Official Luthiers Forum!

Anyone ever used a Sound level Meter to give non subjective volume comparisons between instruments?
What sort of setup did you use?

Yep. I use SPL, an application on my iPhone. It works great, and it's very inexpensive!!

Cheers,
Dave F.

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Cambrian Guitars

"There goes Mister Tic-Tac out the back with some bric-brac from the knick-knack rack"

I use one a lot; an old RadShack analog meter. It's got an output jack for the mic signal, and you can feed it into your computer, or take readings from a remote location using a DVM, and then translate those into dB, or you can take the readings directly from the meter, of course.

I've just been involved with another 'sound port' experiment, trying to figure out why I get different results than another experimenter did. I'm still not sure, but I've narrowed down the possibilites.

Meanwhile, there's a lot of really interesting stuff hidden in the data. I drove the guitar with a constant current (constant force) through a voice coil clamped to the bridge saddle. The whole thing was set up on a turntable in an 'anechoic closet' that I rigged up, and I looked at the output from eight different directions all around the guitar, which was hanging from the headstock. I checked the output every five Hz from 70-350 Hz, with three different configurations of soundholes.

One of the most interesting things I see in the data is how directional the guitar can be, even at these low frequencies. I always knew it would radiate sound in different directions at high frequencies, but even around 200 Hz it can be sending most of it's power off in one direction or another. What's even coler is that the direction can change suddenly: in one setup thre was a 20dB difference in the strength of the signal off to the sides with a frequency change of only 5Hz.

The easiest, and possibly most productive, such test is the 'impulse spectrum'. You tap on the bridge with a light, hard 'hammer' and record the output somewhere out in front of the guitar. If you do the test the same way every time (EXACTLY the same way!) you can compare the results, even if you don't have an anechoic chamber. You don't need a dB meter to do this; most of the small electret capsules are quite 'flat' in response up to 6kHz or so, I'm told. However, using the meter allows you to get calibrated, so you can figure out, for example, which guitar is the most efficient.

!!!WARNING!!!
This stuff is arguably even more addictive than guitar making, if you're at all technically inclined.