Dayton UMM-6 vs. UMIK-1 comparison

Greg Dunn

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I already had been using a UMIK-1 for about 3 years to measure my system, and actually have been pretty happy with it. But because I'm an engineer, and because there's really no way of knowing whether the calibration of a mic is correct without some kind of reference, I decided to buy a Dayton UMM-6 to compare against it and see whether I could learn anything.

The first UMM-6 was DOA, so I sent it back. The second one worked fine, so I set up a comparison. I actually measured the UMM-6, then the UMIK-1, and then the UMM-6 again. I used my system in the basement as a reference, using PR pink noise; I know the actual spectrum isn't totally flat, but the object here was to compare the mic curves, and not to do an absolute calibration on the mics themselves. I quit REW between each measurement, in order to minimize the possibility that it might hang on to the wrong cal file and bias the measurement. I used the moving mic technique with averaging (something I've used a lot over the last couple of years) to minimize position errors and got very consistent results. I actually measured the UMM-6 at both 0° and 90° to see if there was a significant difference caused by orientation; I used one of each orientation in my graph since otherwise the two UMM-6 traces would be indistinguishable - they were that close to each other from run to run.

The result: there's a rather large discrepancy between the mics, which is greatest around 10 kHz. Blue trace = UMIK-1; other traces = UMM-6. Both of the cal files look reasonable (and yes, the cal files from the two UMM-6 mics were actually different, so I don't think they're cheating by sending the same cal file with each mic) and show a max difference of ~2 dB - nothing like the 10 dB I see (which is a sanity check on whether the cal files actually were applied correctly). Maybe somehow there is an error due to the wrong cal file being selected, but that doesn't seem consistent with the results as I view them.

Tonight I'm going to insert a graphic EQ into my system and attempt to verify that the UMIK-1 trace is the more accurate - and if it isn't, I'll be sure to note that. I have no bias toward one or the other of these mics, but I'd sure like to know whether my ears agree. The system sounds OK now, but I recognize that I may just have gotten used to the error and am accepting it as "right". Like the man who has two clocks, I am now worried that I don't have the correct time. :rofl2:

If anyone sees a glaring error here, please chime in.
 

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Sonnie

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I have a UMIK-1 that was calibrated by Spectrum Labs that measured the exact same as another unit that came straight from miniDSP. I did not use moving mic... not sure you could really get an apples to apples comparison with averaging. I use a program to center the mic, and mark the mic holder and measure tip to ceiling to be sure I get it as close as possible. You might see .5dB difference here and there, but for the most part it should be close.
 

Greg Dunn

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The main reason I used MMM averaging is that in this room with this system it's very repeatable. Maybe not within a dB or so, but certainly far better than 10 dB. :) It has done a worthy job of making my system sound right with most music.

I just did a pink noise listening test using a 1/3 octave EQ to check audibility of each band (it's an old soundman trick when trying to balance the EQ without a meter or RTA; you slide each band up and down to see when it starts to become noticeable and then center it by ear). The UMIK-1 calibrated response sure seems close, at least up to 13k where my hearing starts to roll off. So I'm tempted to say that the UMM-6 indeed has a rolloff on the high end - that too measures repeatably despite position or orientation....
 

Greg Dunn

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For completeness, I went ahead and did a swept measurement of the two mics, placed as close to identical as possible and not moved between tests. Once again, the UMIK-1 is the upper trace. Once again, there's a large and consistent discrepancy at 10 kHz. As far as I'm concerned, there's no reason to pursue this any further - the two mics are dramatically different above 2k. I guess I'm going to have to get another one and see how it compares, but at the moment I'm pretty confident that the UMIK-1 I have here is closer to "flat".
 

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Sonnie

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DanDan

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I have roughly tested a UMIK against a Bruel and Kjaer. They were remarkably close in Frequency Response. But the level Cal was off by 1.8dB. Ditto a later UMIK.
 

Greg Dunn

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I'm not too fussed about absolute level, as long as the shape of the curve is known accurately. Was the UMIK more, or less sensitive than the B&K?
 

12outof13

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It appears to me you are measuring a pair of speakers, which is causing the difference in the high frequencies. The left and right channel high frequencies are partially canceling each other out. Measure a single speaker only. Place the tip of each mic in the exact same position, put the mic close to the single speaker to remove room reflections. Do not use the moving moving mic method for this purpose. There is no way these mics are this different Unless one is damaged. It is being caused by the measurement technique.
 

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I'm in the market for a mic to use with REW. These are the two contenders and it is alarming to see the variance between them. Also, the comment about the first UMM-6 being DoA is a concern as well. I think that I will hold my purchase and see how this conversation develops over time. Thanks for the heads-up.
 

AustinJerry

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Like Sonnie, I did not see a significant difference between measurements of my UMIK-1 using the factory cal file vs. the CSL cal file.

Two UMIK-1 mics.png


However, more concerning is the difference between the UMIK-1 and my newly-purchased UMIK-2, both using factory cal files. I am considering sending the UMIK-2 to CSL for custom calibration. I also started a thread on the MiniDSP forum asking MiniDSP Support to comment on the differences, but have not received a reply yet. Several others are seeing the same issues with the UMIK-2, which is supposed to have improved accuracy.

UMIK-2 vs UMIK-1.png
 

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Wow Jerry... that's considerable there. It looks as if the UMIK-2 doesn't have the calibration file applied.

I can't see your UMIK-2 cal file being accurate when CSL calibration matches the UMIK-1 factory calibration as close as it does.

Please keep us posted on what you find out. I suspect miniDSP will be sending out some new cal files.
 

linearphase

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It appears that one of three things is going on here:
1. Wrong measurement technique- both mics must be in exactly the some position (within 1/8") and orientation, pointed directly at a single speaker. Only one speaker should be running. Further I would measure using sweeps at 1M on the tweeter axis
2. Wrong cal file being loaded and /or REQ not correctly recognizing cal file. Use the 0 degree file for both mics and confirm that it is being loaded and recognized.
3. UMM6 is defective, minor assembly errors can cause changes in high frequency response.
 

AustinJerry

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It appears that one of three things is going on here:
1. Wrong measurement technique- both mics must be in exactly the some position (within 1/8") and orientation, pointed directly at a single speaker. Only one speaker should be running. Further I would measure using sweeps at 1M on the tweeter axis
2. Wrong cal file being loaded and /or REQ not correctly recognizing cal file. Use the 0 degree file for both mics and confirm that it is being loaded and recognized.
3. UMM6 is defective, minor assembly errors can cause changes in high frequency response.
When I read your post, I interpret it as "Either you guys don't know what you are doing, or the mic is defective". For a relative newcomer, you are not going to win any friends by being disrespectful.
 
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linearphase

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Sorry to have offended you Jerry. That was not my intent at all. Please let me explain.

I am a relative newcomer here but I am not a newcomer to either acoustics or acoustic measurements. That was my profession for 31 years. I used different measurement tools and only recently switched to REW because it has come so far in the last 5 years or so and now I find it can replicate what the pro tools have offered for years.

Since I have retired 10 years ago, I have been helping people set up their systems , for FREE, mostly in the US but some throughout the world. I like REW because everyone can look at the same data easily so I can often do this over the phone or via email.

What I have learned in all those 41 years is that people often make mistakes, myself included.
I can give specifics about what triggered my response here but will not lest it offend anyone.
So my intent was to merely offer suggestions as to what might be wrong.
 
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AustinJerry

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OK, I'll take you at your word that you didn't intend to offend any one. But in my experience, measurements taken with the mic pointed towards the ceiling, using the 90-degree calibration file, are just as accurate in making comparisons. And you should assume that we are using the proper calibration files, IMO, and that we understand the importance of proper mic placement.
 

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You posted right before me Jerry... fully agree with your comments, although I did not spell it out as you did.

I believe all of those comments by linearphase are pretty basic assumptions that most all of us here will already know, although there are numerous very simple ways to compare mics accurately.
 

linearphase

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Jerry and Sonnie, thanks and I agree. It is never my intent to offend anyone. I admit my response was short and to the point, largely because I am working with three people today and this just popped up between the other two sessions.
The OP is listed as a new member and the feedback was directed to him. Over the years I have helped in excess of 1000 customers make measurements so I am well aware of what can go wrong. I frequently have people make mistakes that have 10's of years of experience. Having two speakers running during a measurement is extremely common. Just as important I have personally seen REW not correctly accept cal files.
Once again just trying to offer suggestions, I do not know the poster or either of you.
Please accept my apologies...
 

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Don't sweat it... and we appreciate you trying to help.
 

Greg Dunn

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OK, I ran one more sweep at 1M, single speaker, on axis, as a final check.

The mics were as close to the same position as they can be without adjusting via laser interferometry. :)

I double checked the cal files, and the proper ones for each mic appear to be loaded. I assume REW is being honest (joking - I trust it as long as I'm not making mistakes).

I'm seeing a ~10 dB difference at 10k between the UMIK-1 and the UMM-6 whether I sweep or average, at 1M or 3M distance, 1 speaker or both being driven. I must assume this is a problem with the mic; if it were position- or technique-related, there's no reason the difference would be consistent and identical.

Incidentally, I double-checked the cal file vs. the edited one I built, and after being sure I purged the cal file from REW's preferences between measurements, I do indeed get a difference in the UMM-6 measurements. I presume it was somehow using the default cal file when I tested it last time, but I'm not sure how. Anyway, I'm going to accept that the UMM-6 is calibrated differently from the UMIK-1 and (sigh) am going to beg, borrow or buy a third mic to end the confusion. Thanks to all who contributed.
 

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DanDan

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That looks like the difference between 0 and 90degrees which most Omni Mics would display. I would be interested to see both mics compared with no Cal Files
 

linearphase

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Greg
Good catch and troubleshoot technique.

These are the the normal deviations of Behringer ECM mics as found by Cross labs. I suspect, but do not know, that they are similar of not the same mic capsule. These are not unexpected variations in a capsule that costs a couple of dollars.
I built several of my own mikes from scratch many years ago using similar Panasonic capsules and found these kinds of deviations. Your idea is probably the best way to resolve these differences if that is important in your application.

1606000513045.png
 
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DanDan

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Decent responses. Good to know Jerry, tx.
 
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