room acoustics in a small house with in wall speakers

[Timothy Golden]

The idea is that by eliminating a speaker cabinet and instead installing speakers either in the walls or in the floor that some gains can be made. The LF resonance of the room is much lower than that of a standard speaker enclosure.

The drivers would be open to both sides either through a wall or through a floor, thus making the rooms out of phase. Some null at the midpoint should be realized, but in the rooms that are driven should this be a good system?

I'm not clear on all the dynamics and am open to doing this experiment though it would be nice to get some prediction of the results ahead of time, which is what a prediction is, so I digress... until someone here straightens me out.

[Fred McKenzie]

Post by Timothy Golden
The idea is that by eliminating a speaker cabinet and instead installing
speakers either in the walls or in the floor that some gains can be made. The
LF resonance of the room is much lower than that of a standard speaker
enclosure.
The drivers would be open to both sides either through a wall or through a
floor, thus making the rooms out of phase. Some null at the midpoint should
be realized, but in the rooms that are driven should this be a good system?
I'm not clear on all the dynamics and am open to doing this experiment though
it would be nice to get some prediction of the results ahead of time, which
is what a prediction is, so I digress... until someone here straightens me
out.

Timothy-

The room's LF resonance may be lower, but you are inside the speaker
cabinet! I think the LF resonance of the space behind the speaker would
have a greater effect on sound inside the room.

Fred

[Timothy Golden]

Post by Fred McKenzie

Post by Timothy Golden
The idea is that by eliminating a speaker cabinet and instead installing
speakers either in the walls or in the floor that some gains can be made. The
LF resonance of the room is much lower than that of a standard speaker
enclosure.
The drivers would be open to both sides either through a wall or through a
floor, thus making the rooms out of phase. Some null at the midpoint should
be realized, but in the rooms that are driven should this be a good system?
I'm not clear on all the dynamics and am open to doing this experiment though
it would be nice to get some prediction of the results ahead of time, which
is what a prediction is, so I digress... until someone here straightens me
out.

Timothy-
The room's LF resonance may be lower, but you are inside the speaker
cabinet! I think the LF resonance of the space behind the speaker would
have a greater effect on sound inside the room.
Fred

OK; yes, but the space behind the speaker is actually another room. The speaker is mounted in the wall so that its back is radiating into another room. A third room connects these two rooms, and some doors can be closed. Let's say these are 12 foot by 12 foot rooms and 8 foot high, tied together by a third room 12 foot by 24 foot so that the three form a square 24'x24'. Somewhere in the third room will be a null, but shouldn't the sound in the two primary rooms be quite strong? I guess the loudspeaker's own resonance will get exposed.

Lets say it's a 15 inch diameter woofer mounted in the high corner of two adjacent rooms which have sheetrock surfaces on a 2"x4" standard studframe interior wall. Being at the corner supposedly boosts bass response and is a strong structural position. Also the only destructive work to the house is to break out some sheetrock and maybe add a bit of framing. Studs 16" on center allow this woofer to mount pretty much onto the studs for experimental purposes. Then sealing in to it should be a matter of boxing it in a bit more. I think preferable the wall cavity would be left out of the puzzle by sealing it with 2x4. I guess a square of heavy plywood 16"x16" would be sensible; cutting the sheetrock back to the center line of the studs leaving a fairly clean look on the best side. The back side will have the magnet exposed which is about six inches deep, so protruding roughly 1-3/4" beyond the wall; just the diameter of the permanent magnet will interfere with the back room.

It's a pretty clean install, and the balanced rooms suggest that the acoustic load to the wall will be symmetrical. The wall as a soundboard seems to be the most immediate problem. I'm not sure what else will be troubling. Will stuff start rattling around in the house and falling off shelves?

[Timothy Golden]

Post by Timothy Golden

Post by Fred McKenzie

Post by Timothy Golden
The idea is that by eliminating a speaker cabinet and instead installing
speakers either in the walls or in the floor that some gains can be made. The
LF resonance of the room is much lower than that of a standard speaker
enclosure.
The drivers would be open to both sides either through a wall or through a
floor, thus making the rooms out of phase. Some null at the midpoint should
be realized, but in the rooms that are driven should this be a good system?
I'm not clear on all the dynamics and am open to doing this experiment though
it would be nice to get some prediction of the results ahead of time, which
is what a prediction is, so I digress... until someone here straightens me
out.

Timothy-
The room's LF resonance may be lower, but you are inside the speaker
cabinet! I think the LF resonance of the space behind the speaker would
have a greater effect on sound inside the room.
Fred

OK; yes, but the space behind the speaker is actually another room. The speaker is mounted in the wall so that its back is radiating into another room. A third room connects these two rooms, and some doors can be closed. Let's say these are 12 foot by 12 foot rooms and 8 foot high, tied together by a third room 12 foot by 24 foot so that the three form a square 24'x24'. Somewhere in the third room will be a null, but shouldn't the sound in the two primary rooms be quite strong? I guess the loudspeaker's own resonance will get exposed.
Lets say it's a 15 inch diameter woofer mounted in the high corner of two adjacent rooms which have sheetrock surfaces on a 2"x4" standard studframe interior wall. Being at the corner supposedly boosts bass response and is a strong structural position. Also the only destructive work to the house is to break out some sheetrock and maybe add a bit of framing. Studs 16" on center allow this woofer to mount pretty much onto the studs for experimental purposes. Then sealing in to it should be a matter of boxing it in a bit more. I think preferable the wall cavity would be left out of the puzzle by sealing it with 2x4. I guess a square of heavy plywood 16"x16" would be sensible; cutting the sheetrock back to the center line of the studs leaving a fairly clean look on the best side. The back side will have the magnet exposed which is about six inches deep, so protruding roughly 1-3/4" beyond the wall; just the diameter of the permanent magnet will interfere with the back room.
It's a pretty clean install, and the balanced rooms suggest that the acoustic load to the wall will be symmetrical. The wall as a soundboard seems to be the most immediate problem. I'm not sure what else will be troubling. Will stuff start rattling around in the house and falling off shelves?

Using http://230nsc1.phy-astr.gsu.edu/hbase/Waves/cavity.html#c4 I am computing a room resonance of around 1/4 to 1/2 Hertz, but that is for a perfect cavity. This freq is a lot to do with the port length and area. This would be with doors closed. Doors open apparently raises this frequency.