Hi there!

I'd like to install in-wall speakers in insulated concrete forms (ICF)
and was wondering about the impact on sound due to the absence of a
cavity. The ICF wall is an 11" wall made-up of 2.5" of EPS (expanded
polystyrene) on each side with 6" of concrete in between. The EPS is
covered with 1/2" sheetrock on the inside. The fairly inexpensive 2-way
speakers (with less than 3" in depth) will therefore sit in a a cavity
that has concrete on the backside and EPS on the sides.

I am wondering whether the absence of a resonating cavity, such as in
an installation in standard framed stud walls, will have an effect on
the sound. Should I add a subwoofer?

Maybe I should also mention that these are part of a six-source,
six-room audio distribution system, so I won't have the amplifier close
by.

I'm not looking for perfect sound, just for simple listening to music
and radio, mostly in the background.

Thanks for any advice or insight!

chrism