# Simple Speaker Calibration - REW & miniDSP UMIK-1



## KarlJohns (Jan 26, 2016)

Hello,

I'm trying to calibrate my simple stereo speaker setup so I can use this setup with Pro Tools for small post-production audio jobs.

I have a smaller room so I want to calibrate the speakers to 78 dB.

I received my miniDSP UMIK-1 mic from Cross Spectrum, which currently I want to use as a SPL meter via REW.

I have a few questions:

(1) I got the sensitivity data from the miniDSP website and I pasted the data into the cal files from Cross Spectrum. Am I correct in assuming the sensitivity data needs to be on the *first line* in the cross spectrum cal files to be used within REW correctly ? Or does it not matter where in the file it is pasted ?

(2) Where should I point the mic to when taking a SPL reading ? directly at the speaker that is being measured or should I point the mic straight ahead in-between both speakers, basically having the speakers at 45 degrees to the mic ? I keep reading different statements about this...

(3) Am I correct in assuming that using the 0 degree cal file from Cross Spectrum should *only* be used when pointing the mic directly at the speaker ? If pointing the mic straight ahead in-between both speakers, should I use the 45 degree cal file ?

(4) when using the mic as a SPL meter using the REW SPL tool, will it function like a standalone SPL meter when using the C weighting function ? Or do we need to use the Z weighting as this is a mic that emulates a SPL meter ? I saw tutorials where Z weighting was used for SPL measuring when *using a mic*, but the general tutorial for speaker calibration with a real SPL meter uses C weighting... 

I just wanna make sure that there are no "special rules" when using a calibrated mic with sensitivity data as a SPL meter inside REW...

Thanks.


----------



## JohnM (Apr 11, 2006)

Put the cal sensitivity figure on the first line of the file.

Use a 0 degree file when pointing directly at the speaker or a 90 degree file when pointing vertically.

Whether you use A, C or Z weighting has nothing to do with the mic, it depends what you are trying to measure. Noise measurements often use A weighting, speaker levels for home theater are usually C weighted measurements. Z weighting (i.e. no weighting) gives an indication of the full spectrum levels, but can be heavily influenced by low frequency noise.


----------



## KarlJohns (Jan 26, 2016)

JohnM said:


> Put the cal sensitivity figure on the first line of the file.
> 
> Use a 0 degree file when pointing directly at the speaker or a 90 degree file when pointing vertically.
> 
> Whether you use A, C or Z weighting has nothing to do with the mic, it depends what you are trying to measure. Noise measurements often use A weighting, speaker levels for home theater are usually C weighted measurements. Z weighting (i.e. no weighting) gives an indication of the full spectrum levels, but can be heavily influenced by low frequency noise.


Hi John, thank you for clarifying.

So what is the 45 deg cal file for ?

Also, would you recommend pointing the mic directly at the speaker when calibrating to a specific dBSPL output ?

Thanks.


----------



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

I don’t know of anything that the 45°file is used for. 



KarlJohns said:


> (2) Where should I point the mic to when taking a SPL reading ? directly at the speaker that is being measured or should I point the mic straight ahead in-between both speakers, basically having the speakers at 45 degrees to the mic ? I keep reading different statements about this...


For a simple SPL measurement, it won’t matter much which way you point the mic with C or Z weighting, as the lower frequencies a speaker generates are “hotter” than the high frequencies, and the mic is truly omnidirectional below 1 kHz or so. However, if using A weighting, pointing at the speaker would probably be best.

That said, for calibrating speaker levels for a full surround sound system, typically C weighing is used. You may find it’s easiest to simply point the mic at the ceiling from a central location (typically the main listening position). That might not get the most accurate reading from an absolute standpoint, but calibrating speaker levels is more about _relative_ level between the speakers.


> (3) Am I correct in assuming that using the 0 degree cal file from Cross Spectrum should *only* be used when pointing the mic directly at the speaker ? If pointing the mic straight ahead in-between both speakers, should I use the 45 degree cal file ?


The calibration files are primarily useful for taking frequency response measurements, not so much for SPL. 



> (4) when using the mic as a SPL meter using the REW SPL tool, will it function like a standalone SPL meter when using the C weighting function ? Or do we need to use the Z weighting as this is a mic that emulates a SPL meter ? I saw tutorials where Z weighting was used for SPL measuring when *using a mic*, but the general tutorial for speaker calibration with a real SPL meter uses C weighting...


John basically covered this, but to add a bit more – a standalone SPL meter contains a built-in mic of its own. Using the a mic with REW accomplishes the same thing as a stand-alone meter, and it also functions the exact same way. So as John said, the weighing selected depends only on what you want to accomplish with or need the measurement for.

For instance, noise readings for jobsite safety (e.g. OSHA regulations) will use A-weighting, as it excludes bass and encompasses only the upper frequencies which can damage hearing. In this situation, any audible low frequencies present may needlessly push the figure higher if C-weighting were used.

However, readings for municipal noise ordinances will probably use C weighing that include bass frequencies, which you would want to be included for noise emanating from a night club or drive-by car stereo.

Hope this helps.

Regards,
Wayne


----------



## KarlJohns (Jan 26, 2016)

Wayne, thank you. Very helpful.


----------

