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Old 11th January 2012, 11:16 PM   #1341
Mark Kravchenko --- www.kravchenko-audio.com
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Quote:
"Has anyone read the AES paper by Don Keele Maximum Efficiency of Direct Radiator Loudspeakers? "
Yes a long time ago when I had hair.

And I concur with djk. Full sized horn in normal interiors are a waste of space!
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Old 12th January 2012, 06:40 AM   #1342
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Hi Art,

Thanks for your comments.

I am not sure that getting more sleep is going to help much at this stage... :-).

I have just been looking at an AES paper which contains graphs showing the SPL of one speaker compared to fifteen speakers connected in parallel, driven by the same voltage. The charts are predictions, but are very close to actual measured values which are also given in the paper. The results are quite different to those generated using any of the three Hornresp models currently under consideration, and donít comply with the coherent signal summing rules discussed earlier.

The first chart attached shows the SPL for one speaker. The second chart shows the SPL for fifteen speakers. The difference between the two at higher frequencies is 13 dB, much less than the summing rules would suggest should be the case.

Until I can find a more robust model to better predict the performance of multiple speakers, I think that it is probably safer to leave Hornresp as it currently is :-).

Kind regards,

David
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Last edited by David McBean; 12th January 2012 at 06:43 AM.
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Old 12th January 2012, 11:29 AM   #1343
Mark Kravchenko --- www.kravchenko-audio.com
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Default Keep your chin up David!

Rules!

They are usually only applicable under very narrow circumstances. What you are trying to cover is real life situations. I think I have seen that paper to. I have a set of three three inch thick binders that are buried up in my attic that I did most of my studying from back in the 80's. If I only remembered half of what I read I'd be somewhat intelligent!

Not as easy as it looks. Hence the rules tend to become rather simplified. Art's observations and Wayne's are most helpful. Djim graphs are priceless.

That you are narrowing down on what really matters is kind of obvious. The math involved is not that obscure. You have cracked tougher nuts before David.

The empirical evidence points in the direction that the current model is wrong. What there seems to be missing is a consensus between the measurements. Your latest paper seems to be a source where it is under very controlled measurement methods. Maybe you have found the information that you are looking for?
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Old 12th January 2012, 12:07 PM   #1344
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Originally Posted by David McBean View Post
Hi klampykixx,

I am more interested in the four hot "mag wheels", stacked to the left of the horns :-).

Kind regards,

David
Hi david, they belong to my jeep. 15inch alloys. If you want to pm me theyre actually for sale.

This sounds completely noobish after reading this page, but if i can make a mount that utilises two twelve inch drivers in the same throat as a single fifteen, what effect would that have on the response?

and second, if i was to put the Jbell horn in a car, would extending the horn path be of any benefit? I tried one in my wagon and it just wasnt that impressive.... are horns any good in cars?
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Old 12th January 2012, 02:19 PM   #1345
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Quote:
Originally Posted by David McBean View Post
Hi Art,

Thanks for your comments.

I am not sure that getting more sleep is going to help much at this stage... :-).

I have just been looking at an AES paper which contains graphs showing the SPL of one speaker compared to fifteen speakers connected in parallel, driven by the same voltage. The charts are predictions, but are very close to actual measured values which are also given in the paper. The results are quite different to those generated using any of the three Hornresp models currently under consideration, and donít comply with the coherent signal summing rules discussed earlier.

The first chart attached shows the SPL for one speaker. The second chart shows the SPL for fifteen speakers. The difference between the two at higher frequencies is 13 dB, much less than the summing rules would suggest should be the case.

Until I can find a more robust model to better predict the performance of multiple speakers, I think that it is probably safer to leave Hornresp as it currently is :-).

Kind regards,

David
One to 16 speakers should be +15, I read about a 12 dB difference in the 1986 Leap version 2.10 simulation, which would be sort of consistent with an incoherent summation and one less(15 instead of 16) speaker.

I have no problem with you leaving Hornresp as it is, itís ďclose enough for rock & rollĒ .

I will continue to point out to the newbies that are counting on a low corner reduction in multiple TH that they will be disappointed .

Perhaps one day someone will actually measure 1, 2, 4 and 8 SH15 cabinets and we can see how they actually perform compared to the simulations people take for granted.

Art
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Old 12th January 2012, 04:18 PM   #1346
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There's definitely an effect (or set of effects) that cause bass to get more increase (or higher frequencies to get less increase) when grouping basshorns closely together. My thinking is it's one or more of these three things, or perhaps a combination of all of them:

1. Mouth size getting closer to acoustical scale at LF (causing an efficiency increase at LF)
2. Reduced summing at HF because of acoustic distance (causing phase/summing reduction at HF)
3. Shift in the movement of the acoustic center (causing distance to change as a function of frequency)

I had considered directivity increase, and it is still a possibility - definitely when groups become large - but I dismissed it in the measurements I posted earlier because the groups were still acoustically small in the passband. However, directivity isn't an on/off thing as size increases with respect to wavelength, it's a gradually increasing thing. So I suppose it may be responsible too, perhaps in part, but I do not think the three items I listed above should be dismissed.

The point is, outdoor measurements of basshorns regularly show more of an increase in the low half of the passband than the high half, even when the combined mouth size is acoustically small. It seems something of a coincidence that the shift appears to happen around the same frequency that the path length is 1/2λ. To me, this is a pretty clear indication that there is more going on than simple coherent summation of wavefronts.
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Old 12th January 2012, 05:28 PM   #1347
Djim is offline Djim  Netherlands
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It's only in relation to 1/4WL 'straight' pipes but it proves there is an impedance (radiation) difference.

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Old 12th January 2012, 05:29 PM   #1348
Mark Kravchenko --- www.kravchenko-audio.com
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But that is exactly what is happening when you stack cabinets together!

Nice.
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Old 12th January 2012, 07:40 PM   #1349
Djim is offline Djim  Netherlands
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I think I need to take back my words about the supposed error in the TH115 measurements from Ivan Beaver...

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Old 12th January 2012, 09:43 PM   #1350
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Hi Djim,

As Hornresp is based on circular cross-sectional areas, the two cases in Post #1347 are Hornresp in Ang=4.0xPi(free space), and in Ang=2.0xPi (half space) (well, kind of).

Post #1349: no, you don't.

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