Found a microphone calibrator on Amazon, thought others might be interested

This might be a handy thing to have in the toolbox?

amazon.com/Decibel-Calibrator-Calibration-Measurement-Microphones/dp/B0786YDF62

Just to a look. Have you tried it or tested it against a known calibrated microphone?

I don't own one, I was just really surprised to find such a tool on Amazon.

All I've ever seen of this style calibrator are used ones.

If the device really works as advertised it could be very useful. The Amazon reviews seem a little fishy though, not one valid one!

Look closely.



The test signal is a 1kHz tone at 94dB and 114dB.

Conclusion: this thing is only useful for calibrating SPL. It is useless for calibrating the full frequency range of your microphone.

Keith_W said:

Conclusion: this thing is only useful for calibrating SPL.

Click to expand...

It is expressly designed to do just that one thing. One would employ this in the situation where the sensitivity of the microphone was unknown and needed to be determined. This has been discussed by John several times here int the past.

Yes if it works it would be helpful as my calibrated Parts Express Dayton mic has no spl calibration or spec. So this could be useful.

Same style/layout as my Cirrus CR511E calibrator. It's manual makes the comments:
The frequency is 1000 Hz, therefore the frequency weighting of the instrument has no influence on the accuracy of the calibration.
The CR:511E Acoustic Calibrator meets the requirements of IEC 942, it corresponds to type 1L, which means, it is type 1 if the correction values for the air pressure are observed.

sam_adams said:

It is expressly designed to do just that one thing. One would employ this in the situation where the sensitivity of the microphone was unknown and needed to be determined. This has been discussed by John several times here int the past.

Click to expand...

One wonders how well that device would work, given that we use free-field microphones. Enclosing the mic in a cavity and playing a 94dB test tone would create a pressure field. And if the purpose if for SPL calibration, SPL meters are much cheaper than that. Just place your mic in front of the speakers, adjust the output of the speaker until the SPL meter reads 75dB, and adjust REW accordingly.

I have this very device, compared against other calibrated devices and found levels within 0.3dB so the specifications are accurate. Good enough for me, and results in measurements in REW that are SPL accurate at any frequency to that level of accuracy. I use it with a few different mics, with access to a 3D printer you can design and print adapters for different styles of mics easily, as long as it fits the orifice.

Process for calibration with REW is easy, just open the SPL meter, hit calibrate, select external reference, wait a few seconds for the SPL to stabilize then calibrate to 94 or 114dB. Don't touch the input gain knob and go about your day.

SPL meters on the other hand, have non-linear frequency response and are not very accurate. Check the specs on those cheap SPL meters, they may be +/- 1.5dB, sometimes even +/-3dB, and only at 1kHz range, for frequency extremes all bets are off. Not what I would use for precision applications.

Keith_W said:

One wonders how well that device would work

Click to expand...

Some of the times John has mentioned using a calibrator. I trust his judgement on its efficacy.

Wrt free-field, the Cirrus calibrator manual comments:
Adjust the Sound Level Meter to the correct level where applicable. There are several factors to be considered when correcting the value generated by the calibrator. These are:
1. A correction for the type of microphone capsule.
2. A correction for any changes in barometric pressure from 1013mBar (1013 hPa).

In most situations, the Sound Level Meter will be fitted with a free field microphone. The correction required for the specific microphone fitted to the Sound Level Meter will be given in the operation manual for that instrument.
Calibration corrections are listed below for the Cirrus Research plc ½" Capsules and two microphone capsules commonly used in test labs:
Microphone Type, Calibration Correction, Effective Calibration Level
MK:202 -0.3dB 93.7 dB
MK:215 -0.3dB 93.7 dB
MK:216 -0.3dB 93.7 dB
MK:226 -0.3dB 93.7 dB
MK:224 -0.3dB 93.7 dB
B&K 4134 0dB 94.0 dB
B&K 4180 0dB 94.0 dB
Example
An example of the procedure used to calculate the value required is shown below:
Level = 94.0dB + Microphone Correction + Barometric/Altitude Correction
Level = 94.0dB + ( -0.3dB) + Correction for 700mBar
Level = 94.0dB + ( -0.3dB) + (-0.8dB)
Level = 92.9dB