Re: How would you calibrate a sound level meter RESTATING THE PROBLEM

From: Walter Harley (walterh_at_cafewalterNOSPAM.com)
Date: 08/25/04 

Date: 25 Aug 2004 21:56:04 GMT

"Norm Dresner" <ndrez@att.net> wrote in message
news:PW6Xc.516007$Gx4.297540@bgtnsc04-news.ops.worldnet.att.net...
> [...]
> But perhaps I simply gave a bad application of a perfectly good instrument
> so let me try again. I have several speakers of differing
> acoustic-electrical efficiency by which I mean that in a free-field
> environment the acoustic energy output per unit of electrical energy input
> differs -- the usual measurements come from the factory in the form of dB
> SPL re 1 meter per 1 watt input but those details are unimportant. What
> is
> important is that I have several speakers, each with a restricted
> frequency
> range, which I want to use to create an array with flat response, i.e. the
> acoustic energy output per unit electrical energy input is approximately
> constant across the relevant bandwidth. This is usually done with
> cross-over networks which are in reality nothing but electical bandpass
> filters. But in terms of matching the acoustic energy from the various
> speakers I also need to attenuate the response of some of them relative to
> the others. In general, tweeters are much more energy efficient than
> woofers, sometimes as much as a decade in power. To do the matching I
> want
> to be able to measure the acoustic energy out of each speaker as a
> function
> of its electrical input. SO ...
> How would one go about calibrating a sound-level meter?

I still don't understand why you need absolute calibration. Seems to me all
that matters is that you get them all equal; for that all you need is a flat
mic and flat electronics (and a free-field testing environment).

But if you insist: there are devices you can buy, for under $100, that
produce reference sound levels (inside a sealed cylinder sized to fit the
reference mic). Check audio gear suppliers, like Musician's Friend,
Sweetwater, etc.; or, I'm sure I saw one in the latest MCM catalog. They're
called "microphone calibrators".

Frankly I'll be awfully surprised if this approach actually leads to a
speaker system with flat frequency response in your listening environment.
Seems to me it would be much more productive to use the spectrum analyzer
approach already suggested, with pink noise. I don't see how you can
meaningfully test the speaker response out of the enclosure and sans
electronics, because those things interact. But I suppose it wouldn't be
the first time I've been awfully surprised.

Relevant Pages