# Microphone Calibration Question



## rokus666 (Jul 17, 2008)

Hello, 

I have managed to go trough calibration procedure on my macbook pro, Radio Shack SPL digital meter and REW. 

The reading on REW DB meter is matching with my SPL meter.

NOw what do i do with it ?:dizzy:

I have Samson MM01 microphone runing trough MOTU 828 preamp into macbook pro's right built in input. 

Since I have read in REW instructions that flat mics do not need calibration, what would i do with this mic in terms of matching levels with REW ?
When I use the measurement mic with REW does C spec have to be unchecked ?
I have connected mic and I couldn't get enough level from it. Do i need to add some gain from mic preamp and feed it into line-in ? If yes what would be the proper way of matching levels with mic and line input ?

I am a bit confused. 
All I want to do is this for now:

* Being Able to put the measurement mic in the sweet spot, shoot some pink noise, Hit measure and get the reading of my frequency response so I can do proper acoustic treatment(bass traps, absorbers, diffusors,...)
*get the waterfall graph of low frequencies(40-250Hz) what test signal is used for this ?

Since I have calibrated the sound card in MacBook Pro, it looks flat, SPL is calibrated to C spec, and have a flat measurement mic, all I need is some help in order to get going and get that frequency response.

I have tried REW manual but soon after calibration of SPL meter, article jumps to hardware setup and other things, so I was uncertain what to do next.


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## brucek (Apr 11, 2006)

> Since I have read in REW instructions that flat mics do not need calibration, what would i do with this mic in terms of matching levels with REW ?


I suspect you've mis-interpreted what it said with regard to calibration. Every mic and SPL meter requires a calibration file - even flat ones. The reason is that even flat ones will fall off at low and high frequencies and require a file to compensate to make them truly flat. The same is true with SPL meters, except they require even more compensation to overcome the internal weighting filters they enjoy.

If you use a Samson MM01 microphone, you require a calibration file (no, the C-Weight box is not checked).

The Radio Shack meter would be fine to use as a mic for REW, except you'er generally limited to low frequency measurements, since it's not consistent enough in its accuracy for high frequency work.



> When I use the measurement mic with REW does C spec have to be unchecked ?
> I have connected mic and I couldn't get enough level from it. Do i need to add some gain from mic preamp and feed it into line-in ? If yes what would be the proper way of matching levels with mic and line input ?


If you had a cal file for the Samson, here is what you would do.
The Radio Shack meter is never connected to REW. Its only one time purpose (when you are using a microphone instead of an SPL meter for measurement), is during the Check Levels routine to set the 75dB at the listening position. After that it's put away. Once the 75dB is set, you adjust the output level of the mic preamp (combined with the input volume control of the line-in) to get a decent level at the input port to REW. Once the levels are set, you run the Calibrate SPL routine to match the REW internal SPL meter to ~75dB.

brucek


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## rokus666 (Jul 17, 2008)

Thank you for the clarification, this explains a lot. 
Actually, I have tried to find the calibration file for Samson MM01 and I couldn't find anything online. 
I also emailed the people in Samson, and they never responded. I'll just wait a day or two and then possibly return the microphone..


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## brucek (Apr 11, 2006)

The microphone that we recommend (because it's relatively inexpensive and we have the calibration file on our download page) is the Behringer ECM8000. Hard to beat for the price...

brucek


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