The drawing in SPEAK is for clarity. I would never build a lever like that. See link below. This construction would only cost as much as a speaker cone with surrounds and spider. Maybe $10 for a 15" one with 2:1 ratio. Most companies charge ridiculous sums for passive radiators. >Some things are unclear for me:
>1. Should the big passive radiator be of the same size as the >speaker?
It should preferably be about 50% bigger.
>2. Did you build the passive radiators yourself?
I was with a big company and we had a suplier build them.
>3. How did you build the lever?
As below with a few mods - the spider did not have a hole in is as shown in the drawing. This gave a larger gluing surface. We sued a frame to hold the parts, although once mounted the frame beomes unimportant.
>4. Which speakers/passive radiators/components did you use to build >the subwoofer?
Again, I was with Ford and we had everything custom made. This project was published in SAE and can be obtained. It shows how the theory worked as expected, the +6 dB gains were achived and the lever with one driver outperformed two drivers in about the same enclosure volume, fewer drivers and watts required with the lever.
If only I could get some company to make the actual lever, I know that this would be a popular approach. Maybe someday I will pay for the tooling and do just that. But I have other interests right now.
If you, or anyone else, wants to have these levers made and sold, I would give you rights, they are patented, to do this since I own them for most configurations of advantage.