User Guide

Sound System Design Reference Manual
7-20
Figure 7-17. Plan view of social area and disco area.
The total level at the test position is thus 82 dB
when all 12 loudspeakers are powered with 1 watt, or
85 dB with 2 watts per loudspeaker. With 20 watts
per loudspeaker, we would have a comfortable 10 dB
margin over our target value of 85 dB SPL. The
system will be “coasting” most of the time, and a
single stereo amplifier, with loads wired in series-
parallel, will suffice.
2. Disco system. There are a number of
possibilities here. A very high-end approach would be
to specify two JBL 4892 Array Series systems at
each corner. They should be mounted near the
ceiling and angled down so that the horns point
toward the center of the dance floor.
The 4892 is a biamplified system, and its
overall sensitivity of 98 dB is limited by its LF section.
The LF power rating is 600 watts. The distance from
each corner to the center of the dance floor is 7
meters:
Level Power Distance
98 dB 1 W 1 meter
126 dB 600 W 1 m
109 dB 600 W 7 m
A total of 8 4892 systems would increase the
output by 9 dB, producing level capability of 118 dB
at the center of the dance floor. The amplifier
requirement would be 4 MPX600 units and 4
MPX300 units. Note carefully that the MPX600 has a
maximum output capability of 400 watts into 8 ohms.
This is approximately 2 dB less than 600 watts, and
we would have to derate the system’s overall output
capability by that amount.