Two Sealed 12's

[DougMac]

I'm thinking of a very non-standard installation and want some feedback.

I'm building a home theater 16wx18dx9h. It will be front projection with a 8' x54" screen. Because of plumbing, I had to build two 2' columns on either side in the front. I built a soffett above the screen to form a proscenium 12' wide x 8' high x 2' deep (think of the arch around your high school auditorium stage). It's 12' to the floor joists above, so I have a lot of room in the soffett area.

Here's my strange idea. I'm thinking of building two sealed boxes in the soffett area and using two 12" subs (e.g. Dayton reference) powered by a Behringer 2400 amp and using a BFD to correct. The subs will be down firing. I used boxplot and worked out a 4^3 ft. box. The numbers from 25hz up look pretty good, when calculating one box.

The advantages: High WAF factor. No big boxes sitting out in the HT. I'm also looking hard at an acoustically transparent screen, so no speakers will be seen, except for the faces of the two subs. It will be easy to build, since only the bottom will be seen. No cabinet finishing needed. I'll do the bottom of the soffett in MDF and either paint black or use a nice matte black laminate.

If they don't work out, I'm out only a sheet or two of mdf. All electronics can then be used in a more traditional box sitting on the floor.

The disadvantages:

No reinforcement from the floor. What will I lose? The back wall may sort of act like the floor, will that be a good or bad thing? Limited placement. I was thinking of placing them to the right of center. I won't be able to scoot them around to find the sweet spot. They may sound great or sound terrible. I they sound terrible, they'll have to be removed. I can probably test before I drywall, so at least I'll know if I'm OK.

Any thoughts? Is this do-able? Am I crazy?

There is one other thought I had for built ins. The bottom of the screen will be 30" from the floor. If I go with an AT screen, it will hang even with the front of the columns. I could build an 8' front 28" or so high and put the two 4^3ft. boxes in it.

Thanks,
Doug

[DougMac]

Here's the soffett to which I refer:

http://picasaweb.google.com/dougbruc...2596424173426.

http://picasaweb.google.com/dougbruc...22600719140770

Doug

[tonyvdb]

I think the one big issue you will have to overcome with that plan is vibration caused buy the sub its self in that area. A floor is always the best place for a sub and this is because its the least effected by this. You may also cause some strange peeks and nulls with them being up so high.

[a1161979]

Anychance you couldd fit larger driver? The 15 Dayton reference series would be better, i dont think two 12 in a sealed box will have enough output in the low stuff for serious Home Theater use...

Also have you considered how you will hang them? If you plan on building them into the wooden subframe then i recomend trying to find some rubber to place between the box and the frame as is done in cinemas

Why not simply have two IXL 18's in a sealed box bellow the center of the screen facing straight towards the seats? Hey if WAF is an issue then completely build them in and have them behind the cloth... Technically placing a sub up the wall is like taking it from a corner so you will lose output doing this, considering those 12s wond have much to begin with i would rethink using larger drivers and placing them on the ground front firing... My 2 cents

[hddummy]

why not put one sub inside each column on either side of the screen? You get floor placement, corner loading and hidden form factor.

[DougMac]

hddummy wrote:

why not put one sub inside each column on either side of the screen? You get floor placement, corner loading and hidden form factor.

First, thanks for all the replies.

Funny how your mind gets stuck in one way of thinking. My original plan was to build in a sonotube sub in each column. I worked out in my mind how I would accomplish it. Essentially, I was going to build the subs and frame around them. My concerns were the permanence of the installation. I was concerned I'd go to all that trouble, then test it and find problems that couldn't be overcome.

Your post has jogged my into rethinking. I felt I needed to have the room completely finished before evaluating. I'm now thinking that I may not be able to fine tune, but I could build the subs, place them in the columns before drywalling and test. If they didn't work, yank them out and go to plan B.

I did some price checking and 15's aren't that much more. The cost of the raw drivers is not a large percentage of the cost compared to the electronics. I'll have to go back and do some calculations on both a box and a sonotube. The Sonotube, especially unfinished, would be a straightforward build.

I had thought of chunking the whole DIY route and just getting an SVS PB12-NSD or a Hsu VTF-3 MK3. For the same money as the VTF-3 (minus cabs), I could have 2400 watts, an EQ and two 15's.

BTW, I'm not after big thump and we don't watch much action, I'm looking towards the musical.

Doug

[hddummy]

yeah man...if I had your room (I wish) I'd put one sonosub in each front corner and put removable acoustically transparent panels on those columns.

[Mike P.]

I have to agree with Matt here. Removable acoustically transparent panels would allow you access to the subs should you need to service them or change something in the future.

[a1161979]

Mike P. wrote:

I have to agree with Matt here. Removable acoustically transparent panels would allow you access to the subs should you need to service them or change something in the future.

And i have to agree with you Mike for agreeing with Matt

We need Steve here because i think two sonotube LLTs on each side would provide awesome performance, i understand you want sealed for music but many make the conclusion that sealed is better for music which is untrue Anyway i think you might be onto something here

Id measure up the space you have then get back to us with the size of tube you can fit and the max height, also the intended driver and we can then start helping you with the nitty gritty design

Go get that tape measure...

[DougMac]

a1161979 wrote:

And i have to agree with you Mike for agreeing with Matt

We need Steve here because i think two sonotube LLTs on each side would provide awesome performance, i understand you want sealed for music but many make the conclusion that sealed is better for music which is untrue Anyway i think you might be onto something here

Id measure up the space you have then get back to us with the size of tube you can fit and the max height, also the intended driver and we can then start helping you with the nitty gritty design

Go get that tape measure...

OK, I did some measurements. The openings in the columns are 21" w x 19" D. Height? 11.5 feet. I don't think height will be a problem.

The internal space of the column is actually bigger, but optimally the access will be from the side, not the front, so 19" looks like the narrowist measurement.

I'm not averse to considering LLT. It does raise some interesting questions, though. But first, let me supply a little more information and describe what to me would be ideal.

The two walls forming the sides outside and rear of the column is 8" poured concrete. The floor is also 8" poured concrete. I don't think floor resonance will be a factor. The room will be a dark green with a flat black acoustic tile ceiling. There will be 30" high wanscotting around the room. It will be oak in a dark stain.

The ideal situation for me would be for the front of the columns to be permanent. Above the wanscotting it will be drywall painted the room color, with sconces on each column. Below the horizontal oak strip at the top of the wanscotting would be speaker cloth, either black or white cloth dyed to the color of the oak stain.

The sides of the columns would be removable panels 8' high, to the bottom of the soffett. They would be covered in black speaker cloth. The area behind the screen will also be painted black.

Since the width of the access is 19", it looks like a 16" tube would be the best size. I think 18" would be too much of a squeeze. I guess my question about LLT is if it would be OK for the output from the subwoofer radiate in essentially 180 degrees, while the output from the port only radiate to the sides, or 90 degrees, since there will be drywall at the height of the port output. Also, how much space above the port is needed? I was thinking it would be a good idea to cover the bottom of the soffett in the columns.

I was considering Titanics or Dayton reference, but I'm open to any suggestions in the ~$200 or less range.

Suggestions and ideas are appreciated.

Doug

[hddummy]

DougMac wrote:

I guess my question about LLT is if it would be OK for the output from the subwoofer radiate in essentially 180 degrees, while the output from the port only radiate to the sides, or 90 degrees, since there will be drywall at the height of the port output.

I don't think it would matter, but I'm not really sure. There really is nothing wrong with building a pair of sealed boxes to begin with. It would be simpler and you can always go back and make LLTs later if you want. Don't forget, LLTs don't have to sonotubes either. I think it is perfectly acceptable to make a square cross section to better utilize your space.

There are a lot of good choices for drivers. Once you decide exaclty what alignment and power requirements you want, we can suggest some good matches for your budget. I'm assuming you mean $200 each not total.

[DougMac]

Yes, that's $200 each. The commercial subs I had budgeted for were in the $699 range. I'm thinking for the same money or a little more, I could have two subs and EQ that would way outperform a single $700 sub.

Doug

[hddummy]

I'd recommend a Behringer EP1500 amp and a Behringer DSP1124 BFD. That leaves $300 for drivers and cabinets. I seem to be suggesting the Torrent Minstals a lot lately, but that is only because I love my dB500s so much. At 90$ each, they are a steal if you ask me. If you model them up, they do well in sealed, vented or LLT alignments. After a pair of those, you'll probably have about $75 left for cabinet materials.

Think you can spend a little more?...look for some 15s, but it'll cost you.

[DougMac]

hddummy wrote:

Think you can spend a little more?...look for some 15s, but it'll cost you.

Yep. I was planning $700 for electronics and drivers. Material costs can be hidden in the framing budget ;-).

Just ran Sonosub on 15" Dayton Titanics. with a tuning frequency of 15 and a tube diameter of 16", it's calling for a 7 1/2 foot tube.

If I could squeeze in an 18" tube, length goes to a tick under 6'. Tune it to 12 and it's 6' 2"

Box size with 6" port ala Boxplot would be 29hx15dx20w. It wants a 44 inch port, though. Hmmm. With a 4" port, it wants a length of 19". Why does a smaller port diameter call for a shorter port?


Doug