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Old 11th February 2007, 06:34 PM   #1
owdi is offline owdi  United States
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Default Measuring harmonic distortion with the ECM8000

I want measure harmonic distortion using my Behringer ECM8000, but I'm afraid the microphone itself introduces distortion, causing invalid results.

Does anyone know what maximum SPL the ECM8000 can measure before distortion starts quickly increasing? Has anyone measured the harmonic distortion introduced by the ECM8000 itself?

I remember reading that the ECM8000 had an upper limit of 92db, but I can't find that reference now.

Below is a nearfield measurement of the Vifa XG18 in an OB. I don't trust the numbers because the noise floor in my room is above the measured distortion.

Dan

Click the image to open in full size.

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Old 11th February 2007, 06:44 PM   #2
Tenson is offline Tenson  United Kingdom
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What program do you use for measuring distortion?

I need to do some disto tests soon and I have previously just done single tone tests and looked at the frequency response in CoolEdit. I canít figure out how to make Speaker Workshop do the tests.
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Old 11th February 2007, 06:44 PM   #3
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Trust me when I say that even a budget mic such as the ECM8000 isn't going to meaningfully influence the distortion measurements taken from a loudspeaker driver.

Just as bit of name dropping to further reinforce that, I believe Zaph uses an ECM8000 for all his testing.

The Behringer will also happily measure SPL levels at 120dB, if really high SPL measurements are needed then take a look at Earthworks range or even those used for car SPL competitions.
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Old 11th February 2007, 06:45 PM   #4
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Quote:
Originally posted by Tenson
What program do you use for measuring distortion?
Its ARTA, brilliant program.
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Old 11th February 2007, 07:43 PM   #5
owdi is offline owdi  United States
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Quote:
The Behringer will also happily measure SPL levels at 120dB, if really high SPL measurements are needed then take a look at Earthworks range or even those used for car SPL competitions.
Well I'm very happy to hear that. I live in an apartment where there is always some type of noise. If I want to measure harmonic distortion levels below -60db, then I need the fundamental to be at least 100db.

I have a generic calibration file for the ECM8000, which I use with Speaker Workshop. I'd like to use it with Arta and Steps, does anyone know how?

Dan
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Old 11th February 2007, 08:21 PM   #6
Svante is offline Svante  Sweden
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One way of testing this would be to measure the same loudspeaker at two different distances, using the same voltage to drive the loudspeaker. If the frequency response remains the same, room effects can be neglected. If the relative amplitude of the distortion components change, there must be distortion components of the microphone that cause the change.

The measurement should be done with a small loudspeaker driver, preferrably mounted in-wall, such that it approximates a point source and has no baffle effects. I predict no large distortion differences between low and highish (<4 kHz) frequencies, so it might be easiest to test this with a mid driver.

Maybe...

Edit: Yet another way: Put the microphone inside a loudspeaker box. For low frequencies, the level easily becomes very high (140 dB or so). This means that if the level is lowered, the signal is almost distortion free. The remaining measured distortion most certainly comes from the microphone, at least for a cheap microphone.

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Old 11th February 2007, 08:36 PM   #7
Svein_B is offline Svein_B  Norway
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Quote:
Originally posted by owdi

I have a generic calibration file for the ECM8000, which I use with Speaker Workshop. I'd like to use it with Arta and Steps, does anyone know how?

Dan
Just select: Setup , Frequency Compensation, and Load File.

SveinB
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Old 11th February 2007, 09:49 PM   #8
ente is offline ente  Germany
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.... have a look on this paper. Maybe it answers some of your questions

http://www.fesb.hr/~mateljan/arta/Ap...r-Rev03Eng.pdf

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Heinrich
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Old 12th February 2007, 12:17 AM   #9
owdi is offline owdi  United States
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Quote:
Originally posted by Svein_B


Just select: Setup , Frequency Compensation, and Load File.

SveinB
Tried that, but that option was not there. Updated the software from version 1.0 to 1.2, now it's there. Thanks :-)

Click the image to open in full size.

Time to retake some of those measurements.

Dan
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Old 12th February 2007, 03:44 AM   #10
owdi is offline owdi  United States
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Svante - I'll try that, although it will be hard to discount room effects. A reflection that is -30db will not show up in the FR, but could affect the readings.

ente - thanks for the link.


I have another question, and don't want to start a new thread. I want to measure the harmonic distortion of my Seas 27TBFC/G tweeters. Can they survive a test at 2.83 volts, without a crossover?

Dan
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