BIG diy woofer for OB

[tinitus]

Could this be a way to do a huge woofer with very low Fs

Drawing shows a huge membrane coupled to one or multiple woofers

[badman]

Long version? REALLY nope.

You'd get a ton of rocking mode distortion from the extended pivot point, and the suspension isn't meant for the type of stress you'd be placing on it.

Better to get woofers more purpose designed for your app. What's wrong with a few Acoustic Elegance IB15s?

[krips]

I'd make an H-frame to lower the point where the bass rolls off so you need less EQ. Have you modeled it in 'the edge'?

[tinitus]

Well, its just an idea that suddenly popped up in my head

Drawing was quickly done, and very incomplete, sorry
I hope this one shows better

Menbrane is suspended by threads
Woofers are mounted in supporting frame

[krips]

What is this membrane you speak of?

[PeteMcK]

Tinitus, have a look at this thread: PIEZO NXT type panel. They're going full range there, but I'm thinking like you, just try it for the bass. some day, I'm thinking of filling the cones of some old drivers with polystyrene foam and coupling then to a large sheet of something, just to see what happens :-)

[MisterTwister]

I have similar idea to make huge dipole sub.
get pro woofer with strong motor, remove its cone, leave spider and coil in place. then build and attach your own cone and frame.
then you'll have subwoofer bigger than 31" fostex for much less money.
flat panel cone is a bad idea, it will resonate way too much.
I actually plan to make deep profile, corrugated cone.

[tinitus]

Thanks for the valuable input
You nailed down some of the obvious benefits

Update
"Cone" might be a 1/2" thick polystyrene sheet, about a square meter
No thread surround, but instead use the flexibility of the polystyrene
Corners are cut away to increase flexibility

Which woofer?
I dont expect this to be a high power speaker
I want a refined sub to be used solely at "normal" SPL
But stilll need a woofer driver with a strong motor and fairly good Xmax, if this thing goes really deep

Beyma SM212 might work, and cost is avarage around 100EUR
Or maybe even a carfi woofer would work fine

[CLS]

That 'felt' surround can be noisy I guess, no? I like the one with thread suspension better

And the motor should be secured in some way, so I think the skectch by MisterTwister make more sense to me.

As to the membrance, how about honeycomb cardboard? Quite light and rigid related to given area. If more than one motors can be used, then it can be driven more evenly.

[paulspencer]

I can see quite a few problems with this. Firstly, two motors driving one cone seems like asking for trouble! Also having no baffle at all makes is horrendously efficient, so you are working uphill negating your gains.

I think you'd be better off starting with some large 15" drivers with a powerful magnet and low Qts. Now remove the surround and simply extend the cone so that it's bigger. Cones are better because they combine stiffness and low mass. Any flat panel will be inferior. So you might turn that 15" driver into a 21" and perhaps use a few of them. Now put it in a H frame to get the best efficiency you can from a dipole.