The lever is not really shown on my site, but is well described in various AES and SAE papers (see my resume for references). The bottom line is that a horn increases the acoustic coupling as the square root of the mouth to throat area ratio, but a lever does this as a direct ratio. So with an area ratio that would double the output due to the horn, the lever would quadruple it. In reality the two things are hard to compare because they both have completely different sets of tradeoffs and problems.

But I stand by my statement that I do not see the advantage of horns at low frequencies.

I am not exactly sure. I have thought about this, but never really decided. I lean towards two ways of saying the same thing.

A spiral is far more difficult to construct with concentric round bends, so it's not a good candidate for wideband use, though as Western Electric proved 70 odd years ago it can be done. But as a spiral allows the longest possible pathway from a finite box size, and complicated reflectors and rounded bends matter not below 200 Hz or so, it makes sense to go spiral for pure basshorns.

The KHorn seems to make the case for the W configuration for a basshorn for corner placement, but I've found that even there a spiral horn has the advantage, as the spiral configuration will allow a far smaller box for equal or better result.

We built several of them when I was at the car companies. I had discussions just last week in LV with a major company who wants to start making them.

Some horns particularly those which are W folded have a relatively short horn length for mouth area. They are often large meaning that low cutoff frequency can be achieved often with only 2 boxes rather than 4 or 6.

These days people will use more cabinets to get more volume as this is what is demanded. Therefore it makes sense to make smaller cabinets which on their own have limited extension but when used in the proper quantity end up being both lower and louder than old designs like w bins because the mouth area is larger and the horn length is longer.

Stu

Your illustration in the book was enough for me to see what you are trying to achieve, and you provided a cursory explanation but you really only dedicated a couple pages to the subject. That may be all that is required to conceptualize it mathematically, but I'd like to see it explored in more detail.

My hunch is that it would be best used in bass subsystems, because of its mass. In that regard, it seems like a relatively small area radiator could be coupled to a much larger radiating lever membrane, on the order of areas similar to a basshorn. That might provide the efficiencies of a horn, but without the peaks from being undersized as basshorns almost always are. It has very intriquing possibilities.

Might be worth asking Eminence to build one, since they are setup to do it. Then again, maybe you can get a better deal through your contacts at B&C. But either way, I'd love to see tests of a few samples made with various size primary and secondary diaphragms.

The Acoustic Lever has been seen before as what was called an "augmented Passive Radiator". It basically has two cones, one larger than the other. As an electrical circuit element it is a transformer and as a mechanical device it would be a lever. It takes in a pressure and volume velocity and outputs a pressure, but with a larger volume velocity than the input (assuming that the output is the larger cone). So it is a volume velocity amplifying device, or impedance matching, whichever you prefer. In the form where all of the sound is forced to go through the lever, it is patented. The prior art all used the lever as a parallel element to a direct radiator.

A lever can produce 6 dB (or more) enhanced acoustic pressure than the same driver in any other enclosure configuration. It takes a little more cabinet volume to do this than a closed box, but nothing like the volume required for a LF horn.

You wrote:

My hunch is that it would be best used in bass subsystems, because of its mass. In that regard, it seems like a relatively small area radiator could be coupled to a much larger radiating lever membrane, on the order of areas similar to a basshorn. That might provide the efficiencies of a horn, but without the peaks from being undersized as basshorns almost always are. It has very intriquing possibilities.

You are right on the money here. The concept is low frequency limited and does work best for a woofer or sub because it is enherently band limited - more so than the horn. As a transformer it transforms as the ratio of the areas of the input and output cones. A horn is also a transformer, but it does so as the square root of the input and output areas. For small ratios the two work pretty much the same, but for a ratio of 2:1 or more the lever is much more efficient than the horn. This is one of the reasons that I often state that I can see no advantage to a LF horn. Levers work a lot better.

You wrote:

Might be worth asking Eminence to build one, since they are setup to do it. Then again, maybe you can get a better deal through your contacts at B&C. But either way, I'd love to see tests of a few samples made with various size primary and secondary diaphragms.

Anybody will make levers for me - if you pay them!! but nobody seems to be willing to build a lever without a great deal of front money. Finding someone to make the levers is not a problem, but making a business case for doing so is.

The problem goes like this. I am now convinced that in small rooms the LF problem is best solved by many small inexpensive lower output woofers placed arround the room. Levers are hard to make small so they favor the single larger woofer approach - not what I recommend. In a large venue, like Pro sound, the lever is ideal, but no one has yet shown an interest in building one for this application and I am not in that business.

When I was at Visteon we built lots of prototypes and this work was all published, mostly in SAE. The bottom line was that it all works as claimed

The catch 22 is that no one wants to make a lever product without consumer demand and consumers don't demand what they don't know exists. I am much more interested in my Summa Loudspeakers at the moment to divert attention rom this project to build some levers just for demo's.

I have always offered to help anyone pursue this, but no one has come forth.