room response exitation source

[Martin Czech]

How can one obtain a room response, or more general the transfer function
of an acoustic environment?

Balloons and starting pistols are easy to carry with, and usually have
loud enough output. Balloons may have considerable different pulse forms
from one explosion to the next.

I think that the basic characteristic of a room still comes out,
even if the impulse response is not deconvoluted (no, I know that!),
or statistically varied.

I think I get myself a new gun (starting pistol, also good for signal
ammunition).

Professional people use spark gaps, or speakers with noise sequences.

If such a noise sequence is generated in a digital fashion (famous shift
register), why use a linear amp?

 I could think of an bass speaker chassis (maybe also tweeter) with a
 switching power stage, i.e. a mosfet pair following the logic level of
 the shift register. All running from 12V battery (automotive type). Of
 course the dc bias has to be kept away from the speaker via caps.

Is there any problem with such an approach?

-no loudness control, always 100%
-perhaps higher frequencies cause coil trouble
-perhaps higher frequencies have inter modulation
-difficulties with recording the shift register output (alias)

You have to record the electronic shift register output, because
you need the reference signal for deconvolution (shift register frequency
and dat-recorder frequency will drift).


If this works, this would be a portable excitation source,
the thing that Magnus asked for...


Maybe I should write a letter to several of the church key keepers
arround here...

m.c.