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homebuilder 6th June 2009 04:54 PM

Suggestions for hidden sub
Seeking some ideas:

We are currently digging up the entire basement floor of our Bed and Breakfast in order to put in a 2700 sq ft Pub. We will end up with 9' ceilings. heated slab floors, etc.
The pub will have areas for pool tables, a bar, two fireplaces, etc. I want good quality sound in the largest room.

I'd really like to do something fun with bury some large diameter PVC pipes, etc. While we have the floor ripped up, it would be easy to put them in.

I found some 12" and 14" tubes, but the local place that sells this stuff charges something like $150 each for large elbows, and about $120 for a cap.

I'm thinking sealed design, and would prefer something like a good 12" or 15" woofer. Does anyone have any good ideas?


chipperman 7th June 2009 07:13 PM

You might want to check with pipe supply yards that sell septic system items. There are some spiral ribbed pipes that are very ridgid and go up to 48" in diameter. Of course, they get very expensive per foot. However, you could bury them and not worry about flexing! If you do put these in the ground, you will have problems with condensation. One way to avoid that issue is to encase the tube with about 4" of sprayed on urethane foam. All this will cost you more than building a box, but you would get that subterranean rumble! There are no shortcuts to this to do it right.

homebuilder 13th June 2009 11:21 PM

spiral ribbed pipe sub
Thank you for the suggestion. I have never seen that pipe..never really looked at a septic system.

I do have my own Graco foam machine, so the urethane foam is almost a given for me.

I also thought about those concrete culvert sections that are widely available, but don't know if concrete is as "Dead" as you would think it is. I suppose that with foam around it, dirt, and then concrete, it really would not matter anyway.

A friend suggested just taking two sonotubes, say one 24" and one 18", and pour in between them. You would just leave the form in place, and foam around it. Since we are going to pour the floor anyway, that would be the cheapest option.

Thanks for the idea.

chipperman 14th June 2009 01:46 AM

Just make sure you seal the separations totally with the foam, sonotube forms will soak up moisture over time (even the waxed ones, and mildew. Seal the cut ends. And, you will need to add some kind of acoustic dampener (acousta-stuff, fiberglass, etc., to kill the standing waves. But if you have a foam machine, anything is possible. I presume you are using closed cell urethane. You could use a heater register over the top. Would that ever give people a thrill!

Moondog55 14th June 2009 04:32 AM

What ever you do may I suggest that you remember to make easy access to replace the driver when ( or if ) it blows.

Howabout a fake fireplace in a corner with the woofer(s) hidden in the brickwork, still utilize the underground box volume with a simple right angle concrete sewer connection for the change of direction.
Use 4 * 12inch car subs wired series /parallel or 2 * 15 in series and a cheap amp bridged.

roger2 14th June 2009 04:52 AM

+1 on sealed design
+1 on the heat register cover
+1 on the future access capability

Here's what I might do:

1) Research potential driver candidates
2) Dig a square hole
3) Line hole (sides and bottom) with blue styrofoam (1 1/2" most likely)
4) Line styrofoam with visqueen (overlapping and taping to ensure good seal)
5) Find a plastic garbage can with internal volume appropriate for driver
6) Put grabage can in hole and fill around outside with concrete, remove garbage can after concrete hardens
7) Build 1 1/2" baffle (2 x 3/4 plywood glued)

Then you have a fairly cheap, watertight chamber which will remain pretty close to the same temperature as the room and avoiding problems related to condensation and heat/cool expansion cycles

IMHO there is no need for foam or damping...but it would not hurt anything.

Of course you would have to do some precise measuring and possibly silicone or some type of efforts to seal the baffle to the concrete chamber.

You could bring wire in through 1/2" Schedule 40 or similar and seal space around wires with that expanding foam stuff (can't think of it's name)

my .02c

I'm jealous, sounds like you are gonna have a really great room there :)

roger2 14th June 2009 05:27 AM


The baffle board would need more than just an airtight seal as mentioned above.

It would also need to be securely physically bound to the concrete "cabinet". If not the baffle would just vibrate, bass would not be solid and the airtight seal would not last long.

What are those things called that are embedded in concrete, are threaded on one end, and used to bolt sill plate to slabs? Several of those with huge washers would be one possible way.

roger2 14th June 2009 06:36 AM


Having thought more, I believe that vented design would be better than sealed. Having a vent would ensure that the temperature and humidity inside the speaker chamber would be the same as that in the room.

With a sealed design any discrepancy in humidity between the room and the speaker chamber would tend to migrate through the sub-woofer...not a good thing for longevity.

Other random thoughts:

Use at least a 15" sub-woofer. 2700 sq ft is a good sized room. Even though, I assume, that the sound system may not be inteded to fully cover the entire area, a 12" in a cubic area that that large may not do enough. An 18" or dual 15's....may be good to consider.

May be good to use sub-woofers with poly cones and rubber surrounds. One reason is to further minimize and potential damage from moisture problems. Another spills.

bjorno 19th June 2009 03:48 PM

2 Attachment(s)

Sorry for my late response to this thread. Here is an idea of using a T-TQWT with the port exiting a wall : Picture 1(2)-2(2)



bjorno 19th June 2009 03:50 PM

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