Theendofday is absolutely right about the cancellation that takes place in the bass summing process that takes place with bass management. This could accurately be described as a loss of bass integrity.

Anytime that two (or more) audio signals (or any AC signals for that matter) of any phase other than absolutely in-phase (zero degrees) are summed, there will be peaks and dips created depending on the phase between the two signals - this is unavoidable in any summing process, and is just textbook engineering. Signals that are of equal amplitude and in-phase in both channels will receive a 3db power boost (6db voltage boost) over bass signals that appear only on one channel. Bass that is between these two extremes will have boosts between 0db and 3db (0db and 6db voltage).

The situation gets far more complex (and worse) when considering 5 active channels being summed in the bass as takes place in a home theater using bass management.

This is one of bass management's dirty little secrets that doesn't get acknowledged by the manufacturers or by any magazines.

Bass management is a compromise solution that allows the use of smaller than actual full range speakers in a home situation. Smaller speakers became popular with the advent of home theater since it was obvious that the vast majority of people (read-wives) would not allow 5 speakers in the (her) living room with 15" woofers. The cost of such large speakers was also a major consideration. Therefore speakers with 6" and below woofers became the norm, and woofers of this size cannot produce real bass below 50Hz or so, and many have difficulty even at that frequency.

A home theater with 5 speakers utilizing 15" woofers for the mains and surrounds, and thus real response to 20-30Hz, would have no need for bass management and could use a subwoofer for the same purpose it's used in a movie theater or on a film dubbing stage: for the LFE channel only (which is a true mono channel and therefore has no phase cancellation issues).