Setting The Controls - PSB HD8 Owner's Manual

as long as a substantial slot (typically 4" by 17" or more) is near the woofers. The best
location for this slot would be at floor level in line with the area to the front of the
cabinet. An inch or so of space between the front firing woofer and the cabinet front
will create enough of a channel for the bass to get down to a floor level slot.
If an HD Sub is within a cabinet, special attention should be given to preventing
rattles from strong bass tones. Rattles can be found by repeatedly playing a
selection with a variety of strong sustained bass tones. Action movies with a lot of
LFE (low frequency effects) content can be helpful as well. With the other speakers
down, turn the level up to the highest level likely to be encountered and listen closely
for rattles. If they occur, find the cabinet panels that are causing the rattle. Usually a
joint or contact area between two surfaces is vibrating and this is the cause of the
rattle. Some foam tape or the commonly available self adhesive felt discs, placed
between the offending surfaces will damp the rattle. Absorptive material, such as
fiberglass, may help damp internal resonances of the cabinet's cavities, but it will
need to be quite thick to have significant effect. Filling the full cavity above the
subwoofer can give a significant improvement, just be sure that the woofers and
their bass exit path are not obstructed. Although it normally runs cool, be especially
sure that any heat generated by the rear amplifier has an exit path and that no
materials are in contact with its metal surfaces.
Multiple Subwoofers—Why Two Subs Are Better Than One
Since the objective of most people who buy subs is to make sure of plentiful low
frequencies, the only situation most of us will run into that makes subwoofer
placement really difficult is the factor we all fear—the "bad" room that just won't let
you get satisfying amounts or quality of bass. There are rooms with troublesome
dimensions, especially as you approach a perfect cube (with closed doors and no
other natural openings). There is unlikely to be any combination of speaker and
listener position that will be free of obvious acoustic anomalies.
In such a case, the best way to iron out those anomalies is with two subwoofers,
placed carefully to work with each other. This can also be true when the problem is
too much, or too uneven, bass. Recent studies have proven that 2 subwoofers
carefully placed will give more even response over a listing area. These studies
show that mounting one woofer in the center (at floor level) of the front wall,
balanced by the second woofer in the center of the back wall will usually give a best
solution. Alternatively, having one woofer at the center of the left wall balanced by a
second woofer centered on the right wall will give similarly good results.
Setting the Subwoofer Controls
Once a reasonably smooth response has been achieved by careful positioning of
the subwoofers, the overall performance can be further improved by means of the
controls found on the speaker. An important one is the low-pass filter, which controls
the upper limit of the subwoofer's frequency range. This should be set high enough
to overlap the low frequency cutoff of the satellite speakers, but not high enough to
localize specific sounds from the sub.
If the frequency response of your satellite speakers is such that the subwoofer's low-
pass filter must be set higher than about 80Hz in order to avoid gaps in the overall
system response, then you might well be able to localize specific sounds from the
sub. This can be very distracting when these sounds appear to come from beside or
behind you. One solution is to make sure the subwoofer is in the front of the listening
area; another is to use multiple subwoofers to make such sounds more diffuse.
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