Measurement microphone calibration

[Daverz]

I have an old measurement microphone, an Audix TR-40 (no longer made), which I would have bought about 2002.

http://recordinghacks.com/microphones/Audix/TR40

It would not have been cheap back then (about $400 IIRC). It hasn't been used much and was always stored in the original instrument case, but it hasn't always been stored in the most temperature controlled conditions (the garage).

I'm wondering if it's worth it to send this off for calibration when a Behringer ECM 8000 is under $60 and a Superlux ECM999 (sold by Acourate) is under $90. Oh, and there's the Dayton Audio EMM-6 for $70. The mic would only be used for room and speaker measurements.

Or maybe it's not worth worrying about absolute accuracy. The correction filters made with the TR-40 measurements sound very good.

I ordered a Behringer UMC202HD to use as a mic pre-amp and ADC. I'm looking specifically for an analog mic so that I can use the same clock for both playback of the excitation signal and recording of the output.

 

[amirm]

If you are using it for room equalization, you don't need to calibrate it. Overall tonality of your room should be set via your ears so it doesn't matter if there is inaccuracy in the measurements that way. The main problem with the room are the resonances in low frequencies and there, the peaks show up regardless of calibration.

 

[Blumlein 88]

Most modern electret microphones will last many, many years. Some older ones would lose some of the "permanent" charge on the diaphragm. Even if this one lost some charge, if it works it would just be insensitive. Not necessarily inaccurate in frequency response.

I've compared multiple versions of recording electrets and condensers and some spanning 20 years of age all measure with response curves falling almost perfectly right on top of each other when they are the same microphone model. For a business or some serious research one would like to see calibration checked. For your personal use I'd not bother having it calibrated. I'd just use it like it is. Like Amir said, it is most useful for straightening out the low end response in your room.

Here is 3 electrets that span more than a decade between the three. Speaker was the same source for each which is why the roller coaster graph. I would imagine the small differences are mostly where I didn't perfectly put the mic in the same exact place though they were within 1/4 inch or so.

 

[Daverz]

I'll admit now that I haven't even been using the calibration file I have for the UMIK-1. While DRC-FIR has an option for loading a calibration file, the time I tried it all it did was change the overall level slightly. Good to know that I don't have to worry too much about the age of the mic, either.

 

[Berwhale]

If I wanted to buy a microphone for REW, should I buy a UMIK-1 as they suggest, or is something cheaper just as good for basic room correction?

 

[GrimSurfer]

If I wanted to buy a microphone for REW, should I buy a UMIK-1 as they suggest, or is something cheaper just as good for basic room correction?

UMIK-1 would certainly give you very good results, but most room correction doesn't require a great deal of precision because you're mostly trying to equalize the large nodes at the lower end of the audible spectrum before ultimately fine-tuning by ear.