ND20FB measurements

[lhwidget]

I have 4 of the little ND20FB-4's and I'm seeing the following amplitude response when I test them in a 1/4 cu ft Dayton enclosure. The response was very much the same on a 3' x 4' baffle board. The measurement is of the driver only with no crossover components installed, 3 ms window @ 1 meter.

Has anyone else seen the broad peak @ about 12500 Hz? Zaph's measurement was practically flat.

Jay

[fjhuerta]

Are you using an ECM-8000? Is it calibrated?

Reason being, I own 3 ECMs, and every one of them has a +6 dB boost starting from 2 right up to 15 KHz, or so.

EDIT: Most of my tweeter measurements looked identical to yours before I had my mic calibrated.

[lhwidget]

That sounds pretty reasonable. I am using the ECM 8000, and I'm seeing a similar hump in the response of a Dayton 1 1/8" fabric dome tweeter.

Are there any calibration services out there?

[dthomas]

I have 4 of the little ND20FB-4's and I'm seeing the following amplitude response when I test them in a 1/4 cu ft Dayton enclosure. The response was very much the same on a 3' x 4' baffle board. The measurement is of the driver only with no crossover components installed, 3 ms window @ 1 meter.

Has anyone else seen the broad peak @ about 12500 Hz? Zaph's measurement was practically flat.

Jay

Not to say you may or may not have a mic calibration issue but it is very likely this is baffle diffraction from your baffle... This is not uncommon and can be handled easily within the crossover.

Zaphs measurements were made on a much wider baffle so it would be expected that diffraction affects were more equally distributed.

[lhwidget]

Thanks Dave.

I'll have fresh measurements tonight or tomorrow with the tweeter mounted in my test baffle. My test baffle is 3' wide x 4' tall with the center about 4' from the floor.

I'm very interested to see if this puts things closer to Zaph's measurements.

The cabinet is 7 1/2" wide x 12" tall. Rough calculations indicate baffle step centered @ 600 Hz and practically finished (ie, 6 dB up) by 1000 Hz or so...

[dthomas]

Well I can see how you get the droop on the smaller baffle but on a 3' x 4' baffle you should not see as much droop. You may need your mic measured so you have a better calibration file.

[fjhuerta]

That sounds pretty reasonable. I am using the ECM 8000, and I'm seeing a similar hump in the response of a Dayton 1 1/8" fabric dome tweeter.

Are there any calibration services out there?

I used Cross Spectrum Labs' services, and I'm very happy with the results.

http://www.cross-spectrum.com

I'd never, ever use an uncalibrated ECM-8000. As I said, I have 3 of them and they are all far from flat.

When I ordered my new mic and sent it to CS Labs, I noticed that Behringer's own calibration graph (the one *inside* the box) has the ~6 dB anomaly, too. At least they are kinda honest (the graph printed on the box is basically flat from 20 to 20KHz).

[lhwidget]

Thanks. I noticed the ECM 8000 tests on their site look suspiciously like my response curve... :rolleyes:

When was the last time you used these guys? Their phone # seems to have been disconnected.

[jims]

I have 4 of the little ND20FB-4's and I'm seeing the following amplitude response when I test them in a 1/4 cu ft Dayton enclosure. The response was very much the same on a 3' x 4' baffle board. The measurement is of the driver only with no crossover components installed, 3 ms window @ 1 meter.

Has anyone else seen the broad peak @ about 12500 Hz? Zaph's measurement was practically flat.

Jay

I haven't used his services, but Kim Girardin has gotten some good recommendations for mic calibration. kmgrdn@luminet.net

Jim S.

[christianb]

I haven't used his services, but Kim Girardin has gotten some good recommendations for mic calibration. kmgrdn@luminet.net

Jim S.

I just had my mic calibrated by Kim and am very pleased.

My ECM8000 has the same increase starting around 10khz. Your mic definitely is the problem.

[lhwidget]

Thanks guys, I appreciate the help.

Fjhuerta, Herb at Cross-Spectrum promptly answered my inquiry, via email; $55 and a 2 day turn-around.

Jims & Cristianb, thanks for the info on Kim.

Jay