The Mysterious Acoustic Turbine

Having come to a dead end in my research into Keely and his machines I decided to try a different approach and suddenly things started to pay off.

Having studied Keely in great detail from available literature I believe I have a fair measure of him, both as a man and as a researcher. Keely did not chase rainbows. He had solid reasons for dedicating his life to his researches and his machines in spite of massive hardships along the way. I reasoned that the only thing that would set him on this path was that he had very early on a workable device (i.e. a functioning motor), albeit in a crude form and of low power. The fact that he continually spoke of "perfecting" his motor seems to indicate this.

I started off with the following assumptions:

1). Keely had a working motor early in life.

2). The motor was of low power, just enough to move, but not enough to do actual work.

3). No man creates something in total isolation. There had to be parallels in research to be found in the work of contemporary experimenters in the field.

4). Someone, somewhere had invented a similar device, only to be brushed aside with a convenient explanation why it could not be developed to do actual work. Such device could possibly still be found tucked away as a scientific curiosity in some museum somewhere. (Like the Crook's tube)

5). The device induced rotation in a tangible body through the medium of sound waves.

All my assumptions proved to be true and verifiable.

The device exists, it works and at least one such device is in the collection of early scientific research instruments in a Toronto museum, though there must be others, as they were used during Keely's time in universities all over the world in scientific demonstrations and were in fact manufactured by at least one scientific instrument maker for sale to universities and other research establishments.

But back to my research.

I started researching the work of Chladni and Helmholtz, knowing that Keely's devices relied heavily on principles discovered by those two eminent scientists.

While researching Helmholtz I came across Rudolph Koenig, a German violin builder who had turned scientific instrument maker and had built a number of Helmholtz devices in conjunction with Helmholtz that were sold to universities and other establishments who were conducting research into acoustics.

I became very excited when I read Koenig's biography and found that he was a contemporary of Keely and that the two must have known each other since Koenig had an exhibit at the 1876 World Exhibition in Philadelphia where Keely was demonstrating his motor.

Koenig manufactured exclusively apparatus used in acoustic research in his workshop in Paris and is, amongst other things, the inventor of the manometric flame (called sensitive flame nowadays), an instrument where a stream of gas is passed through a chamber containing a diaphragm that regulates the flame by regulating the amount of gas feeding it on being excited by acoustic vibrations. These vibrations become visible in the behaviour of the flame and this instrument was invaluable in the research of sound. Undoubtedly Keely had one of these instruments in his workshop.

It is reasonable to assume that both men had visited each other's exhibits and talked at length about their areas of research.

Here was a link worth following up in detail.

Luckily most, if not all, of Koenig's instruments are in excellent condition in collections all over the world. Many are in American institutions having been purchased at the Philadelphia exhibition. Among the instruments are tuning forks, organ pipes, flutes, the above mentioned manometric flame, vibration microscopes and an instrument for Fourier analysis and synthesis which, though stationary and not designed to do any work, exhibits curious parallels to Keely's motor.

All except one.

Amongst his machines is a small device called an acoustic turbine, which is listed in his 1889 catalogue an item No 75 and sold for 60 Franks. (about $15).

The Acoustic Turbine

Alfred M. Mayer (1836-1897) was a faculty member at Lehigh University from 1867 to 1871, and then spent the remainder of his life as a professor of physics at Stephens Institute of Technology in Hoboken, New Jersey. "He invented the sound-wheel in 1876, but very graciously yielded precedence to the Austrian, V. Dvorak, who, it was found later, had quite independently made the same device a few months earlier. This little instrument consists of four small tuned resonators attached to a small cross and balanced on a pivot. When placed near a source of continuous sound of the pitch to which the resonators are tuned, such as an electrically driven tuning fork, the reaction against the closed end by the stationary wave formed inside of each resonator causes the wheel to rotate "backwards." From Dayton Clarence Miller, Anecdotal History of the Science of Sound, (The MacMillan Company, New York, 1935), pg 73.

Acoustic Turbine

The example at the left is at the University of Toronto, and is almost surely some of the apparatus that Koenig brought to Philadelphia
for the 1876 Centennial Exposition.


Thomas B. Greenslade, Jr.
Professor Emeritus of Physics
Kenyon College, Gambier, Ohio 43022

O.K. here is a device that confirms some of Keely's claims. What is noteworthy here is that Keely was attacked for his views by contemporary scientists when the same scientists had already a device they were demonstrating that was the proof of principle of what Keely was saying. No wonder the device disappeared from the textbooks.

This is where it starts to get interesting. In spite of my training in engineering and a life long interest in acoustics and music I had never heard of such a device, in fact no one I knew in the trade had ever heard of it either. It is simply not taught and demonstrated anymore. The explanation given by Dayton Clarence Miller is no explanation at all. I began to suspect that the phenomenon is simply not mentioned anymore because conventional science is not able to explain it. I decided to write to Professor Greenslade, the author of the article, if he could shed some light on this.

I wrote:

.. You describe a device known as acoustic turbine, manufactured by Rudolph Koenig and used in scientific demonstrations. In spite of my training ( I am a qualified engineer, physics major, now retired) I had never heard of the device, nor witnessed a demonstration. As far as I can remember it was never mentioned in class.
What puzzles me here is the explanation given for the phenomenon, which is altogether unsatisfactory. I did notice that in contrast to everywhere else in the project you offered no comment but quoted a source instead.
What I would like to know is by what mechanism does the excitation of a resonant cavity develop a unidirectional force.
It may well be that my inability to understand the phenomenon points only to a massive gap in my knowledge of physics. I can live with that, for no man's education is ever complete (Thank God).
On the other hand there are strange phenomena associated with resonant cavities that have never been fully explained. (Sonoluminescence comes to mind.)
I would very much like to hear your opinion on the subject.

To which Professor Greenslade replied:

Dear Hans,
The usual technique, when you don't understand something, is to quote the source! Let me try to examine the situation...
If the cavity were somehow completely closed on both ends, yet filled with acoustic radiation of the proper (resonant frequency) the forces on both ends would be identical.
Now drill a hole in one end that is smaller than the diameter of the cavity. The standing wave can still be set up, but some acoustic radiation would come out of the hole, and the unbalanced force would drive the resonator forward.
This begs the questions of how the radiation gets into the cavity. Clearly it comes in through the hole. Let me suppose that the radiation comes in almost parallel to the length of the cavity. You can split the incoming radiation into two components -- parallel to the length of the cavity and perpendicular to this direction. The latter component will set up circular standing waves -- I suspect that a Bessel function might be involved here because of the circular boundary conditions. The parallel component will certainly be refracted at the entrance hole -- standard problem of a plane wave interacting with an aperture. This will provide more transverse components -- but there will also be longitudinal components. Having written this, I am conscious of the fact that you just can keep stuffing radiation into the cavity -- eventually an equilibrium situation mmust be reached.
Depending on the entrance angle, some of the incoming radiation has a longitudinal component that must come out of the hole -- and this drives the system forward.
What do you think?

In my next letter I wrote:

.. As to our little problem, I must confess that early on I entertained thoughts similar to yours and would have probably left it at that if it weren't for one awkward fact.
The device is said to move in the opposite direction.

This was over two months ago, I did not get a reply. Perhaps I was a little too forthright and offended the good Professor. This was never my intention. Perhaps he felt that since he had already admitted he didn't know, there was no need for further correspondence.

If you have an explanation for the phenomenon please let me know, I will publish all answers here. Thank you.

Christopher Koveleski writes:

The Acoustic Turbine seems simple enough to build.
I find it hard to believe that it spins "backward" ... and I think that the limited knowledge of sound waves / english jargon when the article was published has defined "backwards" as the opposite direction of the open cavity .. which could be easily proved.
Such as this device:
Nice to see someone else interested in Keely ...

Thanks for the link Chris, interesting stuff. Hans.

Graham Ormiston writes:

I think this may be connected with non-linearity in the air movement in and out of the Helmholtz resonators. At the sort of frequency at which the resonance will occur, the wavelength will be much greater than the size of the resonator, so it is best to think of a resonance between the enclosed air compliance and the 'inertance' of air in the port, causing an alternating stream of air through the port. A lot of thinking has been done on this sort of system by the designers of reflex loudspeaker cabinets. One of the problems that concerns them, of course, is distortion. If the air moves too fast through the port, there will be significant non-linearity. Acting on a sine wave, this will produce both second harmonic and a 'DC' component. I have seen suggestions to the effect that, in a loudspeaker, this may produce a DC pressure shift in the cabinet, causing the drive unit to be displaced from its optimum rest position. Looking at the picture of the turbine, I think the design of the ports, with their sharp edges, may cooperate with the non-linearity to entrain a stream of air with a non-alternating, unidirectional component.
I'm not sure why one resonator is facing in the 'wrong' direction. They look as if they're spot-welded, so this may be intentional
Another physics demo that uses non-linearity in a Helmholtz resonator is the smoke-ring generator.
Graham Ormiston

Good Comments Graham. As to one resonator facing in the wrong direction you will see if you look closely that the resonators are rivetted or screwed to the cross , not too tightly I would suspect, to enable the resonators to be adjusted to their optimum position. Since this device is a museumspiece and in remarkably clean condition after 130 years I would guess that whoever cleaned the device turned one resonator the wrong way before putting the rotor back on the pivot. Hans.

Sam Smith writes:

Dear Mr. von Lieven:
I read your posting about the acoustic turbine with interest. I had not heard of the device before, and it certainly is intriguing.
First, I assume the turbine rotates "nozzles-first", or counterclockwise as seen from above.
Here are my thoughts on a possible operative mechanism:
First, I considered the device as an "air-cannon", ejecting small quantities of air in order to rotate in a jet-like manner.
(Sticking to basics--action and reaction.)
I then considered one container...
Resonance in the cavity may (should) cause the entire container to vibrate. The blunt end (closed end) may flutter as a result. Like a drumhead, so to speak.
If the fluttering of the closed end is more effective at pushing air away from the device than in sucking air back towards it, a net linear force and resulting motion might be created.
On the outward flutter of the container endwall., the air would be displaced linearly--thus causing motion in the correct direction.
On the inward flutter, replacement air would be drawn in from the sides--radially--as the departing pulse of air blocks direct reflux flow by its inertia. This would not affect the previously induced linear motion.
On the inward side of the container base, a similar pulse of air would be formed, but the small diameter and conical shape of the nozzle would act to cancel the motion of the air somewhat in the manner of Tesla's one way pipe--as if the container were closed at the nozzle end. Pressurization rather than ejection of the contained air would be the result.
As a test of this solution, a rigid tube, sealed at one end with a rigid wall, could be fitted with an internal sound generator. The open end of the tube would then be fitted with a flexible membrane of thin metal.
A turbine structure made with four such tubes, upon actuation, should then rotate with the rigid ends "forward".
Best regards,
Sam Smith

Good line of reasoning. The experiment suggested is not difficult to do. I shall get to it as soon as time permits. Hans.

Colin Quinney writes:

I would look for something similar. It's very interesting. Thank you for bringing it to our attention.. Although it's not a microwave cavity, it being a cavity resonance with a mystery, it reminds us somewhat of the unidirectional thrust of EMdrive.
http://www.emdrive. com
What are the similarities (if any) between the Acoustic Turbine and an EMdrive? Other than cavity resonance, (one of sound, the other of microwaves), and end reflectors that are not of equal area, I don't know. Could it be they both operate due to the difference in the energy gradient between the standing wave reflector surfaces?
The mystery remains.. :)

steve edward george writes:

I am not an expert but I believe that sound is a pressure wave that usually involves the rapid back-and-forth movement of air.
My suspicion is that the chambers take the back-and-forth movement of the air (sound pitch) and convert it into a directional pulsed movement much like a whetstone bridge would take AC electricity and convert it into pulsing DC.
The sound (pulsed air) would then exit from the chambers much like the old German V1 Buzz Bomb to cause propulsion.
Steve Edward George
Largo, Florida, USA

nicolaie vlad writes:

mr.Hans von Lieven ,
very interesting 'news' on 'old' Acustic Turbine !
Thanks, Nic


Hans von Lieven, copyright 2007