Four cabinet Bass Array systems go low and provide an unparalleled room lock while using less power and EQ with minimal location restrictions.
Most if not all -3dB subwoofers require standing wave bass mode room (crawl test) positions to providing them the least restrictive path within the room allowing full advantage of their delicate extra low frequency presentation. These are typically side wall locations.
Another point to consider. Using one costlier processor equipped subwoofer as a master to control less expensive basic models or brands.
Any brand -6dB unit is a sub-bass speaker. Like the -3dB subwoofer they will augment your main speakers mid 30Hz region at the expense of the subwoofers delicate sub sonic presentation present on most recordings.
Because of the -6dB sub-bass speakers dramatic low frequency roll off they simply do not excite a rooms standing wave bass modes. This gives them the convenient ability to be located most anywhere in the room with just a volume adjustment.
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