And what are the things that can cause it to become uncalibrated?
So the cheapest calibrated measurement mic a.k.a. Dayton iMM-6 caught my attention. Thinking of buying it while I'm in the States and bringing it back home half a year later. But it would be pointless if the calibration goes out of whack before I can manage to measure anything (and save that measurement for future recalibrations).
So the cheapest calibrated measurement mic a.k.a. Dayton iMM-6 caught my attention. Thinking of buying it while I'm in the States and bringing it back home half a year later. But it would be pointless if the calibration goes out of whack before I can manage to measure anything (and save that measurement for future recalibrations).
I can see how you could check the calibration of a microphone, to see if it meets its standard and so on, comparing against a standard... but can you calibrate (as in alter) a mic that has gone out of spec to bring it back... I can't see how that could be done.
Does just knowing the error count. For example a voltmeter that reads in error by -11% could be used with great accuracy once the initial 'calibration' were known.
There is a fair bit of info around: stick with the video past the first 20 secs or so.
PRSG413: How To Calibrate A Microphone - YouTube
This pretty much confirms what I would suspect would cause a mic to go out of calibration, eg shock and stress beyond its design limits. I would also add magnetic fields to that if appropriate to the mic construction.
Measurement microphone calibration - Wikipedia
Does just knowing the error count. For example a voltmeter that reads in error by -11% could be used with great accuracy once the initial 'calibration' were known.
There is a fair bit of info around: stick with the video past the first 20 secs or so.
PRSG413: How To Calibrate A Microphone - YouTube
This pretty much confirms what I would suspect would cause a mic to go out of calibration, eg shock and stress beyond its design limits. I would also add magnetic fields to that if appropriate to the mic construction.
Measurement microphone calibration - Wikipedia
Good mikes like WE 640AA, you'd have to smack with a hammer to seriously screw the calibration.
What you get for 1/10th the price, I dunno.
However modern electret capsules are VERY robust. I'd expect either a dB shift in the highs after a strong shock (dropping your cellphone), or just quit working.
I think this model comes in a padded case. For travel, put that inside a larger padded case, or wrapped in the socks and sweaters in your hard-side suitcase (but be prepared for quick exposure at the X-ray machine).
What you get for 1/10th the price, I dunno.
However modern electret capsules are VERY robust. I'd expect either a dB shift in the highs after a strong shock (dropping your cellphone), or just quit working.
I think this model comes in a padded case. For travel, put that inside a larger padded case, or wrapped in the socks and sweaters in your hard-side suitcase (but be prepared for quick exposure at the X-ray machine).
Those are active bass absorbers.
They work by putting a mic near a subwoofer and then inverse feeding that signal into the subwoofer. Now, if everything is setup properly, you have no more nasty room modes.
They can be very effective. Instead of covering every corner and wall of your room with bass traps, you can do with 2-4 of these active bass absorbers.
They were subwoofers, with microphones inside to correct their frequency response. My point was, capsules survived the pressure.
First what do you mean by calibration? It can mean sensitivity at 1 KHz. or frequency response. With a pistonphone you can get within .2 dB reliably at 250 Hz. A "normal" calibrator can be trusted to about 1 dB at 1 KHz. However for speaker measurement that is not what you are interested. Frequency response is different but has similar influences. Its affected by the physical size and the diaphragm tension. if you cook a microphone that may affect the diaphragm tension for example. I have had electret based mikes (Panasonic) recalibrated after 5 years with very little effective change. As for the real measurement mikes they are NOT hammer resistant but the metal diaphragm is stable to small fractions of a dB over many years if treated carefully.
The reason for calibrating with a calibrator often is that the sensitivity changes with altitude, temperature, humidity, bias voltage etc. If being within 2 dB absolute sensitivity its not a big issue. If you are going to court over noise complaints it is an issue. If the diaphragm is plastic it will be more sensitive to environment.
The small electrets have excellent performance. The Earthworks measurement mikes are based on the Panasonic wm61(??) now out of production They use a good preamp and have a calibration process. At $500 they are a good value. A GRAS or B&K setup will be $2k to $4K or more. Mems mikes (cell phone) are better for stability and accuracy but noisier and have other limitations.
I would not hesitate to get the Dayton. The Omnimic is a really good package if you want to make measurements.
The reason for calibrating with a calibrator often is that the sensitivity changes with altitude, temperature, humidity, bias voltage etc. If being within 2 dB absolute sensitivity its not a big issue. If you are going to court over noise complaints it is an issue. If the diaphragm is plastic it will be more sensitive to environment.
The small electrets have excellent performance. The Earthworks measurement mikes are based on the Panasonic wm61(??) now out of production They use a good preamp and have a calibration process. At $500 they are a good value. A GRAS or B&K setup will be $2k to $4K or more. Mems mikes (cell phone) are better for stability and accuracy but noisier and have other limitations.
I would not hesitate to get the Dayton. The Omnimic is a really good package if you want to make measurements.
I have seen mikes both inside and in front of subs for feedback. it works quite weel but only to a fairly low frequency. Then the delay through the driver and air will use up all the phase margin and you and a big oscillator.
There are tricks for making the generic electrets to work at high SPL's. For around $1 ea why not? You may need to block the port to get extended LF response.
There are tricks for making the generic electrets to work at high SPL's. For around $1 ea why not? You may need to block the port to get extended LF response.
I just realized something... an alternative way of recalibration
I started with planning to measure two mics just to see how close they are. But then in ECC, one additional bit can only detect but not correct errors, while two additional bits can detect and correct errors.
So if I have 3 mics and I only use one regularly, I can use a majority-wins criteria to correct the response of the outlier, without even needing a source that is accurate or flat or etc.
Kind of similar to using a better mic to calibrate the worse mic. However you don't run into the problem of having to calibrate the better mic.
I started with planning to measure two mics just to see how close they are. But then in ECC, one additional bit can only detect but not correct errors, while two additional bits can detect and correct errors.
So if I have 3 mics and I only use one regularly, I can use a majority-wins criteria to correct the response of the outlier, without even needing a source that is accurate or flat or etc.
Kind of similar to using a better mic to calibrate the worse mic. However you don't run into the problem of having to calibrate the better mic.
Well unfortunately that is also what ECC cannot protect against.
But then besides keeping some of them in storage, the three mics don't even have to be the same. I'm thinking of buying two iMM-6, and use them to calibrate a third normal mic - can be SM57, can be Blue Snowball. And we get a mic that is somewhat calibrated and does not suck entirely for normal recording tasks.
Though issue with SM57 is, the sensitivity is almost 10 times lower than the iMM-6 and I have never successfully recorded speakers at 1m without a lot of hiss.
But then besides keeping some of them in storage, the three mics don't even have to be the same. I'm thinking of buying two iMM-6, and use them to calibrate a third normal mic - can be SM57, can be Blue Snowball. And we get a mic that is somewhat calibrated and does not suck entirely for normal recording tasks.
Though issue with SM57 is, the sensitivity is almost 10 times lower than the iMM-6 and I have never successfully recorded speakers at 1m without a lot of hiss.
SM-57 as a measurement mic? That's an original idea.
It has to be calibrated on different distances and SPL levels, of course in anechoic chamber only! I can imagine the size of that 3-D calibration table. ;-)
The problem with cardioid is that the response varies with distance since there is an interaction between the front and back of the capsule. True for all directional mikes to some extent.
This mike is approx. $1 CMA-6542PF CUI Inc. | Audio Products | DigiKey A 1/4" brass tube and RCA/minijack or cable in the other end and you have a good mike. It would need calibration but I expect the correction factors would be pretty small. the small size makes it less sensitive to orientation. I have measured this type to over 30K. Make a handful and check them against one another and against a calibrated mike.
This mike is approx. $1 CMA-6542PF CUI Inc. | Audio Products | DigiKey A 1/4" brass tube and RCA/minijack or cable in the other end and you have a good mike. It would need calibration but I expect the correction factors would be pretty small. the small size makes it less sensitive to orientation. I have measured this type to over 30K. Make a handful and check them against one another and against a calibrated mike.
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