Jay Kadis wrote:

In article ,
Logan Shaw wrote:

Physics seems to tell me that pressure will be proportional to force,
and force is what accelerates the diaphgram. Therefore, shouldn't
the pressure and the diaphgram's instantaneous acceleration be
proportional? If so, then the diaphragm's velocity is the
integral of the pressure over time.

You seem to be ignoring the restoring force, since the diaphragm is restrained
and not free to move in response to the pressure exerted.

Hmm, I am starting to learn that all this stuff is way more complicated
than I thought it was. Thought I understood it, but apparently only in
a very shallow sense.

How big is the restoring force compared to the force due to pressure?
I'm assuming significantly smaller, so that ignoring it can still give
you a workable first-order approximation. Or is that not true?

- Logan

On Fri, 18 Jun 2004 16:49:08 GMT, Logan Shaw
wrote:

How big is the restoring force compared to the force due to pressure?
I'm assuming significantly smaller, so that ignoring it can still give
you a workable first-order approximation. Or is that not true?

There are two useful choices for the mass/ compliance resonance,
above and below the passband. The usual choice for open (pressure-
differential sensitive) microphones is below passband and the usual
choice for closed (pressure sensitive) microphones is above
passband.

Chris Hornbeck

On Fri, 18 Jun 2004 17:09:56 GMT, Chris Hornbeck
wrote:

There are two useful choices for the mass/ compliance resonance,
above and below the passband. The usual choice for open (pressure-
differential sensitive) microphones is below passband and the usual
choice for closed (pressure sensitive) microphones is above
passband.

This is so poorly worded that I can't let it drop. Imagine a
loudspeaker woofer in a sealed box and driven by a constant
RMS voltage at all frequencies.

If we measure its sound pressure output, we see it rise at
12 dB/ octave from very low frequencies up to its resonant
frequency, where pressure response levels off to flat.

If we measure its diaphragm excursion, we see that it's flat
from low frequencies up to resonance, then it falls at 12 dB/
octave.

There are two components to the diaphragm excursion. The
diaphragm's velocity increases at 6 dB/ octave up to resonance,
then decreases at 6 dB/ octave above resonance. And
wavelength, which falls continuously at 6 dB/ octave.

Microphones are also four terminal devices designed to
translate voltage and pressure. All the same rules apply.
To make non-equalized microphones with flat pressure input vs.
voltage output some strategies emerge:

If our electrical generating mechanism has a flat relation of
excursion to voltage, we simply operate below resonance.

If our generator is velocity sensitive, then our output will
rise at 6 dB/ octave below resonance and fall at 6 dB/ octave
above resonance. Above resonance this is useful with open
diaphragms ("pressure-gradient microphones") whose diaphragm
excursion increases at 6 dB/ octave in their major working
frequency range.

Now I promise the shut the heck up.

Chris Hornbeck

In article ,
Logan Shaw wrote:

Jay Kadis wrote:

In article ,
Logan Shaw wrote:

Physics seems to tell me that pressure will be proportional to force,
and force is what accelerates the diaphgram. Therefore, shouldn't
the pressure and the diaphgram's instantaneous acceleration be
proportional? If so, then the diaphragm's velocity is the
integral of the pressure over time.

You seem to be ignoring the restoring force, since the diaphragm is
restrained
and not free to move in response to the pressure exerted.

Hmm, I am starting to learn that all this stuff is way more complicated
than I thought it was. Thought I understood it, but apparently only in
a very shallow sense.

How big is the restoring force compared to the force due to pressure?
I'm assuming significantly smaller, so that ignoring it can still give
you a workable first-order approximation. Or is that not true?

- Logan


It is the sum of all forces resisting the movement of the diaphragm: it would
depend on the tension applied to the diaphragm in the case of a condensor
element and the stiffness of the suspension for a dynamic element. In the case
of the condensor element, displacement is very small whereas with a dynamic
element, there is more significant movement. This would imply that the
restoring force is large for a condensor element and smaller for a dynamic
transducer.

-Jay
--
x------- Jay Kadis ------- x---- Jay's Attic Studio ------x
x Lecturer, Audio Engineer x Dexter Records x
x CCRMA, Stanford University x http://www.offbeats.com/ x
x-------- http://ccrma-www.stanford.edu/~jay/ ----------x