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Well, then that makes sense, especially if you want absolute correct level matches, also when designing/confirming crossovers. But, as Anechoic mentioned, most users simply want correct FR and Polar response (the two things I looked for). I haven't built speakers in a LONG time. It would be fun to do it again, especially with all the software available.

Ray
 

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When an SPL meter like the Galaxy CM-140 or RS unit is calibrated, does the calibration process simply provide a cal file like what's used for the ECM8000 or is it actually being calibrated so it, as a standalone instrument, measures dB's more accurately, like what you would use one of these for:

http://www.galaxyaudio.com/CMC200.jsp

Maybe I've overlooked something here, but from what I've read the ECM8000 has a wider frequency range (15 Hz to 20 kHz) than the Galaxy CM-140 (31.5Hz to 8KHz), so why would you want to use the Galaxy to do room measurements beyond typical SPL readings?

What I'm getting at is this: Is it worth it to own one of each and have them both calibrated: the ECM8000 with its cal files to correct for frequency response and polar data, and the Galaxy CM-140 to check for SPL? I'd still like to do SPL measurements (level matching systems like my car stereo and headphones, checking noise levels, etc.) w/out having to hook up a whole rig to do this.
 

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Hi Dan,

I have a comparable SPL meter to the one above, but from TENMA. It has the same specs and I only use it for level matching with pink noise. As for doing SPL measurements outside the freq range of this meter, for a stand alone product you can look at Goldline products, but they are expensive.

http://www.parts-express.com/pe/showdetl.cfm?Partnumber=390-815
http://www.parts-express.com/pe/showdetl.cfm?Partnumber=390-805

So, if you have a laptop with REW, that may be the better choice IMO. The 2nd one above from Goldline is an incredible piece, but you can buy a laptop, calibrated ECM8000, and outboard sound card with phantom voltage for less then the Goldline unit.

Ray
 

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When an SPL meter like the Galaxy CM-140 or RS unit is calibrated, does the calibration process simply provide a cal file like what's used for the ECM8000 or is it actually being calibrated so it, as a standalone instrument, measures dB's more accurately
The calibration comes in the form of a calibration file in easily read text form.

Maybe I've overlooked something here, but from what I've read the ECM8000 has a wider frequency range (15 Hz to 20 kHz) than the Galaxy CM-140 (31.5Hz to 8KHz), so why would you want to use the Galaxy to do room measurements beyond typical SPL readings?
The calibration file extends the accuracy range to 20KHz for the Galaxy, just as it does for the ECM8000. So, if your Galaxy was down by 10dB at 20KHz, then the file would show +10dB for the 20KHz entry. This would render the reading flat once the calibration was added in REW (or manually).

brucek
 

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The calibration file extends the accuracy range to 20KHz for the Galaxy, just as it does for the ECM8000. So, if your Galaxy was down by 10dB at 20KHz, then the file would show +10dB for the 20KHz entry. This would render the reading flat once the calibration was added in REW (or manually).
Oops, typo there, it would show -10dB, the cal file contains the actual response of the mic/meter.
 

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First of all, thanks for all the replies here from other members, your input has been very helpful.


Ray,

I checked out that TENMA meter.

http://www.mcmelectronics.com/product/TENMA-72-945-/72-945

All the specs are very similar to the Galaxy meter and actually comes with some nice extras like a hard carrying case, AC adapter, and a USB cable. It seems like the USB connection might actually make connecting it to a computer a little easier. Have you ever used it as a test mic in the REW application?

For all,

Going back to my question about the calibration... I now understand that a cal file is included to show the frequency deviations to adjust inside REW, but I was also hoping to know if the SPL meter calibration can be done for the SPL measurement itself, much like what the Galaxy CM-C200 is used for, to calibrate it at 94 dB and 114 dB.

http://www.galaxyaudio.com/CMC200.jsp

The SPL level calibration device would be nice to have, but it's about $180-$250 on it's own, depending on where you look. I think it would be really handy to have something that could function as a calibrated, standalone SPL meter as well as being able to use it with REW or other programs.
 

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Dan,

Tenma also makes an expensive calibrated model:

http://www.mcmelectronics.com/product/TENMA-72-6635C-/72-6635C

This is more comparable to the Galaxy version, but the model you are looking at is just fine (there is another version of the one you are looking at for a bit more money that can do data logging:

http://www.mcmelectronics.com/product/TENMA-72-947-/72-947

None of them IMO is a flat as using an ECM8000 (calibrated), which is what I use for REW, but it really should be fine if you can get a cal file for it and take that into account as mentioned above.

Ray
 

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When an SPL meter like the Galaxy CM-140 or RS unit is calibrated, does the calibration process simply provide a cal file like what's used for the ECM8000 or is it actually being calibrated so it, as a standalone instrument, measures dB's more accurately, like what you would use one of these for:

http://www.galaxyaudio.com/CMC200.jsp
brucek addressed the rest of your post, but I just wanted to mention that I can do either/both types of calibration (frequency response correction curves and level/sensitivity adjustments) for SLMs with 1/2-inch type microphones.
 

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Hi All,

Just a friendly reminder that prices will change starting on Saturday, Aug 1. If you want measurements at extra angles without paying extra, speak now or forever hold your piece.

That said, I will let slip that it won't be a total loss for HS readers if you miss the deadline. Stay tuned... ;)
 

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Anechoic,

Where can we find your current prices for either buying a ECM8000 with calibration or having our own ECM8000 calibrated. I'd want it accurate to either 10 or 15 hz...
 

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Anechoic,

Where can we find your current prices for either buying a ECM8000 with calibration or having our own ECM8000 calibrated. I'd want it accurate to either 10 or 15 hz...
Click on my name to find prices for pre-calibrated ECM8000 sales. Having your own mic calibrated is $55 for basic calibration, +$10 for polar measurements, +$10 for noise floor/sensitivity. Extra angles are free, but as of Sat, extra angles will be $5 per additional angle. The new price structure for mic sales (again, starting Aug 1) is described here.
 

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I had Herb (Cross Spectrum Labs) test an E-V RE510 for me a few months ago and was very satisfied with the service. The mic, not so much. Herb is the real deal.

Herb, are you able to test mics at frequencies other than the standard third-octave intervals? The reason I ask is because I use a program called Voxengo Curve EQ to approximate the inverse of a mic's measured frequency response and thus "flatten" it, and it has more and different frequencies available on its EQ than the third-octave values.

Thanks.
 

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For those on the fence about getting the calibrated ECM-8000, I recommend going for it. I received mine Friday (thanks for the fast service from Cross Spectrum) and there is quite a bit of difference between it and the generic curve from this website. (To be fair, that generic curve is from one mic and Cross Spectrum has posted the variation among samples of the ECM-8000).

I suppose it all depends on how accurate you want your calibration to be. But, that is why we do this, right?
 

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BTW everyone, if you're in the Boston area, the Boston Audio Society will be holding a "microphone measurement clinic." A bunch of us who do various sorts of measurements (including Joe DeMarinis and possibly someone from Listen Inc.) will be there to talk about mic measurements and actually do some mic measurements. The plan right now is that Joe will be handling the mid-to-high frequency measurements and I'll be doing low-frequency measurements with my low-freq calibration rig.

We're looking at Nov 21 or 22, and when we settle on a date, it will be posted on the BAS website.
 

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FYI, in case anyone was wondering just how accurate my calibration process is, I did I little test to see how my measurement compare with mic calibrations performed by a NIST-traceable lab. I have several professional measurement microphones that are regularly calibrated by Scantek.

One of my more top-of-the-line microphones is a BSWA MP201. Scantek has calibrated this a couple of time using an electrostatic actuator (to get the pressure response) and then applying a free-field correction per ANSI/IEC standards. One such result is shown below (I do have a more recent cal, but I can't find the plot right now. FWIW, the mic FR didn't change):



So I took the data points off that plot, measured the MP201 using my freefield method (which is basically the substitution method using another calibrated mic) and plotted a comparison:



No tricks, no adjustments, no massaging the data, that's what I got using the same software, hardware and scripts I use to generate curves for all the mics I sell. There is a discrepancy at 20 kHz; the problem at those high frequencies is that the wavelengths are so small that every little thing can effect the result, including the microphone mounting method. Without knowing the exact free-field correction process Scantek uses I can't say who is more/less correct but I will note that both measurements are will within ANSI/IEC accuracy standards (which get larger at higher frequencies).
 

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Very nice Herb!!! It gives a lot of confidence in your technique and calibration skills (not that we did not have it before). Thanks again for such a great service!!!
 

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Now this is a great excuse to take the Downeaster to Boston. 2 hours from OOB to Boston, listening to podcast, reading....
Most people I knew from my last meeting I went to at BAS are long gone either in the audio world or dead.

Think I will bring my mic with me too, maybe re-enlist in BAS.

Last BAS I went to, a bit fuzzy... either Acoustic Research, doing car audio tests with a PDP11, or some microphone clinic at BBN, I remember most of us were spending thousands on audio gear mass produced, and the speaker emphasized a microphone is mostly hand made, for only 700.00 or so. (circa 1978ish).
 

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Now this is a great excuse to take the Downeaster to Boston. 2 hours from OOB to Boston, listening to podcast, reading....
Most people I knew from my last meeting I went to at BAS are long gone either in the audio world or dead.

Think I will bring my mic with me too, maybe re-enlist in BAS.
We'd love to have you. The only problem is that it looks like we're going to have the meeting in Winchester, so getting from North Station to Winchester might be a bit of a haul. Although there is a commuter rail stop in Winchester, so I'm sure I or someone else could give you a ride to/from the station.
Last BAS I went to, a bit fuzzy... either Acoustic Research, doing car audio tests with a PDP11, or some microphone clinic at BBN, I remember most of us were spending thousands on audio gear mass produced, and the speaker emphasized a microphone is mostly hand made, for only 700.00 or so. (circa 1978ish).
Wow, you are old! ;)
 

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The calibration comes in the form of a calibration file in easily read text form.


The calibration file extends the accuracy range to 20KHz for the Galaxy, just as it does for the ECM8000. So, if your Galaxy was down by 10dB at 20KHz, then the file would show +10dB for the 20KHz entry. This would render the reading flat once the calibration was added in REW (or manually).

brucek
Sorry I don't understand... why the mic need a calibration? It's not perfect yet?
 
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