3.51 Reducing Multiple-Source Interference. Electro-Voice EVF & EVH

3.0 Designing an EVF/EVH Cluster (cont.)

At higher frequencies, the interference patterns become more densely packed, which essentially eliminates their audibility. Figure 7 shows this effect at 8,000 Hz.

Figure 7:

Horizontal polar response (blue center plot) of two closely clustered 60° x 40° loudspeakers aimed 60° apart, showing multiple, densely packed off-axis nulls at 8,000 Hz caused by multiple-source interference (see text for more details)

3.51 Reducing Multiple-Source Interference

Multiple-source interference cannot be eliminated but it can be substantially reduced. Systems which have radiating devices large enough to hold their rated coverage angles down to relatively low frequencies, such as the horn-loaded EVH series that hold their coverage angles down to 500 Hz, will exhibit less interference in clusters. Also, doubling the distance between the two systems of Figure 8 produces multiple interference nulls which are more densely packed than those of Figure 6, reducing the audibility of the interference.

Figure 8:

Horizontal polar response (blue center plot) of two 60° x 40° loudspeakers aimed 60° apart but with double the distance between grille centers compared to Figures 6 and 7, showing the more densely packed 1,250-Hz off-axis nulls caused by multiple-source interference

(see text for more details)

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3.0 Designing an EVF/EVH Cluster (cont.)

One clustering technique that accomplishes this separation without putting a physical space between two full-range systems is putting a low-frequency or subwoofer system between two full-range systems. Such a cluster is shown in Figure 9, assembled with the optional HRK rigging kits.

HRK-2 Kit

(Sold Separately)

HRK-2 Kit

(Sold Separately)

EVF Full-Range

System

EVF Subwoofer

N ote: Loudspeakers are non-specific and shown as an example.

EVF Full-Range

System

Figure 9:

A way of separating two full-range loudspeakers to reduce the audibility of multiple-source interference by separating them with a subwoofer (see text for more details)

Electro-Voice EVF/EVH User Manual 17

3.0 Designing an EVF/EVH Cluster (cont.)

Finally, another way to reduce interference is to apply signal delay of up to 8 milliseconds to one of the two systems. This requires a separate DSP (digital signal processor) drive to the delayed system. Figure

10 shows the dramatic smoothing achieved at 1,250 Hz. Note that the systems are still close together as in Figure 6.

Figure 10:

Horizontal polar response (blue center plot) of two closely clustered 60° x 40° loudspeakers aimed 60° apart, showing the smoothing of multiple-source interference caused by a 3-ms delay to one loudspeaker

In clusters with more than two systems, adjacent boxes are usually delayed. While the effect can be predicted with appropriate software (such as EASE 4.2), the actual delays are typically established in the field during system setup and commissioning, by ear and measurements.

18 Electro-Voice EVF/EVH User Manual