Found this on another forum discussing the old bucket...
Maybe I can fill in some blanks, being the its inventor and having made the pre-production prototypes for PG, I am familiar with the technology.
The cyclone is a rotary motor and rotary radiator driver (where a normal Servodrive is a rotary motor and piston radiator system. My goal in this invention was to eliminate the problems, losses and non-linearity associated with the edge suspension and spider in a system where a large displacement in a small physical size was needed.
Back in the late 1980’s when I invented this, my job involved making very intense sound, mostly for scientific purposes so the Cyclone is actually the smallest rotary driver I worked on. We had built a number of units that had the displacement of 6, 18” drivers (@1”pp) that were used for active sound cancellation until the Power plant was retired due to an earthquake.
All of the rotary drivers I built had moving magnet motors I designed as well, to produce an “Fs”, a torsion rod is within the center of the shaft and supplies the “restoring force” which gives it the Fs of 10 Hz.
While eliminating all of the flexing / bending parts eliminated those problems, it turned out the torsion spring is also far more linear than spiders etc.
When Tom Nousain reviewed it for a magazine back then, he said it had the lowest distortion of any driver he had ever measured.
This was partly due to the elimination of the brushes which cause low level noise in the servodrive as well as the non linearity’s that normal drivers have.
Like any woofer, the efficiency is set by the T&S parameters and with any application there is a “best” alignment so far as efficiency vs low cutoff.
Why wasn’t this more successful?
At Intersonics, the speakers division was by far second fiddle to the NASA work, when the NASA work died off (a trickle down from the shuttle accident) the company eventually went out of business and the rotary drivers were too labor intensive to pursue in the Surviving speaker div.
PG licensed the technology and got off to a good start. They had good luck molding everything out of plastic and made the Cyclone that way.
Note; do not mold a motor housing out of plastic when the motor has strong Neo magnets inside. Unfortunately, over time, too many of the Cyclone began to rub internally.
While one could usually re-adjust the tension bolts to fix it, it was a rubber glove to fix a leaking pen.
I may resurrect the technology now that I am on my own but there are several other “full range” and “bass horn” things I have to focus on for the time being.
Hope that helps,
Answers to a few questions, the rotary drivers we produced at Intersonics in the late 80’s (the 6X15) was only a commercial industrial device unlike the Servodrive speakers which were for concert / special effects use.
The power plant (in Redondo Beach Cal) was taken off line by the earth quake, not the speakers and in fact nearly all (ideally all of it) of the sound each of the 6 drivers at the perimeter of each fan was “canceled” by the sound the 20 foot diameter fan made.
Unlike a home or “music” application, this had to run 24 hrs a day at full level, part of what made this particular driver a pain in the rear to make.
Perhaps the coolest aspect of the moving magnet motor in general as with this driver and the Cyclone (its huge peak power capacity) was entirely wasted in this application with an “zero head room” signal. Funny, I remember I wanted to set the stinky epoxy the winding was encapsulated in, so I plugged it in to an outlet for a half hour until it was nice and toasty. In operation it was driven by a 3200Watt PWM amplifier and the motor supplied with forced air cooling.
I followed the link one of the fellows had in this thread to the diy rotary driver and thought hey I have been there, pretty cool.
An important thing to keep in mind if playing with rotary “things” is that the obey a different set of relationships so far as how a given force or mass impacts the system.
In the normal “in and out” speakers, the relationship is simple and direct, with a rotary system, force applied at a radius produces torque which is equal to force times radius.
Mass on the other hand is reflected as the radius squared.
For example, in the case of the PG Cyclone, if one used a solid steel center shaft, ¾ inch dia, it would only have a reflected mass on the radiator of a few tens of grams (if I remember off the top of my head). Hence in both of these drivers, I was able to have a considerable amount (mass) of magnet but have a manageable impact on the moving mass. Anyway that different rotary relationship will make these more understandable when you keep it in mind.
What am I doing now?
I had been working at Servodrive / Sound Physics Labs where I have been focused nearly entirely on horn design for the last 6 years or so.
At Servodrive I developed the Unity Horn design which allows multiple frequency ranges to drive a single constant directivity horn. These have the radiation pattern and phase response of a single source even though some of them have as many as 7 drivers on one horn. Also the Bdeap which is a 32Hz horn when placed in the proper location near a corner or can be stacked in multiples of 2 or 4 for as much as 10 dB or more of forward directivity in the bass range (although with a higher low cutoff than in a room).
The 2 on 2 configuration is humorous, it has a measured sensitivity of 97 dB 1 W at 10 Meters (10 meters being –20 dB from 1 Meter) outdoors, halfspace. Add 8 KW of amplifiers and one can “make bass” for several friends.
I resigned from Servodrive in October and have since established a new company called Danley Sound Labs.
That is in its infancy but one can see “what there is so far” at Danleysoundlabs.com
The “Tapped Horn” at the web site is a new horn invention, which allows the size of a bass horn to be reduced significantly for a given cutoff frequency without depending on external loading.
It is to a conventional horn what a vented box is to a sealed box, more or less.
I will be able to describe its operation in detail shortly.
There are some other things coming along too but not enough to talk about.
The companies focus is on commercial sound / installed sound, not the home so I figure indulging my DIY urge every so often is ok. Hey, besides, no one can tell me I can’t anymore come to think of it.
So far as the commutated VC driver, I built a few so I know it can work but at Intersonics there was no interest in pursuing it and no one has approached me about it since.
The patent ought to expire soon if it hasn’t already (I don’t remember when it is) so it may resurface who knows.