Specifications

Better, more uniform coverage will result from spacing the loudspeakers at 1.5 times the ceiling-to-ear distance.

In the lunchroom example, this would require spacing the loudspeakers about 2.7 meters (9 ft) apart.

Some manufacturers now offer ceiling loudspeakers with dispersion angles much wider than 90 degrees. These

allow greater spacing between speakers, and consequently it takes fewer of them to cover the same area,

although each one will require more power.

1 watt in

= 1 meter

= 2 meters

= 3 meters

92 dB SPL

86 dB SPL

82.5 dB SPL

80 dB SPL

= 4 meters

sensitivity = 92 dB, 1 watt @ 1 m

SPL(@ 1 watt) = sensitivity – (20log )

Determining power levels

After you’ve determined where to place the loudspeakers, you need to calculate the power each one requires.

Background music will require an SPL at least 10 dB above the ambient noise. For good paging intelligibility, you’ll

need an SPL approximately 15 dB higher than the ambient noise; 25 dB above ambient will yield excellent

intelligibility. If the installation is in an existing facility already in use, use an SPL meter, set for slow response, to

measure the A-weighted ambient noise at several typical listening positions. Try to take this measurement at the

noisiest time—in a factory, when the machines

are running; in a restaurant, when it’s full of

patrons, etc. You can always make provisions for

turning the system level down for quieter mo-

ments, but it’s difficult to get more level than

you planned for, without a major re-

calculation of equipment needs.

Next, measure the dis-

tance,

, in meters

from the loudspeaker

to the listeners’ ears.

Use D along with the

loudspeaker’s sensitivity

rating (typically expressed as

“

dB @ 1 watt, 1 meter,” which

means

dB of SPL with 1 watt input,

measured at a distance of 1 meter) to deter-

mine how much power the loudspeaker needs to get