Found this with a little searching:
Not what I was thinking, still have not found that, but something...
Not what I was thinking, still have not found that, but something...
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Measurement Microphones - what is the consensus?
- Thread starter stemfencer
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restorer-john
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What does the calibrator output? White noise or a spot frequency? Just wonderin'.
1 kHz tone
restorer-john
Grand Contributor
Someone should stick a mic in and run an FFT. I wonder how 'clean' they are. You know, enquiring minds and all...
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I doubt it would be more accurately calibrating than a Umik with its cal file especially at only 1 khz. For less money the Umik is lots more useful.
Bingo, Specially if your using REW for your measurements. It automatically detects the Umik when attached, asks for it's calibration file and if yours has one with the SPL numbers, it has you all set to go for speaker measurements and use as a SPL level measurement, etc.
Can't ask for much more.
I made a switchable white/pink noise calibrator back in college (professor's project, so he gave it to me 
). It was ridiculously hard to do, not because the generation of the voltage signal was hard (that was easy though a little tricky at very low frequencies), but because creating and measuring the response of a broadband emitter was a royal PITA. I cannot remember exactly what I ended up using, one was some kind of array of small piezo or compression drivers I think in a small box for large mics, and a single compression driver EQ'd (all analog back then, long before DSP chips were common) in a tube(no horn) for pencil mics.
Virtually the only mic calibrators I have seen in recent days are almost all 1 kHz, with some having a 250 Hz option. The only broadband system I found some years back was way out of my price range (thousands of dollars USD). You can get a cheap one for around $100 and a NIST-trace version for around $500 IIRC.
Edit: Same prof had me create a light box the year before, another project that seemed easy but turned out to be incredibly difficult. I learned about Fresnel lenses and a whole lot about how hard it was to get perfectly even, perfectly white light across a 24" x 24" area. You'd think I would have learned to say "no" after that, but he was paying the bills, and it got me an office and lab space in the EE building.
). It was ridiculously hard to do, not because the generation of the voltage signal was hard (that was easy though a little tricky at very low frequencies), but because creating and measuring the response of a broadband emitter was a royal PITA. I cannot remember exactly what I ended up using, one was some kind of array of small piezo or compression drivers I think in a small box for large mics, and a single compression driver EQ'd (all analog back then, long before DSP chips were common) in a tube(no horn) for pencil mics.Virtually the only mic calibrators I have seen in recent days are almost all 1 kHz, with some having a 250 Hz option. The only broadband system I found some years back was way out of my price range (thousands of dollars USD). You can get a cheap one for around $100 and a NIST-trace version for around $500 IIRC.
Edit: Same prof had me create a light box the year before, another project that seemed easy but turned out to be incredibly difficult. I learned about Fresnel lenses and a whole lot about how hard it was to get perfectly even, perfectly white light across a 24" x 24" area. You'd think I would have learned to say "no" after that, but he was paying the bills, and it got me an office and lab space in the EE building.
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Speaking of calibrators, is there any reason to look for a 1/4" capsule calibrator or spend $35-50 for an adapter from iSEMcon or Earthworks? It appears there are plenty of cheap sound level calibrators, but they all have 1/2" openings. I was thinking just use a .5" OD, .25" ID nylon spacer, and bore it out slightly with a 9/32" (~7mm) drill bit, e.g. this $0.65 part:
Use case here is a multi-mike array (4 iSEMcon 7150s) and REW Pro for in-room measurements and hopefully in the future sometime polar speaker measurements. Hence the desire for consistent, albeit not absolute (so a cheap device should be fine) sound level calibration between the mikes.
techsamurai
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How do you use your smartphone for room acoustics?
techsamurai
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I'd like to take REW measurements of my LCR and sub with and without Audyssey. The Behringer 8000 seems like the cheapest way but I will need some sort of USB connector, Can someone point me to the dongle that I need?
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You'll need more than a USB connector with the Behringer 8000. It has an XLR connector and you'll need some sort of audio interface with a mic preamp.
The ubiquitous Umik1 from minidsp is $79, and all you need is to plug it in to a PC usb port. It is very convenient as REW will give accurate SPL readings using it.
The Dayton Audio UMM 6 is another measurement mic with a USB port being all you need for the same price, but it is currently back ordered.
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techsamurai
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Well, the shipping for the Umik1 is $25 which is nearly as much as the 8000 ($35) or the stand ($35) and the results are pretty similar even uncalibrated.
I'm not sure how much I'll get out of this as I only plan to validate my results once or twice so spending $150 is almost overkill when it's half the price of a Dirac license.
I'd like to not waste money on things I almost never use. Paying $100 for a mic is almost ridiculous when the Behringer is 1/3rd the price.
I currently use the app Specdroid on my Android phone and Mobile Tools on my iPad, but I don't use the default settings as the default FFT size in particular is too low for useful low frequency resolution. They are good at showing center frequencies of interest (i.e. resonances, cancelations, and corner frequencies), and to some extent, overall balance, but the overall accuracy will depend on the hardware being used. I have compared those apps with devices I had on hand to one of my calibrated microphones and found that all my Android devices track fairly close between 60Hz and 3kHz, some tracking better than others outside that range. The iPad was an interesting exception in that it tracked well below 300Hz but had a distinct high frequency rise above it.
But if you want to compare before and after of Audyssey, why not use the set-up microphone that came with your receiver and REW? It's basically free for you and it's probably pretty accurate. The little electret capsule's they put in those things are usually pretty flat, the two that I have tested were basically flat up to a couple kilohertz.
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Okay you buy the ECm 8000. Now what can you do with it? It outputs an analog signal over XLR. There is no such thing as an XLR to USB adapter. You will have to purchase an audio recording interface which connects to your computer and has input for the ECm 8000 microphone. That will cost at least about $80. There are some I would not recommend for maybe half that. It will also be a little more complex to use versus a Umik or UMM which simply plugs into to the computer ready to use.
Cheaper options are like suggested using a smartphone or ipad. If you have an Iphone that would work though not directly with REW. Android phones usually roll off low end response. There are some USB lavalier microphones and some that plug into the audio in jack on your computer if it has those. They likely would work for your purposes and some are $35 or so. I haven't used one to recommend. It would work probably.
If you have a little measuring microphone for your AVR, it might plug into the audio input of your computer and work. I've not done that either so not sure it would work, but it might. Of course many newer computers no longer have that kind of 3.5 mm audio input jack. Don't know your particular gear.
You should take the advice give here.
Many times there's more to a deal than an initial low price.
techsamurai
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I just ordered a UMIK-1 to do the measurements.
I'm also buying a microphone stand. Does it need a microphone clip? Here are the stands I'm looking at.
What else do I need? I have a laptop with a USB and HDMI port (I might need to buy a longer HDMI cord).
I'm also buying a microphone stand. Does it need a microphone clip? Here are the stands I'm looking at.
What else do I need? I have a laptop with a USB and HDMI port (I might need to buy a longer HDMI cord).
The umik will plug right into the laptops USB port but you might need a USB extension cord
depending on how far the mic and laptop will be from each other.
Beyond that I think you should be good to go. There is a holding clip with the umik and looks to
also be one with the stand. You can always jury-rig something with a couple rubber bands if needed. LOL
techsamurai
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Thanks! So any of those stands should work then. I'll get the cheapest one ;-)
Yep, that's what I did.
If your not a musician or engineer who will be using it 8 hours a day.
Cheap ones should last us a lifetime.
In case anyone else is going through this same question, get an active usb-extension cord. The active ones can carry standard usb signal far further than passive extensions. That can become very needed when doing measurements and if you cannot carry the computer close to all measurement spots, like with a desktop PC. Active cables are usually usb 2.0, but that's more than what any microphone is ever going to need.
