Handbook for Sound Engineers

1390 Chapter 36

Here the frequency response of two horn loudspeak-
ers is shown. In the upper curve, the sound arrivals are
synchronized and hence add constructively. However, in
the lower curve, the horns are missynchronized by just
300 μs. A series of sharp comb filters occur. Not only is
useful speech information lost in the extensive series of
nulls but also the polar radiation pattern is often undesir-
ably affected as shown in Fig. 36-9. The resultant lobes
may not only result in certain frequencies not being
transmitted to the listeners, but lobes may also be cre-
ated that can cause undesirable reflections to occur.
These may cause either additional unwanted excitation
of the reverberant field or cause the generation of late
reflections (echoes) that may damage intelligibility.

Fig. 36-10 shows the corresponding ETC reflection

sequence for the horns in a reverberant space in and out

of synchronization. Note the increased excitation of the

reverberant field when out of synchronization.

The lobes caused my missynchronization, apart from

potentially reducing intelligibility, may also reduce sys-

tem feedback margin, either by directly radiating sound

back to a live microphone or by causing a strong early

reflection to occur back into the microphone.

36.6 Loudness and Signal-to-Noise Ratio

The sound level produced by a sound system must be

adequate for the intended listeners to be able to hear it

comfortably. If the level is too low, many people, partic-

Figure 36-8. Frequency response of two loudspeakers.
Upper curve shows effect when the sound arrivals are syn-
chronized, lower curve shows effect of 300“s missynchro-
nization.

Vertical: 6 dB/division

Horizontal: 50.33 Hz 

10,001.20 Hz

Resolution: 5.3674E + 02 Hz

Both horns: Near throw delayed 300 Ms

A. Loudspeakers in synchronization.

Vertical: 6 dB/division

Horizontal: 50.33 Hz 

10,001.20 Hz

Resolution: 5.3674E + 01 Hz

Both horns: No delay

B. Loudspeakers out of synchronization by 300 Ms. Figure 36-9. Polar response of two loudspeakers in and out

of synchronization.

140 o

110 o^80 o

160 o

50 o

20 o

10 o

40 o

100 o^70 o

130 o

25 dB

¾

 160 o

140 o

110 o^80 o

160 o

50 o

20 o

10 o

40 o

100 o^70 o

130 o

27 dB

¾

 160 o

A. Two loudspeakers in synchronization.

B. Two loudspeakers out of synchronization.