Specifications

7
Center
cluster
Under-balcony fill
to be understood: this is the “what did he/she
say?” syndrome. In this example, D
C
is approxi-
mately 15 meters.
Not all reverberation is detrimental. A controlled
amount, either natural or added electronically,
can enhance the aesthetics of speech and, to a
greater extent, music. However, adding elec-
tronic reverb on a sound system designed for
mostly utilitarian purposes—e.g., paging or re-
corded background music—is very rare.
The less reverberant the room, the less intense
the diffuse sound field will be, and D
C
will be
greater. Conversely, increased reverberance of a
room will shorten D
C
and sharply reduce the
intelligible coverage area of the sound system.
Increasing the power to the loudspeaker is not a
remedy, because the increased direct field in turn
excites the diffuse field. The result is the relation-
ship between direct and diffuse fields will stay
about the same. And to make matters worse, the
likelihood of feedback through an open micro-
phone increases.
Solutions to maximizing sound system intelligibility in a difficult room include:
• controlling the reverberant nature of the room through acoustical treatment of reflective surfaces, and
architectural means.
• controlling coverage by using loudspeakers with directional qualities (Q) that will help keep sound on
the audience and off the walls and other surfaces.
• using many low-powered loudspeakers close to the audience instead of one (or a few) centrally located
high-powered loudspeakers. This often also requires less total audio power and the
production of less acoustic energy, which further helps reduce the
diffuse field.
The last approach is often best accomplished
through a distributed line speaker system. A
distributed line might also be useful for cov-
ering problematic areas in a room, such as the
under-balcony seating in a theater served by
a center cluster; a line of small speakers under
the balcony, as illustrated at left, could help
provide good sound to that portion of the
audience.
Reverberation and RT
60
A common and useful measurement of a room’s reverberance is its reverberation
time, or RT
60
. It is defined as the time it takes a sound in a space to decay 60 dB (or
one millionth of the acoustic power). The more reverberant the room, the longer the
RT
60
. Reverberation time is most precisely measured with special test gear such as
MLSSA or TEF equipment or the SMAART system.
In general, shorter values tend to be better for speech, while longer ones tend to
make music, particularly instrumental, sound fuller and more pleasing to the ear.
Here are typical targeted reverberation times for various types of venue:
.cte,smoorgniteem,sllahecnerefnoCsdnoces2.1–6.0
sameniCsdnoces2.1–8.0
)swohsyteiravdnalacisumgnidulcni(retaehteviLsdnoces4.1–0.1
smooresu-itlum,sllahloohcSsdnoces5.1–0.1
sesuoharepOsdnoces6.1–0.1
sllahcisumrebmahcdnalaticeRsdnoces6.1–2.1
)lartsehcro(sllahtrecnoCsdnoces2.2–6.1
cisumlarohcdnanagrOsdnoces0.4–0.2