Here is a link that is related to spatial bass. I guess a subwoofer is a bit of overkill for the surrounds, but 60 Hz for an in room FR for the surround speakers is recommended.http://www.davidgriesinger.com/asa05.pdf
"Spaciousness in the front/back direction:
We have examined speaker layouts and room dimensions for the case where the listener
is facing forward. It is however very common that listeners face other directions, at least
some of the time. We can extend the method shown here to other directions. To make
this work we need at least one more degree of freedom in the recording, and at least one
more low frequency driver. Both requirements are met by a professional discrete channel
surround system. In our experience the additional speaker(s) should have low frequency
capability to at least 60Hz.
The extra “independent” rear channels can be in practice derived from the front channels
by adding a time delay. The time delay decorrelates the reverberant component of the
low frequency sound, and can dramatically improve the subjective “feel” of a room."