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

[KSTR]

W.r.t. repeatability I can share a story when I got my Gefell MK301 1/4" capsule which is very low sensitivity. I've used a 1/2" B&K mic body (+supply unit) with 1/4" adapter cone and the whole thing is really damn sensitive to mechanical vibration/shock. I mean, if I barely touch it with a pencil or similar it creates a ringing spike much larger than the true signal even under fairly high SPL (deafening levels). I once had a strange and always the same shape of ringing in a set of measurements of different compression drivers that I could not explain and it turned out it was the resonance of the mic stand (standard K&M, simple metal tubing construction). OK, let's put some isolating foam pads under the feet of the mic stand and all should be well... nope, the ringing was still there, with the only explaination that the direct air SPL was enough to exite the "tubular bell" mic stand. I did not anticipate that the influence would be that strong to make it into the measurement!

 

[DonH56]

I use a shock mount and make sure to loop the cable with some slack. Still not a complete panacea, due to all the various mechanical resonances and pick-up paths, but works pretty well. Precision low-noise measurements are a royal pain... I used to have a mic stand made of solid metal tubing. Heavy as heck but worked pretty well; wish I still had it (long gone). A friend bought a nice carbon-fiber stand with tunes filled with (sand? I'm not sure) for his mic and camera. Works great, but was like $1200 USD for the stand, and I'm too cheap for that. Especially just for measuring my listening room where moving a throw pillow on the couch causes way more variation than the stand adds.

My biggest problem lately is that my old, old $100 boom mic stand is wearing out and the Trinnov measurement mic is bloody heavy (I sold my great big heavy recording mics long ago). I have a couple of times now set it up, left the room to take the measurements, and found the boom had sagged after half an hour or so. Someday I'll break down and get a new stand, or rebuild the one I've got, but for now repositioned it so the boom is not extended as far.

Live sound was always fun; at one concert a guy came up front to take a picture of his kid playing and knocked over the mic stand. Took some talent as it and all the cables to it were taped down. The more insidious issues were things like the mom who held on to the mic stand while recording her kiddo on her phone; a shock mount can only do so much when mommy is shaking the stand. Etc. Then I have to explain why the recording is flawed... Finally they got hanging (overhead) mics for recording purposes.

 

[tochnia]

W.r.t. repeatability I can share a story when I got my Gefell MK301 1/4" capsule which is very low sensitivity. I've used a 1/2" B&K mic body (+supply unit) with 1/4" adapter cone and the whole thing is really damn sensitive to mechanical vibration/shock. I mean, if I barely touch it with a pencil or similar it creates a ringing spike much larger than the true signal even under fairly high SPL (deafening levels). I once had a strange and always the same shape of ringing in a set of measurements of different compression drivers that I could not explain and it turned out it was the resonance of the mic stand (standard K&M, simple metal tubing construction). OK, let's put some isolating foam pads under the feet of the mic stand and all should be well... nope, the ringing was still there, with the only explaination that the direct air SPL was enough to exite the "tubular bell" mic stand. I did not anticipate that the influence would be that strong to make it into the measurement!

So I have to think for better microphone stand then
As for sure this is bringing some resonances for me also...
Which B&K mic body are you using?

I use a shock mount and make sure to loop the cable with some slack. Still not a complete panacea, due to all the various mechanical resonances and pick-up paths, but works pretty well. Precision low-noise measurements are a royal pain... I used to have a mic stand made of solid metal tubing. Heavy as heck but worked pretty well; wish I still had it (long gone). A friend bought a nice carbon-fiber stand with tunes filled with (sand? I'm not sure) for his mic and camera. Works great, but was like $1200 USD for the stand, and I'm too cheap for that. Especially just for measuring my listening room where moving a throw pillow on the couch causes way more variation than the stand adds.

My biggest problem lately is that my old, old $100 boom mic stand is wearing out and the Trinnov measurement mic is bloody heavy (I sold my great big heavy recording mics long ago). I have a couple of times now set it up, left the room to take the measurements, and found the boom had sagged after half an hour or so. Someday I'll break down and get a new stand, or rebuild the one I've got, but for now repositioned it so the boom is not extended as far.

Live sound was always fun; at one concert a guy came up front to take a picture of his kid playing and knocked over the mic stand. Took some talent as it and all the cables to it were taped down. The more insidious issues were things like the mom who held on to the mic stand while recording her kiddo on her phone; a shock mount can only do so much when mommy is shaking the stand. Etc. Then I have to explain why the recording is flawed... Finally they got hanging (overhead) mics for recording purposes.

$1200 for stand is quite a number
Is using shock mount leaving microphone absolutely stable without any movement?
As small change in degree can influence results from what I have read. But it sounds like good solution overall.
Trinnov 3D Mic with 4 capsules integrated looks very interesting especially promising - Freq response: +/-0.1dB and - Freq range: 20Hz - 24kHz
But I guess it can be used only with Trinnov D-Mon 6/8/12?

 

[KSTR]

Which B&K mic body are you using?

Type 2639 (though I'm not sure if it really is original -- using the longer 7pin connector looks suspicious -- but even if it is a copy it is very well made. The supply unit is definitely a clone, though)

Note the scratch marks, those came from trying to open it, not being aware that the two parts (left of the shinier reducer cone) have left-handed threads

I also have an older Gefell MV201 body but I need to build a supply for that one (though a colleage of mine temporarily patched the "B&K" supply/output amp to attach the MV201 for testing).

 

[DonH56]

$1200 for stand is quite a number
Is using shock mount leaving microphone absolutely stable without any movement?
As small change in degree can influence results from what I have read. But it sounds like good solution overall.
Trinnov 3D Mic with 4 capsules integrated looks very interesting especially promising - Freq response: +/-0.1dB and - Freq range: 20Hz - 24kHz
But I guess it can be used only with Trinnov D-Mon 6/8/12?

There's no such thing as "absolutely stable" but it is enough for everything I have done. Some high-SPL testing required special consideration but that is not a reasonable application for the vast majority of us. The shock mount allows the mic to "float" to reduce noise from the mic stand and, to some extent, airborne vibrations. Really for normal measurements a decent stand, mic, and shock mount is plenty. The small changes that affect measurements are far more likely to be from moving the mic or changing the environment (things in the room, speaker positions, and so forth) than from the mic itself.

The Trinnov mic only works with Trinnov (or JBL Synthesis) processors AFAIK. There is a UMIK-2 mic now with larger capsule and higher-resolution ADC (does not really matter for this application but Marketing...) UMIK/miniDSP makes a multi-capsule mic now (Ambisonic or something like that) and a multichannel mic interface but I have no experience with it.

If you are doing laboratory measurements be prepared to lay out at least $5k to $10k USD for your set up. If you want reasonably accurate measurements of your system and typical smaller recording venues then a UMIK-1 (or 2) individually calibrated by CSL or one of the other labs along with REW (free save the learning curve) is more than enough.

I may have missed it, but what exactly is your planned use? What is your budget?

p.s. The B&K I had was the small-diaphragm model, the 4138 (I think, been a while). It had a 1/8" diaphragm IIRC and its own special preamp built into the body, or as a separate attachment, again been so long I have forgotten. It did require 200 V but I'm pretty sure their preamp provided that. It had extremely wide response and would handle very high (160+ dB) SPL. They make a larger (1/2") diaphragm version as well (and probably others now). It was something like $1200 USD and that was 20-30 years ago.

 

[Blumlein 88]

I think the OP is maybe obsessing overly much. Almost any small omni condenser is accurate to around 2 khz. There are deviations above that. Also some of the tolerances over time take into account outliers. I think the majority of microphones are pretty stable over time for uses of home audio measurements. Even electrets are pretty good. I've some that differ in age by 12 years yet are the same.

I wonder if the OP has spent any time with measuring microphones. A few people have said a UMIK-1 is going to be good enough as it is always other factors that play a larger role. If you've done some measurements in various home settings you'll find that to be the case. The microphone isn't the limiting factor. If you feel more comfortable with a better unit the Earthworks 23 or Josephson C550 are probably one to get, and feed it into any decent mid level recording interface. To get better than that will become very expensive.

So my suggestion might be to get a UMIK-1 and use it some. It is inexpensive versus spending $1000 or more. You can get some experience that is very valuable even if you decide to spend the extra bucks. You may find you can do what you need with only the UMIK-1. And I'll mention it again, nearly all small diaphragm condensor microphones are very accurate to around 2 khz.

 

[tochnia]

I think the OP is maybe obsessing overly much. Almost any small omni condenser is accurate to around 2 khz. There are deviations above that. Also some of the tolerances over time take into account outliers. I think the majority of microphones are pretty stable over time for uses of home audio measurements. Even electrets are pretty good. I've some that differ in age by 12 years yet are the same.

I wonder if the OP has spent any time with measuring microphones. A few people have said a UMIK-1 is going to be good enough as it is always other factors that play a larger role. If you've done some measurements in various home settings you'll find that to be the case. The microphone isn't the limiting factor. If you feel more comfortable with a better unit the Earthworks 23 or Josephson C550 are probably one to get, and feed it into any decent mid level recording interface. To get better than that will become very expensive.

So my suggestion might be to get a UMIK-1 and use it some. It is inexpensive versus spending $1000 or more. You can get some experience that is very valuable even if you decide to spend the extra bucks. You may find you can do what you need with only the UMIK-1. And I'll mention it again, nearly all small diaphragm condensor microphones are very accurate to around 2 khz.

I use word "home" but my system is build around studio stuff Studer/SSL/Neumann/Apogee/Klark Teknik. And after spending good amount on audio system why not have proper means for measuring/adjusting/calibrating.
As I said in one of posts above I have Sonarworks Xref 20 Microphone with calibration file but results from it were showing differences between measurements. I have to admit I have to try better stand and shock mount.
Unfortunately I like in UK so there are no CLS calibrated microphones for sale here.

And I believe in long term investment of good measurement mic.
So this is why I wanted to collect information and direction from other people with better that mine knowledge on subject.

Also this forum is very focused on measurements and not "subjective" listening tests so I thought this is best place to ask for advice for measurement microphones.

 

[sweetchaos]

Would the CSL-calibrated UMIK-1 work as well (good enough?) as Earthworks M23/M23R/M30 for CEA-2010 testing?
Brent Butterworth said on his blog:

Everyone I know who does CTA-2010 tests uses the Earthworks M30 microphone

 

[Blumlein 88]

I use word "home" but my system is build around studio stuff Studer/SSL/Neumann/Apogee/Klark Teknik. And after spending good amount on audio system why not have proper means for measuring/adjusting/calibrating.
As I said in one of posts above I have Sonarworks Xref 20 Microphone with calibration file but results from it were showing differences between measurements. I have to admit I have to try better stand and shock mount.
Unfortunately I like in UK so there are no CLS calibrated microphones for sale here.

And I believe in long term investment of good measurement mic.
So this is why I wanted to collect information and direction from other people with better that mine knowledge on subject.

Also this forum is very focused on measurements and not "subjective" listening tests so I thought this is best place to ask for advice for measurement microphones.

My Umik-1 seems very consistent on measurements. I also have one of the little EMM devices for a phone which is better than I expected. I've some recording microphones which aren't for measuring, but I've calibrated them against the Umik or used published response curves and found them to nearly overlay the Umik results. At least those in some cases are expensive well made bits of kit.

 

[Blumlein 88]

Here is a Umik1 (pink), an Avantone CK1 omni (green), and CAD M179 omni(blue). These are 1/6th octave smoothed. The CK-1 and M179 used calibration curves I constructed from published frequency response curves provided by the manufacturer. I was measuring a small bookshelf speaker and placing the mic diaphragms as close to the same spot as possible. I have pairs or even three of the recording omnis. Compared to each other they all just give a curve that lays right on top of each other. Even in some cases with microphones that are years different in age. I could of course cal the other mikes to the Umik1 if I wished to do so. I was surprised using published curves these recording mikes were this close to the Umik 1. I'd have to think using an Earthworks leaves very little on the table in terms of quality of the measurement you can do.

 

[Dave Zan]

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...

Who makes P48 powered mic bodies that can use a 200V capsule?
Similarly to the OP, I want a nice stable measurement system*, even if I don't really need it.
So I can't really justify top dollar but am prepared to pay more than a basic electret mic.
A P48V powered body that can run a classic capsule seems like a nice solution but I am unaware of their existence.
Bruel and Kjaer only seem to do proprietary bodies or ICP.
And all their spin-offs and clones (DPA, GRAS, Norsonix) likewise.
Gefell maybe? Found a Gefell preamp that does this, not exactly much "choice" yet but a nice start.
ACO Pacific have 200V capsules but their P48 body only works with the pre-polarised capsules.
At least I think so, the ACO Pacific website is worthless, doesn't seem to have a clue about how to sell. or even inform.
Perhaps explains why they are barely mentioned on this site (or anywhere much) despite what looks like decent products.
Anyone dealt with ACO Pacific?

I had hopes that Rode would do a reasonable measurement mic and undercut the overpriced products of the lazy established companies, just like they did with their "Neumann" clone and subsequent vocal mics.
But years after their announcement of a "Measurement" division" there's no mic in prospect.
You would think the Measurement division of a Microphone company would make a measurement microphone but apparently not (?!?)

Best wishes
David

*It's for the DIY Klippel system that was started at DIYaudio and that I haven't entirely abandoned.
Just need to finish some speaker cabinets first...and some horns... and the horn tool cutter...and some more amps....and...

 

[KSTR]

Who makes P48 powered mic bodies that can use a 200V capsule?
Gefell maybe?

Correct. Microtech Gefell MV 225 P48.
And I've seen another one but can't recall. It wasn't from a major manufacturer.

200V caspule and P48 output is a compromise, one can hardly get max SPL capability and lowest noise at the same time from this.

 

[Dave Zan]

Correct...

We cross posted, I eventually found it on the Gefell website.
It's not as useless as the ACO Pacific site but still tediously makes one click on every individual product to see the information..
Any idea of the price. approximately?
Expensive.

And I've seen another one but can't recall. It wasn't from a major manufacturer.[

Probably Josephson.
I also discovered DPA do a P48 body that will use standard (B&K style) pre-polarised capsules.
Code is MMP-A and costs ~$500 so the whole mic could be <$1000.
Not bad for B&K reference standard.

200V caspule and P48 output is a compromise, one can hardly get max SPL capability and lowest noise at the same time from this.

Why? They claim the polarisation is internally derived, apparently not just a 200V capsule run on 48V.
If properly done the power supply shouldn't influence the noise.
And I would expect 48 V to be sufficient to drive the output to max SPL.
Is there some problem I have missed?

Best wishes
David

 

[KSTR]

Is there some problem I have missed?

A capsule can provide way more voltage than you can practically transmit via P48. 10Vrms is about the limit (wrt low distortion), even when actually driving the pins symmetrically. The more power you need internally the more the output level is restricted. So you'd have to pad the cpasule buffer outoput down to allow full SPL and that compromises noise limit at least from the circuit side of things. Does in matter in practice? Most often I'd say no.

 

[Dave Zan]

But some inexpensive Class 1 Microphones like BSWA MP215 /200GBP/ show:

You prompted me to have a look at what was available in inexpensive Class 1* so thanks.
I found the MicW M215 which looks quite nice.
The number code implies it is is similar the BSWA MP215 but there are some inconsistencies.
Not sure if the MicW specs are just optimistic or if it really is an improved product.
Other inexpensive options seem to be to adapt an old B&K style measurement mic and preamp via an interface/power supply with XLR output..
This actually looks reasonably easy for the pre-polarised capsules like the B&K 4189 or Gefell MK255.
The Gefell 255 is what Amir uses for his Klippel measurements, maybe considered as a benchmark.

*To be pedantic, Class 1 only applies sound level meters, for precision measurement microphones the IEC standard 61094-4 equivalent is a work standard 1/2" free field microphone, abbreviated to WS2F.

A capsule can provide way more...than you can practically transmit via P48. 10Vrms is about the limit (wrt low distortion)...

A typical sensitive 1/2" capsule is 50 mV/Pa. so 10 Vrms is 140 dB SPL.
Even on the rare occasions when this is insufficient, I can't see the P48 as the limitation.
10 V will drive practically any audio ADC to full scale, or overload a mic preamp.
Why would the use of P48 compromise the system?
I expect it would be possible to put out more than 10 V if necessary.
Do you have any B&K mic body pre-amp (buffer really) schematics?
I would be very interested to see one.

Best wishes
David

 

[tochnia]

You prompted me to have a look at what was available in inexpensive Class 1* so thanks.
That BSWA MP215 looks quite nice, where is it available for 200GBP?

Here it is listed for 208 Euro: https://shop.elkome.com/en/mp215-free-field-microphone
But even they write "microphone" it is only capsule, without preamplifier.

 

[Dave Zan]

Here it is listed for 208 Euro: https://shop.elkome.com/en/mp215-free-field-microphone
But even they write "microphone" it is only capsule, without preamplifier.

That explains the price, also the MP215 is only class 2, which explains the poorer stability numbers you quoted in your initial post.
The Class 1 version is the MP201 or MP231 and the specs are much closer to the MicW 215, despite the less similar codes.
Hope I haven't missed my chance to buy a MicW due to the delay while I checked the competition.

Best wishes
David

 

[Dave Zan]

You prompted me to have a look at what was available in inexpensive Class 1* so thanks.
I found the MicW M215 which looks quite nice.

Ok, ordered a MicW M215

Lower noise than the 1/4" electrets but still with frequency response to >31 kHz for tweeter resonances.
Decent maximum SPL.
And it's a stainless steel capsule so the stability should be excellent.
Well, not B&K excellent but at least it has proper specs so it should be better than a plastic mic.
There is a Tech Note with a cut away of the capsule, looks like another B&K clone.
Link here http://www.micwaudio.com/series.php?cid=51.
About $400 US or just under.
I am really pleased to have found this between the "cheapos" and the full professional financial catastrophe.
Now to learn if it lives up to the claims, report as soon as I have it in my hands, theoretically in a couple of weeks.

Best wishes
David

 

[Graph Feppar]

Any opinions on 1/4" microphones from G.R.A.S, PCB and Aco Pacific? I want B&K but that price is brutal, or should I just take a risk and buy used from ebay?

 

[DVDdoug]

I don't know but I'd say the most important thing is that you trust the calibration curve...

If you were doing "serious" pro work with a used mic it should be re-calibrated, and even a new mic should be periodically calibrated.

If absolute SPL level is important to you a USB mic is better because otherwise you have to calibrate the preamp/interface gain.