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Model 172 PBM
Using the Subwoofer Lo-Pass Control
When used with the complete System 170, the 172 PBM Lo-pass control should be set at 1/3 of its
range to begin with. The goal is to optimize the performance of the system by ensuring that the sub-
woofer and satellites produce a cohesive and well integrated sound “picture.” The low frequency
response of the System 170 satellites has been optimized to work with approximately a 90Hz crossover
point. This provides maximum performance and smooth integration with the subwoofer.
Higher crossover frequencies pass more bass but can sound boomy and may be more easily localized to
the subwoofer. Higher crossover frequencies may be suitable, however, when using very small satellites
that have no real low frequency performance. Settings lower than 90Hz should be employed if you are
using larger speakers that have extended bass response. This way, the subwoofer will only reproduce
the very lowest bass frequencies that are in the range where the large main speakers begin to roll off.
It’s generally undesirable to have the main speakers and the subwoofer overlap too much. Larger
speakers means a lower Lo-pass crossover frequency, smaller speakers means a higher Lo-pass crossover
frequency. Consult the manufacturer’s specified low frequency response for your main speakers to
determine the appropriate Lo-pass setting on your subwoofer. In the end, however, a little time spent
experimenting will generally result in dramatically better bass response.
The Phase Invert Control
A subwoofer operating out of phase with the rest of the system won’t provide optimum low frequency
performance. Also, the correct subwoofer phase can enhance room acoustics. Since there is so much
variation in the industry regarding phase, and no standards have been established, a switch that will
reverse the phase of the subwoofer is provided on the amplifier panel. Listen to a monaural musical
source with strong bass content. (For example, you can use the mono switch on an FM tuner or
preamp, or use a Y-connector on the outputs of one of your source components to get a mono signal.)
Experiment with the position of the phase switch to get the most extended bass. It should be obvious
which is the correct setting. In particular, there will be a smother more integrated transition between
the satellites and the subwoofer when they are properly phased.
Figure 5:
Assymmetrical
arrangement for
2 subwoofers in
a home theater,
for example, one
closer to a corner
than the other.