multiple spacing on ESL...possible to avoid directionality?

[thadman]

Im aware that one of the main issues concerning ESLs is directionality, and I'd like to combat that somewhat. Would it be possible to build an ESL with multiple panel widths (say (1) .5", (2) 2", (2) 6") while running all of them fullrange to avoid directionality? Would there be any comb filtering, or other negative effects?

How much excursion can I expect from an ESL? .1mm? (FYI im modeling it in SL's spreadsheet)

[Paul W]

Sanders book

In terms of directionality, running all of the segments full range would be virtually the same as 1 large panel running full range. The largest difference would be the work involved

Audioxpress has a sale on now, so a good resource would be Roger Sanders book.
Paul

[thadman]

wouldnt a 12" panel be abyssmal directive? (I own Roger Sanders book btw...seems Ive misplaced it though)

[Paul W]

Achieving a broad radiation pattern requires a narrow radiator in terms of wavelength. In other words, to minimize lobing, radiator physical width must decrease as frequency increases.

So, yes, a full-range 12" driver would be very directional at HF; as would a segmented version if all of the segments are run full range. Segmenting an ESL doesn't gain anything unless the wider/outer segments are low-passed.

For your hypothetical ESL with (1) .5", (2) 2", (2) 6", you would roll off the 2x6" at relative LF, 2x2" would roll off at MF, the .5" could run full range (though many designs use closer stator spacing and high-pass the tweeter).

[thadman]

Is the BG RD75 directive (>6000hz) because of its radiating area (1.1" should become directive at 6000hz in the nearfield) coupled with the fact that you're listening in the nearfield, or is there another reason?

[Paul W]

You could say a 1.1" source will begin to become directional at 6k. But the operative word is "begin"...it isn't like throwing a switch. Just consider the horizontal directional tendencies of linesources the same as a cone or dome of the same width. 12" will beam more than 2" and so on.

Near/farfield discussions are usually more concerned with vertical line height vs distance. In practice, nearfield/farfield transition from a line source to a point source is across a broad region...again, not throwing a switch. Best near/far reading I've come across are the array and linesource papers on the JBL Pro site.

The FRD Consortium has a lot of freeware you can use to explore these subjects visually.