Hi
The power cooling trick in the patent you mention was used on all Servodrive BT-7’s and most SDL-4 and SDL-5’s and proved to be very effective.
It can also be applied to a normal loudspeaker if configured as shown in the patent.
Intersonics inc, the company I worked for at the time licensed the patent to Bond acoustics in Canada who was headed by Steve Hutt, now director of R&D at Harmon Motive.
While I was prohibited from using “conventional drivers” most of the time, Steve applied it to a range of products and got more than a factor of two in increased RMS power capacity.
As the power to the fan tracks the input power, it is not difficult to make the fans operation inaudible.
It is important to do the venting as show or risk cone offset proportional to air pressure.
On the other hand, if the air is withdrawn from the VC pocket, then the cone is not affected.
Also, it doesn’t take much flow past the coil to cause a large increase in PHC.
Keep in mind that the “un-glued” temp in a modern VC is around 300 – 350 deg C. that is darn hot and any net flow across that coil causes a nice temperature drop.
In the patent drawing, is shown the power cooling applied to a conventional VC driver, note where the air is drawn out.
Attached is a photo from the “Olden days” back at Intersonics (around the time I applied for the patent).
I was demonstrating a switching amplifier and control circuitry on a subwoofer at the time.
In the foreground was the Eminance 12 inch driver I had modified to add power cooling.
This driver (like most) did not have access to the VC pocket, I drilled a pair of holes and pressed in he copper tubes sticking out the back.
I am on the far left side and John Halliburton (a lab poster) is on the far right.
Hope that helps
Tom Danley