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Speaker, distances and horns – Electro-Voice Microphone User Manual

Page 89

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89

Dispersion Angle distance for same coverage

Inverse Square law (point source)

- 22 db

- 28 dB

- 34 dB

- 37.5 dB

- 40 dB

B

(246.1 ft)

12.5m

25m

50m

75m

100m

(41.01’)

(82.02’)

(164’)

(246.1’)

(328.1’)

This graph should help you to get a feeling of coverage angles, loss in SPL and covered areas.
The following questions can be answered:

1. Question: “What coverage angle is needed to cover a width of X meters by the maximum possible distance to the audience

of Y meters?” Helpful when the install position of the speakers and the area to cover are predetermined.

Solution: Possible distance to the audience is a maximum of 12 meters. Covered width should be approx. 36 meters
(2 x 18 meters). A system that provides 120 degrees coverage is needed.

2. Question: “Which system is needed when the distance to the audience and the target SPL is known?” Helpful when the

install position of the speakers is known and a pre-defined SPL is required.

Solution: Inverse square law of a point source (-6dB when doubling the distance) helps to define the loss in SPL at a distance
of X meters. The pre-determined SPL at listening level (the audience) should be 100 dB. Distance to the speaker is approx. 50
meters (I.E. open-air, arena etc). The loss in SPL after 50 meters is approx. 33 dB, therefore the system has to provide a
continuous SPL of 133 dB/1m.

3. Question: “At what distance is a (i.e.) 75 meters width reached, using different loudspeakers with different coverage angles?

Solution: A 120 degrees system provides a covered width of 75 meters after approx. 22 meters. A 40 degree system provides
same width after approx. 100 meters.

4. Furthermore (based on point 3): “What´s the loss of SPL in both cases?”

Solution: Approx. 25 dB for the 120 degrees and approx. 40 dB for the 40 degrees system. To achieve a pre-determined SPL of
105 dB, when an area of 75 meters needs to be covered, the 120 degrees system has to deliver > 130 dB and the 40 degrees
system > 145 dB. In explanation: A job for MH 4020 which provides 146 dB maximum.

5. And others…

Dispersion angle versus distance for same coverage

Inverse square law (point source)

Speaker, Distances and Horns