Measuring harmonic distortion with the ECM8000

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owdi

owdi

Member
Joined 2003
ente - thanks for that chart. It is exactly what I was looking for.

Jmmlc - agh! I should have read the entire article when ente posted the link. Great info, thanks.

Svante - 1% is -40db.. ouch


This thread has been very informative.

According to the chart on page 15 of the Arta Application note, the ECM8000 will have .30% (about -50db) distortion at 300hz and 111db. The sloping chart indicates it could be less at lower spl levels.

The chart ente posted shows slightly higher distortion than the Arta Application note, but it's at 200hz instead of 300hz. At this lower frequency it measures .25% (about -52db) at 105db. It looks like distortion starts to level off around .15% (about -56db) below 100db.

I took my harmonic distortion measurements of the XG18 at 85db, and it still looks they are around the same level as the ECM8000 would be. Maybe I am measuring the distortion of the microphone only... meh, I don't know. Maybe I should quit worrying about things happening below -60db, since my ears will not be able to distinguish it.

Dan
 
B

bidland

Member
Joined 2004
I'd say for most DIY'ers you could just as well skip the calibration curve if it isn't from your own mic. Just not trust it above 20 kHz.

I have less deviation than the calibration curve above. See my measurements below:

BehringervsBruelKjr.gif



Relativsammenlikning.gif


Please disregard deviation below 30 Hz. This is caused by poor S/N (did not bother to close both doors to the anechoic chamber...).

I have not done any distortion measurements with the ECM8000, so I can't comment on that.


Bjorn
 
Vikash

Vikash

Ex-Moderator
Joined 2003
vikash.info/audio/
Jmmlc said:
Most often electret capsule as the MCE2000 possess an integrated fet inside.

THis fet is used at very small drain-source current in an operating zone called "quadratic", this means that it's transfer function is in power 2 creating a second order (H2) distortion.
Click to expand...

Time to mention the Linkwitz mod. About 2/3 down this page: http://www.linkwitzlab.com/sys_test.htm
 
owdi

owdi

Member
Joined 2003
bidland - thanks for posting that response curve. I think the calibration file I've been using may be slightly overcompensating. I found the manufacturers response curve, loaded it up in SPLTrace, and got the following.

Vikash - can that same mod be applied to the ECM8000?


An externally hosted image should be here but it was not working when we last tested it.



An externally hosted image should be here but it was not working when we last tested it.



Link to SPLTrace ecm8000-Manuf.SPLTrace.mic

Dan
 
ShinOBIWAN

ShinOBIWAN

diyAudio Member
Joined 2004
Svante said:
So, the measurements seem to suggest in the order of magitude a percent of distortion or so at 120 dB SPL.

That is not very little. :)
Click to expand...

Run a 200hz test tone at 120dB and see if the mic at just over 1% THD or the driver has more distortion ;) Comparatively it is very little which was my point all along.

The issue of THD contributed by the ECM8000 being a factor that would call distortion measurements into question is mute, there is an error margin but if your sensible about this then you realise that its all relative. If you take issue with that then you better email Zaph and John K to tell them they're misinforming the DIY community with their efforts.

My point is that the data captured by the ECM8000 is more than good enough to be informative.
 
Svante

Svante

Member
Joined 2004
ShinOBIWAN said:


Run a 200hz test tone at 120dB and see if the mic at just over 1% THD or the driver has more distortion ;) Comparatively it is very little which was my point all along.

The issue of THD contributed by the ECM8000 being a factor that would call distortion measurements into question is mute, there is an error margin but if your sensible about this then you realise that its all relative. If you take issue with that then you better email Zaph and John K to tell them they're misinforming the DIY community with their efforts.

My point is that the data captured by the ECM8000 is more than good enough to be informative.
Click to expand...

Well, ok, let's agree on the numbers, the distortion is about 1% at 120 dB. Really, that is all the information needed.

As you say, if this is much or little depends on the context. For measurements at 1 m distance, it sure is less than most speakers produce. For close field measurement, I'm not so sure, and for measurements inside the box (which can be a great method for FR measurements) it is definitely too much.

Ok?
 
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