Rich Andrews. wrote:

A Bessel array is usually a horizontal array.

Strange that one of the two forms of Bessel array that work well is 5 x 5.

The other Bessel array that works well, 5 in a row, has the same
directional characteristics no matter which way it's roated.

Effective Performance of Bessel Arrays 2366218 bytes (CD aes5)
Author(s): Keele, Jr., D. B.
Publication: Volume 38 Number 10 pp. 723·748; October 1990
Abstract: The Bessel array is a configuration of five, seven, or nine
identical loudspeakers in an equal-spaced line array that provides the same
overall polar pattern as a single loudspeaker of the array. The results of a
computer simulation are described, which uses point sources to determine the
effective operating frequency range, working distance, efficiency, power
handling, maximum acoustic output, efficiency·bandwidth product, and
power·bandwidth product of the array. The various Bessel configurations are
compared to one-, two-, and five-source equal-spaced equal-level
equal-polarity line arrays. As compared to a single source, a five source
Bessel array is 14% (0.6dB) more efficient, can handle 3.5 (+5.4dB) more
power, and has 4 times (+6dB) the maximum midband acoustic output power, and
is usable for omnidirectional radiation up to the frequency where the
overall length is 11 wavelengths long. As compared to a two-source
equal-level in-phase array, a five-source Bessel array is 43% (2.4dB) less
efficient, can handle 1.75 (+2.4dB) more power, has the same maximum midband
acoustic output power, and is usable for omnidirectional radiation 10 times
higher in frequency. A working distance of 20 times the length of the Bessel
array was assumed, with the length of the Bessel array (center-to-center
distance of outside sources) being four times that of the two-source array.
Analysis reveals that the three Bessel arrays have equal maximum acoustic
output, but that the five-element Bessel array has the highest efficiency
and power·bandwidth product. The seven- and nine-source Bessel arrays are
found to be effectively unusable, as compared to the five-source array, due
to much lower efficiency, requirement for more sources, and poor
high-frequency performance. Judging polar peak-to-peak ripple and
high-frequency response, the performance of the Bessel array is found to
improve in direct proportion to the working distance away from the array.
Unfortunately the phase versus direction and phase versus frequency
characteristics of the Bessel array are very nonlinear and make it difficult
to use with other sources.