Vocal Motors: Sound Mills and Phonomotors
Compiled by Gerry Vassilatos
by Silvanus P. Thompson
Nature 29 (363-364), 14 February 1884
AFTER the notable researches of Crookes on radiation, which culminated in the discovery of the radiometer, or lightmill, it was a natural transition of thought which suggested to several minds almost simultaneously the possibility of devising an apparatus which should rotate under the influence of sound waves as does the radiometer under the influence of the rays of light and heat. Such instruments were indeed devised independently about six years ago by Lord Rayleigh, by Prof Alfred M. Mayer of Hoboken, by Mr Edison, the well-known inventor, by Prof Mach of Prague, by Dr A. Haberditzel of Vienna, and by Prof Dvorak of the University of Agram (in Croatia). These researches, though of great scientific interest, have been somewhat overlooked in the rush of scientific inventions during the intervening years. During the course of the past year, however, Dvorak has given to the world, in the pages of the Zeitschrift der Instrumentenkunde (vol. iii, Heft 4), a detailed account of his experiments, together with figures of various piece of apparatus hitherto undescribed. We propose to give a resume of the principal points of Dvorak’s researches.
Four kinds of sound-mills are described by Dvorak, two of them depending on the repulsion of resonant boxes or cases, and two others on different principles.
The first of these instruments is depicted in Fig. 1, and consists of a light wooden cross, balanced on a needle point, carrying four light resonators made of glass. These resonators are hollow balls of 4.4 cm. diameter, with an opening of 0.4 cm. diameter at one side. They respond to the note G (392 vibrations). When the note G is forcibly sounded by an appropriate tuning fork, the air in each of the resonators vibrates in response, and the apparatus begins to rotate. As a resonator will respond when placed in any position with respect to the source of sound, it is clear that one single resonator properly balanced should rotate; and this is found to be the case, though, naturally, the action is more certain with four resonators than with one.
Before proceeding to the other forms of sound-mill devised by Dvorak, it may be well to explain briefly the cause of the phenomenon, and to describe Dvorak’s particular method of exciting the appropriate sound, Dvorak has pointed out, as indeed has been done elsewhere both by Lord Rayleigh and by Prof A. M. Mayer, that, when sounds of great intensity are produced, the calculations which are usually only carried to the first order of approximation cease to be adequate, because now the amplitude  of motion of the particles in the sound wave is not infinitely small as compared with the lengths of the sound-waves themselves. Mathematical analysis shows that under these circumstances the mean of the pressures in the condensed part and in the rarefied part of the sound-wave is no longer equal to the undisturbed atmospheric pressure, but is always greater. Consequently at all nodal points in the vibrations of the air in tubes or resonant boxes, the pressure of the air is greater than elsewhere, and therefore any resonator closed at one side and open at the other is urged along bodily by the slight internal excess of pressure on the closed end. The apparatus, Fig. 1, therefore rotates by reaction, in the same way as the top and bottom, while the air cavity was tuned by enlarging the circular opening in front. In the later researches the box stood on four feet made of India rubber tubing. The note of the fork so mounted was very strong. At 40 cm. distance it would set the sound-mill in motion.
Dvorak’s second apparatus, a “rotating resonator” consists of a short cylindrical box, constructed of stiff glazed paper, having four projections, shown on plan and elevation in Fig. 3, each of which bears at its side a short open tube of paper. It is, in fact, a resonator with four openings, arranged so that it can be hung upon a silk fiber. A fine needle projects also below to steady the motion during its rotation, which occurs whenever the apparatus is brought near to the sounding-fork. For the note G the dimensions were: diameter, 7 cm.; height 8.6 cm.; diameter of openings, 0.6 cm.
The third apparatus is the “sound radiometer” described by Dvorak before the Imperial Viennese Academy in 1881. Its cause of action is less readily explained, though its construction is even more simple. Its form is shown in Fig. 4, D; there being, as before, a light cross of wood, pivoted by a glass cap upon a vertical needle. To the four arms of the cross are cemented four pieces of fine white card, about 0.08 cm. thick, perforated with holes which are depressed conically at one side, and raised at the other. These holes may be made by punching the card upon a lead block with a steel perforating-punch of the form shown in Fig. 5A, the dimensions of which are: a b = 0.38 cm.; c d = 0.2 cm. The holes should be from 0.6 to 0.65 cm. apart from one another. When a card so perforated is held in front of the opening of the resonant box of the tuning fork, it is repelled if the smaller ends of the conical holes are toward the box. A better but less simple way of perforating the cards is by the use of the conical steel punch shown in Fig. 5B; and the matrix, Fig. 5C. The angle of the cone is 55′, and the narrow projecting nose of steel is 0.2 cm. For this purpose he places between the prongs of the fork an electromagnet constructed of the following plan. Two plates of iron separated by a sheet of paper are used as a core. They are cut of such a breadth as to lie between the prongs without touching them. This core is overwound with insulated copper wire, as shown at E, Fig. 2, and the electromagnets then mounted by a bent piece of wood, a b c, upon the sounding box, K, of the fork. The wires are connected in a circuit with a battery, and with the electromagnet of a self-exciting tuning fork of the same note. Dr. Dvorak is extremely particular about the arrangement of the resonant boxes of his tuning forks. They must not touch the table, the arm, a b c, being clipped at about the point b in a firm support. Moreover, the resonant boxes themselves require to be specially tuned, for all are not equally good. Dr. Dvorak points out that, besides the tone of the fork, and the tone of the air column in the cavity of the box, there is also a tone proper to the wood of the box itself which in most of the forks used in acoustic researches is too base, the wooden walls being too thin. To hear this tone the prongs of the fork should be damped by sticking a cork between them, and the cavity should be filled with cotton wool while the wooden box is gently struck with the knuckle or with a cork hammer. It is important that the wood tone should be tuned up to coincide with the tone of the fork and with that of the air in the cavity. Dr. Dvorak himself used the box depicted further on in Fig. 6, in which drawing F is the socket into which the stem of the fork was screwed. The rotations are more rapid if the cards are set on obliquely in the fashion shown in Fig. 4E, the burred sides being outward. Cards with twenty five perforations so mounted rotate briskly when the “mill” is set in front of the resonant box.
The fourth apparatus of Dvorak is called by him an “acoustic anemometer”. It is shown in Fig. 6. This is merely a little “mill” of simple construction, the valves being small pieces of stiff paper or card slightly curved. The sounding box previously described is placed a little way from it, and between them is held an ordinary Helmholtz’s resonator, with its wide mouth b turned toward the box, and its narrow opening a toward the mill. From what has been previously said it will be understood that the internal increase of pressure in the resonator at a has the effect of driving a jet of air gently against the sails of the mill, which consequently rotates. Dr. Dvorak also suggests that this two-aperture resonator may be replaced by one having but one aperture, as shown, as shown as R, with its open side i, turned toward the mill. This resonator is formed of a glass ball cut away at one side and cemented to a glass plate having a small hole in the center. It may be remarked that when the air ejected from the mouth of this resonator is examined by the method of mixing smoke with it, and then viewing it through slits cut in a rotating disk, the currents are seen to consist of a series of vortex rings.
A second kind of “acoustic anemometer” may be made by taking a card pierced 100 conical holes, as previously described, and placing this between the resonant box and the “mill”. The latter rotates in the wind which passes through the conical holes.
Space does not admit of a comparison being drawn between these instruments and those of Mayer, Mach, and others, which are very closely akin in their design and mode of action, interesting though, such a comparison might be. Nor can we here compare the action of these instruments with the “phonometer” with which Mr. Edison literally accomplished the feat of talking a hole through a dead board. But this remarkable machine was a purely mechanical toy, which converted the vibrations of the voice, by means of a very finely cut ratchet wheel, into a motion of rotation round an axis. – Silvanus P. Thompson
Dvorak’s Sound Radiometer
The Electrical World
14 June 1884
A very interesting conversazione was given in London by Prof. Huxley as President of the Royal Society, on the evening of the 7th ult. One of the most interesting contributions to the objects exhibited was Herr Dvorak’s sound radiometer, which we illustrate on the next page, and which was exhibited by Mr. W. H. Preece, F.R.S. In this apparatus, which attracted considerable attention, a wheel is set into rapid rotation by the sound waves produced by a vibrating tuning fork. Referring to the figure, T is a large tuning fork mounted on a resonating chamber R, and maintained in continual vibration by an electromagnet C fixed between its prongs, to which an intermittent current of electricity is transmitted by a contact breaker consisting of a similar fork timed in unison with T, with which it is connected by the wires x and y. Opposite the orifice of the resonating chamber R, and on the same horizontal axis, is placed a Helmholtz resonator K and in front of its small end is placed the instrument shown at L, which consists of six little Helmholtz resonators fixed round the circumference of a wheel which is poised at its centre on a needle point so as to be capable of rotation in a horizontal plane after the manner of a compass card. The little resonators are attached to the wheel in such a manner that their axes are tangential to their circle of rotation, their smaller ends pointing in the direction in which they revolve. When the tuning fork T is set into action the air within the chamber R takes up the vibration and the sound is greatly reinforced, and this is more marked if a mass of cotton wool or soft rubber be interposed between the chamber R and the table. The action of the Helmholtz resonator K, is to take up the sound waves and to concentrate them in the direction of the revolving instrument L, and this effect is so strongly produced that, if the finger be placed a short distance in front of the smaller orifice of K, a sensation is felt which if indistinguishable from that which would be produced by a rapid  intermittent jet of air issuing from the nozzle. The rotation of the wheel L may be due to the fact that as the air within each of the little resonators L is thrown into vibration under the influence of the sonorous vibrations, and in the direction of its axis, and as it is freely open to the external air toward one end of that axis, it is probable that the energy of motion expends itself partly on the envelope and partly on the air, and the former receiving a greater proportion over that part of its surface which is opposite to the large orifice than in the contrary direction, rotation takes place.
We are, however, rather inclined says Engineering, to which we are indebted for these details, to place the phenomenon in the same class with those discovered by Professor Bjerknes, and illustrated in the beautiful experiments of himself and his son, and to attribute the action to the effect of one vibrating body upon another through the intervention of a common vibrating fluid medium.
United States Patent Office.
THOMAS A. EDISON, OF MENLO PARK, NEW JERSEY.
IMPROVEMENT IN VOCAL ENGINES.
Specification forming part of Letters Patent No. 210,767, dated December 10, 1878; application filed November 27, 1878.
To all whom it may concern:
Be it known that I, Thomas A. Edison, of Menlo Park, Middlesex county, State of New Jersey, have invented certain new and useful Improvements in Vocal Engines; and do hereby declare the following to be a full, clear, and exact description of the invention, such as will enable others skilled in the art to which it pertains to make and use it, reference being had to the accompanying drawings, which form part of this specification.
The object of my invention is to transform the vibrations of a diaphragm or other body capable of being set in-vibration by soundwaves into continuous rotation of a shaft, to act as a prime motor, for various light mechanisms.
My invention consists in the combination, with a diaphragm sensitive to sound-waves, of a shaft between centers having a fly-wheel attached, and combining the diaphragm therewith by a friction-clutch, which, when reciprocated by the vibration of the diaphragm, acts upon a shaft so as to continuously rotate the same when the diaphragm is actuated by sound-waves.
Figure 1 is a front view of my apparatus. Figs. 2 and 3 are side views of the same.
In Fig. 1, C is the diaphragm, of any convenient material, which is secured to the frame A by the ring D and screws XX. B is a mouth-piece for concentrating the air-waves upon the diaphragm. F is a cork secured to the center of the diaphragm. 2 is a rubber tube, into which a pin is secured. This pin connects the rubber with the reciprocating lever G, whose fulcrum is upon the shaft 3.
P is a click or pawl resting upon the wheel H, and pressed against its surface by the spring O. K is another click, secured to the upright M, which serves to prevent a backward motion of the shaft. E is a fly-wheel, for storing, by momentum, the intermittent power, and thus keeping the shaft in continuous rotation. The shaft 3 runs in centers between the uprights M and N. The whole is secured to the base W.
The action is as follows: When the mouth is placed in proximity to the mouth-piece B, and several words are spoken, or a musical note given, the sound-waves, striking the diaphragm, set it in vibration. This, in turn, reciprocates the lever G, causing the shaft to be carried forward a small distance at every vibration, and the momentum of the fly-wheel transforms these minute impulses into continuous rotation of the shaft. A small grooved pulley, 4, Fig. 1, is attached to the shaft, in the groove of which a continuous thread or band may pass to any light mechanism, and thus give motion.
I do not wish to confine myself to any particular mechanism for transforming the vibratory motion of the diaphragm into continuous motion, as a ratchet-wheel and click and many other well-known mechanical equivalents may be used. If either do I wish to confine myself to a pulley and cord for connecting the prime mover to the apparatas to be set in motion, as a worm and wheel or toothed wheel or friction-wheel may be substituted instead.
A large cone may be inserted in the mouthpiece B, for collecting extraneous sounds and causing them to move the diaphragm.
This apparatus is useful for giving motion to clocks and other small apparatus requiring minute power.
I claim as my invention—
A vocal engine consisting of a diaphragm or other body capable of being set in motion by sound-waves, a shaft, and reciprocating mechanism, substantially as and in the manner set forth.
THOMAS A. EDISON.
by Gerry Vassilatos
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