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Join Date: Dec 2000
Location: Venice, Florida, USA
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OK. Into the fray regarding wall, ceiling, and floor treatments to tune the room. Construction of the walls and ceilings (assume a concrete floor) is a whole different issue.
The screen wall wall should be soft absorptive. Ditto for the first couple of feet from that wall along the sides. The side wires generally should hard absorptive, say absorptive below 1000 cycles, reflective above. However spot soft absorptive is absolutely required. The placement is determined by the first reflective point for each of the three front speakers for each seat in each row of chairs. The idea is that each seat wants to hear only direct sound from each of the front three speakers. NO refctive sound please. Go to a commercial theater. You will soft absoeption just above your head on each side. That is there to ensure that the row behind you just like the row in front of you hears onle direct sound. LCR speakers in a commercial theater and hopefully yours as well have wide horizontal dispersion and narrow vertical dispersion. I assume risers for the second and more rows in your HT. Dependent on room dimensions and seat locations, you will need some spot soft absorption for the first row, and behind it but higher some for the second row and so on. Assuming close rear wall location to the last row, the rear couple of feet of the side walls and the rear wall should be diffusion on the top half and hard absorption below that.
The ceiling is another issue and is dependent on ceiling hight (I assume about 8 ft) and whether your center speaker is above, behind, or below the screen. High mounted left and rights enter also. Basically, with an above screen center (i.e., with the center mounted very close to the ceiling), you will need some soft absorption right in front of the center (a 2x4 ft) panel. With high mounted left and rights but with some distance to the ceiling, you will need some soft spot absorption (say four 2x2 ft panels) probably 2 spots just in front of the center two chairs and above the chairs on either end assuming a four chair row of HT type recliners.
Side and rear surrounds are generally mounted near the ceiling and these locations cry out for ceiling diffusion in front of each speaker. The rest of the ceiling depends on the type of ceiling. You do not want a painted sheet rock surface. At a minimum use some acoustical bubble filler in the paint or a textured sand. Hard absorption is good but expensive. Acoustical tile say with an NRC of .75 but you should weight down the tile by gluing sheet rock to the back and then you should put some fiberglass wall or ceiling insulation over that. Treatment of the space between the joists is an issue of room isolation rather than room tuning though it will affect the tune.
Your floor should be carpeted but do not use a foam or rubber pad. Horse hair jute is the best but is generally no longer available because of youths smoking it for the hemp. 1/2 inch felt padding to me is the next best thing BUT put the bonding surface side down (normal carpet insulation is to put it up so that the tape the installers use to hold pad sections together will not tear the pad).