Underground Sub

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In the not too distant future I plan to build a new house and I want to build the house around the home theatre room. I have already started a thread here about the room http://www.diyaudio.com/forums/everything-else/231732-your-chance-help-build-ultimate-home-theatre-listening-room.html , but I would like to spawn a separate thread to discuss just the underground sub part of the room.

I have attached some very rough thoughts (size of room hasn’t even been determined yet but thinking around 6 meters wide and 8-10 meters long) but I don’t have a track record of building successful subwoofers, and I would really appreciate the experience of those that have built wild subwoofers before.

For drivers I am thinking of a pair of TC Sounds Ultra 5400’s, but even those are subject to suggestion. I have seen several websites with underground horns and different types of cavities but based on the drivers I want to use can you please suggest what an ultimate box for this purpose might look like.

Please bear in mind that a concrete floor needs to be poured over the sub enclosure.


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Thanks xrk971 that website was linked in the other thread. I would like to do a tapped horn but I really don't know how to use Hornsresp properly.

The main advantage I would have over that guy, is he is working with an existing building and is limited by what he has. If I could work out how to design the horn I could do the horn without the turn.

I probably wouldn't want to go over the top with 16 drivers, but a couple of nice 18" TC sounds drivers in the right enclosure would make for a tidy home theatre :)
Here's my similar but bit smaller scale IB sub project.

For your size theather I'd go with 4 x IB318 located at front wall, 2 x 2 manifolds at 1/4 and 3/4 along front wall should eliminate rooms width mode and give similar response to all seats at same row (in theory).

I guess back wall location could cause challenges to phase with front speakers.

IB sub FAQ
IB subwoofer FAQ page

and dedicated forum
"Cult of the Infinitely Baffled"Hear The Bass, Not The Box The definitive online resource for Infinite Baffle subwoofer designEstablished 1999 - Home
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Hi more10 the problem is I can't even get a decent result out of Hornresp as it is, there is no way I could ever design anything that involved.

Using OB speakers I really would like to get the subs out of the room to give me better speaker placement, and being that I have the option to build whatever I want before the house get put on top, it would be best to try use one of the space hungry designs first.

Not sure which design is going to give the best results...
bjorno that looks very interesting... imagine an 8 horn loaded DBA flush mounted in cavities behind the front and rear walls. You would just see 8 square holes in the walls and no subs.

What I do like about the idea is no pressurization of the room. Which I am sure OB speakers would greatly appreciate, especially the RAAL dipole ribbons.

Just doing the math on a 6 meter wide room and it is reduces the horizontal room mode cut off to 172 / 3 = roughly 57Hz. Starting to loose much of the advantage of this type of design.

With 3 meter center to center screen size will be touch and go depending on the size of the outlets.
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Not sure what you mean by manifolds.... but how about this?
You should read IB FAQ I posted.

Manifold is kind of connection box for IB sub elements, usually mounted to back space side. Normally 2 or 4 element is connected to opposite sides of box...
IB subwoofer picture gallery page 1

Don't build that kind horns from your head, result would suck without good design.

Don't understand what benefits much complicated horn have over very simple IB for hometheater subwoofer. Maybe you save two driver price and can use smaller amp, but construction is so much complicated that you lose many times that to material costs and time used.
Hard to say which would sound better, because probably no one have build both to same room.
I tried modeling the DBA bjorno suggested and it just won't work, using a modest 600mm square outlets, it only gives a 100 inch diagonal 16:9 picture, which is not enough, and I don't want to try material over the ports to make the screen bigger, so that leave me back at either IB or TH.

Thanks Ile I will investigate the IB option in greater details.


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I'm not sure you would get the same effect if you deviate from the 1/4 - 3/4 placement, but there is no reason I couldn't still use the idea even if its not perfect for more even bass distribution.

Just working with the IB idea for a moment I could use the master bedroom directly above the home theatre room to provide a chamber for the IB.

Perhaps with it vented it would result in non pressurization of the room as it would be a back and forth motion with a large air buffer in between.


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I am going to build LeCleach bass horns, to go with a 4 way horn build. After hearing the effortless dynamics and detail fr horns I just have to try a 20hz concrete bass horn. I will detail the build and feel free to jump on a cheap flight for a listen when complete.
Sounds interesting 3GGG.

The boss expressed her displeasure with me using the master bedroom to vent the home theatre room, on the account of she says it should be separate for privacy reasons...

With just the two of us in the house I don't see who we are going to upset :)

I asked if it was ok to build it into the 3 x 6 meter walk in wardrobe, and that was far more acceptable, as it would be separate from the bedroom.

I could use the whole room, but there's no point in rocking the boat unnecessarily when it is still just an idea...


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If you're going to build such an extreme build then you might consider to use twice as many drivers and slot mount them where one is reversed. This would reduce driver significantly distortion and cancel mechanical forces. Your house will thank you when playing lots of LFE content ;)

There is a thread about this, also some information on Linkwitzlab since he uses the technique himself a lot.

If you go this route you could compensate by using smaller less fancy drivers since the strain on each driver is reduced.
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