# Is an SPL meter required?



## ghova (May 5, 2011)

I am new to REW and this is my first post.

I have a Crown GLM-100E Miniature Omnidirectional Microphone, and a Turtle Beach Audio Advantage SRM USB sound dongle. Are these sufficient for room equalization, or is an SPL meter required? To what extent is REW self calibrating?

I am a software engineer, a Java programmer. and a hardware engineer with a good general knowledge of analog and digital electronics, though not of digital signal processing. Please provide technical details if appropriate.

Thanks
Ghova


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## JohnM (Apr 11, 2006)

You don't have to have an SPL meter, it is used to give REW a reference level so it knows what SPL figures to show on the graph axis for a given input signal level from the soundcard. You can simply guess an acoustic level in the SPL calibration stage, i.e. adjust the level so it is not too loud and tell REW that is 75dB (say). The only effect is on the position of the graph on the y axis, the shape is not affected.


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## Wayne A. Pflughaupt (Apr 13, 2006)

But keep in mind that if you don’t have a calibration file for your Crown mic, your x axis won’t be accurate. So any equalization you attempt will be based on a flawed measurement.

Regards,
Wayne


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## ghova (May 5, 2011)

Hi Wayne,
Thanks for the advice. Re microphone calibration, I think I understand how to produce a .CAL file for the Crown mic, and that it is a relative, not an absolute calibration.  The data sheet with the crown shows it to be ruler flat from 40 Hz to 7 kHz, falling off 5 db at 20 Hz, having a 2 db peak at 13 kHz, and falling off 3 db at 20 kHz. This could be an idealization or average response, but I'm inclined to believe it -- the mic is a very small electret design and should be relatively free of diffraction effects. I'll mount it on a thin boom.

I'll try getting by without buying an SPL meter per your post. My plan is to use the eq with a miniDSP board, and insert it in the mag tape loop of my Denon stereo amp.
Regards,
George


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