Q&A with David Allen of ML. You asked the questions.. Here are the answers.

[User211]

Not sure what that diagram means, really, MotorToad.

Consider this. Like forces repel, opposite attract. If I am in the middle (the signal) and I go positive, the +guy on my left will move left and the -ve guy on my right will be attracted to me (er - no thanks!) and move left as well. Therefore they both move in the same direction, therefore, IT IS A DIPOLE!

 

[amey01]

Excellent post, JonFo, I agree with your assertions entirely.

I guess the question is, what does this dipole dual force arrangement actually provide in terms of advantages? On a "forward push" towards the listener, he will surely only hear the results of the mylar diaphragm closest to him. So what is the following diaphragm actually doing? Given that air doesn't compress that easily, and "if" there is an airtight gap between the two, I expect it allows greater overall excursions and hence volume and lower frequency reach.

Anyone have any thoughts on this? Particularly the airtight gap? I am just sitting here guessing, really. Beyond all the hyperbole surely this is just the relatively simple arrangement as described above? Or am I wrong?

Justin

Yes, I've wondered the same thing myself. What is this actually achieving? More exertion is achieved through higher bias voltages. I don't see how this arrangement could make greater SPLs (or provide greater control), or anything of benefit. The "EFFECTIVE" driven area is exactly the same as a regular double-panel.

 

[miljac]

Yes, I've wondered the same thing myself. What is this actually achieving? More exertion is achieved through higher bias voltages. I don't see how this arrangement could make greater SPLs (or provide greater control), or anything of benefit. The "EFFECTIVE" driven area is exactly the same as a regular double-panel.

I would tend to think of this being a clever method of canceling out the phase cancellations (acoustical short circuit). Good trick for a panel bass driver. I would assume that this is the reason for such a remarkable bass of the CLX.

 

[MotorToad]

Ah, man, I misinterpreted "charged opposite of each other" as "moving opposite (from the charge)." Mea culpa.

 

[tonepub]

Hey Tom:

Good questions!

I've got to pass on my trip this weekend, family member in the hospital, so I'm not going to get to see the CLX till the 12th in Seattle! Arrgh.

 

[User211]

Yes, I've wondered the same thing myself. What is this actually achieving? More exertion is achieved through higher bias voltages. I don't see how this arrangement could make greater SPLs (or provide greater control), or anything of benefit. The "EFFECTIVE" driven area is exactly the same as a regular double-panel.

Hm - one guy pushing a car is not the same as two guys pushing a car, if you get my drift. Also, won't the air in between the diaphragms add to inertial effects and therefore lead to more extended excursions than a single diaphragm?

 

[JonFo]

Yes, I've wondered the same thing myself. What is this actually achieving? More exertion is achieved through higher bias voltages. I don't see how this arrangement could make greater SPLs (or provide greater control), or anything of benefit. The "EFFECTIVE" driven area is exactly the same as a regular double-panel.

Close, but the real secret is that while there is the same effective radiating surface as a single diaphragm, there is 2X the effective driven area. Ergo the name 'DualForce', as there is twice the motive force that is applied to moving the diaphragms and therefore the 15 PSI of air resting on either externally facing diaphragm.

More force, more excursion for those large wavelength bass notes. :rocker:

This arrangement, while totally novel implementation in an ESL, is actually a derivation of something that's been around a while for bass reproduction: the isobaric woofer alignment.

This is a commonly used method to reduce harmonic distortion in woofer designs, with the use of two woofers mounted in a push-pull alignment as shown in the figure below.
When one driver is connected with inverted polarity in this push-pull format the result is that even order distortion components will be 180 degrees out of phase and should cancel in the summed acoustic response. This is fundamentally true and can be realized for dipole (like the DualForce ESL) or infinite baffle woofers and other woofer systems, provided the air mass load on both sides of the woofers is identical. However, in boxed woofers there is an additional distortion generating element which is unaffected by the driver mounting. This is the nonlinearity of the compliance due to the air in the box. If the box is large, or the excursion of the woofers is small, this source of distortion may also be small, thus cancellation of the majority of even order distortion is possible.

This distortion canceling approach has been routinely adopted to isobaric or compound woofer systems as well, but has encountered many an application challenge with sealed chambers due to choices around the volumes of trapped air (make it too small and distortion rises).

ML’s use of a dipole configuration allows the realization of all the theoretical advantages of isobaric, with the added benefit of having extremely low-mass ‘drivers’.

Very clever :bowdown:

 

[User211]

I wonder whether they are using thicker mylar at a lower tension to allow long excursions in these new ESL drivers....

Justin

 

[TomDac]

Hey Tom:

Good questions!

I've got to pass on my trip this weekend, family member in the hospital, so I'm not going to get to see the CLX till the 12th in Seattle! Arrgh.

Hey Jeff,

sorry to hear that. Hope it's nothing serious.

Tom.

 

[JohnA]

...
More force, more excursion for those large wavelength bass notes. :rocker:
..

That's how it appears to me as well.
Similar to using a car engine with twice the capacity to produce the same bhp.
On first sight it is inefficient, since max bhp has not changed.
But you've got twice the torque at low revs, it pulls harder without using the gearbox. Effortless.
Same as the bass frequencies here.