Under-floor subwoofer

Thinking of sinking my subwoofer in the suspended timber ground floor under the sofa as a space-saving exercise.

Rather than it being attached to the suspended timber floor and causing excessive vibration which could travel and annoy the neighbours, I was thinking of building four walls in the void under the floor (from ground up to floorboards) and placing the subwoofer in there cushioned in some suitable material, looking up.

I could fit a 'trap door' on top with holes drilled in.

Does this sound a sensible idea?

Interesting idea. It has been done before, but in a slightly different way. Some Americans have been putting huge speakers in their basements.... effectively turning the basement in to a giant sub.

First thoughts...

...you'll need to decide how to handle the bass port for air flow...
...and think very carefully about positioning since you won't be able to move the sub if it's bricked in
...how are you going to stop debris and muck landing in he upturned bass cone and rattling when played?
...you'll need to allow some way to get at the controls of the sub

Quite a few people seem to do this on AVForums - one guy turned his barn into a cinema and done the very thing your talk about!

http://www.avforums.com/forums/home-cinema-diy/657443-bat-barn-begins.html

I can't remember which page it's on, but I'm sure you'll get sucked into reading the whole thing anyway.

The whole idea of a sub is to move lots of air in the room that you're listening in. Submerging it and allowing the air into the room via holes in a trapdoor negates this. Mounting it on cushions is also a bad idea.

If the sub is working properly, the speaker cone should be moving, but the cabinet isn't to any great degree.

If the sub has spikes, then drive crosshead screws into the floor and sit the sub on top with the spikes resting in the centre of the crosshead. This gives a rigid base and minimises vibration transfer to the floor.

GRC said:

The whole idea of a sub is to move lots of air in the room that you're listening in. Submerging it and allowing the air into the room via holes in a trapdoor negates this. Mounting it on cushions is also a bad idea.

Click to expand...

I agree with what you're saying there, but I have to add one thing: wave formation.

If the OP does submerge his sub, I would suggest that he custom builds an enclosure with a horn. A big, fat horn. Otherwise, a typical living room just doesn't have the size required to <<properly>> build a bass wave.

I've never built my own speaker enclosures, but if I was going to the effort of building a sub into the floor I would definitely do it. To appreciate the effects, put on something continuously bassy (dance music, hip hop etc) and wander about your house. You may notice that deep bass sounds a lot better formed when you're a few rooms away from your subwoofer.

Undoubtedly the easiest way of taking this idea forward is with an infinite baffle subwoofer. Essentially infinite baffle requires that one side of the cone faces to the listener in free air (into the room, and the other side is separated from the listener by an infinite barrier but also in free air. These type of subs work well for home listening because whilst efficiency is poor (bad sound per watt ratio), low frequency response is good (they play plenty of sub).

The simplest implementation of an infinite baffle would involve cutting a hole in your floor and mounting the driver (speaker unit) facing up. Assuming the crawlspace is sealed from the room, this would work fine as the size of the crawl space is effectively putting the rear of the driver in free air. It is obviously not ideal though as you would trip over the sub and would need to be careful not to damage it. More common is to mount a manifold of sorts hanging from the joists and mount the driver(s) into it.



This type of system has the advantage that all amps and controls can be mounted remotely and you just need to run a speaker cable under the floor to the driver(s).

Beyond infinite baffle there are innumerate options but essentially they will all involve mounting an enclosure under the floor rather than integrating the drivers into the floor.

If you want maximum efficiency and SPL the a horn subwoofer is really unbeatable, Unfortunately an exponential horn need to have a length of ¼ of the lowest wavelength you want to play. Assuming you want to reproduce 30Hz special effects in films, this equates to a horn length of approximately 2.8m and a mouth area of 10.4m2! This makes it unfeasible for all but the most diehard bass fans... see below!

http://www.royaldevice.com/custom.htm





You can use a smaller mouth area or horn path and correct the defficiencys with EQ but it compromoises various things and you would better using a different enclosure type.

That last picture: is that what a subwoofer would look like if drum'n'bass had been around in the 1920s?

Seriously, either that's a massive gramophone or that's a picture from inside The Borrowers' home cinema...