Academic question for the Bose guys:

I was very skeptical about the claim that the volume from a PAS drops off much more slowly than it does from a conventional loudspeaker, because basic physics tells us that sound intensity diminishes according to the inverse square law.

But having heard it with my own ears, I can attest to the fact that indeed, the sound intensity over distance decreases much more slowly with the PAS than it does with a conventional loudspeaker.

So I'm missing something here. I thought that was physically impossible.

Does this have to do with the fact that the PAS is a line array and not a point source? In other words (let me see if I can articulate this correctly...) the sound energy at any given distance is spread uniformly (?) over a wave front, which with a conventional speaker is spherical, but with a line array is cylindrical. A sphere of a given radius has more surface area than a cylinder (I think) so the same amount of sound energy at a given distance is spread over a greater area, which means it will have a lower sound pressure level at that distance.

Is this close to the reason why?

That's actually a very good description of how it works. You are right on track. Basically the surface of a sphere (which is proportional to the sound energy for a spherical source) is proportional to the square of the radius. Hence the "inverse square law".
The surface of a cylinder (which, not counting top and bottom, is roughly proportional to the sound energy of a line source) is only proportional to the radius (no square here).
There is actual a third form of sound field called a "plane wave" which doesn't diminish at all with distance. That would require not a line source but a "rectangular source". Unfortunately, this is very impractical.
All these three type of sound fields are perfectly in compliance with basic physics. In fact, most physics text books start out with plane waves first, since they are mathematically much easier to tackle than spherical waves.
If you want to see some actual data on "spherical" vs. "cylindrical", you can look at this post in our FAQ section.

Hope that helps

Hilmar

Thanks for the prompt reply, Hilmar. I had seen that FAQ, but it does not address the reasons why it works. Nice to know I'm thinking more or less clearly about this.

Plane wave radiators, eh? Hmmm...Bose shoji screens? Bose drywall? Bose ceiling tiles?

If you had a perfectly cube-shaped room, made all four walls, floor and ceiling out of plane wave radiators and fed them all with a good, loud kick drum signal could you accomplish nuclear fusion at the exact center of the room?

Not only in the center of the room but pretty much everywhere. In fact, you get the most energy close to the walls and the center is probably the weakest point (based on the acoustic modes of the room).
At some point I was hanging out in a lab in Denmark that has an "infra-sound" chamber. That's pretty much what you describe. Cubical room with all six walls packed end-to-end with 15" woofers. The chair is suspended in mid-air in the room. I can't remember the exact numbers but it was something like 140 dB SPL at 8 Hz or so.
Quite a bone shaking experience. Literally !!

Wow Hilmar, that's wild!

So what would make a plane wave radiator impractical if it was a permanent install?

Lee and all the ships at sea

A plane wave is not localizable (same sound everywhere). You wouldn't be able to tell where the sound is coming from and you would basically get The Conference Call Effect everywhere. Ewwwww. And so, the Cylindrical Radiator (TM) is sort-of the best of all worlds: imminently portable and the best sound coverage of any acoustical radiation device that is localizable. It's one of those rare ultimates. Practically speaking, a plane wave system would be prohibitively expensive and annoying to set up (see earlier posts on "acoustic weaponry"), unless you had a big budget, enough electrical outlets, enough room, a big truck and a crew willing to set up for you. Basically, it don't get no betta than the L1.

Cylindrical Radiator, you complete me.

quote:

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unless you had a big budget, enough electrical outlets, enough room, a big truck and a crew willing to set up for you.

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That sounds eerily familiar...oh yeah, you just desribed my "old" band before we got PAS'd

Hi Cliff-at-Bose,

Did a "Find" for "acoustic weaponry", but it returned only this thread. Which thread were you referring to?

-Carl

Carl,

I remember something about "acoustic weaponry" in a thread titled, TOTALLY NEW APPROACH, EXPERIMENTING FOR LARGE VENUES, under the "Technical" heading. You may have to go back a page or two to find it.

Oldghm

Acoustic weaponry?
Try this link. Scroll about half way down the page.
weapon