TOA bs-1030 Mode D'Emploi

TOA Electronics Speaker Guide

 

Amplifier Selection

33

A multi-purpose room needs high-quality sound for video and A/V presentations, speech rein-
forcement, and background music for company functions. The room is 40 x 80 ft with a 12 ft 
ceiling. TOA model F-121CM speakers are selected for their ability to meet the wide-ranging 
requirements. 

From the F-121CM’s coverage and spacing table (page 37), we see that spacing recommenda-
tions range from 10–21 ft for standing listeners (h – l = 6 ft.) and 14–28 ft for seated listeners 
(h – l = 8 ft). Selecting a square pattern and spacing the speakers at 20 ft intervals puts us within 
both ranges and allows a simple layout of two rows of four speakers (8 total).

To deliver convincing, distortion-free movie sound, the system should be designed for a max-
imum average level of 85 dB at the listeners, with 10 dB of headroom for transient peaks, for 
a L

req

 of 95 dB.

The F-121CM has a rated sensitivity of 90 dB, 1 W @ 1 m. Using the attenuation with distance 
chart (see Figure 5-1 on page 22), we find that this gives us 82 dB with 1 W at the listener. 

Using the level change with power input chart (see Figure 5-2 on page 22), we see that 20 W 
per speaker provides the 13 dB to reach the L

req

. Adding them up yields a speaker total of 

160 W. Multiply by 1.2 (120%) to yield the minimum amplifier power: 192 W.