HT Systems - Bass response question

Currently putting together a design for a 3 way active system - later to develop into 5.1 with smaller surrounds.

Something I've been curious about for a while...

Seen many HT speaker packages sold with Bass reflex setup all round. Some of the more up market systems have 'large' front speaker and smaller satellites.

Whats happening to the lower bass here.

Say the Satellites / centre rolls off at 100 Hz
... the Fronts roll off at 50 Hz
... Sub goes down to 20 Hz rolling off at 80 Hz

All these 24 db/oct roll-offs with their attendant phase shifts must be mangling the overall low freq response at the seating position. At these largish wavelengths the respective phase shifting must be causing cancellations and sums all over the place .... or have I got it all wrong. Anyone care to comment.

Cheers,
Simon C.
 
Can't comment on the center channel, but there is very little low frequency output coming from there.

THX specs have the mains roll off at 80 hz, and the sub picks up below there. Very little low frequency material is sent to the surrounds.

I have the option of following the THX specs, but I opted to go the route of having my mains roll off naturally, and crossing the sub over starting at the low 40hz range. I have little problems with cancellation; those that I do experience are primarily due to room interactions. However, speakers that aren't crossed over properly would likely experience the problems you mentioned.