classical recording?

Bob Cain wrote:
Scott Dorsey wrote:

It's not the noise that is the problem in that case, so much as the wonky
phase response.

A lot of those mikes either use Panasonic electret capsules, or some
cheaper clones of the classic Panasonic design. These mikes have a
diaphragm resonance of around 18 Khz. To get the response out flat
to 20 KHz, they put a Helmholtz resonator tuned to around 20 KHz or so
in front of the diaphragm.


Scott, do you have a reference that derives that from the physical
parameters? I've heard it claimed and I've heard it intelligently
disputed that the volume in front of the diaphragm could be a resonator
tuned that low.


I might have a paper by Juha Backman about compression effects in
condenser microphones, which refers to this. It doesn't do actual
measurements.

Try and open up the hole in the front of the capsule and see what happens
to the frequency response, though. The top end sags down. So it's clear
that the chamber in front is in _some_ way acting to increase the top end.

I dunno. Those Panasonic capsules also tend to have gritty top end.
Whether this is due to the group delay or not, I don't know.


I don't even know what gritty means. It's one of those things like
"warmth" and "space." Can you put any kind of parameters to it?


Probably it's a result of distortion products. Some of that may be due to
the FET and the crappy biasing scheme on the FET. Some small amount might
be due to compressability of air in such tiny spaces. It's _possible_
some of it could be the result of group delay, but I'm willing to bet it's
really all distortion.

Distortion products from the top half of the spectrum aren't audible
even if they could make it through the anti-alias filter at the front of
converters. Could be that you are hearing upper half distortion
products from the lower half and if a source follower is not used to
buffer the capsule (many circuits for those capsules are common source)
then the front end (highly non-linear) FET could be responsible.


Sure. Or intermodulation distortion products too.

But
I'd suggest avoiding them for impulse measurement and for recording.
They are cheap, though, and just fine for swept sine measurements.


My only reservation would be with respect to noise. The capsules in the
Earthworks TC30K (and others of their models) are Panasonics, btw. I'm
pretty sure that they employ source follower FET buffers. Have you
heard them and do you consider them gritty?


SOME of the Earthworks mikes use standard 2-terminal Panasonic capsules,
and those mikes do sound gritty to me. Many of them (and I think pretty
much all the newer ones) use a three-terminal variant that allows external
biasing, and those sound less gritty. None of them sound as smooth on top
as say, the Schoeps or DPA mikes.
--scott


--
"C'est un Nagra. C'est suisse, et tres, tres precis."
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Bob Cain
 
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Default Gefell measurement mics for classical recording?

anahata wrote:
Bob Cain wrote:

Distortion products from the top half of the spectrum aren't audible
even if they could make it through the anti-alias filter at the front of
converters.


Intermodulation products could be all over the audio spectrum.


True. I was speculating as to why the artifacts Scott hears would be in
the high end.


Bob
--

"Things should be described as simply as possible, but no simpler."

A. Einstein


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Bob Cain
 
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Default Gefell measurement mics for classical recording?

Scott Dorsey wrote:

Try and open up the hole in the front of the capsule and see what happens
to the frequency response, though. The top end sags down. So it's clear
that the chamber in front is in _some_ way acting to increase the top end.


I've heard of people doing that (with considerable difficulty) but not
of actually measuring it afterwards. It just occurred to me that it
would be easier, for experimental purposes, to reduce the hole size with
a punctured cover. I might just make comparative measurements doing
that one of these days because I've long been curious about the truth of
the Helmholtz cavity theory. I can't, however, imagine what else could
cause any kind of weird phase characteristics given how small and simple
(acoustically and mechanically) the capsules are.

Probably it's a result of distortion products. Some of that may be due to
the FET and the crappy biasing scheme on the FET. Some small amount might
be due to compressability of air in such tiny spaces. It's _possible_
some of it could be the result of group delay, but I'm willing to bet it's
really all distortion.


Yeah, me too. Especially if using the common source buffer
configuration they (Panasonics and the like) ship with. I'm sure I'm
not telling you anything you don't already know but FETs are terribly
non-linear in common source and in this application signals can easily
be large enough to cover a significant region of the gain curve.

SOME of the Earthworks mikes use standard 2-terminal Panasonic capsules,
and those mikes do sound gritty to me. Many of them (and I think pretty
much all the newer ones) use a three-terminal variant that allows external
biasing, and those sound less gritty.


It's not difficult to obtain source follower configuration using two
wire capsules (or to further enhance signal loop gain with something
more sophisticated than a resistor in the source leg.) I've got matched
TC30K's but the way they are constructed I've never been able to figure
out how to expose the capsule or get the electronics out to see if they
do this kind of thing or not.


Bob
--

"Things should be described as simply as possible, but no simpler."

A. Einstein
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