backbox or no?

[rabbit_ears]

i'm putting a pair of Sonance Symphony in-ceiling speakers in my kitchen. Half of the kitchen has a second floor above it, the other half has nothing above (essentially attic space). so one speaker would be in a 2x10 joist bay (16" OC), the second would be open is a 2x4 truss system (24" OC). the attic area has blown in fibreglass insulation with no vapor barrier.
i have the backbox dimensions that sonance uses for their 6&1/2" speakers. would you recommend i build my own boxes uses their dimensions so ensure both boxes have the same internal volume (one will be 16" wide and the other 24")? of course i will ensure the boxes are properly braced.
is this a waste of time or worthwhile?
incidentally if anyone is looking for some good in-ceiling speakers Vann's has the thinline 622's on for $99.

 

[Rickster71]

I would use some type of enclosure.
You mentioned blown in insulation; with that you will need the box to keep the insulation
from impeding the movement of your drivers.
Since one will be in a closed joist cavity, and the other open.
The box would also allow them to sound the same.