One advantage that a Bessel array might have over a conventional array is diminished wind effects in outdoor applications. Since lobing is greatly reduced (when compared to parallel-wired transducers), the “prism effect” of the sound moving through the temperature gradients of a passing breeze would be greatly diminished. Another possibility is the building of arrays that can be switched between conventional and Bessel wiring, allowing either controlled and/or spurious radiation from the array.

The Bessel arrays in this Tech Topic are made up of small diameter cone transducers (4-inch), however, about any transducer could be implemented in this manner. The 25-loudspeaker unit is actually a Bessel array of Bessel arrays. These can be built using large-format horns, full-range systems, subwoofers, etc. The actual effect is a function of the piston diameter, driver spacing, and frequencies (wavelengths) being reproduced.

As a result, our mid-band examples could be scaled either up or down in frequency as the application dictates.

One Loudspeaker Only... The polars at right are for the center loudspeaker of the Symmetry is assumed in the horizontal and vertical planes. Compare this data to the measured polars of 25 loudspeakers in parallel and a 25 loudspeaker Bessel array. Note the simlarty between the Bessel array and single loudspeaker.

The Bessel array is another valuable tool in the sound system designer’s toolbox. The actual implementation of these interesting devices is left to the ingenuity of the system designer. We feel that there are applications for it in all areas of audio - from the small house of worship array to huge touring systems.

Don & Carolyn Davis offer more discussion of Bessel Arrays in their book
Sound System Engineering. Click here to order this valuable reference text.

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