Cross-Spectrum Microphone Calibration Service - USA - Page 23 - Home Theater Forum and Systems - HomeTheaterShack.com

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post #221 of 368 Old 12-18-12, 12:07 PM
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Re: Cross-Spectrum Microphone Calibration Service - USA

Quote:
Anechoic wrote:
The standard uncalibrated CM-140 tends to be within 1-3 dB of the actual SPL value out-of-the-box. That said, the verified meters I sell have been adjusted to the correct value and sell for about the same price you can get a CM-140 elsewhere (and a little cheaper with the HTS discount).
So in other words, 75 dB on the CM-140 might be 77-78 dB in reality?
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post #222 of 368 Old 12-18-12, 12:23 PM
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Re: Cross-Spectrum Microphone Calibration Service - USA

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Vaughan100 wrote: View Post
So in other words, 75 dB on the CM-140 might be 77-78 dB in reality?
72-78 dB, yes. Most are within +/- 1.5 dB or so, but I've seen a few outliers.
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post #223 of 368 Old 01-11-13, 12:22 PM
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Re: Cross-Spectrum Microphone Calibration Service - USA

Just a question, as I heard a member talk about a calibrated CM-140 in the UMM-6 thread (not sure if was referring to the cross-spectrum calibration or not) but :

"i was previously considering the calibrated galaxy cm-140 (just to skip phantom power and mic pre) but after looking at the posted calibration result i decided to cancel. the meter have too much attenuation at the low frequency that it's not exactly precise anymore. -6db down at 20hz, -12db down at 10hz and -22db down at 5hz. it's only flat to 100hz."

Is this true? I just received my CM-140 calibrated by cross-spectrum. Is it still inaccurate? I'm confused by the above comments.
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post #224 of 368 Old 01-11-13, 01:00 PM
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Re: Cross-Spectrum Microphone Calibration Service - USA

The CM-140 is a sound level meter that only has A- and C-weighted settings. Both of those weightings roll off the high and low frequencies, with the A-weighting setting producding sharper rolloff, but C-weighting is still down 14 dB at 10 Hz. The correction curves I ship with those meters (in theory) will correct for those extreme rolloffs and flatten the response. However boosting the levels that much (as much as 25 dB at 5 Hz) can create distortion problems similar to what you would get if you boosted the level of a graphic equalizer by 20 dB. That's the potential issue one might have to deal with.

The meter and the calibration aren't inaccurate, it's just a matter to the degree that it needs to be corrected to produce a flat response.
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post #225 of 368 Old 01-11-13, 01:46 PM
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Re: Cross-Spectrum Microphone Calibration Service - USA

How do I know how much you boosted my curve by so that I know that there is low distortion as opposed to a lot of distortion?

I'm just trying to understand this. You mention distortion, but how do I know that my meter doesn't have gross distortion due to huge correction? What does that mean for me? How does this distortion influence the results?

I'm not clued up, clearly, but I wasn't aware there would be potential problems. I just thought I would get my meter calibrated for accurate results. Please try to clarify these things for me ...

Last edited by Doctor X; 01-11-13 at 01:52 PM.
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post #226 of 368 Old 01-11-13, 04:26 PM
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Re: Cross-Spectrum Microphone Calibration Service - USA

Are you the Vaughan from SA? If so, you got a "Verified" meter, so I didn't provide you with a correction curve (as opposed to the "Verified+" meters which are provided with correction curves). If you use your meter as a microphone with a computer program (REW, etc), the low and high frequencies will be rolled off. There's not much you can do about it except to find a generic correction curve someplace and use that to compensate. But as a sound level meter reading absolute C- or A-weighted SPL's, it will be accurate.
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post #227 of 368 Old 01-12-13, 07:21 AM
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Re: Cross-Spectrum Microphone Calibration Service - USA

Hi there,

Yes, that's me. I'm using this meter purely for setting levels, so you say that everything is accurate for that application and definitely more accurate than the standard meter? Correct me again, what does the "Verified" option do? I've clearly gone off the rails here as I must have assumed something else.
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post #228 of 368 Old 01-12-13, 07:27 AM
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Re: Cross-Spectrum Microphone Calibration Service - USA

Quote:
Anechoic wrote: View Post
The CM-140 is a sound level meter that only has A- and C-weighted settings. Both of those weightings roll off the high and low frequencies, with the A-weighting setting producding sharper rolloff, but C-weighting is still down 14 dB at 10 Hz. The correction curves I ship with those meters (in theory) will correct for those extreme rolloffs and flatten the response. However boosting the levels that much (as much as 25 dB at 5 Hz) can create distortion problems similar to what you would get if you boosted the level of a graphic equalizer by 20 dB. That's the potential issue one might have to deal with.
There aren't any distortion problems if using a meter with software like REW, since the signal isn't actually being boosted in a hardware sense, the displayed level in measurement responses is simply scaled up to reverse the attenuation of the C weighting curve. The main problem is that signal and noise both get scaled up, so the measurement result at the very lowest frequencies has more noise than if measured with a mic. None of this is an issue if using a meter to measure SPL, however.
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post #229 of 368 Old 01-12-13, 09:52 AM
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Re: Cross-Spectrum Microphone Calibration Service - USA

I just need reassurance that a) this verified meter is more accurate than the standard meter b) more accurate than the RS meter for measuring levels. That's it.

For measuring REW I'll get a UMIK-1 at a later date.
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post #230 of 368 Old 01-15-13, 12:46 PM
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Re: Cross-Spectrum Microphone Calibration Service - USA

No response?
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