# SPL calibration issues (M-Audio mobile pre + ecm 8000)



## morik (Mar 15, 2011)

My setup:
- M-Audio mobile pre as soundcard
- mono line out from left channel going to RCA splitter going to L/R aux input of my AV
- XLR cord to left channel input from the ecm 8000
- the ecm 8000 is calibrated (by cross-spectrum), and I loaded the 0 degree narrow band calibration file
- radioshack analog SPL meter for calibration purposes

I did the sound card calibration (looked fine), did the sound level measurements, got everything set up well according to the directions (levels at -18.4 db fs)

When I do the sound level calibration, it seems fine (I got 77 db on my radioshack meter, and entered that)

However, now when I measure SPL with no sound on, I'm getting around 74-76 as a reading.

My radioshack meter reads 54 dbC by the mic.

If I mute the mic input via my OS control panel, the dbC reading in REW goes down to 60.7, and stays there.


I'm assuming this isn't normal?

Is there anything I can try to get this working? I had to turn up my volume knob on the mobile-pre quite a bit to get to the -18 dbFS (and boost mic gain to the max, +12). Might this be causing the issue I'm seeing?

EDIT: Hmm, I appear to be measuring with the wrong channel... when I check levels in the measure dialog, the left channel does show -18 dbfs, but the right channel shows -73. I'm then told levels are too low (-73). I guess I forgot to switch it while I was using it for the feedback loop 

A different question then:
My max SPL level that can be read is 95 dB because I had to pump my input sensitivity so high to get to the -18 dbfs level... so should I lower the input sensitivity a bit? (I think I read that -30 dbfs is an acceptable minimum?) I'd like to measure up to 105 at least... preferably 115. What is the downside?


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## mechman (Feb 8, 2007)

Sorry for the late response, but have you got this setup working yet? Sometimes posts do slip through the cracks. :doh:


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## morik (Mar 15, 2011)

Yeah I did, thanks for the response though!

(I ended up going to radioshack and getting a 1/4" to dual RCA plug, and using the mono out instead of stereo out. Everything is much better now)


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