On Tue, 29 Sep 2015 02:32:16 -0700 (PDT), Phil Allison wrote:
snip
The standard way of calibrating mics in an anechoic room uses a
test speaker and a known flat response mic ( normally a small
diaphragm omni ) placed on axis and connected in a gain control
feedback loop with the amplifier as you described, BUT the test
signal is a slow swept sine tone. When set up and adjusted
correctly, the signal level from the reference mic is the same at all
frequencies - so it can be assumed the SPL at that spot remains the
same.
The mic to be calibrated is simply placed close to the reference mic
and its signal level recorded during a sweep, which gives its response.
If time is no object, one could do a large number of spot frequency
tests instead, noting the difference in level between the reference and
mic under calibration at each spot and plot a curve manually.
If 1/3 octave pink noise signals were available, they could be used
instead of sine tones, with the disadvantages of less precision and
unsteady levels at low and mid frequencies.
The Windows software from
http://www.artalabs.hr/ might help in such
a
case (it's originally for loudspeaker measurements). It can make
measurement based on a known response of a measurement mic, which
doesn't have to be flat if the deviations are documented. It uses a
variety of noise and sine signals. You don't need necessarily a dead
room, just a large one: it can use only the sound up to the first
reflection, at least in some cases.
Mat Nieuwenhoven