Vertical dispersion on planars. How much?
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bolserst
diyAudio Member

Join Date: Jun 2005
Location: Fort Worth, Texas
BG8 directivity for long axis, measurements vs theory

Quote:
 Originally Posted by bolserst I thought the data you posted was actual measurements...I see now that you stated it was simulation results.
Me being me, just couldn't leave things hanging like that.
So I borrowed a BG8 from a friend and took a quick set of measurements to compare with the calculated theoretical off axis response.

Measurements were taken at 1m from the BG8 mounted in free air on a pole attached to rotating platform.
I estimate the width to be about 5 15/16" = 0.1508 m.
Theoretical response calculated using the sinc function mentioned in post#3, and the cos(theta) response for a dipole radiator.

Plot #1
The measured off axis response for the BG8 on the long axis.
Note that I didn't bother to notch out the cavity resonance.

Plot #2
Same data set, just normalized to the on axis response.

Plot #3
Normalized measurements compared to theory for 5, 10, & 15 degrees off axis.

Plot #4
Normalized measurements compared to theory for 30, 45, & 60 degrees off axis.

NOTE: Due to length of measurement window, ignore measured data below about 350Hz.
Attached Images
 BG8_dim.jpg (213.8 KB, 626 views) BG8_resp.gif (78.5 KB, 627 views) BG8_norm.gif (39.2 KB, 614 views) compare_01.gif (43.1 KB, 606 views) compare_02.gif (50.3 KB, 597 views)

 13th August 2010, 06:01 PM #12 twest820 diyAudio Member   Join Date: Jun 2009 Sweet! That's excellent agreement to the first null. Did you happen to measure distortion as well? So far as I know, if anyone's taken data to assess how much dipole compensation the Neo8 can handle it's not posted anywhere. But since the dipole "peak" is at 2kHz establishing how low the Neo8 can run due to excursion and Fs limitations is pretty important for assessing its use as a dipole mid. Assuming the Neo8 behaves like the Neo3 and Neo10, Fs is right around 400Hz and the intrinsic distortion should be OK about the same frequency. However, my experience with the Neo3 is equalizing it flat below 2kHz exhausts its excursion capabilites fairly quickly. Since the Neo8's essentially a line array of Neo3s I'd expect similar problems to crop up. Last edited by twest820; 13th August 2010 at 06:08 PM.
 14th August 2010, 04:23 PM #13 applehorn   diyAudio Member   Join Date: Jul 2008 twest820. re post #9 What software are you using for the fem plots. Haven't seen this before. TIA Iain.
 15th August 2010, 12:27 AM #14 twest820 diyAudio Member   Join Date: Jun 2009 Edge. (As mentioned in post #9. )
bolserst
diyAudio Member

Join Date: Jun 2005
Location: Fort Worth, Texas
Quote:
 Originally Posted by twest820 Sweet! That's excellent agreement to the first null.
Note too shabby as a first cut approximation of dispersion, which was what Armand, the OP, was after.

Quote:
 Did you happen to measure distortion as well? So far as I know, if anyone's taken data to assess how much dipole compensation the Neo8 can handle it's not posted anywhere. But since the dipole "peak" is at 2kHz establishing how low the Neo8 can run due to excursion and Fs limitations is pretty important for assessing its use as a dipole mid. Assuming the Neo8 behaves like the Neo3 and Neo10, Fs is right around 400Hz and the intrinsic distortion should be OK about the same frequency. However, my experience with the Neo3 is equalizing it flat below 2kHz exhausts its excursion capabilites fairly quickly. Since the Neo8's essentially a line array of Neo3s I'd expect similar problems to crop up.
I didn't measure the distortion, but had many years ago.
If memory serves, with reasonable input level 3rd order distortion rose dramatically below 500Hz rising past 10% by resonance.
It wasn't very pleasant to listen to test tones.

Oh, and Fs was about 300Hz I believe, with Q of roughly 2.

twest820
diyAudio Member

Join Date: Jun 2009
Quote:
 Originally Posted by bolserst If memory serves, with reasonable input level 3rd order distortion rose dramatically below 500Hz rising past 10% by resonance.
Dipole or closed box operation?

 16th August 2010, 01:49 PM #17 bolserst   diyAudio Member     Join Date: Jun 2005 Location: Fort Worth, Texas dipole.
 16th August 2010, 03:22 PM #18 twest820 diyAudio Member   Join Date: Jun 2009 Thanks. That's with the SPL equalized flat, I assume?
bolserst
diyAudio Member

Join Date: Jun 2005
Location: Fort Worth, Texas
Quote:
 Originally Posted by twest820 Thanks. That's with the SPL equalized flat, I assume?
All measurements were performed with constant voltage/frequency input, no EQ applied.

 16th August 2010, 09:27 PM #20 twest820 diyAudio Member   Join Date: Jun 2009 That makes a bit more sense. I'll stick to my guesstimate that once equalized for dipole roll off the Neo8 wouldn't cross happily below 1.1kHz or so when operated nude. Appreciate the confirmation I should probably be looking at a cone mid for the nude dipole build I have going.

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