# 3 db too hot with SPL meter?



## PoorSignal (Jul 23, 2009)

Is it true when using Radio shack SPL meter if you set volume to 75db it is actually 78db?
So should I just set it to 72db instead. Or set the trim to -3db in the receiver settings?

What about when using a calibrated mic and REW, is the db displayed in the software accurate?


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## tesseract (Aug 9, 2010)

Thread moved, Jeremy, your question will get more exposure here. :T


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## stereo2.0 (Sep 25, 2009)

PoorSignal said:


> Is it true when using Radio shack SPL meter if you set volume to 75db it is actually 78db?
> So should I just set it to 72db instead. Or set the trim to -3db in the receiver settings?
> 
> What about when using a calibrated mic and REW, is the db displayed in the software accurate?


Even Radio Shack attempts to calibrate their SPL meters fairly accurately, so if you're reading 78dB on your meter when your receiver is set to 75dB, then that just means you're getting 3 extra dB of volume either because your speakers are a little more efficient or you're just located nearer to your speakers than what's needed to make it match perfectly. (I'm surprised the readings are that close to begin with!)

Sure you can adjust your trim to -3dB to make it match up. It's a cool and easy way to know how loud you're playing back a movie. (Music from CD's, mp3, etc, won't be calibrated though, they don't adhere to any standards)

Even if you get a calibrated mic, the SPL meter on REW won't be correct until you adjust your computers soundcard levels to get the bargraph readings close, and then you have to click the calibrate button to make it exact. (Read the help instructions to get the details:T)


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## PoorSignal (Jul 23, 2009)

Sorry, the post get moved, and the context was loss
I was only referring to the subwoofer test tone.
Because in the SVS manual it also asks you to trim the receiver sub out to -3db first and then calibrate all speakers and sub to 75db


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## stereo2.0 (Sep 25, 2009)

PoorSignal said:


> Sorry, the post get moved, and the context was loss
> I was only referring to the subwoofer test tone.
> Because in the SVS manual it also asks you to trim the receiver sub out to -3db first and then calibrate all speakers and sub to 75db


Sorry, I can't figure out why SVS would want you to trim the sub out to -3dB before calibrating.

Do they ask you to raise it back up to 0dB after calibrating? That would give you some kind of house curve to help compensate for the ears reduced sensitivity to low frequencies.

If they expect you to keep it at -3dB then maybe they're worried about clipping and want to provide some headroom. I don't know - seems odd. Does the manual provide any explanation of why it's necessary?


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## tesseract (Aug 9, 2010)

PoorSignal said:


> Sorry, the post get moved, and the context was loss
> I was only referring to the subwoofer test tone.
> Because in the SVS manual it also asks you to trim the receiver sub out to -3db first and then calibrate all speakers and sub to 75db


You asked for help with the meter and the SPL/Mic's/Calibration/Sound Cards is the best place to get that. Sorry for the confusion.

Did you ask SVS? We have an SVS forum here, too. :T

http://www.hometheatershack.com/forums/svsound/


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