Has anybody seen this type of driver before?

i can understand how the dual coils can reduce distortion. that is what jbl is doing with their differential drive.

other than that, it looks like a sub without a dustcap and a rod connected to a diaphragm behind the woofer.

the explanation isn't very scientific either (sounds kindof amateurish) and no measurements of anything. seems like some random idea that some guy thought up and got a patent on it. just because he got a patent on something doesn't mean it is better. it just means in the eyes of the poor clerk who was examining it that it appeared sufficiently different from other designs.

That exploded view you posted looks like the car audio example further down the page. The very first woofer they are talking about looks alot different. A better diagram is shown on this page: http://www.codrive.com/bassp.htm

It looks like down the throat is a sealed chamber with another physically linked cone. Seems kind of cool but the prices are insanely high.

So the lower cone plays into the box and through the senter of the front cone?

I'm not ready to make fun of it. Makes sense.

there is no T/S mentioned, so i have no idea how much throw this has. It looks like its a 15" with a 12" ish firing through a 3" ish hole... i wonder if its any chuffing? seemes kinda small that hole.

Keith Yates tested this odd-duck long ago. Of course the output was pretty weak, even compared to what we would consider a good 12" woofer these days.

Way Down Deep CoDrive CB1
Edited by Mark Seaton - 11/28/12 at 9:41am

The home version uses 12"/10" cones, and while interesting the results are not any better than current conventional systems.

it looks like he was trying to pump some midrange through the center of the woofer. these days, we call that a co-axial design. unfortunately, the slightly smaller "back" driver isn't going to perform anywhere near as well as a compression driver, which is what is used today.

Actually I believe the cones are locked together to the common former. I believe the intent was for increased Sd from a given frame diameter. A quick guess suggests at best he could get close to the Sd of a 15", but with some silly complexity and no other benefit I can see.

"Actually I believe the cones are locked together to the common former. I believe the intent was for increased Sd from a given frame diameter. A quick guess suggests at best he could get close to the Sd of a 15", but with some silly complexity and no other benefit I can see."

that is what i thought at first, but if the cones are moving together, there is no differential in air pressure behind the front cone and the back cone, so no spl would actually be coming out of the "hole" in the front cone.

No. Mark is right.



The frame infront of the back cone is closed so it can only escape through the hole in the senter.

OP linked to this, but im "bumping" it:
http://www.codrive.com/tech.htm

oh i see.

So I guess bigger is not ALWAYS better.......

Whats the Mms on that thing like 2Kilograms!?

That might have been the intent but I'm pretty sure it doesn't work that way. You can stack as many cones as you want and it won't increase Sd at all (no matter if there's a hole in the outside cone or not), in the same way that a cone shape vs a flat round shape with the same diameter both have the same Sd, since they push linearly straight in and out. The cone has more surface area but doesn't push any more air than a flat plate.

As I see it, this alignment makes no sense, it does not increase Sd, it increases Mms significantly and it has a dead chamber in between the two cones that really serves no purpose at all.

But it does look a lot like the Geddes acoustic lever, which he was granted a patent for. (One that he didn't really deserve, as he just changed one extremely small detail in existing prior art patents.) The only difference being the outside cone in the acoustic lever doesn't have a hole in it.

It does increase SD.

I don't think so. Think about a tube of silicone for instance. In that case the "cone" would be the plunger thing you push on to make the silicone come out. No matter what shape that plunger thing is (cone or flat or multi cones with a ported chamber in between) the same amount of silicone is going to come out for a given input stimulus (like a squeeze on the trigger).

Sd is cross sectional area of the diaphragm, regardless of the diaphragm geometry, regardless of whether you you make a cone with an internal chamber inside of it.

The air inside the cavity is a static load, it's not going to do anything, certianly not increase Sd. The speculations about high velocities coming through the outer cone center hole are wrong - the two cones are connected and moving back and forth together. There's going to be no air flowing in and out of the cavity, the cavity and it's air load will not pressurize and depressurize. In short, the cavity is going to do absolutely nothing but add unnecessary weight.

I welcome you to refute this, but please back up your statements with... anything really.
Edited by diy speaker guy - 11/30/12 at 10:28pm

Guess I don't see the need to back up anything. And I don't see anything worth refuting. Its just the way it is.

How do you measure Sd? Do you measure the cross sectional area or do you measure the actual surface area of the cone? If the latter, you are the only one and your calculated Sd and simulations will be wrong. If you glued an extra dust cap (a very large one) on a regular driver and cut a hole in the middle of it, would that increase your Sd? This is a ridiculous notion and that's basically the same thing as this driver - two cones that are attached to each other, the outer cone having a hole in the dustcap.

This is very basic theory and physics. All you need to understand is the basic definition of Sd.
Edited by diy speaker guy - 12/1/12 at 12:26am

To some extent it resembles a pair of drivers in an isobaric alignment, the difference being the sealed back on the inside 'driver' and the open pole piece. Whatever. As is always the case what matters is how it works, and the results of the linked review says no better than a standard driver.

You mean, the type of stuff I might have picked up while earning a MS in mechanical engineering? Oh.

Look, your analogies are all misguided. I don't have the inclination to enter a lengthy back and forth over something that seems so obvious.

EDIT - Sd = diaphragm cross sectional area. It alwasy has and it always will. No matter what crazy inventions claim otherwise. Sd has NEVER been calculated by diaphragm surface area. I would hope that even the beginners among us know that. But I guess not.

Regardless of your education I don't appreciate being called misguided unless you can back up your claim with ANYTHING AT ALL and show me my error.
Edited by diy speaker guy - 12/1/12 at 11:26am

To save some hassle, let's describe Sd to be the cross section of air displaced per Xmax of the motor. This means Sd x Xmax = Vd .

A perfect comparison to this would be the consideration of 2 12" drivers in a face to face manifold. If the manifold had a 13" x 6" opening, is the Sd equal to that of 2 12" woofers or the 13" x 6" opening (close to a single 12")?

The rear side (facing motor) of the internal cone is open to the internal box volume, just as the rear of the 12" cone is through the openings on the front basket. The forward side of the internal cone is confine/funneled into the center hole of the 12" cone in the same location we might place a phase plug or coaxial tweeter. The hurdle is that the Vd of the internal cone has to exit through the center opening, but it does not communicate to the rear of the 12" driver.

The 2 cones do add for effective Sd at low frequencies, while internal reflections and directivity issues would cause the model to fall apart above some frequency related to the diameter of the inner cone.

I agree wholeheartedly with the first sentence of this post, it's this quoted part I don't agree with.


This is super easy to test, like I said, just glue a big dustcap with a hole in the middle on a regular driver. That is the SAME THING, since both cones are attached and moving together in the device we are discussing. You will notice a decrease in performance, not an increase, and no increase in Sd or the amount of air pushed for a given input stimulus.

You can also easily test this with liquid and a tube with a plunger. No matter the shape of the plunger or if you have dual plungers with a hole in one of them, a given squeeze will push out plunger CROSS SECTIONAL AREA X plunger excursion.
Edited by diy speaker guy - 12/1/12 at 2:00pm