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Front LED Switch
The Front LED Switch, located on the rear panel, is used to enable or disable
the LED located on the front of the enclosure near the bottom of the grill. Slide
the switch to the ON position to enable the front LED and slide it to the OFF
position to disable the front LED.
Most applications merit the use of the Front LED so power status can be visu-
ally confirmed, easily and quickly. For applications where the LED may distract
audience members, it is easily disabled by sliding the FRONT LED switch to
the OFF position.
Polarity Switch (HPR151i and HPR181i)
When all loudspeakers in system are properly polarized, a positive polarity
drive signal results in a forward excursion of all loudspeaker cones. This, in
turn, sets up a positive reinforcement of the sound wavefront (each loud-
speaker reinforces the actions of the other loudspeakers). This effect is most
pronounced at low (bass) frequencies.
If a loudspeaker is not properly polarized, its cone moves inward while the
properly polarized loudspeaker’s cones move outward. The inward movement
will effectively cancel the bass response of a similarly-sized driver in the sys-
tem, resulting in a reduction in the bass content.
It is critically important to maintain correct phasing in a loudspeaker system in
order to realize maximum performance. Polarity can be altered by miswired
input cables, interconnecting cables, mixer polarity switches set incorrectly,
just to name a few likely culprits.
To make matters a bit more complicated, phasing is also influenced by the
position of loudspeakers with respect to one another and by their position in a
given room. It is possible to have all loudspeakers polarized properly (electri-
cally) and yet achieve better bass response by having the subwoofer reverse
polarized. It is even possible to achieve improved bass response from the sys-
tem with multiple subwoofers polarized differently. Be aware that perceived
bass response also will change with the listener’s position, so move around
the room (venue) when testing your setup.
Because phasing problems can so drastically effect the bass output of a sys-
tem, the subwoofers are equipped with a switch marked POLARITY. When set
to NORMAL, the polarity is such that a positive going input will cause the cone
to move outward. When set to REVERSE, the input signal has its polarity
reversed and a positive going input will cause the loudspeaker’s cone to move
inward.
How to Use the Polarity Switch
When using QSC subwoofers and QSC full range loudspeakers, NORMAL
polarity will result in the best bass response IF the full range loudspeakers are
sitting on or very close to the subwoofers. If the subwoofers are some dis-
tance away from the full range loudspeakers, polarity change may be of bene-
fit.
Start with all subwoofer POLARITY switches in the NORMAL position. This
applies to systems with one subwoofer as well. Then, with your system at or
near expected operating levels, change the polarity of each subwoofer INDI-
VIDUALLY. Then walk around the venue and assess the overall bass response.
Select the polarity that results in the best overall system bass response.
Polarity switch.
IMPORTANT! If using full
range loudspeakers from
another manufacturer,
we recommend they be
connected to the QSC
subwoofer’s 100 Hz LOW-
CUT OUT. This will
ensure proper polarity of
the full range loud-
speaker with respect to
the subwoofer.
Front LED switch.
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