Hoping that this community can help me choose a very accurate mic to purchase for loudspeaker measurements.
Wishlist is as follows:
- current production (not discontinued by manufacturer)
- 5Hz to 30KHZ bandwidth (1/4" capsule)
- dynamic range around 150dB
- free field response
- external polarization
- amplitude response calibrated from the manufacturer using reciprocity, substitution or electrostatic actuator with uncertainty =< 0.25dB; NO spark calibration
Was looking at B&K 4135 + 2633 but they are obsolete and no interest in buying these used.
All recommendations very appreciated!
Wishlist is as follows:
- current production (not discontinued by manufacturer)
- 5Hz to 30KHZ bandwidth (1/4" capsule)
- dynamic range around 150dB
- free field response
- external polarization
- amplitude response calibrated from the manufacturer using reciprocity, substitution or electrostatic actuator with uncertainty =< 0.25dB; NO spark calibration
Was looking at B&K 4135 + 2633 but they are obsolete and no interest in buying these used.
All recommendations very appreciated!
Now there's a brand I haven't heard of but I will investigate further! Thanks for the suggestion.
Thanks for the link.
After buying two Earthworks mics and confirming their frequency response calibration is well outside my requirements (up to 4dB with their "calibration" file compared to a reciprocity calibrated B&K 4135), I won't use them for any speaker measurements. Even my $50 EMM6 Dayton mic calibration was closer than the $700 EW M30 although the latter has slightly lower noise.
EW uses a spark gap to calibrate their mics which I have read is not an accurate method due to the inconsistent nature of the spark.
Aco Pacific, Inc. - Microphones
G.R.A.S. Measurement microphone sets
https://www.bksv.com/~/media/literature/Catalogue/bf0236.ashx?la=en
TestMic.com - the best in Precision Mics. (ACO Capsule)
Measurement Microphones M2230, M2211, M2210, M2215, M4260, M2010, M2015
My 1" mics are B&K, I have both an ACO and Gras 1/2" also I bought 6 Earthworks and am down to 1 or 2 somewhere around here. I have the coupler to test the preamps, a pistonphone etc. I would look at ACO for a 48V phantom unit.
G.R.A.S. Measurement microphone sets
https://www.bksv.com/~/media/literature/Catalogue/bf0236.ashx?la=en
TestMic.com - the best in Precision Mics. (ACO Capsule)
Measurement Microphones M2230, M2211, M2210, M2215, M4260, M2010, M2015
My 1" mics are B&K, I have both an ACO and Gras 1/2" also I bought 6 Earthworks and am down to 1 or 2 somewhere around here. I have the coupler to test the preamps, a pistonphone etc. I would look at ACO for a 48V phantom unit.
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You have several challenges. First the 140 dB Dynamic range is pretty extreme. Second a 1/2 " mike will do 30 KHz accurately.
I have a 4145, 4135, 4136, 4165, 4133. The 4135 has a current cal so I use it as a reference, the others are all older but they seem to still be within calibration. Not sure why you want new? Comparing microphone sensitivity does require lots of care and proper correction. The Earthworks adapter is a must for use with a pistonphone. The HF calibration is a much bigger challenge since the mike influences the sound field around it and at short wavelengths its significant. The Earthworks mikes are compared to a Microtek Gefell MK301 1/4" pressure mike for the calibration. Its not presuming that the spark is an absolute. Here is more than you ever wanted to know about mike calibration: https://www.nist.gov/sites/default/files/documents/calibrations/aip-ch8.pdf
The Microtek capsules are good. So the the Tokyo Rico. There are other vendors as well.
What is the application and why such a focus on calibration?
I have a 4145, 4135, 4136, 4165, 4133. The 4135 has a current cal so I use it as a reference, the others are all older but they seem to still be within calibration. Not sure why you want new? Comparing microphone sensitivity does require lots of care and proper correction. The Earthworks adapter is a must for use with a pistonphone. The HF calibration is a much bigger challenge since the mike influences the sound field around it and at short wavelengths its significant. The Earthworks mikes are compared to a Microtek Gefell MK301 1/4" pressure mike for the calibration. Its not presuming that the spark is an absolute. Here is more than you ever wanted to know about mike calibration: https://www.nist.gov/sites/default/files/documents/calibrations/aip-ch8.pdf
The Microtek capsules are good. So the the Tokyo Rico. There are other vendors as well.
What is the application and why such a focus on calibration?
Demian
As a general rule the Bruel and Kjaer capsules are good until they are dropped. Change due to aging is so little on the metal diaphragm capsules that is barely measurable.
The plastic diaphragm capsules usually have significant absolute level vs temperature change so require level calibration before use.
The biggest issue I ever had was with an eBay Bruel and Kjaer power supply. It was improperly repaired and had lots of hum. Not very hard to fix, but the guy who sold it to me never noticed!
Now your list hints to me I probably should do an inventory of my test equipment!
As to frequency calibration I do have a General Radio calibrator that does a few different frequencies.
As to accuracy I have the barometer to know how much to correct the calibration for the weather.
But realistically trying to get repeatable measurements to better than one dB is really tough.
As a general rule the Bruel and Kjaer capsules are good until they are dropped. Change due to aging is so little on the metal diaphragm capsules that is barely measurable.
The plastic diaphragm capsules usually have significant absolute level vs temperature change so require level calibration before use.
The biggest issue I ever had was with an eBay Bruel and Kjaer power supply. It was improperly repaired and had lots of hum. Not very hard to fix, but the guy who sold it to me never noticed!
Now your list hints to me I probably should do an inventory of my test equipment!
As to frequency calibration I do have a General Radio calibrator that does a few different frequencies.
As to accuracy I have the barometer to know how much to correct the calibration for the weather.
But realistically trying to get repeatable measurements to better than one dB is really tough.
Chasing 1 dB accuracy in other than a very controlled laboratory is futile.
I have collected lots of this stuff. I'm not sure why any more but its nice to have.
I have 3 pistonphones, two fully operational, 2 different GR calibrators (including an Omnical) a GR reciprocity calibrator (I have never figured out how to use) and some CEL calibrators. The pistonphones are the best standards in practice but big and clumsy. The CEL's are small and easy to use so why not?
I have two B&K measuring amps, something like 6 2219 preamps. (I got all this stuff years ago in various fire sales) I also have 2 HP sound level meters and 3 HP mikes and preamps. The HP has significantly lower distortion than the B&K's. It has lead me to questioning many of the distortion measurements of speakers and headphones.
I just realized I also have a B&K probe microphone. With so much stuff its easy to lose track.
I use one of Kim Giradin's mikes (Panasonic mike in a tube) for almost all my measurements, its just easier.
I do wonder whether new stuff would give me any different results or experiences. Using all this stuff does highlight how many ways you can make it lie to you.
I have collected lots of this stuff. I'm not sure why any more but its nice to have.
I have 3 pistonphones, two fully operational, 2 different GR calibrators (including an Omnical) a GR reciprocity calibrator (I have never figured out how to use) and some CEL calibrators. The pistonphones are the best standards in practice but big and clumsy. The CEL's are small and easy to use so why not?
I have two B&K measuring amps, something like 6 2219 preamps. (I got all this stuff years ago in various fire sales) I also have 2 HP sound level meters and 3 HP mikes and preamps. The HP has significantly lower distortion than the B&K's. It has lead me to questioning many of the distortion measurements of speakers and headphones.
I just realized I also have a B&K probe microphone. With so much stuff its easy to lose track.
I use one of Kim Giradin's mikes (Panasonic mike in a tube) for almost all my measurements, its just easier.
I do wonder whether new stuff would give me any different results or experiences. Using all this stuff does highlight how many ways you can make it lie to you.
I'll raise you and go to my Western Electric gold diaphragm mic!
I bought 3 eBay piston phones and when all showed the same level 2 went away as calibrated! In theory you use the piston phone to calibrated your best sound level meter and then use that to calibrate your calibrators. They should hold calibration for a year before being rechecked.
I have lost count of how many sound level meters I have!
The oldest one still working and in cal is from April 1952.
But we both are gear hogs!
Demian, thanks for your reply. The NIST paper was a great read.
My application is HF transducer development. It would be advantageous to have confidence in the frequency response curves of the transducer and the final loudspeakers that will use it. Most of us can hear lower Q changes in FR of 0.5dB. If the mic calibration is +\- 1 or 2dB, the end product requires additional correction to address this.
My application is HF transducer development. It would be advantageous to have confidence in the frequency response curves of the transducer and the final loudspeakers that will use it. Most of us can hear lower Q changes in FR of 0.5dB. If the mic calibration is +\- 1 or 2dB, the end product requires additional correction to address this.
You are confusing accuracy of frequency response with level. If you look at the frequency response curves most of them show limits equal to or better than your requirements. Absolute level meadurements require issues like barometric correction.
I think hes right to be concerned about response variations. However above about 15KHz the measurement technique can have a significant impact on he measurements. You start with the microphone affecting the measurements. Its size alters the sound field. Distance from the source since the source is a finite and most likely larger than the wavelength size moving in any axis will change things. Where lies the truth?
I have been playing with a Pioneer ribbon tweeter for the extended response stuff. It seems to be good to 70 KHz. It does enable some degree of learning about these HF issues. I'm less confident in the Piezo tweeters since they were not originally conceived for reproduction.
I have been playing with a Pioneer ribbon tweeter for the extended response stuff. It seems to be good to 70 KHz. It does enable some degree of learning about these HF issues. I'm less confident in the Piezo tweeters since they were not originally conceived for reproduction.
https://www.bksv.com/~/media/literature/Product Data/bp2212.ashx
Is the data sheet for a 1/2" Bruel & Kjaer capsule. It does wiggle a bit at the top end, but look at the divisions! 2.5 dB per line so the wiggle by carefully exploding the data sheet it =/- 1/2 dB!
I expect similar results for most quality measurement microphones.
Even better https://www.bksv.com/~/media/literature/Product Data/bp1844.ashx
Is the data sheet for a 1/2" Bruel & Kjaer capsule. It does wiggle a bit at the top end, but look at the divisions! 2.5 dB per line so the wiggle by carefully exploding the data sheet it =/- 1/2 dB!
I expect similar results for most quality measurement microphones.
Even better https://www.bksv.com/~/media/literature/Product Data/bp1844.ashx
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The second B&K is a pressure response mike. Its free field response is different from the chart. When I started down this road I did not realize how complex it would be. The free field mikes are calibrated with a cap fixture that creates the equivalent of a pressure response which is corrected to get the free field response. The microphones have a self resonance at the top of the range that's tweaked to extend the response on the free field mikes. However you end up with a pretty sharp low pass filter with its attendant effects on transient response. Still lots to learn on this.
My bad didn't notice it was the wrong type. Yes an important to note and get right.
I made a correction curve for my pressure response mike which flattens the response and should have less of the transient issues.
I wonder how much of the sound of a large diaphragm mike comes from its HF tuning and transient response. I know a lot has to do with the screen over the mike. Scott W was going to dig up the stuff on using a spark for calibration and I would like to see it.
I wonder how much of the sound of a large diaphragm mike comes from its HF tuning and transient response. I know a lot has to do with the screen over the mike. Scott W was going to dig up the stuff on using a spark for calibration and I would like to see it.
Less so than you think, just like you can make a +- .1dB piston phone out of a $15.00 medical grade pressure transducer. The same one Jim Willams used for his barometer. You might need a piece of mailing tube, etc.
I now see that this is the case with some of the more expensive and smaller diameter/ higher frequency mics. My EW mics are not in that category.
The following paper I found on the PCB Piezotronics website contains many measurements and includes IEC + manufacturer tolerances confirming why good FR calibration may be useful.
https://www.pcb.com/Linked_Documents/3P03218condensedreport.pdf
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