6
Room Acoustics
The SR151z loudspeakers are designed to sound as
neutral as possible; that is, to reproduce the input signal
as accurately as possible.
Room acoustics play a crucial role in the overall per-
formance of a sound system. Here are some additional
placement tips to help overcome some typical room
problems that might arise:
• Avoid placing loudspeakers in the corners of a
room. This increases the low frequency output and
can cause the sound to be muddy and indistinct.
• Avoid placing loudspeakers against a wall. This, too,
increases the low frequency output, though not as
much as corner placement. However, if you do need
to reinforce the low frequencies, this is a good way
to do it.
• Avoid placing the speakers directly on a hollow
stage floor. A hollow stage can resonate at certain
frequencies, causing peaks and dips in the fre-
quency response of the room. It’s better to place the
loudspeakers on a sturdy table or stand designed to
handle the weight of the SR151z.
• Position the loudspeakers so the high-frequency
drivers are to feet above ear level for the audience
(make allowances for a standing/dancing in the aisles
audience). High frequencies are highly directional
and tend to be absorbed much easier than lower
frequencies. By providing direct line-of-sight from the
loudspeakers to the audience, you increase the over-
all brightness and intelligibility of the sound system.
• Highly reverberant rooms, like many gymnasiums
and auditoriums, are a nightmare for sound system
intelligibility. Multiple reflections off the hard walls,
ceiling, and floor play havoc with the sound. Depend-
ing on the situation, you may be able to take some
steps to minimize the reflections, such as putting
carpeting on the floors, closing draperies to cover
large glass windows, or hanging tapestries or other
materials on the walls to absorb some of the sound.
However, in most cases, these remedies are not possi-
ble or practical. So what do you do? Making the sound
system louder generally doesn’t work because the
reflections become louder, too. The best approach is to
provide as much direct sound coverage to the audience
as possible. The farther away you are from the speaker,
the more prominent will be the reflected sound.
Use more speakers strategically placed so they are
closer to the back of the audience. If the distance
between the front and back speakers is more than
about 100 feet, you should use a delay processor to
time-align the sound. (Since sound travels about
1 foot per millisecond, it takes about 1/10 of a
second to travel 100 feet.)
THERMAL CONSIDERATIONS
The SR151z has two powerful built-in amplifiers
capable of producing a combined 500 watts of power.
As amplifiers produce heat, it is important to dissipate
the heat as quickly as possible. This results in increased
reliability and longevity for the amplifier.
The amplifier module is mounted on a large heatsink,
which is cooled by convection where cool air is drawn
through it’s fins, carrying the heat away. In order for this
convection cooling to work efficiently, it is important
to provide adequate airspace behind the loudspeaker.
When you position the SR151z, we recommend leaving
at least six inches of air space behind it.
In the unlikely event of the amplifier overheating, a
built-in thermal switch will activate, which mutes the
signal and lights the THERMAL LED. When the amplifi-
er has cooled down to a safe operating temperature, the
thermal switch resets itself, and the SR151z resumes
normal operation.
If the thermal switch activates frequently, try turning
down the level control a notch or two on the mixing con-
sole (or the back of the SR151z) to avoid overheating
the amplifier.
If the temperature in the room is too high, it could
cause the amplifier to overheat. In this case, you should
try aiming a fan at the rear panel to move more air
through the heatsink fins.
AC POWER
Be sure the SR151z is plugged into an outlet that
is able to supply the correct voltage specified for your
model. If the voltage should drop below 97% of the spec-
ified line voltage, the built-in amplifiers will no longer
be able to supply rated power. (They will continue to
operate down to 80% of the rated line voltage, but won’t
reach full power, resulting in lower headroom.)
Be sure the electrical service can supply enough am-
perage for all the components connected to it.
We recommend that a stiff (robust) supply of AC
power be used because the amplifiers place high cur-
rent demands on the AC line. The more power that is
available on the line, the louder the speakers will play
and the more peak output power will be available for
cleaner, punchier bass. A suspected problem of “poor
bass performance” is often caused by a weak AC supply
to the amplifiers.
Never remove the ground pin on
the power cord of the SR151z or
any other component. This is very
dangerous.
