Is a line source always a vertical array?
Is a Bessel array always square?
What are other arrays that make sense?

Yes, they have a very very narrow vertical dispersion, while maintaining a wide horizontal dispersion.

>>Is a Bessel array always square?

Usually, or close to it, so you can do some neat things with them, like high SPL's or for beam steering applications and frequency shading and some other things. JBL has a tech paper on beam steering and freq. shading for bessel arrays and the principles behind it, see link below.

Phillips corporation holds the patent and licensing for Bessel arrays so if you're going to use them commercialy(sp) you may need a license.

HTH
Bill W.

• JBL tech paper on bessel array layouts

Well Bill answered some of your questions but let me weigh in and give you another viewpoint. My viewpoint comes from application of line arrays for home usage (vs. the usual pro sound use).

First of all, let me say that Bessel arrays are not a very smart idea for most applications. How many current home or pro sound applications have seen that utilize Bessel arrays? Very, very few. Bessel array ideas are like urban myths--they come around every few months but quickly fade as they are shown to be plenty dumb ideas.

I doubt that Philips's Bessel array patent has paid them much money over the years. Bessel arrays operate in the far field (listening position would be typically 20 to 30 times their height away from them). Their efficient is typically little more than a single driver source within the array so why do it? Don Keele published an excellent paper on "Effective Performance of Bessel Arrays" in the Journal of Audio Engineering Society in October 1990. He studied 5, 7 and 9 source Bessel arrays. His conclusion was that only the 5 source Bessel array made any sense at all and even that array has shortcomings versus a 5 element linear array.

For my applications I really like near field line arrays (NFLA)--especially for home usage. See my white paper on NFLA design considerations for more details. NFLA provide effortless sound which has a huge image field plus nearly constant sound level within the room. NFLAs come the nearest to having the impact of a live sound venue that I have experienced.

Let us hear about your line array application and perhaps a more detailed answer can help you reach a solution.

Jim

• Near Field Line Array White Paper

What frequency do you crossover the larger pair at? About 2kHz or so I'd guess? How about the smaller pair? Maybe 3.5kHz?

The larger array is crossed at 2300 Hz while the smaller array crosses at 2000 Hz. I wanted the smaller array to be crossed at 3500-4000 Hz but the array gain falls enough that a lower crossover was necessary.

Jim

Is the array gain a function of driver-to-driver spacing?

http://www.creativesound.ca/details.php?model=NEEDLES

The larger array is the Linus 2 for which parts and plans are available through Rick Craig at:

www.selahaudio.com

The Linus 2 doesn't show up on Rick's hot keys on the home page but you can e-mail for details. Take a look at some more Linus 2 examples in his Gallery photos.

Thanks for the interest. Contact me for any more general line array details.

Jim