ECM8000 Orientation for Speaker Measurements

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Dave Bullet

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Joined 2002
Therefore, rather than paying someone $100+ to calibrate your mic, buy a couple of consistent and well published tweeters then calibrate yourself. Not only will it be cheaper, but you could convince yourself you are getting a couple of "free" tweeters for your next project.

Attached are various ECM8000 calibration charts. The cyan coloured (light blue) is the one I created. The double hump in the 10K+ could be an artifact of the measurement distance. I will try a greater distance to see if it evens out.

Cheers,
David.
 

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Pano

Pano

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The ECM8000 is almost certainly a mic that is meant for "Diffuse Field" measurements.

Most of use wanting to measure loudspeakers and drivers are trying to use it in a "Free Field." That is going to change the response of the mic.

Last summer I came across a couple of websites that offered really good explanations of this Free Field vs Diffuse Field use. But of course I can't find them any more!

But if you take a look at pages 17-18 of the Bruel & Kjaer magazine of Nov. 2007, you will find an explanation. Not as clear as some of the stuff I've read elsewhere, but the info is there.

(You need Flash to see the pages).
 
D

djarchow

Member
Joined 2007
As long as your microphone is calibrated in the orientation you will use it to measure the loudspeakers you will get valid results. Especially when doing the gated measurements usually done for loudspeaker design which eliminate reflections from the room from the measurement anyway.

Regards,

Dennis
 
Pano

Pano

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djarchow said:
As long as your microphone is calibrated in the orientation you will use it to measure the loudspeakers you will get valid results.
Click to expand...

Quite agree!

So for practical purposes, if you use the ECM8000 pointed straight at the source you should use a calibration file, as the response will not be flat.

If you can't use a calibration file, turn the mike about 70-80 degrees off axis for the flattest response. (But you'll get more reflected sound)
 
D

Dave Bullet

Member
Joined 2002
Good idea.

I'll measure my ECM8000 without a calibration file and find what angle gives a similar response to the on-axis with calibration measurement.

Specifying an angle "range" for the ECM8000 might be a valid alternative for those that cannot get their mic calibrated somehow.

To correctly identify peaks in the upper treble and correct, you need to have a mic with a flat response.

David.
 
xiphmont

xiphmont

Member
Joined 2007
xiph.org
For purposes on information... I'd not seen this come up yet...

I have some ECM8000s I bought for a job a few years back and, honestly, had found them too noisy to use for anything other than simple not-very-versatile room calibration, not particularly sensitive and although flat, not even as flat as some other mics we had already anyway (Lots of AT853a and AT4051).

Too bad too, because I wanted some rugged, dedicated calibration microphones, especially for near field.

I decided to carefully open one up today to look inside-- easy, BTW, gently punch the capsule free with a 6mm rod and remove three screws, opens right up--- and found a tiny little phantom powered preamp board and... a panasonic WM61A capsule or a clone so close I can't tell the difference. I'll compare the electrical specs of the two in a bit.

I'll see if I can piece together a schematic of the preamp, but it looks like the Linkwitz mod could work nicely on the ECM8000--- and if you screw up, the capsules are only a buck anyway! I'm not sure how much of the self noise comes from the little preamp, but I'm about to find out.

Even if it's a complete loss, $40 isn't too bad for a few weekend's fun.
 
xiphmont

xiphmont

Member
Joined 2007
xiph.org
Speedskater said:
Different vintage ECM8000's may use different circuits and/or components. Older units had a transformer.
Click to expand...

Good information-- is there a way to tell the difference from the outside?

I was actually a little surprised, as my boxes all have a simplified schematic that clearly shows a transformer... but opened up, I found a semiconductor preamp. I'm not sure which would have made me happier.

Do you know if the preamp has changed/been revised over time?
 
S

Shawn Parr

Member
Joined 2008
Zero Cool said:
BUT, for home speaker builders and Sound system guys there are a number of mics under $250 and one under $50 that have specs as good and in one case much better then a B&K 4010! and much flatter then the Earthworks we tested!

If someone was going to purchase a budget mic today. contact me off list and i might be able to influence your decision.
Zc
Click to expand...

Zero Cool,

I'm currently researching these things for myself and my students (Sound Designers/Engineers in Theatre). I'm not able to send emails due to my newbie-ness. Could you please either post a link to the article, or where we could get it, or drop me an email, as I'm curious what your results were, especially those better than a 4010....

Thanks! :)
 
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