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attic horn subwoofer
attic horn subwoofer
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Old 14th April 2019, 04:11 PM   #1
Lewis Goudy is offline Lewis Goudy
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Join Date: Apr 2019
Default attic horn subwoofer

The listening room is the master bedroom of a single story saltbox with the ridge running E/W. It is on the SE corner and the mains will be on the W wall which is 16' with an adjoining bath to the N adding 6' which flows into the BR through a 30"x74" aperture. Listener seating will be 14' from the wall but there will be live performance interiorly sometimes on top of recorded program. The BR/Bath combo reaches to the ridge line with an attached garage to the N taking up the rest, with the service panel and ground at the end.

I have two Altec Lansing 515 (no suffix, i.e. 20 ohm Hollywood) and eight RCA MI-9449 15" drivers. All have been reconed so the Thiele-Small parameters are uncertain but I can measure them.

The attic plenum has loose fiberglass to the top of the (6") joists. l can do whatever I want. I play rock organ and want concert SPL as close to the bottom as I can get, but I don't want to spend a lot of money on different drivers for the sub 20Hz region. I just want to squeeze as much as I can out of what I've got with stuff from Home Depot.

One question up front: it seems like I could get design geometry easier using plane facets with polyurethane foam fill in the corners, rather than bracing bent plywood. Is there a reason not to? I will use a tractrix with the speaker wall extending the mouth, which can include the entire ceiling if that is what is called for.
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Old 15th April 2019, 12:09 AM   #2
PRR is online now PRR  United States
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Location: Maine USA
If you have EIGHT fifteens, and a 30"x74" hole, there's little advantage in a horn.

*Maybe* for rock organ. However I think you should get a 30"x74" cut of 3/4" plywood, cut the eight holes, and try it. (I have done 500-head venues with less woofer.)
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Old 15th April 2019, 06:38 AM   #3
Lewis Goudy is offline Lewis Goudy
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Join Date: Apr 2019
No, you are misunderstanding--the room is about 14x16 but it adjoins a bathroom about 6x12 and the doorway is 30x74. I just added that detail for completeness, it doesn't matter much. Total of ten 15" (2 Altec and 8 RCA). These are all short throw (underhung, i.e. voice coil never protrudes from the gap) drivers designed for horn enclosures with fairly low power handling (~75 WRMS) and XMAX. The idea is to frame in the horn in the attic and remove part or all of the ceiling for the mouth. I thought a reasonable throat configuration would be an elongated hexagon with the Altecs side by side facing forward and pairs of RCAs firing up and down on the near-horizontal panels with the other four loading the same volume obliquely from the sides. I know that the non-vertical mounting can cause them to take a set (they have been stored vertically and rotated 180 degrees every six months) so I will arrange it so they can be rotated periodically (T-nuts and access to them if they don't simply speak to the entire attic from the rear, which is one of the things I hoped to get advice about).
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