Housing Floorstanders in Cabinets

A soffit mount is intended to isolate the backwave (the soffit is effectively an extention of the speaker's front baffle), so it must be "flush" or "sealed". This will eliminate certain irregularities in bass response, but also has a broader effect on a speaker's sound that may (or may not) become an issue for any given listener. If you don't isolate the back wave, it's likely to be a mess. As an example, you could visit my den where Silverline Sonatinas are being mistreated by their in-cabinet location.

Good Luck

Marty

It is going to be a lot of trouble and very likely to screw up the sound. Given that even the supplied grill cloth degrades the sound you are probably asking for trouble. The old 70s foam was the most transparent acoustically but lacked aesthetic appeal. The speakers you are talking about are, I think. intended to be mounted with the wall acting as an infinite baffle. This is a good approach but only for speakers constructed with this in mind. It all depends on your relative valuation of sight and sound, I once knew an artist who committed atrocities on his speakers to make them look the way he wanted. He took the legs off his Quad 57s and wrapped them in black burlap. Not a success from a sonic perspective.

As Marty says you need to make a seal and a smooth transition between the front baffle and the edge of the cabinet and you need to ensure the cabinet is as flat or as wall like as possible. Any gaps or any sharp edges will create edge diffraction. You can see an example on my virtual system of how to minimize edge diffraction by building a tight fitting frame around the speaker to snugly fit.

Minimizing edge diffraction and ensuring the enclosed space you create is well sealed and stuffed with acoutic fibreglass is critical. The cabinetry needs to be extra thick walled heavy mdf and heavily braced using shelving - as anything loose or flimsy will rattle or create unwanted resonances. If the cabinets are left hollow then this is bad - make sure everything is stuffed with books or jewel cases, dvd's etc. as completely hollow spaces can resonate.

Note that a soffit mount is akin to placing your speakers close up against a wall and you will get some bass boost which can be beneficial (gives you more dynamic range) but may also be detrimental in the form of too much bass or excessive room modes.