Subwoofer Design

[Sounder]

Nearly finished with my 11 cu ft speakers (with GPA 604s)and already an organist wants me to build them a subwoofer to "go as low as possible", say 20 Hz, for a 20 x 40 ft, carpeted room.

I have no idea what woofers to use, size of enclosure, etc. I would appreciate any leads. Thanks.

John

[Todd W. White]

Altec 411A's in a 9-cubic foot sealed enclosure.

INCREDIBLE sounding sub!

[GM]

Greets!

Subs are about moving air, so how much can they afford to move sets the performance goals.

GM

[bigjunglejim]

How do the Servodrive Contra Bass and Basstech 7 work for home use? Anyone out there have any experience with these two models?

[bfish]

Don't know about the Basstech, but have a buddy with a Contra ServoDrive. Unless your home sits on a slab and has double-rocked, 6" walls, you won't likely keep a ServoDrive in it long unless you're planning on remodeling soon anyway.

[Sounder]

OMG these subs are frightening (in a good way). I'll check them out but I suspect that you may have to re-mortgage the house to get one.

Seriously, CAN they destroy a stick built house?

Truly awesome equipment! Thanks, guys, for your advice.

John

[GM]

Greets!

I've seen used CBs for as little as $1 k, but if they need repairs they're not cost effective IMO. Last time I heard, they were retailing at $3.5 k and the DTS-20 at $3 k. If either extreme SPL isn't a requirement or you're willing to build two or more folded TLs similar in size to the DTS-20 depending on peak SPL required you can DIY for a few hundred - $1 k. For example, here's a 12 Hz TL project in the works for only ~$230: http://www.decware.com/cgi-bin/yabb/...330259;start=0

The CBs did a number on mine. It's a floating floor design (concrete block perimeter with block pillars under load bearing walls) built at the beginning of the drywall era, so only 3/8" thick. Other than behind the few kitchen wall cabs, literally every tape joint split and the majority of nail joints tore, so the least effort was to lay up new drywall on top of the existing. One concrete pillar supporting a load bearing wall shattered near the right channel CB's location causing the roof to bow down, driving the floor down, buckling the wall and bending the in-wall galvanized steel water pipes, which in turn stressed the joints at the then new heater, hastening it to a very early demise.

This of course caused water leaks that ultimately required stripping the entire roof to its 1x8 slats and replacing all the ones that split either from the initial sag or from me j-a-c-k-i-n-g it back up. All this roof ridge sag pulled in the living room exterior wall from end to end, buckling both end walls and a section of hardwood flooring and destroying several windows. I was able to jack the roof back up to within ~1/2", but couldn't do anything about the now inward sloping front wall and its attached now out of plumb walls beyond what shifted back with the roof j-a-c-k-i-n-g. I could have, but all things considered I couldn't justify the extra cost that would have ~doubled my already too expensive for the locale 'renovation' bill. A new neighbor that hadn't met me yet called the cops when I sledgehammered the windows out and fired up the chainsaw to square up/re-frame the buckled openings so I could fit the nearest size new pre-hung assemblies. The conversation/debate between the two about my sanity/actions added a little comic relief to my plight though.

Pretty high price to pay for an evening's entertainment IMO. On a similar 'note' , a dude and his buddies coupled one up under his trailer home to act as a whole house bass shaker and promptly blew it apart. Fortunately, they escaped with only cuts and bruises, though probably only because they were all ~commode hugging drunk at the time.

That said, I've since designed subs that's every bit as powerful and installed in the typically much better constructed homes of the 'landed gentry' and/or located north of the Mason-Dixon Line, various and sundry rattles and/or the female's LF tolerance seems to be their limiting factor, at least on the short term.

As always though, YMMV.

GM

[GM]

Greets!

Indeed I do......... I pretty much destroyed my old stick built post WWII G.I. tract home with a pair of CB kits/500 W ~7 yrs ago and still haven't finished all the repairs. Anyway, they are the cleanest/tightest subs I've ever auditioned and were an excellent blend to the much modded 210s and could keep up SPL-wise, but I had to sell them with the 210s along with some other audio and biker goodies to support the greedy medical cartel. I kept two unbuilt kits though just in case I'm ever able to build another HE system.

Tom Danley says the BT7 is way too much horn for any reasonable HIFI or HT app.

Since you seem to only be interested in getting down to 15-20 Hz though, his new single driver DTS-20 Tower of Power horn 'blows the doors off' the CB, so this is his current recommendation for a 'full tilt boogie' home system: http://www.danleysoundlabs.com/DANLEY_dts20.htm

GM

[Jim Butler]

I am dumbstruck GM. A had NO idea that it was possible to do this to a house (concrete block!!!Blowing up a house trailer!!!) with a sub system.

What kind of SPL's are at work and at what HZ to cause this kind of destruction?

I will go ahead with the 411 pipe plans but you say the calcs indicate similar effects as the CB's are possible. My studio building is a 1904 stick jobber that has already had a rebuild...

[GM]

Greets!

Well, look at it this way, 16 Hz in a large enough space will expand to a ~22.53 ft diameter oscillating pressure 'ball' moving along at the speed of sound, so if its amplitude is high enough it's going to literally jackhammer anything in its path at 16 cps. Now try to contain this 'jackhammer' inside a typical room and why room gain rolls off down low in a typical room/home as it forces it way through any airspace as well as bleeding off energy exciting everything that doesn't have a Fs lower than whatever the lowest frequency is being generated.

It was the low 'B' (~16 Hz) on St. Saens and I had to cradle the CD player in my lap to keep it from mis-tracking at what sounded like ~live levels. I don't know what the actual peak SPL was since it was bouncing off the peg on the 120 dB scale. It didn't sound excessively loud, just real, and when I told TD about it he said it was because they are so low in distortion that when they first started selling them the FOH engineers would keep raising the gain on them till they popped drive belts waiting to hear the distortion point.

The trailer dudes were watching U-571, so I assume the depth charges claimed another 'kill'.

Anyway, you live up where they build them to last in a much harsher climate than down here around Hotlanta and my (once) low rent unit was built out in what was the 'sticks' at the time when there were few building codes. Because of the damage and the desire for a larger room, I extended it and today's building codes wouldn't let me match the existing, so the extension is both better built and odd looking since I wasn't allowed to tie into the existing foundation, though planting some wild shrubbery masks it somewhat.

Obviously, the sub's SPL can be regulated and things rattling is distracting, but sub-bass is addictive and the lower a system goes, the 'richer'/'fuller' the rest of the BW sounds and even though it's an illusion, the highs seem more extended if your hearing is still youthful.

GM