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Old 12th November 2005, 10:19 AM   #1
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Default Subwoofer enclosure under floor

Hello all!

I have been searching forums for some information on this subject, but haven't found exactly the information I am looking for yet.

I am custom residential homebuilder, and I am looking at incorporating plasma televisions and audio in all of my future spec homes. In my earlier years, I installed car audio for a living for approximately 5 years, and was a car audio fanatic from 1985 - 1997 or so. I recently got back into car audio somewhat and am looking at expanding my knowledge to the "home side" to where I can have fun with it and make some profit!

The question of the evening for me has to do with subwoofer cabinets underneath the floor of the listening room. In a spec home, there is no furniture. In the house I am currently framing, I plan on having the plasma mounted over the fireplace mantle and running RBH front/rear/center in-wall/ceiling speakers (most likely the MC line). I would also like to install a sub, but make it stealth, not just have a cabinet sitting in the corner of a room (That would look pretty stupid for a consumer to walk into a spec home and see a sub just sitting in the corner). My question regards subwoofer enclosure attachment to floor joists. I do not have a clue as to how much energy would be transferred to the floor if the subwoofer enclosure was directly attached to the floor studs and vented through the floor via a register. My guess is that it would be a lot, and possibly cause a lot of vibrating/rattling. I have an idea and would like to get some opinions on what I am thinking. My idea is this:

I would build the custom enclosure for the subwoofer of my liking. I would pour a concrete slab in the crawlspace (None of my homes are built on slabs) approximately the size of the speaker cabinet. The small concrete slab would be positioned directly under where the subwoofer is desired to be vented into the room (most likely a corner). I would install masonry block on top of the slab with some treated lumber attached to the top of the masonry blocks via anchor bolts. The cabinet could then be attached to the treated lumber with screws, bolts, etc.. The overall height would be adjusted to give my cabinet a 1/4 - 1/8 inch clearance between the face and the subfloor. I would provide some gasket material to couple the cabinet opening to the subfloor. The subwoofer would be mounted inside the cabinet, and access to the driver would be via a removable end on the cabinet. The driver would vent into the room through a register. In this manner, I feel I would provide sufficient support for the speaker cabinet as well as eliminating virtually any transmission of energy to the floor in the house from the cabinet touching the floor.

I would appreciate any/all comments or constructive criticism regarding this.

Thanks!!
Steve
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Old 12th November 2005, 03:53 PM   #2
Volenti is offline Volenti  Australia
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A simpler option would be to use 2 drivers set up so their mechanical movement cancels, think tripple chamber bandpass box, vented center chamber.

That will remove the majority of mechanical energy transfer to the structure and allow for simpler and cheaper construction.

The sub will shake the floor/walls regardless at certain frequencies/volume just from air pressure.
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Old 12th November 2005, 10:09 PM   #3
morbo is offline morbo  Canada
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This would be the perfect application for an infinite baffle install, have a look here:

http://home.comcast.net/~infinitelyb...B-Gallery.html
http://home.comcast.net/~infinitelybaffled/
http://home.comcast.net/~infinitelyb...Bmanifold.html


It needs more woofers and some EQ, but is unparalleled in terms of sound quality and flexibility. All you need is a small hole venting into the listening room, no sign of the woofers or electronics anywhere.
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Old 13th November 2005, 05:52 AM   #4
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I will agree that IB is probably the BEST way to go, but doing a bandpass enclosure which is vented to the room via registers would also be simple enough. I wouldnt say a concrete slab in the crawlspace would be required, or that it be attached to the floor joists structurally. The most important thing is that the sub radiates the full energy of the frontwave into the listening space and not into the crawlspace. What you do with the backwave can depend on your tates, the woofer(s), and application goals
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Old 14th November 2005, 02:19 AM   #5
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Steve,

With an IB subwwoofer there's no need to pour a concrete pad or use masonery construction. The rear wave will be absorbed by the crawlspace

If you use a manifold design IB the mechanical vibrations of the drivers themselves are canceled.

However ANY sub regardless of the design, will excite the room it's firing into if the SPL is high enough.
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Old 14th November 2005, 02:41 AM   #6
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An IB is not an option. The subs would be exposed to the elements, moisture, bugs, etc., in the crawlspace, and there is a room directly over the listening room - thus no space for ceiling mounting.

Steve
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Old 14th November 2005, 05:10 AM   #7
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There are many, many crawlspace IB subs, and no there aren't problems with them. Believe me I'd hear about it if there were.

Drivers are designed for use in a car. Temperature swings in a crawlspace are nothing compared to those in a car or attic. Humidity isn't an issue.

BTW, insects don't hangout where there are LFE vibrations.
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Old 14th November 2005, 05:34 AM   #8
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yeah... any bug that wants to can crawl inside the voice coil gap on my sub... it will be crushed!
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Old 14th November 2005, 03:09 PM   #9
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yeah, dont worry about temps, humidity, or bugs. i kept my 12" philips sub, in a plywood enclosure, on the dirt under my house for 10 years. no problems. when i moved, the sub ended up in the living room. i ended up getting a 15" audiosource driver for the enclosure, and i boxed in an 8 foot section of floor joist under my new living room for the philips driver. the 15" in the room provides air motion, and the 12" in the floor shakes the house. neat combo!
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Old 14th November 2005, 03:51 PM   #10
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Default OT

How would a sub handle the temperature difference in the winter; having heat on one side of it, and cold on the other? Would condensation be a problem?
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