ECM8000 Orientation for Speaker Measurements

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arc2v

Member
2007-05-09 7:15 pm
I have noticed many pictures online of people using the ECM8000 to measure speakers and aiming the mic right at the speaker in question.

However, I have discovered that many of the calibration files floating around out there are for the mic oriented vertical.

so my question is: what's the proper way?

how do you all do it for measurements?

The reason I ask is that I'm seeing weird results in my top and bottom octaves that seem to correlate with the calibration file. So what I hear flat seems to measure way bright.

I'm considering paying for the calibration, but at $100+ I'd like to research my options more first.

Any thoughts on this?

Thanks,
A
 

ShinOBIWAN

diyAudio Member
2004-02-25 9:13 pm
UK
Good question.

Personally speaking I point the mic at the driver/loudspeaker when aiming to measure loudspeaker performance. But point the mic vertically, at the listening position, when doing room correction or looking into performance at the listening position.

I have no solid reasons for working this way, it just feels sensible I guess.
 

arc2v

Member
2007-05-09 7:15 pm
that may be correct, but I see the same effect when using swept-sine (Room EQ Wizard), so it is definitely a frequency response thing -- regardless of signal type.

I will have an easy night tonight, so I'll measure the room and a few drivers vertical and horizontal -- with correction file and without, and see what the results look like.
 

Ron E

Member
2002-06-27 10:41 pm
USA, MN
arc2v said:
I have discovered that many of the calibration files floating around out there are for the mic oriented vertical.

so my question is: what's the proper way?

The reason I ask is that I'm seeing weird results in my top and bottom octaves that seem to correlate with the calibration file. So what I hear flat seems to measure way bright.

Which calibration files are you speaking of? Can you show us some graphs?

You would want to point it at the speaker and calibrate the mic for on-axis measurements if that is what you are measuring. The vertical orientation is more used for a random incidence type measurement that you might use to measure reverberation in a room, etc.

I think you can still get your mic calibrated for ~$40 from Kim Girardin.
 
You will always get faster HF roll-of if you orient the mic at 90 degrees to the source, compared with pointing straight at it. B&K have information on their site about this. It's much worse with large diaphragm mics.

When the wavelength of the signal gets small enough to be significant compared with the diaphragm diameter you'll get some signal cancellation on the mic output if the acoustic waveform is passing across the mic diaphragm.

I don't know if the Behringer calibration data is with the mic at 0 or 90 degrees to the signal source. I guess it's with it at 0 degrees.
 

arc2v

Member
2007-05-09 7:15 pm
Actually, what I've seen coincides with that statement.

The behringer plot shows a fairly flat response that humps a bit (0.5 db) in the upper midrange and then just a very slight rolloff above 15 kHz.

The other cal file, from HomeTheaterShack was calibrated vertical and it shows a flat response across with a steep rolloff at 10 kHz. I confirmed that they tested theirs vertical.

so it may be that the Behringer is pretty flat for direct sound and needs that compensation for vertical use. I'll see if my measurements agree with that statement tonight.
 

ShinOBIWAN

diyAudio Member
2004-02-25 9:13 pm
UK

arc2v

Member
2007-05-09 7:15 pm
Svante,
Just to be clear: 90 degrees is up and 0 degrees is right at the target?

If so, that would follow what I've seen with this particular mic's cal files.

Your 90 degree one looks like the HomeTheaterShack's newecm.cal file, while your 0 degree one looks like the old ecm8000.cal (which looks like the cal curve on the box of the microphone).

It may just be that I need two cal files: one for horizontal (driver) and one for vertical (free field) testing.

Thanks for the help -- all of you.
 

Pano

Administrator
Paid Member
2004-10-07 6:05 am
Panama
There was a thread about this last year, but I'll be darned if I can find it.



Anyway, it was pretty much agreed that the ECM8000 is meant for room measurements, thus not flat when pointed right at the source. For drivers it should be turned about 70-80 degs. off axis.

However, looking at Svante's graphs, it does seem that 90 off axis kills the top end. It does also kill the 10K peak, but that high end drop is a problem.

Svante, if you ever get the chance, it would be nice to see the same graphs at angles of about 60-90 degrees. Thanks!
 
panomaniac said:


Cool! Thanks.

Are those curves with the ECM pointed at the source? (0 degs). And the Earthworks as reference?

Why are the plots so rough?

On all the plots I see that rise at about 10K that is the signature of a mic capsule this size.

Yes, the Earthworks i pointed towards the source, just as in the calibration chart.

The reason for the roughness of the curves is that the microphones are spaced a bit apart (4 cm as I recall it). This combined with that I used a tweeter in an ordinary box lead to slightly different responses at the two positions. I would have liked to have the tweeter mounted on a big surface so that there was no edge reflections from the box, and also, I would have liked to measure one microphone at a time (reference/ECM8000) instead of having the interfering reflections from the neighbouring microphone.

This would have lead to smoother curves, but the big picture would still be the same, ie that the Behringer mic shows a hill around 5-10 kHz.

BTW, I believe that the size of the front of the behringer mic is a big part of the hill. Here is a plot of one of the responses compared with the baffle step of a circular baffle with a diameter if 12 mm:

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

Zero Cool

Member
Paid Member
2004-09-20 6:10 am
MN
I just finished testing 7 RTA type mics for a future magazine article. the ECM-8000 included as well as the Nady, Superlux, Earthworks M23, Beyer MM1, Naiant, & DBX mics and we referenced the B&K 4010 and several other B&K mega buck measurment mics.


Several things to note. 1- not all ECm-8000's are created equal. there are several revisions of this mic. and a very large unit to unit variance between mics of the same series. The Behringer mic was no shining star in our test's. but there was some surprising results! stay tuned for more info.

most of the mics we tested had the bump at 10-18K. typically less then 1db.

when measuring a direct source. the mic inline with the source is generally the best way to go. when measuring room response. the mic at various locations and angles and averaged, is what is normally used.



Zc
 
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