Microphone reliability below 20Hz

[tisimst]

Budget measurement microphones, such as the miniDSP UMIK-1 and Dayton Audio EMM-6, state some functional frequency range (i.e., 20Hz to 20kHz). My question is specifically on the low end of these claims. In spite of such published specifications, I've seen many demonstrations online of knowledgeable users doing subwoofer frequency sweeps often from 10Hz on up, for example. So, where the published specs do not claim to go that low, what kind of reliable measurements can I expect to get from such microphones for ultra low frequencies? The real reason for asking, is that there are some microphones that cost much, much more that do have published specs down to below 10Hz, even down to 5Hz in some cases I've seen, but is that really necessary to get mostly accurate low frequency measurements? I admit that I'm an audio enthusiast and that I can probably live without incredibly precise measurement microphones. Still, I'd like to at least learn so I can make the judgement call from there. I'm grateful to any and all who are willing to share their experience.

 

[John Mulcahy]

For the UMIK-1 20 Hz to 20 kHz is the +/1 dB spec range, the mic of course remains useable well outside that range. The calibration file extends to 10 Hz. There is no need for an expensive microphone for low frequency measurements.

 

[Wayne A. Pflughaupt]

What John said. The frequency response of the mic ultimately isn’t what’s important. A proper calibration file will make up for what’s lacking below 20 Hz.

Regards,
Wayne

 

[AudioCAT]

I used a measuring microphone made by WM-60AT. I calibrated it myself. The low frequency limit is 6Hz. I am very satisfied.：p

 

[tisimst]

That makes a lot of sense. Thank you @John Mulcahy & @Wayne A. Pflughaupt for that insight. I guess I'll not worry quite as much about that. What if I can't get a calibration file for whatever microphone I end up choosing?

@AudioCAT, how did you perform the calibration yourself? That would be very interesting to learn about.

 

[DanDan]

Nearly all the manufacturers of cheap measurement mics supply Cal files now. I can see no reason to buy one without. Unless you want to go up market. The higher grade mics, including those used for recording, DPA and such, often have very tight frequency response specs, probably better than those factory Cal files.
There are other decent mics in the middle market. studiosixdigital W-Mic Isemon.
Full list here https://www.avnirvana.com/threads/some-guides-to-rew-and-acoustic-measurement.121/page-2#post-49827

 

[AudioCAT]

@AudioCAT, how did you perform the calibration yourself? That would be very interesting to learn about.

Calibrating the microphone is indeed more troublesome, the reason is not the operation, it is required to have a reference microphone with reliable frequency response.

The calibration operation is relatively simple.
First measure the same sound source with the reference microphone and the microphone to be calibrated separately.
(I use a 3-inch full broadband speaker as the sound source, and the measuring distance is 200mm)

Then use the REW to Division calculation the two frequency response files to obtain the microphone calibration file.

The lower limit of the frequency of the calibration file obtained in this way is limited, and it is generally not very low.
Therefore, it is necessary to calibrate the low frequency band again (Replace sound sources with better low frequency performance)

Using near-field measurement, repeat the above steps.

In this way, we got the calibration file of low frequency band.

Finally, using REW's Merge calculation function, the low frequency band is Merge from the previous calibration file, and the calibration file with the full frequency bandwidth will be obtained.

 

[DanDan]

Thank you AudioCat, that is well, amazing. As it happens I do have a B&K 2250, so a Lab standard reference. But a lot, most of my work these days is done using a PMik and a UMIK, so the ability to do my own Cal is of great interest to me.