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Determining sound direction


I've been playing a bit more with datalogging (check out the fantastic tips from Brian in the forums) and I've always wanted a robot that could come to me when I called it. The sound sensor is great for 'detecting' sound but no good for deciding where the sound came from. One way to figure out where the sound is coming from is to use 2 sound sensors.

So I built myself a little NXT head that had 2 sound sensors and a bit of foam in between.

"Sure it's pretty" I hear you say, but whats that foam in between the ears for?

Well I figure that if I had 2 ears, with some sort of dampening material in between, the ears would hear the same sound source, but at different volume levels.

ie. If I clapped my hands very loudly on the left hand side, then the left 'ear' would hear a certain volume and the right 'ear' would also register a sound, but at a much quieter level.

So I set up my head and start writing sound readings from both the left and right ears to a text file as fast as I can. I'm not too concerned with the sampling rate, as I'm more interested in the difference in sound levels for the same 'clap'

I take the results and put them through Excel where I subtract the value of the right ear from the value of the left ear to give me a difference.

Now if the clap happens directly in front (or behind) my NXT head, then the sound levels will be the same and the difference will be 0. But if I clap off to the left hand side, then the left reading will be higher than the right reading and my difference will be a positive number. If I clap on the right hand side then I'll get a negative number.

This graph shows the difference between the left and right ears with 3 test claps, once on the left, once in the center and once on the right.


From this I can see anything under -40 is a definite clap on the left and anything over +40 is a clap on the right.

So now I can write a program that takes the two sound sensor readings and subtracts one from the other. If the result is more negative than -40, I turn clockwise a small amount. If it is greater than 40, I mover counter-clockwise for a small amount.

I think with more sound dampening, I could probably get it to respond a little more accurately.

--
Damien Kee

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