A stealth subwoofer project

[-=Rudy=-]

When I move in a couple of months, I plan on redoing my folks' living room into sort of my "bachelor pad" home theater/audio room/computer room. I've got more than enough pairs of speakers to do a matched surround sound system.

The only thing I want to tackle that might be a big task is bass. Subwoofer bass. Gobs of deep, low bass that shakes the *neighbor's* house. :D OK, not *that* much, but I want it clean and low. I won't be buying a pre-built subwoofer, though...I'm going to roll my own, since I can save a lot of money and also get something that I can tune and tweak to get the type of bass I want.

Here are some options:

1. I can get a kit, or just get a driver and build my own cabinet, and build a pair of basic subwoofer cubes.

2. To keep things stealthy, I may decide to do a subwoofer that mounts under the floor. (I have basement access.) The first sub-floor option is to build a speaker box that would fit between the joists. There is a kit I saw somewhere where you can build such a box. The output of the woofer would blow through an open floor vent.

3. The other sub-floor option I saw: there is a bass speaker available made for open-air mounting...aka "infinite baffle". So basically, I could mount it under the floor and not even have to worry about a cabinet. The disadvantage is that I don't know how it would sound.

I can buy 250-watt subwoofer amps for a fair price, or I may hit eBay and find a couple of decent bridgeable amps to power these with. Advantage to the subwoofer amp is that it has a continuously variable crossover frequency.

Still debating different enclosures (sealed, vented, bandpass, etc.), but I reallly like the in-floor idea. Has anyone ever done anything like this here?

[Gary]

Hmmmm. I think you should not spend too much cash on this idea. With all that house shaking bass, your folks will be kicking you out pretty quick, Rudy.

You'll have to move back to A&M Corner!

[Claviusb]

Rudy, two points-- first, you need a structure (box or cylinder, my vote being a cylinder because it eliminates standing waves) to help generate the most potent bass wave possible, and too big or too small a box (or cylinder) and the effect diminishes. The math involved for figuring out the optimum enclosure area is very important. Consider looking at the Adire (I believe) site or one of the Home Theater Forums in the DIY section.

Second, if you really want some gut-rattling bass, also consider bass shakers attached to the couch and under the chairs in the room. Like having your own Sensurround™ setup! :)

[-=Rudy=-]

Originally posted by Gary
Hmmmm. I think you should not spend too much cash on this idea. With all that house shaking bass, your folks will be kicking you out pretty quick, Rudy.

You'll have to move back to A&M Corner!

I live at the Corner enough as it is. ;) No worrry about the folks' house, though--Mom's been gone since 1995, and Dad's going to be living in assisted living or a nursing home from now on. I'll probably buy the place at any rate, once I sell this shack we're in now.

I'd taken over the basement when I used to live at home, so they would have been used to the loud noises anyway. :D

[-=Rudy=-]

Originally posted by Claviusb
Rudy, two points-- first, you need a structure (box or cylinder, my vote being a cylinder because it eliminates standing waves) to help generate the most potent bass wave possible, and too big or too small a box (or cylinder) and the effect diminishes. The math involved for figuring out the optimum enclosure area is very important. Consider looking at the Adire (I believe) site or one of the Home Theater Forums in the DIY section.

Second, if you really want some gut-rattling bass, also consider bass shakers attached to the couch and under the chairs in the room. Like having your own Sensurround™ setup! :)

I'll skip the Sensurround™ for now ;) . There is actually a speaker enclosure that was made to install between the joists of the floor...it's either a vented system or one of those bandpass enclosures. Standing waves aren't a big deal--a couple of well-placed baffles and damping inside the box help to reduce them, along with reducing cabinet resonance. A tube is also a giant resonator, so some care needs to be taken there as well. I've seen speakers actually built out of PVC pipe! If I could find a big honkin' 12" diameter piece of PVC, I could probably wedgie that up under the floor. ;)

That 'open air' woofer concept actually has some advantages. Other than not needing a cabinet, there is no problem with standing waves, loading, etc. It is a special woofer design, which was developed so it could be used in open environments (specs are way different than a woofer for sealed or vented use)...such as having the woofer's back opening into another room, or on a very large baffle. Not sure if it has a high efficiency rating or not, but it probably needs a lot of power to drive it to a decent level.

I still have some formulas from an old issue of Speaker Builder for vented and sealed systems, as well as transmission lines. I'm almost thinking that a transmission line might be what I'm after...they're notorious for having very clean bass, but not as efficient as vented. In fact, a tube of the correct length (1/4 wavelength, based on the Fs (free-air resonance) of the driver, would be ideal. As far as math goes, it's the easiest to make, but can grow to a large cabinet size in a hurry.

[Khorn]

There have been some successful "furniture" designs like coffee or end tables. The thing invoved here would be cabinetry and finishing skills.

My choice? One left and one right box consisting of an 18" JBL Med Efficiency driver in 8(small) 12(probably the most realistic) or 16(pretty massive) cu ft vented enclosure and augmented by electronic bass eq from JBL that will provide high output capability to - 3db to 23Hz. Problem is amplification which I would think to be at least 500wpc in a good solid amp like McIntosh or a Bryston 14B or the old standby of a couple of Bryston 7B monos. I sure these will provide the house (block) shaking capability you're looking for.

[-=Rudy=-]

I've always laughed at the idea of 'furniture' subwoofers. Could I automatically stir my instant iced tea? Ultrasonically clean jewelry? Would the lamp vibrate right off the subwoofer 'end table'? Could one of the ladies sit on it for a cheap thrill?? ;) :D :love:

One good thing about subwoofer amps is that if it does the bass right, it should work well. Fast and clean, with plenty of reserve. Fast so it does the attacks well, clean meaning not muddy, and reserve to hit those attacks without running out of power. The living room doesn't have a lot of room for large sub boxes.

Hey, I once saw a picture of a slot-loaded subwoofer that a guy used for his living room. it was like a narrow duct to which he had about eight large woofers attached, which came down from the basement ceiling. The bass traveled up this duct to the living room.

I'd like to tease some listeners with stealthy subs...think about it, get a small pair of speakers, hook them up, and there's this 32Hz bass note coming out of nowhere. ;)

[Khorn]

Hmmm...how about buyin' a house and the two houses across the street.
You could then take those houses across the street and......

I think the stealth idea has some intriguing possibilities and I think that was the idea behind some of the furniture subs and actually some were built so well that vibration wasn't a problem, the cost of the cabinet was. One of the downfalls to the coffee table design was counting on the idea that at low enough frequencies you could get away with a single low bass source as it wouldn't be directionally detectable. While this may be true if x'd over at a low enough subsonic noise level it is not so with most bass musical reproduction.

Infinite Baffle designs using walls and closets have always been interesting concepts and worth exploring if you have the space to spare.

Another property that helps a good bass amp is a high enough damping factor to control heavy woofer motor movement precisely.

[PMC7027]

In the "old" days of high end audio one or two Hartley 24" drivers in the floor were considered the "ne plus ultra" of bass.

[Jack Keck]

http://www.hometheatertalk.com/DIY_Projects/IB_Sub/ib_sub.html

I've heard his one. The builder played a THXlogo scene fro a movie on it. It does just what the subs in the theaters do. Grat forum, too.

[-=Rudy=-]

Jack--was it a similar design, or was this a local project pictured? Looks pretty darned impressive! Although I personally would have covered it up. I would also give it a name...probably something like "The Beast". :D

My idea's similar, but would be through floor vents, and only one woofer in each location...maybe two, if I shoot two vents up through the floor. I don't think I could bring myself to knock a hole that large into wet plaster walls! :)

[Jack Keck]

I was privlidged to hear this when I had to pick up a foster child from Tampa, FL.. I wish it was local. Like at my house :D

A few years ago, Tom Nousaine from everyone's favorite mag, Sound & Vision, wrote an article about a sub that he built in his basement with 8 twelve inch drivers that fires up through a vent in the floor. The article might be available on their site. If it isn't, I might still have the magazine.

[-=Rudy=-]

Originally posted by Jack Keck

A few years ago, Tom Nousaine from everyone's favorite mag, Sound & Vision, wrote an article about a sub that he built in his basement with 8 twelve inch drivers that fires up through a vent in the floor. The article might be available on their site. If it isn't, I might still have the magazine.

Hey, I think that's the one I remember! There's not room for something like that in the basement, but I remember looking at that article and thinking, "Oooooh yeah!" :D

Just thinking about it, though, it would be much easier to pull of an infinite baffle system in a basement listening room, since I could build a wall to my specifications.