Dual / Opposed driver(subs?) theory learn on

[jinjuku]

Where can I do a bit more reading or can we discuss in thread?

[MGrant1957]

What are you wanting to know?

[AR3A]

Are you referring to Iso Baric design or just want more info on dual woofer configurations ?

[jinjuku]

I am wanting to know:

1. If you have an inert cabinet do you benefit from dual opposed drivers?
2. What is the efficiency gain in dB?
3. What is the proper wiring (how do they null cabinet resonance)?

[fbov]

1) if by "inert cabinet" you mean one that properly deals with sonic energy off the cone, dual opposed is no advantage. If you're talking about a massive cabinet that makes cone mass a very small fraction of the total (like 100+ kg.), you would reduce the benefit of dual opposed.
2) I know of no efficiency gain from dual opposed above that of adding a second sub.
3) Wire in phase, so both pull in from the same polarity voltage, and with voice coil axes co-linear, so forces are aligned. It don't work if the drivers aren't facing directly away from each other.

The advantage of dual opposed in-phase woofers is that the mechanical force imparted to the cabinet through the woofer frame by cone acceleration of one woofer is cancelled by a simultaneous and equal-but-opposite cone acceleration from the second woofer. (Simultaneous is the in-phase part, equal-but-opposite is the co-linear part.) As a result, the cabinet will only vibrate due to sonic energy, which is isotropic, not mechanical energy which is highly directional.

I'm building a spring-isolated sub to achieve same sort of result. I fully expect mine will bounce like a happy baby when driven at the resonant frequency, due purely to the mechanical forces moving the cone. Dual opposed wouldn't bounce, nor will mine above 10Hz.

Have fun,
Frank

[Face]

Want to help eliminate resonances...

http://i.imgur.com/PaTZt.jpg

KEF does something similar in the Blade.

http://i.imgur.com/uW9mN.jpg

You can find similar threaded inserts at Home Depot and Lowes.

As for efficiency, it depends how they're wired, in series or parallel. They should both be wired in phase with each other, so they don't cancel each other out.

[AR3A]

I did a design like this with some buy out drivers and was unsuccessful. Although I would recommend a driver with a large x max. Mine had a small x max and would of done better as a single or dual driver in a sealed configuration.

That is one cool looking speaker, always wanted to make a glass speaker :D

[jinjuku]

Does the cabinet volume remain unchanged or does it double?

I am thinking opposed Kappa 100.9w's. Working on a W/M/T/M/W where the MTM is dipole and wondering if I should go dual opposed on the W/W (so four 10's per speaker) to bring up the fidelity through a lower distortion woofer section (X-over somewhere in the 250-300Hz region). 1.2 cubic foot sealed originally.

[jinjuku]

1) if by "inert cabinet" you mean one that properly deals with sonic energy off the cone, dual opposed is no advantage. If you're talking about a massive cabinet that makes cone mass a very small fraction of the total (like 100+ kg.), you would reduce the benefit of dual opposed.

So what problems does a dual opposed driver configuration solve?

[Face]

Volume doubles, only with a Isobaric will volume decrease.

I would think twice about crossing those woofers that high, due to them being dedicated subs and side firing.

[jinjuku]

Volume doubles, only with a Isobaric will volume decrease.

I would think twice about crossing those woofers that high, due to them being dedicated subs and side firing.

They measure a usable frequency response up to 400Hz. Having heard the 120.9w and playing around with the X-Over they play comfortably above 220Hz.

I wouldn't be side firing them. Front/Back.

[biff]

Dual drivers of course gets less distortion at the same output, and the normal sensitivity increase of around 6 db if they are paralleled. Opposed drivers will reduce the cabinets share of contribution to the audible output especially if they are braced to each other as in the examples. As one driver moves forward, the other is doing the same in the opposite direction and that means that the perpendicular faces are subject to canceling fotces, only the baffles have their own vibration to deal with. Internal pressure isn't helped. Only if you use a very long cabinet will you get the benefit of distributed room mode reduction that you get with two sepatate subs well ditributed in a room. Someone a few years back had a 6 foot or so long cabinet with drivers on each end tucked behind his couch and that should have been a killer sub set, but at that length it's unlikely the drivers were braced to each other.

Always a compromise, but my next set has opposed woofers FWIW.

[Paul Carmody]

Here was my experiment with it. I think it went very well.

http://techtalk.parts-express.com/showthread.php?t=213731

[billfitzmaurice]

So what problems does a dual opposed driver configuration solve?Sub 'dancing', which can happen when the mechanical force created by the driver is enough to overcome the inertia of the cab, causing it to move. Opposed drivers cancel out that mechanical force.

[edlafontaine]

http://www.linkwitzlab.com/woofer.htm

read on...

[jinjuku]

Thanks guys. That confirms what I wanted to know.

[tedwilt]

http://www.diyaudio.com/forums/subwoofers/177905-thread-those-interested-ppsl-enclosures.html
http://www.audioasylum.com/forums/hug/messages/13/139292.html
http://forum.audiopsychosis.com/viewtopic.php?f=6&t=60
http://www.avsforum.com/avs-vb/showthread.php?t=1301337