Do-it-yourself measurement of reverberation time RT60 · 12.02.10
One basic parameter describing room acoustics is the reverberation time. The RT60 is defined as the time elapsed when the acoustic signal vanishes 60 dB below the direct sound after the sound source has been turned off.
Goofing around, I measured the sound of clapping hands with laptop microphone and wrote a Matlab program to automatically determine the RT60 for each clap. So just record a dozen hand claps, read the wav into Matlab signal and off you go:
s = wavread('clappinghands.wav');
rt60(s, 44100);
A living room nearby measures
Analyzed 12 sounds, mean RT60 = 0.773016 +/- 0.100988, median RT60 = 0.765757
while a bedroom
Analyzed 26 sounds, mean RT60 = 0.301507 +/- 0.017670, median RT60 = 0.300696
Have to concentrate on more consistent hand claps in the living room measurement the next time. Stay tuned for the inverse problem of determining the absorption coefficients of the surfaces in the room…
Update May 15th 2010: RT60 measurement app for Macs
— ajv
:D
It seems that you have too much time on your hands.
Anyway, looking forward for detailed description of the solution to this inverse problem :)
— weksu · Feb 13, 01:14 PM · #
This is the kind of code I do before breakfast using left hand only; I would not call myself as someone having too much time right now :)
I just got a call from a acoustics expert saying that 0.3 s reverberation time is a typical for a well designed room, so maybe there is a systematic error somewhere. On the other hand, that statement is not in line with Sabine’s equation if you think of quite small room with ceiling and walls covered with a thin layer of absorbent. Say, 15 square meters, 2.5 m high, wooden floor and 20-30 mm wool on walls and ceiling is only 0.17 s on 500 Hz. Something else on subwoofer frequencies though.
In the first place I’m interested in having the reverberation down on the voice freq 300-3500 Hz.
— ajv · Feb 14, 01:01 PM · #