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Discussion Starter · #1 ·
Am about to embark on my very first home sub build and am looking for some advice. I have done car subs (long ago) with fiberglass, MDF, but certainly not at the level that you guys or even the car guys are doing it nowadays.

My room will be (currently being built) a decent sized dedicated HT with good sound isolation (double drywall, green glue, isolation clips). I don't recall the exact volume but it will be around 3500 cuft or more. There will be a screen wall with an AT screen behind which I will hide the drivers. So I only have to make them pretty enough to not be seen :) ... So I will paint the rough frames matte black. There will be about 33" from the back wall to the front of the AT screen, so given the false wall thickness, about 29" will be available for speakers. The plans call for two relatively small reinforcement subs in two of the side pillars that I am also DIY'ing with 10" shallow Peerless XLS drivers, one on each side of the listening area.

Main bass was going to be, at least initially, an existing SVS 12" subwoofer that currently sits in the corner of my family room.

Then I got a load of you all :yikes: and got another DIY bug. I decided to build an 18" subwoofer and then saw the DIYability of the SI HT drivers and ordered two. I ordered yesterday the SI HT-18D2 thinking that I could pick a suitable amp, but may change that to D4's on Monday.

I would like to follow some of the designs here and on AVS but would like to get some official plans. To that end I will be contacting Graham for some help, but thought I could refine the design here first before doing so.

I thought of building two sealed enclosures pointed out at the listening position, but then decided to do a single dual opposed instead. In addition to the apparent inherent benefits to dual opposed, I have the option (and space) to build another if I want more bass or to improve room response. I don't think it will be a problem, but I assume having the drivers pointed sideways on opposite sides of the sub box would be acceptable, as they do have to go behind the screen wall. I don't want it out in the open as the only visible speaker.

So, dual 18" drivers dual opposed. I will probably get a Crown XLS1500 to power it, if i used D4 drivers, that would be 775w x 2 channels.

Thoughts?
 

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Discussion Starter · #3 ·
Thanks Mike! 12 cubic feet is larger than I was thinking, but I guess the tradeoff of smaller volume is more power needed. I should have the space for it in any case, about 24" x 24" x 48" exterior dimensions is 13.6 cubic feet without double/triple baffles, braces, and driver displacement losses. Does the Qts go up if the volume of the box goes down?
 

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Discussion Starter · #5 ·
You know, they say a little bit of knowledge is a dangerous thing. So, to that end I tried learning more about subs and their application in home theater, particularly as it applies to the theater that I'm building. So I think that I'm now in the dangerous category :)

I have not totally ruled out the dual opposed idea, but have been thinking more about the room and getting a good baseline FR before EQ. I am now thinking of setting up two subs on the front wall of the theater behind a false wall and AT screen. There is maybe 6' of height and 22" of depth after 2" thick broadband absorption is applied to the front wall behind the screen.

I am proposing placing two subwoofers about 1/4-1/3 in from the corners to minimize room modes, but also proposing to build the subs tall to try to position the drivers at the center of the height of the room. I could vent the subs upwards but not sure if direction of venting matters at all in affecting room modes.

Soooo ... how does that sound? I will build two tall subs, each having two front facing SI-18 dual 4ohm drivers and appropriate power positioned as above.

To make things more complicated, I also had plans for two reinforcement subs placed in the same rear side columns as the side surround speakers. To that end I bought two Peerless XLS10 shallow mount drivers, as the box is less than 6" thick. I don't have the amp for these either yet. Depending on how the fronts sound and measure (I also need to get into REW), I may or may not install the reinforcement subs. These would be 1/3 in from the back corner walls and close to center of the height of the room, given that this column is on a riser in the back of the room.

Some other relevant information .... The large riser in the back of the room is a bass trap filled with R19 fiberglass batts. There are no corner bass traps but there are specific aborbers and diffusors spread throughout the room, but these are not bass specific.

Here's an overall room plan if that helps.:

 

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I should have gone with the 2 si 18" insted of the tc sounds 5400. Feel I would be some where by now. Congrats on the purchase! Looking forward to seeing some pictures.
 
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