# REW as a class 1 SPL Meter



## supersonic (Aug 11, 2008)

Hello everyone,

After having done some research into professional, class 1, 1/3 octave SPL meters and realizing that their costs ranges anything from 2500€ to 8000€, I begun looking for alternative solutions. Here's my question. Could REW with a high quality sound card (MOTU Traveler), a good measurement mike and a SPL calibrator do as a good a job as a dedicated, stand alone unit?

Thank you very much for your insights


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## Sycraft (May 21, 2009)

Well... Maybe. It would, of course, not be certified as a class 1 SPL metre so if this is for official measurement, then it wouldn't work. Now if this is just for you then possibly. First thing is, as you said, the hardware backing it up has to be good. In particular, you need a good mic that is accurately calibrated. One thing to make sure of is that the mic is stable over a range of pressure levels. If it's response changes as volume goes up or down then it won't work unless you have multiple ocrrection curves and load them at the appropriate range.

There's also the issue of weighting both with regards to frequency and time. A real SPL metre will let you choose what frequency weighting you want. With REW you may have to build calibration curves to do that. Also I'm not sure how REW weights with respect to time.

More or less it comes down to what you want/need. If you are out to get something that can just give you some good analysis for your own use, then it'll probably work. Might have to spend a bit on a microphone, and maybe deal with multiple calibration curves, messing with gain settings and so on. If you have a need for an actual class 1 device for any reason, then no it isn't a substitute.


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## steely (Mar 17, 2008)

Hey Mate

What do you require Type 1 accuracy for?

It's certainly possible - although Room EQ Wizard probably isn't the best software for this task - it's awesome at doing what it is made for but not for what I think you have planned. 

Check out this site - fesb.hr/~mateljan/arta/
That program has some functionality towards what you're after - relatively low cost. There may be better though..

Apart from software (easy part) I think your main problem will be the hardware - preamp and mic + interface with pc so that it confoms to Type 1 spec. There are a few IEC standards (IEC defined what Class 1, Class 2 are etc) below that should help you:

For example a B&K 2250 siting here has this printed on the back:
Conforms to IEC61672-1:2002 Class 1
IEC 60804:200 Type 1
IEC 60651:1979 Type 1
IEC 61260:1995 1/1 & 1/3 Octave Class 0

Let us know what you want to use it for - and then we'll have a better idea of your setup requirements.


Andrew


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