ECM8000 microphone measuring techniques and usage discussion - Page 6 - Home Theater Forum and Systems - HomeTheaterShack.com

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post #51 of 170 Old 01-26-09, 06:03 PM Thread Starter
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Re: MobilePre ECM8000 oddities

But still, you figure the ECM would show a better top octave than the RS meter and yet they still both show that steep drop above 15kHz.

Hmm, I think my next project may be to build one of those condenser mics from scratch and see how it performs. If for no other reason, to learn more about what goes into all this. I've had enough tweeter crossover problems that I want to make sure I have something I trust up there (and I don't have $500 for a EarthWorks )
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post #52 of 170 Old 01-26-09, 06:33 PM
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Re: MobilePre ECM8000 oddities

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So I believe we've ruled out the mic, and via nearfield measurements ruled out the speaker. It's not the calibration or loop, but it seems to be the soundcard.
I don't see how it could be the soundcard if your loopback measures flat to 20KHz. That completely eliminates the soundcard. It's the only thing you can be sure of...

I don't think you can be 100% sure of the mic until you have it calibrated.

How have you ruled out the speaker?


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post #53 of 170 Old 01-26-09, 07:10 PM
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Re: MobilePre ECM8000 oddities

I just find it to be too much of a coincedence that both anthony and I are showing a steep roll-off in the HF above 15KHz. I show it when using both an ECM Mic and DBX mic.

Here are a series of nearfield plots I took using the DBX mic. The different plots represent on-axis, slightly above, slightly below, and to the left and right. (I was trying to find some axis, any axis, that I would get flatish treble response above 15KHz).



I'll be getting my calibration files for my DBX mic this week, but Cross Spectrum has already sent me a preview of the plot, and there is no roll-off in the HF, so I don't expect the cal file to fix this problem. In fact the DBX mic's response looks very similar to the ECM, just with less of a hump at 10KHz.

Last edited by hifisponge; 07-19-09 at 02:22 AM.
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post #54 of 170 Old 01-26-09, 07:33 PM
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Re: MobilePre ECM8000 oddities

Anthony -

I'm not sure that the Maggies are a good reference for this test. I've read in the past that it is difficult to get an accurate FR reading of panel speakers because of the way they project sound.

For reference, I looked for FR measurements done by AV mags on the maggies and found these:

Magnepan MMG W (measured by Ultimate AV Mag)


Magnepan MG 3.6 (measured by Ultimate AV Mag)


As you can see, they are showing a fairly steep roll-off in the upper HF. Do you have any other more conventional speakers around to test?

Here's what my speakers are supposed to be doing in the HF.

Wilson-Benesch speakers (measured by Hi-Fi News UK)

Last edited by hifisponge; 07-19-09 at 02:23 AM.
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post #55 of 170 Old 01-26-09, 10:11 PM Thread Starter
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Re: MobilePre ECM8000 oddities

Heh, I wonder if Ultimate AV is using our mic

That's a good point, though, about testing other speakers.

I have some Adire HE10.1's (don't know why that number is in both of my speaker sets ) in the tube system upstairs. I can bring one downstairs and remeasure.

Panel speakers radiate in a "middle finger" lobe pattern (for lack of a better image). The on-axis is very strong but narrow then flanked by weaker lobes around the 15 to 30 degree mark, then another null and another set of even weaker nodes around the 45 degree mark. Overall it looks like the classic figure 8 pattern of a dipole, but with nulls inbetween the fingers. A neat trick to getting a great center image is to aim the speaker so the second lobe is aimed at the listening position (about a 30 degree toe-in). It's weird but it keeps a pretty stable center image across the stage without the dreaded "sweet spot".

Anyway, I was measuring about 8 inches from the panel, which should be enough for the ribbon and panel to integrate, but you are right, all it takes is for the mic to be in the wrong null and the FR goes all wacky.

I'll try the other speakers tomorrow night. I can also try a raw BG Neo3PDR and Neo8PDR tweeter/panels to see how they fare.

Thanks for the input guys, it'll be great to get to the bottom of this.
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post #56 of 170 Old 01-26-09, 10:49 PM Thread Starter
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Re: MobilePre ECM8000 oddities

Well, I just looked through some old measurements and this is not apparent in all of them -- just the ones of the Magnepans. Some random measurements don't seem to have it (like almost touching the panel nearfield), but almost all of the 1m to 3m measurements do. Hmm, I guess I started with a bad assumption, since the speaker was supposed to be flat to 24kHz. But dipoles are tough to measure, tweeters are tough to measure, and in-room is tough to measure. So dipole tweeters in room must be really tough to measure

My guess is it's some sort of cancellation effect from position or frame/panel. Sorta like a broad comb filter effect. It's too high to be dipole cancellation and the likelihood of me putting the mic in an exact null every time is slim. I'm just thinking out loud here to try and find a solution that fits your problem as well, Tim.

I'll test those horn tweeters tomorrow and check back. Seems we're at least a bit closer.
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post #57 of 170 Old 01-26-09, 11:47 PM
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Re: MobilePre ECM8000 oddities

Hmmm ....

I ran some more measurements, and I don't know what I did differently but I'm able to get respectable HF extension when I use the mixed cal file for the ECM mic, BUT only when I point the mic at the speaker .

Yellow plot is horizontal mic position, blue is vertical.

Last edited by hifisponge; 07-19-09 at 02:24 AM.
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post #58 of 170 Old 01-27-09, 05:51 AM
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re: ECM8000 microphone measuring techniques and usage discussion

I have been prototyping a new setup, which is why I found this forum. I have never had a tool like REW before! All I can say is WOW. Anything else I said would ensure that the moderators would delete it.
Anyway, I would not be in a position to comment without REW, So...
I couldn't get the ECM8000, However the local shop did have a JBL re-badged DBX TRA M for a similar price. So I bought it and a small mixer to supply power and set about measuring my new speaker. (singular)
I have been extremely happy with the JBL as my Shiva X measures (close field) to what was modelled in WinISD for a 120 litre cabinet. ie ~7 Db down at 20Hz.
As for the top end, this mic happily did a good job of following the Raven 3.2's response with no major anomolies.
If you cannot find the ECM then I can quite happily suggest using the JBL.

Last edited by robbo266317; 01-27-09 at 05:54 AM. Reason: spelling
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post #59 of 170 Old 01-27-09, 07:30 AM
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re: ECM8000 microphone measuring techniques and usage discussion

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JBL re-badged DBX TRA M for a similar price.
What microphone calibration file are you using for it?

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post #60 of 170 Old 01-27-09, 10:51 AM Thread Starter
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Re: MobilePre ECM8000 oddities

Nice measurements there. Interesting that the JBL tweeter has that top octave falloff as well -- not exactly a cheapo tweeter in its own right.

I'll post mine tonight in this exact same format. You said 1 foot, 6ms gate (from zero, or from first impulse received?). The candidates will be the MG10.1 ribbon tweeter and the compression tweeter used in the Adire speaker. I do not remember the brand name on it, but it screwed into the back of the Eminence woofer.
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