Single voice coil, two cones

Would it be beneficial in a push-pull subwoofer for example, with opposing cones, to have a single voice coil handling the movement of both cones?
So in the magnetic gap a single voice coil conjoines the cones, essentially is this not a single driver then?
Now we don’t need a parallel load of two drivers so could this be more “current-efficient”?

Please tell me if I’m missing something critical here, it just started to confuse me, why haven’t I seen this ever done?

Hello It wouldn’t work with just one voice coil for two speakers.
Two opposing diaphragms with a voice coil would result in cancellation.

There are speakers like Manger or tweeters that drive a dome and cone membranes with a voice coil. At high frequencies only the middle part vibrates and at low frequencies the outer part is also excited. Greetings Andrew

Not necessarily. How to avoid this, what say you?

60 foot long horns going in opposite directions from each side perhaps, would look good in the mountains too :slight_smile:

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It doesn’t work. I’ve been building speakers for 35 years. Try it yourself. Set up your speakers like Pushpull. Cross one. The bass will cancel each other out as the cones work in opposite directions. Greetings Andrew

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What if the other cone of the driver is walled for isobaric tuning?
Essentially would the isobaric loading principle work with a push-pull single voice coil driver?

I don’t know what the ifs and buts are supposed to lead to. The second membrane would be nothing more than the back of the first. Rebuild for what? It would amount to splitting a membrane and would offer no advantages. On the contrary, it would double the membrane mass with no advantages with a lot of disadvantages. Greetings Andrew

There was a company called Codrive that did this in the early 2000’s, though their website is still up.

codrive cut

They did this with a single motor or dual motor (and sincle or dual cones). The inner cone fires through the opening the apex of the front cone (where the dustcap would normally be).

This adds a lot of complexity and is mostly (pointless versus using a single, larger cone, unless baffle space is at a huge premium. Possibly, this could be resurrected for a line array box where the height of the front face of the cabinet is critical.

The dual opposing motors aren’t quite as good as the JBL approach of a single differential motor with dual coils, where the coils cancel the flux modulation. However, this codrive approach is potentially capable of more excursion.


What a concise throughput of information on something so at first glance questionable and trivial as a single voice coil. Apparently, not entirely trivial?

I was going to mention the KEF KC62 and LS60, but they in fact use two separate voice coils and one central magnet/pole piece.

Apparently this is easier to implement efficiently, that way with the shared pole structure. Interesting results those too mentioned above nonetheless, those with a single voice coil. How about cobbling all these ideas of shared unity and symmetry together even more efficiently?
I hope to see more of this type of development either way.

Chris, care to elaborate on this more deeply with your personal insight? You seem to be insinuating this as a rather pioneering solution.

I don’t think you would gain any efficiency going to a single coil, dual cone system. The coil would have to be “beefed up” in order to cope with the added mass of the second cone.

Well, at their core, the JBL and KEF approach are a little similar in that, instead of a backplate, you put a split in and create a second top plate and magnetic gap on the back side of the motor and hang a second coil there. You have to wind the coil the opposite direction (since the flux is flowing in the opposite direction there), so you have a sort of “push-pull” system from one motor. The benefit for subwoofer is that, while they are physically separated somewhat counterround coil modulates the total flux in the system down as the other coil modulates it up, cancelling a lot of the flux modulation (one of the major factors in distortion for high power, deep bass, applications. Shorting rings are not effect down below 100 Hz and this approach is.

You can also bias the coils apart for longer excursions and flatter motor force over excursion (further lowing distortion) and the dual coils give increased power handling.

Kef essentially took this split backplate approach and added concentric coils so they could drive two cones. They still benefit from the reduction in flux modulation but they also get a reduction in cost/depth versus a par of equivalent subwoofers. The KEF design was patented but the JBL patent has expired and it is now in the public domain.

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Cone-Specific Tuning: Voice coils are tuned to a specific cone based on its mass, size, and material. Using a single coil for two different cones could negatively affect the performance of both.

Cancellation of Vibrations: The opposing cone design in a push-pull subwoofer is meant to cancel out mechanical vibrations. Using a single voice coil could compromise this effect due to both cones moving in the same direction.

Increased Load on Amplifier: A single voice coil moving two cones might increase, not decrease, the load on the amplifier because it needs to exert more force.

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