Vertical dispersion on planars. How much?

[bolserst]

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.

[twest820]

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.

[applehorn]

twest820. re post #9

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

TIA

Iain.

[twest820]

Edge. (As mentioned in post #9. )

[bolserst]

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.

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]

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?

[bolserst]

Originally Posted by twest820

Dipole or closed box operation?

dipole.

[twest820]

Thanks. That's with the SPL equalized flat, I assume?

[bolserst]

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.

[twest820]

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.