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3.0Designing an EVF/EVH Cluster
3.1General Aiming and Placement Guidelines
Loudspeakers should be “pointed at the people” and away from reflective room surfaces. Since people are excellent absorbers of sound and room surfaces are often not, this practice insures not only that the audience will receive the high frequencies necessary for good voice intelligibility and musical clarity but also that the reflective surfaces do not energize the room with
Loudspeakers for sound reinforcement are usually located high above a stage or platform and aimed down and out into the audience. This minimizes the difference between the longest throws to the rear of a venue and the shortest throws to the front rows, promoting coverage uniformity. Note that the typical portable loudspeaker on a short,
Level loss (dB) = 20log10(closest distance/farthest distance).
See comments on the audibility of different dB differences in section 3.4
3.2 Choosing between the EVF
When the reverberation time of a room (formally called T60 and the time it takes sound, once the source has stopped, to decay by 60 dB) exceeds
3.21 Directivity Break Frequency Defined
Below a certain frequency, the mouth size of a waveguide is no longer large enough to maintain the nomi- nal coverage angle and the coverage angle gets wider and wider as frequency is decreased. The fre- quency at which this occurs is called the “directivity break frequency” (fb) and is inversely proportional to the size of the waveguide mouth and the nominal coverage angle of the waveguide. The directivity break frequency can be approximated by the following formula:
fb (Hz) = 1,000,000/[angle (degrees) x dimension (inches)].
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