Shopping for a measurement mic

[Blumlein 88]

I use the Dayton Audio iMM-6, super small. It needs a TRRS extension cable and TRRS usb audio. The lot is less than the other mics and calibrated.

I've one of those too. It isn't far from the Umik. Let's you use a smartphone or tablet for some measures. However, I've found a few oddities using it with Android stuff. Some of it works, and some truncates the response past 8 khz. It isn't the microphone as an iPhone can do good work using it.

 

[headshake]

I've one of those too. It isn't far from the Umik. Let's you use a smartphone or tablet for some measures. However, I've found a few oddities using it with Android stuff. Some of it works, and some truncates the response past 8 khz. It isn't the microphone as an iPhone can do good work using it.

No probs with a PC and a USB TRRS audio adapter.

 

[RayDunzl]

However I've seen studies showing that you need really good mics to test loudspeaker distortion since you need high spls and close micing to get the speaker to distort and to diminish room sound.

My limited experience here is that speakers can and will produce measurable harmonic distortion starting below 80dB at a 10 foot listening position, which isn't terribly loud at the driver in a typically reflective residential room.

I don't have nor am I building any specialized speakers/drivers, but here's a 1998 MartinLogan electrostat vs 2016 JBL LSR 305.

I leave it to you to guess which is which, for now.

I figure since the observed SPL is the same, the frequency is the same, but the distortion products are quite different, it isn't the mic -- UMIK-1 ---that is causing the distortion in the readings.

Plus, you can hear the more distorting speaker distort vs the lesser distorting unit...

Were I designing drivers, I suppose a quiet microphone would be handy, surely quieter than the UMIK-1, and, of course, a quiet room, as the residential low frequency ambient noise messes with lower SPL low frequency measurements.

 

[Blumlein 88]

My limited experience here is that speakers can and will produce measurable harmonic distortion starting below 80dB at a 10 foot listening position, which isn't terribly loud at the driver in a typically reflective residential room.

I don't have nor am I building any specialized speakers/drivers, but here's a 1998 MartinLogan electrostat vs 2016 JBL LSR 305.

I leave it to you to guess which is which, for now.

I figure since the observed SPL is the same, the frequency is the same, but the distortion products are quite different, it isn't the mic -- UMIK-1 ---that is causing the distortion in the readings.

Plus, you can hear the more distorting speaker distort vs the lesser distorting unit...


View attachment 40337

View attachment 40338

Were I designing drivers, I suppose a quiet microphone would be handy, surely quieter than the UMIK-1, and, of course, a quiet room, as the residential low frequency ambient noise messes with lower SPL low frequency measurements.

Assuming some considerable similarity, I believe much of the distortion in the LSR is from the amplifier. Look at this data sheet for the amps in the mkII version which I believe is more or less the same.

https://www.jblpro.com/ProductAttachments/308P_MkII_SellSheet_2page_Final.pdf

.2% thd (-54 db) at 2.83 vrms output with SNR of 70 db at that output level. < 1% thd (-40 db) at full rated output at 1 khz.

Using Revel F12's driven by a fairly clean amp, I've measured around or just below .1% thd in REW at 85 db spl. Or just about the same as the Soundlabs will do. 11 ft LP in my case.

 

[RayDunzl]

Here's what I believe to be the amp chip:

https://www.st.com/resource/en/datasheet/sta350bw.pdf

Same in LSR 305 and 308, but the 308 gets a little heat sink stuck on top of it.

http://rdimitrov.twistedsanity.net/blog/show.php?entry=JBL LSR305 Teardown and Analysis

It's fine for casual listening, and very economical at an average of about 5W draw, but can't keep up with the mains... like right now...

 

[trl]

Just installed last weekend several acoustic panels inside a friend's small auditioning room and for the measurements I was using Superlux ECM999 connected to a Focusrite Solo 3.

​

The orange line represents the sound before acoustical panels installation, the green one is after. There's still some work to do there on the next weekend, but overall I think a cheap measurement mic should do the job. I've also tested this microphone with a sweep 20-20KHz audio file and it was showing quite a flat freq. response when pointed directly on the speakers.

 

[Gnasherrr]

ii went for an isemcon 7150. seems like the most reliable measurement mic that's somewhat comparable to earthwork's offerings.

 

[JRT]

I've seen studies showing that you need really good mics to test loudspeaker distortion since you need high spls and close micing to get the speaker to distort and to diminish room sound.

Outdoor ground plane measurements allow more propagation distance, and -6_dB SPL at the microphone with each doubling of propagation distance in the far field. You would need a portable test rig, and would need to find a suitable outdoor test location.

 

[Dave Zan]

...the Scarlett + EMC8000 instead of UMIK-1?

Hi Matias

There is one issue that no one seems to have mentioned.
USB mikes have their own clocks and thus have synchronisation issues in certain test set ups or with some software.
For instance VituixCAD is nice crossover CAD freeware that mentions this issue.
This may not be a problem for you for simple measurements but may limit your ability to switch software or step up to advanced measurements.
So just a point to keep in mind if you haven't already purchased your mike (sorry if you have, I'm a newish member, just saw this).

Best wishes
David

 

[Dave Zan]

...mics to test loudspeaker distortion...
What is it about these...?

One aspect is that the old reference standard Bruel and Kjaer microphones used a 200 V polarisation supply.
This provided more freedom to optimise the capsule for extreme SPL and still retain acceptable sensitivity and low distortion.
Newer electret based capsules are more convenient since they don't need a specialised power supply (and connectors etc.)
But there is a performance trade off.
Stability is also minutely worse but not likely to matter unless you are a national standards level lab.

Best wishes
David

 

[q3cpma]

I personally use the Behringer, but it's worth noting the Beyerdynamic comes with an individual calibration file (you just have to register it on their website).

 

[mitchco]

ii went for an isemcon 7150. seems like the most reliable measurement mic that's somewhat comparable to earthwork's offerings.

Great choice! One of the few measurement mics that actually has a published distortion specification: http://www.isemcon.com/datasheets/EMX7150-US-r04.pdf The only other mic that I know that has a published distortion spec is the Earthworks mic. Maybe the B&K's do as well, did not look. Important if you want to take speaker distortion measurements. Also one needs to check the distortion spec on the mic pre and ADC as an example here.

The UMIK-1 makes it real easy, but as @Dave Zan points out it does have it's own clock and there have been issues with clock drift and clock sample rate mismatch, but this have been fixed in the later software versions of REW, Acourate, and Audiolense.

 

[Dave Zan]

...The UMIK-1 makes it real easy, but as @Dave Zan points out it does have it's own clock and there have been issues with clock drift and clock sample rate mismatch, but this have been fixed in the later software versions of REW, Acourate, and Audiolense.

Hi Mitch, do you have more information on this?
AFAIK there is a "work-around" to use an acoustic time reference but this is not always practical.
For example - the Klippel scanner clone discussed in a thread here and in DIYaudio needs time lock but can't use the work-around.
There are probably other, similar situations.
A true "fix" would be nice.

Best wishes
David

 

[Matias]

After I got my UMIK-1 I think it is so convenient that I would recommend everyone to start with it, and only upgrade if needed. It is that good.

 

[Dumdum]

Oddly I bought a umik-1 and am now branching out to a m-audio mobilepre and a Dayton mic as I heard a fair few people say that the beginning era of late had some issues of some description I can’t recall with the capsule or some such... so I got the Dayton and have yet to get it working properly, mainly due to a lack of understanding I reckon, time needs to be spent with it I feel I’ve just got some 1/4” jacks to rca adaptors to suit the car audio environment more and enable measurements to be taken

 

[617]

Unless you're testing drivers or trying to design loudspeakers, the USB mics offered by Dayton and minidsp are great products.

 

[Dumdum]

Unless you're testing drivers or trying to design loudspeakers, the USB mics offered by Dayton and minidsp are great products.

The only thing you can’t do with a usb mic that I want to try is a loopback measurement in rew, using an acoustic signal seems to wander and when I’m in the milliseconds it can be a bit inaccurate, now it may be a setting or something but I’ve not bottomed it as yet

Its purely for timing drivers with my dsp in a car environment, it’s hard enough with reflections so close by

 

[scott wurcer]

One aspect is that the old reference standard Bruel and Kjaer microphones used a 200 V polarisation supply.

Just FYI, I measured 90-100V equivalent on some better electret elements. If you have raw capsules without FET's you can buck the built-in polarization and measure the loss in sensitivity.

 

[mitchco]

Hi Mitch, do you have more information on this?
AFAIK there is a "work-around" to use an acoustic time reference but this is not always practical.
For example - the Klippel scanner clone discussed in a thread here and in DIYaudio needs time lock but can't use the work-around.
There are probably other, similar situations.
A true "fix" would be nice.

Best wishes
David

Hi Dave,

I think @JohnPM should be able to comment on using UMIK-1 with REW and whether those clock drift/sample rate mismatch problems have been fixed. I believe they have been...

Wrt Acourate, there is a standalone Log Sweep Recorder that takes the UMIK-1 issues into account and the software can be downloaded here. ASIO4ALL is required though. Wrt Audiolense, there is a feature built into the software to "use clock drift correction" and Audiolense is also able to "use separate play and recording streams" and does not require ASIO4ALL.

These software can export impulse responses as required.

Merry Xmas!
Mitch

 

[JohnPM]

I think @JohnPM should be able to comment on using UMIK-1 with REW and whether those clock drift/sample rate mismatch problems have been fixed. I believe they have been...

There are no systematic issues with UMIK I'm aware of, the rate errors seen were isolated cases. REW can compensate for clock rate differences if required, the setting is under the Analysis preferences, but when measuring in a car there are so many close reflections that the acoustic timing reference could easily be affected.