Raimund Specht wrote:
> Walt,
>
> I'm afraid, that you can not compare the ability of small diaphragm
> microphones to pick-up low frequencies with the physical effects,
> that occur in a parabola. A small diaphragm microphone detects the
> variations of air pressure only (it does not need to reflect
> sounds). The size of the diaphragm has no impact on the lower cut-
> off frequency (only on the sensitivity and on the upper corner
> frequency, that is caused by undesired reflections of higher
> frequencies). In contrast to such a pressure detector, a parabola
> relies on the reflection of sound waves, which heavily depends on
> the size of the reflector. This would be the theory.
> However, there might be also other physical effects which lead to
> some additional gain at lower frequecies, as you have experienced.
> Perhaps, the air pressure field is influenced in some way.
Take your thinking one layer deeper.
What is pressure? What is reflection? On the level of molecules of air.
Which are what transports sound.
Pressure is the combined impact force of the air molecules.
Reflection is the air molecules bouncing back off after impact.
Reflection and pressure are directly related to the same thing. We are
not dealing with waves, but particles.
Finally, sound in air does not occur as transverse waves as you are
clearly thinking. It occurs as longitudinal waves. What are those?
Molecules of air moving back and forth along the axis of the sound
travel. They will impact on anything their size or larger that's in
their path.
The only real difference between the microphone diaphragm and a perfect
reflector is that the diaphragm absorbs energy to move it. A perfect
reflector returns all the energy. I'm sure that any real world parabolic
reflector only approaches a perfect reflector.
Don't believe me? Go read some of the accounts of designing microphones.
You will find quite a few comments on controlling reflections from the
parts of the microphone. All of which are smaller than the wavelengths
involved. If there are reflections there, they are no different from
those from the parabolic reflector. Or take a look at a PZM boundary
microphone, where only reflected sound reaches the mic. The boundaries
are much smaller than the wavelengths involved.
And, yes I do know the next level too, at the atomic level there is no
such thing as simple impact. Nothing ever really touches.
Walt
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