Full range sweep - odd graph

1985 Views 7 Replies 4 Participants Last post by davidbrn, Feb 16, 2012

davidbrn

Discussion Starter · Feb 4, 2012

I've just been having a go at doing some full range sweeps, with a view to producing some convolver filters for use in J River. The graphs though look really odd - there's a 25db drop off from 7k to around 250. My speaker should roll off at around 55, so I can only assume I've done something wrong.

I'm measuring with a Behringer ECM8000 mic connected to a Behringer MIC100 valve pre-amp, and an M-Audio Audiophile 2496 soundcard. The sound card calibration looks 'normal' i.e similar to others on here, no mic calibration file.

Any suggestions?

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davidbrn

Discussion Starter · #3 · Feb 5, 2012

Thanks for the suggestions. Tried both, no appreciable difference. I've also tried my on-board sound card instead of the M-Audio, again, no difference. I'm going to get hold of another mic preamp to see if that makes a difference, and if not, another mic.

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davidbrn

Discussion Starter · #6 · Feb 5, 2012

Ah-ha!

I have the XLR output of the MIC100 connected to the RCA in of the sound card with an XLR-RCA adapter, which is what your describing. I'll report back when I've got a 1/4" - RCA adapter to use the preamps other output.

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davidbrn

Discussion Starter · #8 · Feb 16, 2012

Update on what I’ve found.

I ditched the XLR-RCA converter and got a mono ¼” plug to RCA socket converter. This was plugged into the MIC100 and then an RCA cable to the PC. Disappointingly the result was no different to the first graph.

I did note that using this method the “Gain” and “Output” dials on the MIC100 both had to be turned to their maximum setting to get a usable reading, which I suspect is not normal.

Next attempt was to swap the MIC100 for an ART Micromix, again using the ¼” plug to RCA socket converter. Instant success. I only did a quick uncalibrated test to see what the shape of the resulting graph would be, and it looks much like expected, with a largely flat response. The massive drop off has gone.

I think that either
a. There is an incompatibility somewhere with the MIC100, but I have no idea what it could be.
b. I have a faulty MIC100

Thanks for your suggestions, all I need now is to get the house to myself for a morning to do some proper measuring.

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