Bessel Arrays

14 BESSEL ARRAYS Loudspeaker systems that use a relatively large number of identical drive units unfortunately provide a highly directional beam of sound. Depending on the alignment of the drive units, frequency `holes" occur at a number of positions. Arranging the drive units in a Bessel array results in even sound distribution. It should be noted that for the commercial use of the systems described in this article the permission of the patentee, Philips Export BV, Eindhoven, the Netherlands, is required The requirement for frequency-indepen- dent even distribution of sound in large rooms can be met only approximately. Radiation patterns at different frequencies but equal magnitude are shown in Fig. 1. From these diagrams, it is clear that the pattern approaches the ideal at low fre- quencies and that the higher the frequency the more chaotic the distribution. Assu- ming a maximum sound pressure of 85 dBm, the sound pressure in the "eyes" of the 1600 Hz diagram is some 40 dB down...