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I just had an idea for an invisible distributed sub. Moved into a house that was built in the 80s. Walls are about 7 in. of brick + 2 inches of styrofoam on the outside + some mortar & paint. However, the window openings go all the way to the floor, and from about 3 ft. downwards, there is a sandwich of about 1 cm baltic birch on the inside, 1.5 cm stryrofoam and 1 cm of some stone/plastik/fibre compound on the outside. While this sandwich may well have the same insulation rating as the double pane, dry-gas filled windows, the baltic birch is painted dark brown, and is situated about 5 in. behind a radiator. It will heat up to about 100°F and conduct more heat to the outside than it radiates back into the room.
I have started putting two inches of styrofoam (or rather, Styrodur, a super tough version which is used a lot in construction) with aluminum foil on top into the niches. The difference is immediately noticable.
While I was thinking about using spacers between the Styrodur and the sandwich to further improve the insulation, I realized that I was looking at an enclosure with a potential volume of 70 to 150 l, depending on the size of the window. It is also deep enough for flat 10 inch drivers like a Vifa M25 to live in comfortably. I could probably spread half a dozen of those along the short side of the living room and hence get a pretty uniform excitation of modes.
Of course, I will have to use at least 3/4 in of MDF, OSB or particle board instead of Styrodur for the outside layer ("baffle"), and due to the large surface area of this sub, substantial bracing will also be needed.
While rockwool is as good a thermal insulator as styrofoam and certainly better as acoustic stuffing, styrofoam sandwiched to the MDF might provide better stiffness. The Styrodur stuff is actually so tough it'll make great braces, too. So I am looking at lining the inside of the baffle with 1.5 in of styrofoam and/or use 1 in. Styrodur braces that would be about 4 in. wide (i.e. join "baffle" and the rear sandwich board.
So my question is:
Does anybody know how acoustically transparent the regular white, lightweight styrofoam is below 100 Hz? Or, for that matter, the Styrodur stuff, which might be closed cell? I am not looking into damping standing waves (will XO at 100 Hz or below), and I have plenty of enclosure volume, so I don't need to enlarge it by stuffing. I just don't want to make it any smaller by using styrofoam.
I have started putting two inches of styrofoam (or rather, Styrodur, a super tough version which is used a lot in construction) with aluminum foil on top into the niches. The difference is immediately noticable.
While I was thinking about using spacers between the Styrodur and the sandwich to further improve the insulation, I realized that I was looking at an enclosure with a potential volume of 70 to 150 l, depending on the size of the window. It is also deep enough for flat 10 inch drivers like a Vifa M25 to live in comfortably. I could probably spread half a dozen of those along the short side of the living room and hence get a pretty uniform excitation of modes.
Of course, I will have to use at least 3/4 in of MDF, OSB or particle board instead of Styrodur for the outside layer ("baffle"), and due to the large surface area of this sub, substantial bracing will also be needed.
While rockwool is as good a thermal insulator as styrofoam and certainly better as acoustic stuffing, styrofoam sandwiched to the MDF might provide better stiffness. The Styrodur stuff is actually so tough it'll make great braces, too. So I am looking at lining the inside of the baffle with 1.5 in of styrofoam and/or use 1 in. Styrodur braces that would be about 4 in. wide (i.e. join "baffle" and the rear sandwich board.
So my question is:
Does anybody know how acoustically transparent the regular white, lightweight styrofoam is below 100 Hz? Or, for that matter, the Styrodur stuff, which might be closed cell? I am not looking into damping standing waves (will XO at 100 Hz or below), and I have plenty of enclosure volume, so I don't need to enlarge it by stuffing. I just don't want to make it any smaller by using styrofoam.
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