Phase Cancellation
When two speakers in the same frequency range produce sound waves that are inverted from one another or 180° out of phase, the sound waves will cancel each other out to some degree. This effect will be heard as a drop in the output level and/or a muffled or muddy quality in the Bass Response.

The source of this Phase Cancellation can be at any point in the signal path. The obvious cause of this problem would be a speaker connection that was reversed in polarity, but that is not always the case. Sometimes amplifier channels will shift phase 180° for no good reason, or a signal processor could have a setting for phase that has been set incorrectly or the source material could just be recorded in error. No matter what or where the cause is located, the solution is an easy one.

Disconnect all but one Bazooka® from your system. Be sure that any loose wire connections are insulated to avoid the chance of short circuiting any of the electronic equipment. Listen to the system and take note of the level of the Bass Response. Connect the next Bazooka® and compare the level of the combined output to that of the single unit. If the Bass Response increases, the Phasing is correct and you can repeat this process on the next Bazooka®. if the level of the Bass Response drops, the Phasing is incorrect and you should reverse the speaker connections to this Bazooka® and compare again. In short to INCREASE IS GOOD, to DECREASE IS BAD!

Using this method, any number of Bazooka® subwoofers can be kept in absolute phase.