How Many Subwoofers - Niles CM8SW Installation & Operation Manual

How Many Subwoofers?
For most applications a single CMBSW is
appropriate. However, in large rooms, high
performance listening rooms or in home
theaters, an array of two or more CMBSW
will deliver astounding results. Unlike
other subwoofer systems, a Niles
Subwoofer Array is concealed. Consider
the distance between the subwoofer and
the listener, the size of the amplifier and
the desired quality and volume of sound
when deciding how many CMBSWs to
install in your home.
Decibels and Power
65dB
Conversation at three feet.
75dB Sewing Machine at three feet.
95dB
Vacuum Cleaner
at IO feet.
95dB Subway Train entertng a station
at 20 feet.
3dB
The smallest difference of sound
the human ear can easily detect.
1OdB Perceived as twice as much loud-
ness if it is an increase (half as
much if it IS a decrease).
Any speaker requires twice as much
amplifier power to increase 3dB and ten
times as much power to increase IOdB.
Comparison of 1,2 or 4 Subwoofers
16' x 18' x 8' Room @ 12'
25 Watts 100 Watts
1 Sub 95dB 1OldB
2 Subs 1OOdB 106dB
VLSA of 4 Subs l03dB 109dB
2 x Watts = 3dB Increase rn Volume.
2 x Subs = 3dB Increase in Volume.
2 x Subs = I/2 the subwoofer excursion for
the same volume.
If you double the distance from the sub-
woofer to the primary listenlnfi position
you decrease the volume by 4 to 6dB.
Single Stereo Subwoofer
One CMBSW can produce the bass sound
from both the left and the right channels
because of its unique dual voice coil
design. One voice coil powers the left chan-
nel and the other powers the right channel.
A stereo crossover divides the signal and fil-
ters it according to the position of the
switches on the front panel. A single stereo
subwoofer is compatible with any 4 ohm
stable amplifier. Eight ohm stable amplifiers
may be used with a Niles IM volume con-
trol (see Impedance section on Page 7)
Dual Subwoofer Systems
Using two CM8SW subwoofers in a system
raises the maximum attainable volume of
the system by 3dB. Additionally, at lower
volumes, excursion - and therefore distor-
tion levels - are reduced. In a large room,
or a home theater system, the effect on
bass quality is extremely desirable.
Another 2dB increase is possible if the
voice coils of each are CM8SW paralleled.
This requires a multi-channel amplifier or
an amplifier capable of driving the 2 to 2.6
ohm load of the overall system.
VLSA Installations
A Very Large Subwoofer Array (VLSA)
installation lowers the amount of excursion
requrred to achieve a high sound pressure
level. Lowering excursron dramatically
improves the quality of the sound. VLSA
installations are most appropriate when the
listener appreciates detail and bass exten-
sion, but must have a concealed installa-
tion. A VLSA of four subwoofers must have
a multichannel amplifier with one channel
assigned to each subwoofer.