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Old 2nd August 2010, 02:33 AM   #101
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Old 2nd August 2010, 12:11 PM   #102
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Quote:
Originally Posted by bear View Post
I seem to recall the McIntosh line source speakers - too bad the technology wasn't really "disclosed" in the marketing... although perhaps I am thinking of much earlier speakers from them??

_-_-bear
The array in question was only used in the XRT24 and 25. I don't think in anything after, although the have used the Bessel arrays as described in the paper (after Keele and others).

There have been a lot of audiophile line array systems that could be significantly improved by proper tapering. Yet I am not aware of any high-end designer that has understood or used the technique. This includes electrostatic and planer magnetic designs. I've tried to explain the approach and benefit to numerous designers and always get the blank stare.

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Old 2nd August 2010, 02:08 PM   #103
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Thanks David...

My stare is not blank... more like that confused look a cat or dog can give you??

No, seriously I "get it"... but as i said, McIntosh seems (ed) to keep this "feature" unstated. At least I never noticed it in anything i ever read, not that I read everything... but I have never heard it mentioned...

Speaking of Bessel arrays - my impression is/was that they are frequency tapered from a "center" point (up and down) not amplitude tapered?

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Old 2nd August 2010, 02:15 PM   #104
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Now, any expert comments on:

It may be that I do not understand what I am seeing in Don's paper. But I am comparing the Legendre shaded 50 driver array figs 62-5 with 41-3 for the straight line source.

I seem to see energy going up vs. energy not going up??


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Old 2nd August 2010, 02:42 PM   #105
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speaking of the inverse (??), I was at Wallmort the other day and I walked past a spot in the aisle in the cosmetic section and suddenly heard sound. I stared up at the high black metal truss work overhead and saw what looked like an array of small (computer sound sized) speakers, in a line, behind black perf metal grille. Very very very directional from about 20 feet above. Oh, parallel to the aisle...

Reverse tapering?? Or??

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Old 2nd August 2010, 03:28 PM   #106
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Default Fun with Arrays

Quote:
Originally Posted by bear View Post
speaking of the inverse (??), I was at Wallmort the other day and I walked past a spot in the aisle in the cosmetic section and suddenly heard sound. I stared up at the high black metal truss work overhead and saw what looked like an array of small (computer sound sized) speakers, in a line, behind black perf metal grille. Very very very directional from about 20 feet above. Oh, parallel to the aisle...

Reverse tapering?? Or??
This is another interesting applications of arrays: using super directivity to focus a beam to a narrow audience. I think some museums are using this where you can walk from painting to painting and a large area array gives you comentary that is only audible in front of the painting. (Either that or WalMart just had a few plasma TV speakers left over!)

Somewhat related are the panel arrays that One Digital (Pioneer) and Yamaha are selling. A single rows-and-columns array can create multiple sharp beams that might reflect off your walls to create 5 surround sources. All they have to do is create tight, wide frequency band pencils of sound, that fire in the appropriate directions of the room.

Multi antenna deep space arrays are also the same technology.

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Old 2nd August 2010, 03:43 PM   #107
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Quote:
Originally Posted by bear View Post
Thanks David...

My stare is not blank... more like that confused look a cat or dog can give you??

Speaking of Bessel arrays - my impression is/was that they are frequency tapered from a "center" point (up and down) not amplitude tapered?

_-_-bear
The Bessel array is a weighted coefficients or shaded array. The common example is 5 elements with coefficients of:

+0.5 -1 +1 +1 +0.5

In other words the outter elements are 6dB down and one element is out of phase. It turns out that such an array has no extra directivity in spite of being 5 elements long. Mac has some speakers with 5 tweeters mounted sideways using the Bessel weighting. Because of one tweeter out of phase and two at half strength, you get minimal extra output from your 5 tweeters, so it seems like a marginal benefit to me.

I think what you are thinking of would be like the 3 element arrays that have been designed for THX approval or elsewhere when a little more directivity was desired. (Another Mac product like the HT1) In that case the outer tweeters of the trio would be rolled off in the right amount and you can achieve good response and no lobes.

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Old 2nd August 2010, 05:48 PM   #108
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Post re #103

Quote:
Speaking of Bessel arrays - my impression is/was that they are frequency tapered from a "center" point (up and down) not amplitude tapered?
Bear,

To add to David's reply. The Bessel array was initially designed, as a spherical radiation solution. At the time Philips (the Patent holders) were involved in sound reinforcement. The Bessel array was a cost effective solution to reduce interference effects, caused by positioning multiple adjacent drivers, or systems, side by side. At the time a step up from the usual cheap and nasty column speakers.

Iain.

bessel arrays.

McIntosh XRT18 Speaker System history
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Old 2nd August 2010, 07:59 PM   #109
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Thanks for that input...

Odd, my brain must be misfiring, not an uncommon occurance (!!) but I seem to recall reading about Bessel Arrays in Berenek's Acoustics textbook... obviously I got it wrong. (grrrr...)

Ok so what then is a frequency tapered line array??

All of my reading on this - not a lot at that - predates anything like THX, and is (omg!!) LAST CENTURY!!

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Old 2nd August 2010, 09:03 PM   #110
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Don't know if the group delay steering used in the JBL CBTs works worth a whit yet, but I think it's darn clever and easy to implement DIY.

Is that a Keele or a Button innovation?

[They're obviously WAY smarter than the Zilchster, who is more like 10,000 monkeys by comparison.... ]

Last edited by ZilchLab; 2nd August 2010 at 09:07 PM.
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