Electro-Voice EVID Appendix B - System Design Guide, Ceiling Systems Size vs Coverage

Appendix B — System Design Guide

Selecting and Positioning Ceiling Loudspeakers

Several key criteria determine the type and quantity of ceiling speakers to employ in a job. Specific EVID™ Ceiling Series models accom- modate each job, depending on how these cri- teria are specified.

•Room size

•Coverage density desired

•Coverage angle specification of the speaker

•Ceiling height

•Audio program material being played The information below,and the free design

program downloadable from www.electrovoice.com (under downloads/speak- ers),will help you optimize your EVID design.

In the traditional approach to overhead- distributed systems, loudspeakers are placed in a grid whose dimensions are dictated by the room height and the directivity of the speaker ele- ments.Two basic placement patterns prevail: square spacing and hexagonal (or crisscross) spacing. See Figure 22.

Grid	Edge-to-edge Minimum￿	Center-to-￿
	overlap	center

Hexagonal Square

Figure 22: Coverage patterns

In addition to the spacing pattern, the designer must choose between three coverage density types, designated respectively as edge- to-edge, minimum overlap and center-to-center. The greater the overlap, the more uniform the coverage.The illustration below shows these various layout patterns.

Ceiling Systems: Size vs.

Coverage

In the past, system designers usually specified 8- inch cone loudspeakers for distributed overhead

systems,at least in part because they represented the traditional choice. EVID systems,however, allow for far more flexible options.

In many cases,you can achieve excellent results — at a significant savings — by using 4- inch transducers.This is especially true in jobs that do not require extended low-end response or high SPL levels. 4-inch transducers,such as those used in the C4.2,offer wider dispersion to allow for fewer speakers to be employed in the job. For example,due to its smaller cone diameter,the C4.2 exhibits significantly wider dispersion (130 degrees) than the C8.2 (110 degrees) at the -6 dB points.

The effect of this characteristic on an overhead system is indicated in Figure 23. In replacement applications where existing speaker positions are used,the C4.2 (shown in angle A) offers greater overlap and,thus,more uniform coverage than an older conventional 8-inch unit (shown in angle B).When specifying a new system,you can take advantage of the C4.2’s wider dispersion to decrease the number of speakers required to

Ceiling

A A

B B

Figure 23: Size vs. coverage

cover a given area.This will result in even greater savings.

Of course, the C4.2 is somewhat less sensitive than the 8-inch C8.2.The difference is

–5 dB.The C4.2 will also have slightly reduced low-frequency capabilities below 65 Hz. However, neither of these factors is a significant problem in many distributed systems.The C4.2 is conservatively rated to handle 80 watts of con- tinuous power equal to or greater than most other brands of 8-inch units, so its continuous SPL output will be more than adequate. Moreover, its low-frequency output can easily be augmented with the addition of the C10.1 sub- woofer. For these reasons, the C4.2 represents a great way for you to provide good audio cover-

10 EVID™ Ceiling Series Installation and Operation Manual