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Old 22nd January 2002, 11:00 PM   #21
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Assuming that I'm following what you're saying, it sounds as though you're taking a line source and making it behave somewhat like a point source. The wavefront that launches from the middle will not be met by an equal strength pressure and will begin to bend upwards and downwards from the center.
I'm reminded of the way that Quads trigger (comparatively) large panels in order to make them approximate a point source. No, I'm not saying it's the same, just that it sounds as though you're taking one sort of speaker and making it behave like another.
This may or may not be a good thing, but I'm not sure that it qualifies as a line source any more. Perhaps new nomenclature is required.

Grey
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Old 22nd January 2002, 11:46 PM   #22
Bill F. is offline Bill F.  United States
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I already took my best swing at new nomenclature in the long post above: Quasi-not-really line source. That's the best I can do.

You wanna talk about a line source not behaving like a line source, have you ever checked out bessel array theory?

Craziness!

(Won, here's another idea to stoke your mental furnaces regarding short arrays.)

Here's an example--a five-driver bessel line array.
(numbers show relative power and polarity for each driver in the bessel row.)

1:2:2:-2:1

It gets even crazier for a seven-driver row:

1:2:2:0:-2:2:-1

Yes, the middle 0 means no driver there, just a blank (though necessary) space. I guess you could drop a tweeter in there for coincident sound.

Don't ask me how, but you can mathematically solve for a bessel row of any lenght, even for bessel matrices.

I've never played with bessel arrays, but the claim is that they approximate a point source. I think Philips holds the patent.

I hear that coherence isn't good till you move back to 3x-5x array hight, then it sounds smooth.
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Old 22nd January 2002, 11:54 PM   #23
Won is offline Won
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Interesting. Would you mind telling me where you found that info on Bessel Arrays, Bill? Those multiples seem pretty easy to deal with, although now they seem rather arbitrary. The 7 speaker bessel (or really, 6 with a hole) seems to be perfect for my MMMTTMMM plans. I wonder what a bessel array of order 2 looks like, and how it relates to the D'Appolito (sp?)

Thanks, Won (off to Billy Joel/Elton John concert...)
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Old 23rd January 2002, 12:27 AM   #24
Bill F. is offline Bill F.  United States
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Two links to get you started:

http://www.prosoundweb.com/install/s...t25_4_p1.shtml

http://yu-ra.tripod.com/audio/array_wiring.gif

Bill
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Old 24th January 2002, 07:40 PM   #25
Bill F. is offline Bill F.  United States
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Oops, I see the second link is no longer good. Sorry, I didn't turn up much more on a google search.

Won, just a word of warning about your MMMTTMMM idea:

You might run into problems with your tweeter dispersion pattern.

One of the unavoidable characteristics of line arrays is that driver interactions cause cancellation that narrows dispersion along the axis of the line. For instance, vertical line arrays tend to have wide horizontal dispersion and narrow vertical dispersion. This is just fine if your head stays at a level between the array ends. In fact, it can be a plus in that it tends to limit floor/ceiling reflections.

However, in your case you have a tweeter array that's maybe three inches tall. As frequency increases, line array driver interactions become more pronounced as overall dispersion narrows. If you line your two tweeters up vertically, the vertical dispersion will be quite pinched. String them side by side and you'll rotate that pattern 90 degrees. Neither makes for a very big sweet spot.

It may work just fine for you depending on your expectations, it's just something to be aware of.

Bill
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Old 25th January 2002, 12:05 AM   #26
JohnR is offline JohnR  Australia
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Hi Bill, sorry I didn't read your post properly! I was thinking of a floor-to-ceiling array :-) Won't the matrix give you frequency-dependent lobing in the horizontal as well as vertical direction?
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Old 25th January 2002, 02:50 PM   #27
Bill F. is offline Bill F.  United States
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Yes, it will.

But lobing should start higher in the band. I'd planned to cross the array over as low as possible to a high efficiency horn or bullet tweeter. I don't know how great a tonal match that would be, but it would be a fun experiment. I'm intrigued at the thought of 102 dB/W system efficiency.

I poked around at SpeakerBuilder for info about Wayne J's "insane" matrix array, but all I could find was his note that he was dropping the project. Anyone know if/where I could get the full scoop?

Bill
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Old 26th January 2002, 06:25 AM   #28
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Hello,

Will creating a curved baffle, with the center point of the radius for each baffle being at the listener's respective ears (puting each speaker the same distance from the listener's ears at one listenting location), reduce the problems of lobing, nodes, and such, at the listening location? I realize that this is only a solution for one position in the room (maybe), but the end is satisfatory to me if I could get the efficiency of the line array without the downfalls.

Thanks,

Dave
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Old 30th January 2002, 04:58 PM   #29
Won is offline Won
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Bill -

How do you compute the volume for a sealed bessel array? Does the volume "displaced" by out-of-phase drivers "cancel?" Or should each driver be in a separate sub-enclosure? Or each set of drivers in a particular phase?

-Won
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Old 30th January 2002, 05:13 PM   #30
Bill F. is offline Bill F.  United States
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Good question.

All I can say is that the safest way to go would be seperate enclosed spaces. That way driver interactions will be purely electrical and the speaker will end up behaving closer to the T/S model.

By the way, I found another good line array link:
http://www.meyersound.com/products/c...ray_theory.htm

Bill
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