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
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.
Front LED switch.
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.
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