# A question about dynamic and condenser microphones and maths

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Anonymous
June 29, 2005 8:48:14 PM

Hey. This might be a stupid question, but here goes.

A dynamic microphone's output, in voltage, is proportional to dx/dt (where x
is diaphragm displacement), right? And a condenser's output is proportional
to x, right?

So in theory (disregarding, for the moment, differences in capsules,
components, sensitivity, etc), if you differentiated the signal from a
condenser in terms of t, you'd get a dynamic-like signal, and if you
integrated the signal from a dynamic mic in terms of t, you'd get a
condenser-like signal, right?

In some applications, a condenser might sound better but a dynamic might be
more practical due to high SPL or the risk of damaging an expensive
condenser etc. Has anyone ever tried to design a plugin that could integrate
or differentiate a sound file's signal (numerically, obviously, not
analytically)? Maybe even in realtime?

Or am I just being stupid... and is this how mic/speaker simulators work?

I'd be interested to hear any thoughts.

--
tj hertz
Anonymous
June 29, 2005 8:48:15 PM

TJ Hertz <tjhertz@gmail-HOLDTHESPAM.com> wrote:
>Hey. This might be a stupid question, but here goes.
>
>A dynamic microphone's output, in voltage, is proportional to dx/dt (where x
>is diaphragm displacement), right? And a condenser's output is proportional
>to x, right?
>
>So in theory (disregarding, for the moment, differences in capsules,
>components, sensitivity, etc), if you differentiated the signal from a
>condenser in terms of t, you'd get a dynamic-like signal, and if you
>integrated the signal from a dynamic mic in terms of t, you'd get a
>condenser-like signal, right?

Yes.

>In some applications, a condenser might sound better but a dynamic might be
>more practical due to high SPL or the risk of damaging an expensive
>condenser etc. Has anyone ever tried to design a plugin that could integrate
>or differentiate a sound file's signal (numerically, obviously, not
>analytically)? Maybe even in realtime?

That's more or less what a high-pass filter does.
--scott

--
"C'est un Nagra. C'est suisse, et tres, tres precis."
Anonymous
June 29, 2005 8:48:15 PM

"TJ Hertz" <tjhertz@gmail-HOLDTHESPAM.com> wrote in message
news:ihAwe.78140\$Vj3.68395@fe2.news.blueyonder.co.uk
> Hey. This might be a stupid question, but here goes.
>
> A dynamic microphone's output, in voltage, is proportional
to
> dx/dt (where x is diaphragm displacement), right? And a
> condenser's output is proportional to x, right?
>
> So in theory (disregarding, for the moment, differences in
> capsules, components, sensitivity, etc), if you
differentiated
> the signal from a condenser in terms of t, you'd get a
> dynamic-like signal, and if you integrated the signal from
a
> dynamic mic in terms of t, you'd get a condenser-like
signal,
> right?

No.

If you differentiate a signal with some reference frequency
response characteristic, you'd get a signal with frequency
response that is rising at 6 dB/octave as compared to the
signal you differentiated.

But, in the real world both dynamic and condensor
microphones have nominally flat response.

IOW, there is *something* in a dynamic mic that causes a
level of integration that compensates for the
differentiation function you've noticed. I think that
*something* is the mass of the diaphragm and voice coil,
which is obviously far greater than the mass of the
fantastically thin diaphragms used with condensor mics.
Related resources
Anonymous
June 30, 2005 5:56:29 AM

On Wed, 29 Jun 2005 16:48:14 GMT, "TJ Hertz"
<tjhertz@gmail-HOLDTHESPAM.com> wrote:

>A dynamic microphone's output, in voltage, is proportional to dx/dt (where x
>is diaphragm displacement), right? And a condenser's output is proportional
>to x, right?
>
>So in theory (disregarding, for the moment, differences in capsules,
>components, sensitivity, etc), if you differentiated the signal from a
>condenser in terms of t, you'd get a dynamic-like signal, and if you
>integrated the signal from a dynamic mic in terms of t, you'd get a
>condenser-like signal, right?

Cool, so next you want to be thinking about pressure response vs.

Two frequency-invariant models arise. Quiz on Friday!

Chris Hornbeck
"Chief Assistant to the Assistant Chief" -F&S
Anonymous
June 30, 2005 1:20:38 PM

Arny Krueger <arnyk@hotpop.com> wrote:

No.
>
> If you differentiate a signal with some reference frequency
> response characteristic, you'd get a signal with frequency
> response that is rising at 6 dB/octave as compared to the
> signal you differentiated.
>
> But, in the real world both dynamic and condensor
> microphones have nominally flat response.
>
> IOW, there is *something* in a dynamic mic that causes a
> level of integration that compensates for the
> differentiation function you've noticed. I think that
> *something* is the mass of the diaphragm and voice coil,
> which is obviously far greater than the mass of the
> fantastically thin diaphragms used with condensor mics.

Or to put it another way, the (relatively massive) diaphragm + coil
system of a moving coil mic resonates, heavily damped, in the audio
band. It behaves as a resistance-controlled system.

The diaphragm of a condenser mic is much lighter and resonates on a mass
of entrapped air at a frequency well above audio. In the audio band it
is operating below resonance in compliance-controled mode, which is 90
degrees phase shifted from the resistance-controlled mode.

....That's where the compensating phase shift and consequent 6 dB/octave
slope comes from.

For a much more erudite description than that, try to get hold of a copy
of "Microphones" by A.E. Robertson. I believe it was published on both
sides of the 'pond'.

--
www.poppyrecords.co.uk
Anonymous
June 30, 2005 10:25:24 PM

> Or to put it another way, the (relatively massive) diaphragm + coil
> system of a moving coil mic resonates, heavily damped, in the audio
> band. It behaves as a resistance-controlled system.

Don't you mean mass-controlled?

Bob
--

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

A. Einstein
Anonymous
July 1, 2005 1:41:09 PM

Bob Cain <arcane@arcanemethods.com> wrote:

>
> > Or to put it another way, the (relatively massive) diaphragm + coil
> > system of a moving coil mic resonates, heavily damped, in the audio
> > band. It behaves as a resistance-controlled system.
>
> Don't you mean mass-controlled?

No, it also has a stiffish mounting, so the uncontrolled resonanace
would lie slap in the middle of the audio band - that's partly why they
were so popular, because the resonance made them sensitive and it could
be tuned and damped to cover the frequencies of interest.

The resistance control was by means of close-fitting air baffles (often
formed from the front of the magnet assembly) with restricted-flow air
vents. Modern moving coil mics also use all kinds of extra resonances,
damping and venting to flatten and extend the useful range. Of all the
mic types, they are the most difficult to get 'right' for high fidelity
because the technology is 'wrong' to start with - the manufacturers have
done a brilliant job to design them so well.

A mass-controlled mic, such as a ribbon, would have the resonance below
the frequency band of interest and there is a further 90 degrees of
phase shift.

(Before you say it, I know the mass of a ribbon is less than the
diaphragm and coil of a moving coil mic, but the suspension is *lot*
softer).

--
www.poppyrecords.co.uk
Anonymous
July 1, 2005 2:08:13 PM

Bob Cain <arcane@arcanemethods.com> wrote:

>
> > Or to put it another way, the (relatively massive) diaphragm + coil
> > system of a moving coil mic resonates, heavily damped, in the audio
> > band. It behaves as a resistance-controlled system.
>
> Don't you mean mass-controlled?

Sorry to follow-up twice but:

I didn't explain properly, the 'resistance' is air resistance, not
electrical resistance.

Electrical damping can also make a difference but it is only loosely
coupled to the diapharagm and has far less effect. Some moving coil
mics do need particular terminating resistor values if they are to
perform exactly as specified.

--
www.poppyrecords.co.uk
Anonymous
July 1, 2005 6:55:20 PM

"Bob Cain"
>
>
>> Or to put it another way, the (relatively massive) diaphragm + coil
>> system of a moving coil mic resonates, heavily damped, in the audio
>> band. It behaves as a resistance-controlled system.
>
> Don't you mean mass-controlled?

Bob 0.

.......... Phil
Anonymous
July 1, 2005 6:55:21 PM

Phil Allison wrote:
> "Bob Cain"
>
>>
>>
>>>Or to put it another way, the (relatively massive) diaphragm + coil
>>>system of a moving coil mic resonates, heavily damped, in the audio
>>>band. It behaves as a resistance-controlled system.
>>
>>Don't you mean mass-controlled?
>
>
>
>
>
> Bob 0.

What is the "heavy-damping" mechanism that makes a dynamic
mic resistance controled and not sensitive to its mass?

Bob
--

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

A. Einstein
Anonymous
July 1, 2005 9:37:10 PM

"Bob Cain"
> Phil Allison wrote:
>>
>>>
>>>
>>>>Or to put it another way, the (relatively massive) diaphragm + coil
>>>>system of a moving coil mic resonates, heavily damped, in the audio
>>>>band. It behaves as a resistance-controlled system.
>>>
>>>Don't you mean mass-controlled?
>>
>>
>>
>> Bob 0.
>
> What is the "heavy-damping" mechanism that makes a dynamic mic resistance
> controled and not sensitive to its mass?

** Got news for you Bob - a mic is not electrically driven.

............. Phil
Anonymous
July 2, 2005 7:18:38 AM

Phil Allison wrote:
> "Bob Cain"
>
>>What is the "heavy-damping" mechanism that makes a dynamic mic resistance
>>controled and not sensitive to its mass?
>
>
>
> ** Got news for you Bob - a mic is not electrically driven.

And that is relevant to my question how?

Bob
--

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

A. Einstein
July 3, 2005 4:27:44 AM

Bob Cain <arcane@arcanemethods.com> wrote in
news a2ouf02c2a@enews1.newsguy.com:

snip....snip

> What is the "heavy-damping" mechanism that makes a dynamic
> mic resistance controled and not sensitive to its mass?
> Bob

If you got off your high horse and did a little reading, you might learn
something and eventually dispel your long-standing reputation as being
someone whose arrogance is only matched by his technical ignorance.

The answer to your question can be found on page 262 of Harry Olson's
classic text "Acoustical Engineering" which was first published in 1957.
If you don't have a copy, perhaps you should get one. If you do have a
copy, perhaps you should give it a read, as it clearly isn't doing you any
good by simply collecting dust on your bookshelf.
Anonymous
July 3, 2005 9:37:52 AM

On Thu, 30 Jun 2005 18:25:24 -0700, Bob Cain
<arcane@arcanemethods.com> wrote:

>
>> Or to put it another way, the (relatively massive) diaphragm + coil
>> system of a moving coil mic resonates, heavily damped, in the audio
>> band. It behaves as a resistance-controlled system.
>
>Don't you mean mass-controlled?

the compromises necessary in conventional (voice coil plus diaphragm)
dynamic mics, and Bob is talking about loosely suspended pressure-
differential mics like classic ribbons.

The former has a resonance in the pass band that must be dealt
with as well as possible; the latter must try to push the
resonance below the pass band.

Both are dynamic mics. Both are resistance controlled and both
are mass controlled, just varying in emphasis. But y'all know
all this.

Chris Hornbeck
"You been good to me, Baby,
Better than I been to myself"
-Isley, Isley, Isley
Anonymous
July 3, 2005 12:42:31 PM

Here's a little but info-packed booklet from Neumann that contains most
mic types and nearly all the physics equations necessary to describe
their operation:

TJ, it sounds like what you're concentrating on is the dependence on
output of veleocity vs. position/displacement of the mic element. This
property of a microphone depends on several factors, and often one
predominates the other at certain areas of the frequency response
depending upon the mic design. Iirc, this booklet goes into that a
little bit.

Cheers,
Chris
Anonymous
July 3, 2005 1:42:30 PM

Chris Hornbeck <chrishornbeckremovethis@att.net> wrote:

> On Thu, 30 Jun 2005 18:25:24 -0700, Bob Cain
> <arcane@arcanemethods.com> wrote:
>
> >
> >> Or to put it another way, the (relatively massive) diaphragm + coil
> >> system of a moving coil mic resonates, heavily damped, in the audio
> >> band. It behaves as a resistance-controlled system.
> >
> >Don't you mean mass-controlled?
>
> the compromises necessary in conventional (voice coil plus diaphragm)
> dynamic mics, and Bob is talking about loosely suspended pressure-
> differential mics like classic ribbons.
>
> The former has a resonance in the pass band that must be dealt
> with as well as possible; the latter must try to push the
> resonance below the pass band.
>
> Both are dynamic mics. Both are resistance controlled and both
> are mass controlled, just varying in emphasis. But y'all know
> all this.

I wasn't brought up on the American terminology "dynamic", but had
assumed it only referred to moving coil mics (and speakers).

So as to keep my answer on absolutely safe ground, I slightly changed
the wording and referred to the mic I was talking about as "moving coil"
- althought I wasn't aware that the term "dynamic" might have had such a
wide application as to include ribbon mics.

I suppose, in a way, nearly all mics are 'dynamic' because something in
them has to move. Is it possible, without starting another flame war,
to ask what the American terminology is for *only* a moving coil mic -
and how broadly the term 'dynamic' can be used ?

--
www.poppyrecords.co.uk
Anonymous
July 3, 2005 4:38:36 PM

Chris Cavell wrote:
> Here's a little but info-packed booklet from Neumann that contains most
> mic types and nearly all the physics equations necessary to describe
> their operation:
>

Thanks, Chris. From page 26:

"Dynamic directional microphones, which respond to pressure
gradients or particle velocity and therefore are subject to
increasing forces as frequency rises (as shown in Fig. 3),
must be operated at the top of the downslope of their
resonance curve in order to yield a flat frequency response,
i.e. above their mechanical resonance frequency. This means
that they must be “low-tuned” and predominantly
mass-controlled in operation."

It was from memory of this principle that I questioned
"resistance-controlled" being an appropriate description of
a dynamic's operation. The quote and the figure 3 applies
to the gradient type which is by far the predominant dynamic
design and thus the default when I think about them.

Bob
--

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

A. Einstein
Anonymous
July 3, 2005 7:13:22 PM

On Sun, 3 Jul 2005 09:42:30 +0100, poppy.uk@ukonline.invalid.invalid

>I wasn't brought up on the American terminology "dynamic", but had
>assumed it only referred to moving coil mics (and speakers).
>
>So as to keep my answer on absolutely safe ground, I slightly changed
>the wording and referred to the mic I was talking about as "moving coil"
>- althought I wasn't aware that the term "dynamic" might have had such a
>wide application as to include ribbon mics.
>
>I suppose, in a way, nearly all mics are 'dynamic' because something in
>them has to move. Is it possible, without starting another flame war,
>to ask what the American terminology is for *only* a moving coil mic -
>and how broadly the term 'dynamic' can be used ?

The American use comes from "dynamo", and so includes, most broadly,
any motor with a conductor moving within a fixed magnetic field. But
many Americans would restrict use as you have, so there's no