# How to read peak SPL on REW SPL meter?



## Saturn94 (Jun 8, 2013)

I was using the REW SPL meter to get a peak reading of a particular movie scene. I set the meter to C weighting and fast response.

I noticed it gave two peak readings; LCFmax and LZpeak.

What do these mean? Which one do I use?

Btw, the scene I was checking was the "Darla taps aquarium" in Finding Nemo. With my processor set to -3.5, I was getting these readings;

LCFmax 106.9
LZpeak 113.8

It was very loud and felt like the whole room was shaking.


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## JohnM (Apr 11, 2006)

LCFmax is the highest level seen in the C-weighted, Fast (125ms) filtered measurement.
LZpeak is the peak instantaneous value seen in the input with no weighting and no filtering.


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## Saturn94 (Jun 8, 2013)

JohnM said:


> LCFmax is the highest level seen in the C-weighted, Fast (125ms) filtered measurement.
> LZpeak is the peak instantaneous value seen in the input with no weighting and no filtering.


Thank you.

So in terms of how we hear, would the C weighting figure be the appropriate number to use? How about in determining the output capability of my sub?


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## JohnM (Apr 11, 2006)

Saturn94 said:


> So in terms of how we hear, would the C weighting figure be the appropriate number to use?


Better of selecting 'Z' weighting (i.e. no weighting) for a subwoofer as the C weighting curve rolls off below 31.5 Hz (see SPL meter help).



> How about in determining the output capability of my sub?


Output level is best assessed using the CEA-2010 methodology, which applies limits to harmonics in establishing the max level when using a special test signal. REW's signal generator (in the V5.01 beta version) can produce a CEA-2010 test signal, this can be used with the REW RTA, which should be set up with FFT Length 65536 if running at 44.1k or 48k, or 131072 if running at 88.2k or 96k, in all cases with Rectangular window - the generator has a checkbox to loop the burst to make testing and capturing the results easier. You would need to do some googling or buy the spec to get the details of how to do the test though.


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## Saturn94 (Jun 8, 2013)

JohnM said:


> Better of selecting 'Z' weighting (i.e. no weighting) for a subwoofer as the C weighting curve rolls off below 31.5 Hz (see SPL meter help).
> 
> Output level is best assessed using the CEA-2010 methodology, which applies limits to harmonics in establishing the max level when using a special test signal. REW's signal generator (in the V5.01 beta version) can produce a CEA-2010 test signal, this can be used with the REW RTA, which should be set up with FFT Length 65536 if running at 44.1k or 48k, or 131072 if running at 88.2k or 96k, in all cases with Rectangular window - the generator has a checkbox to loop the burst to make testing and capturing the results easier. You would need to do some googling or buy the spec to get the details of how to do the test though.


Thanks.


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## pdxrealtor (Jun 30, 2013)

JohnM said:


> Better of selecting 'Z' weighting (i.e. no weighting) for a subwoofer as the C weighting curve rolls off below 31.5 Hz (see SPL meter help).
> 
> Output level is best assessed using the CEA-2010 methodology, which applies limits to harmonics in establishing the max level when using a special test signal. REW's signal generator (in the V5.01 beta version) can produce a CEA-2010 test signal, this can be used with the REW RTA, which should be set up with FFT Length 65536 if running at 44.1k or 48k, or 131072 if running at 88.2k or 96k, in all cases with Rectangular window - the generator has a checkbox to loop the burst to make testing and capturing the results easier. You would need to do some googling or *buy the spec* to get the details of how to do the test though.


John, what do you mean 'buy the spec' ? Could you elaborate.


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## 3ll3d00d (Jun 6, 2006)

pdxrealtor said:


> John, what do you mean 'buy the spec' ? Could you elaborate.


Brent Butterworth has a good overview on his site - http://brentbutterworth.com/cea-2010-bass-output-measurement-manual/

The idea is you play the tones at specific frequencies (12.5, 16, 20, 25, 31.5, 40, 50, 63, 80, 100, 120, 125) & raise the level until harmonic distortion breaches a given limit (-10dB for 2nd harmonic, -15dB for 3rd, -20dB for 4th and 5th etc). To produce comparable numbers, there are a set of rules you have to follow for how the measurement is done but I don't think that really matters for just checking what is going on in your room.


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## JohnM (Apr 11, 2006)

Here is what buy the spec means: http://www.ce.org/Standards/Standard-Listings/R3-Audio-Systems/CEA-2010-(ANSI).aspx but you will probably find good enough info on the procedure through Google, such as Matt's link (which looks very useful).


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## pdxrealtor (Jun 30, 2013)

Thanks both. Interesting....

Matt- I'm working on tuning still, but when I'm done will give this a go using the information in the other thread too. Looks fun!


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