Cross-Spectrum Microphone Calibration Service - USA - Page 18 - Home Theater Forum and Systems - HomeTheaterShack.com

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post #171 of 366 Old 04-28-12, 08:37 AM
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Re: Cross-Spectrum Microphone Calibration Service - USA

Quote:
Anechoic wrote: View Post
There are two issues with calibrating the omnimic microphone:
  1. 2
  2. The version I saw last year only worked with the Omnimic software. I've heard rumors that has changed with recent versions and that now the Omnimic shows up as a USB audio device - if that's true, than I can use it with my rig, otherwise I can't measure it (at least not easilly)
  3. The diameter of the Omnimic mic I played with wasn't a standard diameter (I don't understand why mics manufacturers do this, the industry has standardized on 1/4", 3/8", 1/2", and 1" for decades now), which makes it harder for me to use in my low-frequency jig.

Assuming the mic does show up as a USB audio device, if someone wants to send one to me, I'll check it out.
Tell me where I should measure for the diameter of the mic. If its one of the standardize ones you listed, I'd be interested in sending it in for testing. It is the more recent version of the mic, not the original one.
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post #172 of 366 Old 05-25-12, 12:48 AM
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Re: Cross-Spectrum Microphone Calibration Service - USA

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JimP wrote: View Post
Tell me where I should measure for the diameter of the mic. If its one of the standardize ones you listed, I'd be interested in sending it in for testing. It is the more recent version of the mic, not the original one.
At the "business end" of the mic, at the capsule (it's just over 1/4-inch IIRC).
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post #173 of 366 Old 05-25-12, 10:23 PM
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I must be doing something wrong

Hi Herb,

I am a recent owner of a calibrated Galaxy meter (verified +).


How reliable is calibration at the extremes supposed to be, specifically in the sub-10Hz region?

The reason I am asking is that results I am getting do not look realistic at all.

As you can see in the attached REW measurement snapshot I am getting 30dB jump from 70db at 15Hz to almost 100dB at 5Hz. Is it even theoretically possible?


The calibration file I amusing with REW is called "one_third_octave_band_response_random-incidence_C-wtd.frd". Is this correct file to use?

Here's the content of the file:


5 -30.49 0
6.3 -23.99 0
8 -19.35 0
10 -15.72 0
12.5 -12.62 0
16 -10.03 0
20 -7.9 0
25 -6.16 0
31.5 -4.74 0
40 -3.58 0
50 -2.66 0
63 -2.01 0
80 -1.65 0
100 -1.29 0
125 -1.04 0
160 -0.83 0
200 -0.73 0
250 -0.62 0
315 -0.5600000000000001 0
400 -0.48 0
500 -0.4 0
630 -0.28 0
800 -0.07000000000000001 0
1000 0 0
1250 -0.24 0
1600 -0.38 0
2000 0.44 0
2500 0.38 0
3150 0.36 0
4000 1.54 0
5000 2.55 0
6300 3.05 0
8000 2.2 0
10000 -0.19 0
12500 -5.07 0
16000 -10 0
20000 -15.2 0
25000 -19.97 0

I am not sure what it is that I am doing wrong. Any guidance you can offer is much appreciated.
Attached Thumbnails
Cross-Spectrum Microphone Calibration Service - USA-problems-measurements.jpg  

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post #174 of 366 Old 05-25-12, 10:40 PM
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Re: I must be doing something wrong

Quote:
zheka wrote: View Post
Hi Herb,

I am a recent owner of a calibrated Galaxy meter (verified +).


How reliable is calibration at the extremes supposed to be, specifically in the sub-10Hz region?

[snip]
I'm not an REW expert, but I would recommend trying the "narrow_band_response_random-incidence_C-wtd.frd" instead of the one-third octave band file. Also, do you have the meter set to C-weighting when you make the measurement? The data you quoted looks plausible - the Type 1 C-weighting value at 5 Hz is -25 dB, at 8 Hz -17.7 dB, at 10 Hz -14.3 dB, at 12.5 Hz -11.3 so it's certainly in the right ballpark.

What is the serial number of your meter?
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post #175 of 366 Old 05-25-12, 10:58 PM
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Re: I must be doing something wrong

SN 110508226

I am using C weighting and response slow.

I will try the narrow band cal file and report back.

Thank you very much!
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post #176 of 366 Old 05-25-12, 11:30 PM
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Re: I must be doing something wrong

results using both cal files look very close to me.
Attached Thumbnails
Cross-Spectrum Microphone Calibration Service - USA-narrow.jpg  

Cross-Spectrum Microphone Calibration Service - USA-one-thir-octave-5-50.jpg  

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post #177 of 366 Old 05-26-12, 01:10 AM
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Re: I must be doing something wrong

Quote:
zheka wrote: View Post
results using both cal files look very close to me.
The cal files for your meter look kosher. Try checking in the REW forum to make sure there isn't something wrong with the software settings. If that's not it, maybe your meter went bad - if the REW forum folks can't clear it up, you can ship the meter back to me and I can take another look.

(also, did you take advantage of the HTS discount for your meter?)
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post #178 of 366 Old 05-26-12, 01:40 AM
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Re: I must be doing something wrong

Quote:
Anechoic wrote: View Post
The cal files for your meter look kosher. Try checking in the REW forum to make sure there isn't something wrong with the software settings. If that's not it, maybe your meter went bad - if the REW forum folks can't clear it up, you can ship the meter back to me and I can take another look.
sounds good, thank you very much.
Quote:
Anechoic wrote: View Post
(also, did you take advantage of the HTS discount for your meter?)
no, I did not
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post #179 of 366 Old 05-26-12, 03:01 AM
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Re: I must be doing something wrong

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zheka wrote: View Post

no, I did not
Check your PMs.
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post #180 of 366 Old 05-26-12, 08:20 AM
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Re: I must be doing something wrong

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Anechoic wrote: View Post
Check your PMs.
Thank you!
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