Class 1 Measurement Microphone 1/2", 1/4" vs class 2 calibrated

[tochnia]

I want to get opinions on what kind of microphone we need to get accurate measurements?

This mean to get same result if we next 6 or 12 months later with different temperature in room.
As cheaper class 2 microphones deviate with time, humidity and temperature.

Some class 1 1/4" Microphones even having great initial calibration result will require continuous calibration over time for accurate results, which will bring costs up.
Some class 1 1/2" Microphones show stability of 250 year / dB.

Class 2 usually don't show temperature coefficients.

But some inexpensive Class 1 Microphones like BSWA MP215 /200GBP/ show:
Dependence on temperature: ±0.2 dB
Dependence on humidity: ±0.2 dB
Dependence on pressure: ±0.6 dB
So this is ±1dB which is quite substantial and cannot be count as close to accurate.

So lets have some graphs and food for thoughts:

In graph:

Class 2 NTI Audio - M4261 - 400GBP
Class 2 Sonarworks Xref 20 Microphone - one of better samples - 70GBP
Class 1 NTI Audio - M2211 - 940GBP


Also graph for deviation of Brüel & Kjær microphone deviations /taken from B&K presentation/:

I expected less deviations, which can go up to ±1dB at higher frequencies.

But even super expensive Neumann U87 is having quite a deviations acceptance: ±1dB over whole spectrum.

So which microphone do you see as one which will provide long term accurate results without need of continuous calibration?

 

[KSTR]

@tochnia , Get a true high-voltage condensor type, not a back-electret one. The latter are much more prone to change specs over time (top of all: loosing sensitivity) and under varying environmental conditions. Speaking of which, those are in general not the key issues for repeatability and the conditions will be more or less the same for "typical" measurements... if only that the transducers to be tested/recorded will have much much more drift from temperature and humidity than any mic. Humity also impacts frequency response vs distance in air.

If you really need extended flat frequency reponse (without calibration) and true omni behavior, you need a 1/4" capsule and typically those are really flat only without protective grille. Otherwise, just dial in the calibration as per the individual on-axis frequency response plot delivered with the mic.

EDIT1: The U87 is the antipode to a measurement mic... it is goodwill from Neumann to actually use a tolerance band for production... and 1dB is really quite narrow to catch small tilts and sensitivity changes.

EDIT2: The Sonarworks is a generic off-the-shelf phantom-powered back-electret, it is available in this exact shape under different names from various suppliers (including Behringer etc). Their unit-to-unit variation is gross ususally, but you may be lucky and get a good one with a moderate calibration curve .... which is only as good as the reference they used, of course. Some people/companies offer calibration services at reasonable cost.

 

[Trell]

Earthworks Audio has a number of measurements microphones, and one of them (the M23R) has a fr response of +- 0.5dB.

https://earthworksaudio.com/measurement-microphones/m23r/

Seems that recalibration is not necessary:

"Build your own matched array of reference microphones at your own speed. Simply add more M23Rs whenever you need them. They’ll match tomorrow or ten years from now. "

 

[dfuller]

The U87 is not meant to be a measurement mic. It doesn't need to be that accurate. Neumann's capsule spec is I believe +/-2dB from spec which as recording mics go is quite close tolerance.

 

[Trell]

The U87 is not meant to be a measurement mic. It doesn't need to be that accurate. Neumann's capsule spec is I believe +/-2dB from spec which as recording mics go is quite close tolerance.

Indeed, the U87 is a studio microphone that can switch between three polar patterns. I've the Earthworks Audio SR314 that is a very nice vocal microphone with a cardioid polar pattern and a "flattish" fr response , but I would not use that one for measurements.

 

[tochnia]

I know that Neumann U87 is not measurement microphone
It was just example how even very expensive microphones have quite a deviations.

I haven't seen this statement about stability of Earthworks microphones before, but is encouriging.

"Build your own matched array of reference microphones at your own speed. Simply add more M23Rs whenever you need them. They’ll match tomorrow or ten years from now. "

 

[KSTR]

M23R's are just cherry-picked M23's, me thinks.
As mentioned, precision engineered and carefully handled capsules with high voltage polarization are extremely stable. And the pre-polarized stuff is getting better as well, just don't expect that they retain sensitivity over several decades.

 

[tochnia]

M23R's are just cherry-picked M23's, me thinks.
As mentioned, precision engineered and carefully handled capsules with high voltage polarization are extremely stable. And the pre-polarized stuff is getting better as well, just don't expect that they retain sensitivity over several decades.

With high voltage polarization you mean 200V ones like B&K which need special preamplifiers providing this polarization voltages?

Even one decade of stability will be fine, but not microphones which need calibration every 6 or 12 months.
I understand that this regular calibration is fine for manufacturers of equipment, but will be too much for hobby testing and tuning of audio systems.

Should I be worried about noise floor/self noise of measurement microphones?

 

[PKAudio]

Earthworks recommends re-calibration every five (5) years.
https://earthworksaudio.com/wp-content/uploads/2020/11/Earthworks-Audio-M23-User-Guide-V2-1.pdf

 

[tochnia]

Earthworks Audio has a number of measurements microphones, and one of them (the M23R) has a fr response of +- 0.5dB.

https://earthworksaudio.com/measurement-microphones/m23r/

Seems that recalibration is not necessary:

"Build your own matched array of reference microphones at your own speed. Simply add more M23Rs whenever you need them. They’ll match tomorrow or ten years from now. "

View attachment 129592

Now I checked and also in user guide for M23R is written: Earthworks recommends re-calibration every five (5) years.
https://earthworksaudio.com/wp-content/uploads/2020/11/Earthworks-Audio-M23R-User-Guide-2021.pdf

 

[KSTR]

@tochnia , for hobbyist purposes I wouln't freak out over high grade measurement mics, let alone with traceable calibration and such.

Of course, a good mic is a life-time investment and then initial and follow-up costs might be justified, especially in a commercial setting.

200V capsules can be used with either classic proprietary buffers and supplies but today there is a choice of P48-powered mic bodys as well. Some are even with digital output.

W.r.t. noise, that all depends on the application. 1/4" capsules go high in frequency and max SPL but ouf course are much noisier than a 1" diaphragm (which has at least 10x the active area).

 

[Trell]

Now I checked and also in user guide for M23R is written: Earthworks recommends re-calibration every five (5) years.
https://earthworksaudio.com/wp-content/uploads/2020/11/Earthworks-Audio-M23R-User-Guide-2021.pdf

Clearly I didn't read the user manual carefully enough.

 

[DonH56]

Metal-diaphragm mics will be more stable over (long) time but I am not sure what those are these days. I have an M30 but am pretty sure it is not metal diaphragm.

1 dB variation is actually very good for a microphone and many include individual calibration files. Sound velocity is a function of temperature, humidity, density, etc. so calibrations may vary with environmental factors. Smaller capsules tend to be less sensitive IME but this is decidedly not my day job. Smaller capsules typically have more extended (and often flatter) frequency response but higher self noise as @KTSR said.

I compared the measured response from my CSL-calibrated UMIK-1 to my Earthworks M30 and the curves virtually overlaid. A mixed blessing given the cost difference. The Earthworks has lower noise and greater dynamic range but the UMIK-1 is way easier to use and more than adequate for typical measurements in a home or even typical commercial setting. A UMIK-1 and REW replaced about $10k worth of HW and SW as my main measurement system a long time ago (with the caveat that I rarely did any commercial jobs, mainly home, church, and venues for the local youth and volunteer orchestras and bands, and for years now have very rarely pulled it out -- just when something in my system changes).

What is the application (use-case) for this mic?

Edit: CSL link for UMIK-1 calibration: https://cross-spectrum.com/measurement/calibrated_umik.html

 

[tochnia]

Use-case for mic is precise calibration/equalisation of speakers - mostly home/small studio setups.

I know that most people will tell me to settle with cheap class 2 mic with calibration file, but given the serious amount of money spend on speakers, amplification, digital audio conversion, clocking, equalisers I want to achieve accurate measurement results and don't mind to spend some money on good microphone.
I started with Sonarworks Xref 20 Microphone with calibration file in REW but measurements tends to differ for same setup so I wanted more stable and precise microphone.

But I faced problems with which microphone to go ahead and what exactly to look for.
So far among good choices I see: Earthworks M23R 1/4", NTi Audio M2211 1/2".
B&K prices are very expensive and most of them are designed to work with their analysers, and not having XLR outputs.

 

[PKAudio]

Here is comparison of EMM-6 CSL and Earthworks M-30.
EMM-6 CSL calibration file applied (5Hz-25kHz). Mic is ~4years old.
M-30 new mic, cal file not applied.

For acoustic measurements or crossover design EMM-6 is perfectly fine (cal file is neccessary so it is why I chose CSL, CSL calibration is reliable). On the other hand, these mics are not good for distortion measurement, that basically includes all cheap EMC-6, ECM8000 etc, and I think USB mics as well.

 

[DonH56]

Use-case for mic is precise calibration/equalisation of speakers - mostly home/small studio setups.

I know that most people will tell me to settle with cheap class 2 mic with calibration file, but given the serious amount of money spend on speakers, amplification, digital audio conversion, clocking, equalisers I want to achieve accurate measurement results and don't mind to spend some money on good microphone.
I started with Sonarworks Xref 20 Microphone with calibration file in REW but measurements tends to differ for same setup so I wanted more stable and precise microphone.

But I faced problems with which microphone to go ahead and what exactly to look for.
So far among good choices I see: Earthworks M23R 1/4", NTi Audio M2211 1/2".
B&K prices are very expensive and most of them are designed to work with their analysers, and not having XLR outputs.

Honestly, given variances in speakers and rooms, and guided by my experience comparing them, I would just go for the CSL-calibrated UMIK-1 and REW. CSL also calibrates some Dayton and Behringer mics (or did, have not looked recently), but they both had higher self-noise and in some cases less dynamic range than the UMIK-1 so I stuck with it. An Earthworks or any high-end measurement mic plus good preamp and interface (ADC) is going to run at least several thousand dollars (USD). I know, been there. I had B&K and Sennheiser (I think) measurement mics in the past in addition to the Earthworks I have now. The mics cost around $1k or more (and that was years ago) and a quiet preamp was in the $2k to $3k range, plus analysis software. I think my M30 is around $600~$700 USD now. I got rid of my high-end preamps when I quit doing serious recording and have not touched my inexpensive "field" recorder (a little Roland unit) in years now. I have inexpensive PreSonus and mAudio interfaces I used with the M30, but given the hassles of setting everything up, these days REW and the UMIK-1 are perfect for my needs. For in-room measurements I don't need the greater dynamic range and lower noise, and hauling the preamp and interface is a chore when I need to measure at some venue.

Measurement differences can happen if you move the mic (or anything else) just a tiny bit; getting repeatable measurements is one of the banes of any acoustician. While environmental changes have caused me some variation in the past, by FAR the biggest repeatability issues were mic placement and making sure everything else in the room was placed identically (including me) from measurement to measurement. A quarter wavelength at 10 kHz is a fraction of an inch so it does not take much for a measurement to change.

 

[SIY]

M23R's are just cherry-picked M23's, me thinks.
As mentioned, precision engineered and carefully handled capsules with high voltage polarization are extremely stable. And the pre-polarized stuff is getting better as well, just don't expect that they retain sensitivity over several decades.

AFAIK, the M23R has its eq and sensitivity tweaked internally to give a flat response.

https://audioxpress.com/article/fresh-from-the-bench-earthworks-m23r-measurement-microphone

 

[KSTR]

AFAIK, the M23R has its eq and sensitivity tweaked internally to give a flat response.

https://audioxpress.com/article/fresh-from-the-bench-earthworks-m23r-measurement-microphone

Ok, so fiddled to fit rather than blunt cherry-picking. Fixed components have been used for many decades for capsule EQ and sens. trim so making them adjustable or simple to fit and replace is a logical step forward.

 

[KSTR]

I started with Sonarworks Xref 20 Microphone with calibration file in REW but measurements tends to differ for same setup so I wanted more stable and precise microphone.

As mentioned by others, the microphone itself most proably is not the limiting factor here.

 

[SIY]

Ok, so fiddled to fit rather than blunt cherry-picking.

Great way to put it!