# SPL reference level



## dougsmith (Aug 21, 2008)

Is there easy way to establish an SPL reference level for a setup with an ECM8000 mic, M-Audio USB sound card and Acoustisoft measurement software that would obviate the need for a separate SPL meter?


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## lsiberian (Mar 24, 2009)

dougsmith said:


> Is there easy way to establish an SPL reference level for a setup with an ECM8000 mic, M-Audio USB sound card and Acoustisoft measurement software that would obviate the need for a separate SPL meter?


Well generally a 3khz measurement is used for reference measurement.


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## glaufman (Nov 25, 2007)

Without having a calibrated reference to compare to, such as the separate SPL meter, there's no way to calibrate the SPLs. That being said, to many people, the exact SPL doesn't matter nearly as much as the comparison between SPLs at different frequencies, such that playing around until you get reasonable readings and making reasonable scans is all that's needed.
I'm not familiar with the Acoustisoft software.
Also, the EMC8000 mics show a few db variation between individual units at 3kHz, whereas they all seem to hit almost exactly with each other at 1kHz, so without a custom cal file, if you just want a reference, you may do better at 1kHz.


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## dougsmith (Aug 21, 2008)

Ok; thanks... I didn't think so. The RplusD software is quite good, but the free stuff available now (REW or Holm Impulse) probably works just as well. I got my system optimized nicely, but I may just go out and get a Radio Shack meter so I can tell how loud it is really playing at various settings. It doesn't really seem worth it to me to get my mic calibrated, because I am only doing critical measurements and applying filters below 200 Hz to smooth out the modal region (and applying the ECM generic correction file doesn't have much impact there). 

- Doug


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## Doug Plumb (Mar 16, 2007)

dougsmith said:


> Ok; thanks... I didn't think so. The RplusD software is quite good, but the free stuff available now (REW or Holm Impulse) probably works just as well. I got my system optimized nicely, but I may just go out and get a Radio Shack meter so I can tell how loud it is really playing at various settings. It doesn't really seem worth it to me to get my mic calibrated, because I am only doing critical measurements and applying filters below 200 Hz to smooth out the modal region (and applying the ECM generic correction file doesn't have much impact there).
> 
> - Doug


Its a better idea to measure SPL with noise than it is to use pure sine, pure sine calibration has to be done under careful conditions. RPlusD uses noise that can be band filtered to read SPL. You can use any noise source, you can make a noise CD from RPlusD.

The only thing that matters is relative SPL, SPL is NOT loudness and the fact that it is measured in dB shows this (Loudness is measured in "phons")


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## tonyvdb (Sep 5, 2007)

Generally narrow band pink noise is used to achieve reference level settings, I personally like using full band pink noise and set it to 75db with the sub at 85db.


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## glaufman (Nov 25, 2007)

And REW's generator allows basically full customization of the pink noise band with a low cut and high cut.


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## glaufman (Nov 25, 2007)

Also, despite the generic cal file not showing much effect in the low end, look at the graph comparing different serial numbers and the variation they show under 200Hz. the only path to true accuracy is a custom cal file.


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## dougsmith (Aug 21, 2008)

Thanks for the feedback. I did get the RS meter, so now I can tell if I am likely to be damaging my ears when I turn it up at least (no worries, the average reading is rarely more than 85 db). So what is the recommended SPL level to take measurements at? The R+D manual recommends "normal conversation" levels... I would interpret that to be around 65 db.

-Doug


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## tonyvdb (Sep 5, 2007)

You should take them at 75db


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## Doug Plumb (Mar 16, 2007)

Use the hybrid signal and play it at a comfortable level. Your s/n ratio on the graphic should be above 15 - 20 dB.


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## dougsmith (Aug 21, 2008)

Thanks. That's where I had it without checking the reference level. I was just wondering if there was a more specific recommendation.


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## Doug Plumb (Mar 16, 2007)

Its not really that important. What is important is your hearing and you may do damage to it if you play it too loud.

The quality of the measurement is as good as it gets for practical purposes if your S/N graph is above 20 dB over your range of interest.


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