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Loudspeaker directivity by Roy Allison


Howard Ferstler

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What you and Toole advocate is narrow dispersion by my standards.

As I recall, we previously agreed that wide dispersion began at 120°. It's real easy - 0 -60, 60-120, 120 - 180, 180+.

Geddes agrees with you, actually; he calls his designs "narrow," and when I attempted to correct him on that, he advised, in his case, 90° refers to the flare angle, the actual -6 dB dispersion being 70°. Go figure.

[He's not buying my suggestion that narrow is 60° or less, either, obviously. ;) ]

Actually, my own home-built jobs are certainly narrower in broad-bandwidth dispersion than my IC-20 models, and with some recordings, especially smaller-scale stuff, I think that my units actually sound better.

Who'd have guessed...? :P

And, sure, in that particular picture the drapes will obviously absorb some sound, although not much treble energy gets behind a speaker in the first place. The Toole room, as shown in his diagrams, also had drapes partially down the side walls, and those drapes WOULD have an impact. The photo of the LvR concert does not show the side walls, so we have no idea if they were draped. Also, as I have noted, the AR-3 is a more directional speaker than, say, the later AR-3a, AR-LST or any Allison model, and so in an auditorium environment it would be able to aim more direct-field energy and not have it dissipated by open space (or drapes) well to the sides.

Again, the Toole room drapes stop at the speakers, and do not damp the lateral reflections.

SO, we now argue that the success of Villchur's LvR presentations was in some significant part attributable to dominance of the direct field.

COOL! :blink:

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As I recall, we previously agreed that wide dispersion began at 120°. It's real easy - 0 -60, 60-120, 120 - 180, 180+.

Geddes agrees with you, actually; he calls his designs "narrow," and when I attempted to correct him on that, he advised, in his case, 90° refers to the flare angle, the actual -6 dB dispersion being 70°. Go figure.

[He's not buying my suggestion that narrow is 60° or less, either, obviously. ;) ]

Who'd have guessed...? :P

Again, the Toole room drapes stop at the speakers, and do not damp the lateral reflections.

SO, we now argue that the success of Villchur's LvR presentations was in some significant part attributable to dominance of the direct field.

COOL! :blink:

"SO, we now argue that the success of Villchur's LvR presentations was in some significant part attributable to dominance of the direct field.

COOL! "

What a strange lot audiophiles are. Among the advocates of narrow dispersion tweeters, one poster tells me that the reflection of a perimeter wood molding on the baffle only a couple of inches wide will change the output 10 db and create horrible distortion while another such advocate says that a speaker with a tweeter whose highest octave starts falling off appreciably just a few degrees off axis can successfully emulate the sound of a guitar whose radiation of all of its sound including higher harmonics is so wide, you practically have to stand behind the musician before enough harmonics are blocked to change the timbre. And you expect me to believe that an audience over a fairly wide angle will not hear this difference. Yes a strange lot.

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What a strange lot audiophiles are. Among the advocates of narrow dispersion tweeters, one poster tells me that the reflection of a perimeter wood molding on the baffle only a couple of inches wide will change the output 10 db and create horrible distortion .

So we are making up facts now to support our argument? Find me the quote please.

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I was looking at Olson's study on enclosure diffraction/reflection and he showed a worst case peak to trough of 10dB (I'm guessing that would be audible) for drivers mounted dead center in a square or circle. Typically 2 to 3 dB effect for other cabinets.

David

And then:

You need to read what I said again. I was refering to Olson's study and his measurements of a small driver on the face of a variety of cabinets. Worst combinations, with the unit in the center of a highly symmetical cabinet, gave 10dB peak to trough. More typical cases gave 2-3dB. These are diffraction related edge reflections alone. Perimeter dams would be a seperate additional issue. I'm not sure I would lump these in with cables and vacuum tubes. Olson didn't strike me as a tweak..

I twice explained that the reference was to Olson's experiments with cabinet diffraction which showed as much as 10dB peak to trough ripple.

I guess reading comprehension is a problem for some.

David

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And then:

I twice explained that the reference was to Olson's experiments with cabinet diffraction which showed as much as 10dB peak to trough ripple.

I guess reading comprehension is a problem for some.

David

"I guess reading comprehension is a problem for some."

I'd guess extreme exaggeration, unwarranted generalizations, and focusing minutely on the irrelevant are problems for others.

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