# LAeq/LCeq over defined time span



## BrechtDM (Mar 18, 2011)

Hi, 

Can anyone recommend a way (preferably using REW) to measure the LAeq and LCeq over 15 minutes instantaneously and at all times? I suppose this is not possible with REW because that means it basically has to remember all the pressure levels of the past 15 minutes (whereas it just sums and rescales now for calculating the Leq). 
Since it's a pretty common measure, I would think it should be possible with some (cheap or free?) software though. 
Thank you very much in advance and best regards, 

Brecht


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## JohnM (Apr 11, 2006)

Easiest would be to open two instances of REW and set one meter to A weighted and the other to C.


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## BrechtDM (Mar 18, 2011)

Thanks, that would solve the problem of needing both A- and C-weighted Leq. 
However, my main concern is how to get a Leq over a certain time span, instead of the time that has passed since the start of the measurement (as is now the case in REW). This means that 45 minutes into the measurement, I would need a Leq from 0:30 to 0:45. 
I also need to log these values.


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## JohnM (Apr 11, 2006)

Couldn't you just work it out from the logged SPL values across the span? The REW SPL meter can log up to 24h of data which you can save to a text file and import to a spreadsheet for further processing. REW's data is generated from 8k FFT's with 2/3 overlap.


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## BrechtDM (Mar 18, 2011)

Sadly, for this particular application (due to very strict guidelines on noise) I would need instantaneous measurement, registration and display of LAeq,15min and LCeq,15min. So I think the SPL log file would only help me for the 'registration' part. 
Maybe it's simply not possible with this software (suggestions other applications - and even not insanely expensive hardware - are very welcome, or so I hope at a forum that's actually about REW - oops  )

Thank you for your help, John. Congrats on this great app.


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

Surely there’s a professional-grade SLM that can do this (or does that fall under the “insanely expensive hardware” designation)?

Regards,
Wayne


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