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Old 13th August 2010, 02:34 PM   #11
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Default BG8 directivity for long axis, measurements vs theory

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Originally Posted by bolserst View Post
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
File Type: jpg BG8_dim.jpg (213.8 KB, 398 views)
File Type: gif BG8_resp.gif (78.5 KB, 394 views)
File Type: gif BG8_norm.gif (39.2 KB, 384 views)
File Type: gif compare_01.gif (43.1 KB, 382 views)
File Type: gif compare_02.gif (50.3 KB, 380 views)
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Old 13th August 2010, 06:01 PM   #12
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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.
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Old 14th August 2010, 04:23 PM   #13
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twest820. re post #9

What software are you using for the fem plots. Haven't seen this before.

TIA

Iain.
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Old 15th August 2010, 12:27 AM   #14
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Edge. (As mentioned in post #9. )
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Old 15th August 2010, 07:34 PM   #15
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Quote:
Originally Posted by twest820 View Post
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.
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Old 16th August 2010, 05:22 AM   #16
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Quote:
Originally Posted by bolserst View Post
If memory serves, with reasonable input level 3rd order distortion rose dramatically below 500Hz rising past 10% by resonance.
Dipole or closed box operation?
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Old 16th August 2010, 01:49 PM   #17
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Quote:
Originally Posted by twest820 View Post
Dipole or closed box operation?
dipole.
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Old 16th August 2010, 03:22 PM   #18
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Thanks. That's with the SPL equalized flat, I assume?
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Old 16th August 2010, 05:19 PM   #19
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Quote:
Originally Posted by twest820 View Post
Thanks. That's with the SPL equalized flat, I assume?
All measurements were performed with constant voltage/frequency input, no EQ applied.
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Old 16th August 2010, 09:27 PM   #20
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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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