[Scott Dorsey]

Jerry Steiger wrote:
"Scott Dorsey" wrote in message

If people are using the thing from three feet away, you need to be able to
measure response with a sound source three feet away. Because it may be
very different than the response up close, especially if you are using a
directional microphone.

Yes, I was thinking that I would just measure the microphone and speaker
response from three feet ( or a meter, since that is the "standard" distance
for measuring sensitivity), knowing that the response would only be better
at closer distances. Perhaps I should consider doing multiple tests to cover
more of the usage scenarios.

It may not actually be better at closer distances.

If you're going to do it from three feet away, buy one of the Tannoy dual
concentric loudspeakers and try it. You can buy one of the nicer Series 600
monitors for good money, or buy a used i6 for cheap, and they will probably
do what you want. The nice thing about these speakers is that they are as
close to constant directivity as you can get, and the pattern is the same
in all directions; it has radial symmetry.

Do the measurement outside, in an open field, high off the ground on
a ladder if possible. You will be able to do good measurements at lower
frequencies more effectivity in an open field than with a small chamber.
Even voice frequencies.

My guess is that under typical surveying environment, at three feet away
from the mike the environmental noise problem is going to be severe. And
anything you do to make the mike more directional is going to make wind
noise problems worse.

I hadn't thought about the interaction of wind noise and directionality in
the microphone. I was thinking that a directional microphone would be better
since the user is almost always in front of the unit and the noise is liable
to be coming from any direction. Just mounting the microphone in the unit
compromises its omnidirectionality by some amount. How much effect does
directionality have on wind noise pickup?

It is a substantial difference. A pressure microphone will be much less
sensitive to wind noise than a cardioid. And yes, mounting the pressure
mike in a housing means the pattern will be altered and you'll have issues
with wind noise on the housing too.

Incidentally, let me commend the Gentex omni capsules to you. They are
very resistant to rain and mud. They also sell noise-cancelling mikes
for close-talking use, but that does not sound useful to you.

Great! I hadn't run across them. An inherently waterproof microphone is a
distinct advantage. (I actually used Panasonic capsules that were exposed on
the front side in the first product we made, since they seemed to survive
our dunk testing without any problems, but we got nervous about their
long-term health and sealed them from water in later products.)

The Panasonics are interesting because they have a Helmholtz resonator in
front of the diaphragm, with a very small entrance hole. Because the hole
is so small, it's hard for water to get into it. Soapy water, though, will
penetrate it very easily.
--scott
--
"C'est un Nagra. C'est suisse, et tres, tres precis."