See the mdf board faq for more information on obtaining and using mdf along with safety issues.
In wall speaker box build.
You will probably need 2 sheets.
Cover the back top and bottom of the speaker box with 1 inch 2 1 2 cm of poly fill to minimize resonance.
Set up the speaker box.
In wall and in ceiling speakers use the surface they are mounted in as their baffle front part of speaker box using a cabinet door for a mount will likely result in a boomy echoey sound.
I have also seen insulation stuffed around the enclosure.
I would think the easiest way to build a box for these would be to put insulation in the stud bay and then screw on a 5 8 drywall panel to the back of each of the 3 stud bays containing speakers.
Build a couple of test boxes of varying sizes starting with one just large enough to mount the speaker in with an inch or two free space in the back beind the drivers.
It would probably serve you well and cost less than dynamat.
Inwall speakers and inceiling speakers typically do not need to have boxes built or spaces constricted.
You could also use scrap lumber if you have enough laying around.
If you want to make a box it helps to use wood glue and caulk to seal all of the edges.
These types of speakers are designed with american homes in mind.
The speaker box should be constructed from medium density fiberboard mdf.
You should use minimum 3 4 mdf which is sold in 4x8 sheets.
Hook up the speaker wires.
Seal up any holes in the framing first.
Insert the speaker and run the connectors through their appropriate holes.
A back box is usually a flimsy plastic box that fits behind the speaker in the wall or ceiling.
The larger the box the lower the tuning to a point.
It usually is not very rigid has no acoustical material inside of it and it hasn t been designed with the proper internal volume needed for best bass performance with no adherence to the theile small parameters of loudspeaker design.