A New Speaker Principle
by Edgar Villchur
September 27, 1952
Taken all together, the weakest link in the chain of audio reproduction remains the one which seems, to the lay eye, to have the greatest exterior efficiency—the speaker itself. Trim-looking, functional in design, with clearly evident components to do the specific job involved, it seems as satisfactory a solution to the problem as can be devised. But it has several inherent weaknesses, to which a engineer has recently addressed a new mode of procedure, with some potentially startling possibilities.
The stylus-diaphragm assembly of the early phonograph (an assembly then properly called a “speaker” after its function) was made to vibrate in recognizable imitation of any number of different voices. So uncanny was this seemingly unnatural phenomenon that when the Edison phonograph was first demonstrated before the French Académie des Sciences, suspicions were voiced that the operator who cranked the machine was using ventriloquism. However, a mechanical-acoustical device subjected to forced imitative vibration has inherent limitations in its fidelity to the stimulating force. Ideally the device must be entirely passive, speaking only as continuously directed, without asserting any oscillatory life of its own; like a good actor it must efface its own personality in favor of the characters it plays. But actors do not entirely lose their own personality characteristics. The mechanical device retains some of the behavior patterns determined by its inherent inertia and restoring force, coloring the imitation and making it less than perfect.
Today electronics dominates all fields which are primarily concerned with the transmission and reproduction of oscillatory energy, and many formerly mechanical functions are now performed electronically. The scanning wheels of the first television receivers have been replaced by deflection coils and cathode-ray tubes; the mechanical amplifier has been replaced by the electronic audio amplifier. But the electrical output of the amplifier must be changed back again to mechanical and then acoustical, form before it can be heard, and we return to the use of a mechanical speaker.
The modern moving-coil loudspeaker converts the electrical output of the amplifier into mechanical vibrations through the interaction of magnetic and electric fields. Although the tendency of the speaker’s mechanical system to lapse into natural modes of behavior is partly counteracted electrically by the amplifier, the disadvantages of a suspended mechanical device still operate. Resonances formed by the inertia and elasticity of the system, uneven restraint exercised by the elastic supports during the course of the cone vibration, and the fact that elements which must transmit vibrations cease to be rigid at higher frequencies, introduce distortions which make the loudspeaker the weakest link in the reproducing assembly.
Loudspeaker engineers have made great advances, and the current emphasis on careful design of the mounting device (to provide good acoustical coupling between the speaker and the room) is well placed, but speaker distortion and frequency response ratings are still significantly worse than those of other audio components. Information on speaker amplitude distortion is conspicuously absent from the multitude of technical data appearing in audio component advertisements. The reason is not difficult to discern: while amplifier manufacturers vie with each other in boasting, justifiably, of distortion percentages that are only a fraction of 1 per cent at rated power, the very finest speakers introduce as much as 5 per cent harmonic distortion in the neighborhood of certain frequencies. The frequency response of most amplifiers is kept within a maximum variation of one or two decibels, but the output of speakers in the 150 dollar class varies over the reproduced frequency spectrum within a range of at least ten decibels. Contemporary loudspeakers perform admirably, but the buying public is used to ratings with smaller numbers. What, then, of the new French thinking on this subject?
In October 1946 a potentially revolutionary idea in loudspeaker design was described in L’Onde Electrique by M. S. Klein. Klein called his invention the “ionic” loudspeaker. In it the electro-mechanical stage is bypassed, and there are no moving mechanical parts. The Gordian knot created by the imperfections of the vibrating machine is cut rather than untangled.
The ionic speaker reproduces the vibrations of the acoustic medium which were created by the original sound, but it does not reproduce the mechanical vibrations of the original source. The molecules of air which are set into oscillatory motion are not pushed and pulled by a mechanical diaphragm or cone acting as an intermediary agent between the electrical signal and the sound, but are controlled directly by a varying electrostatic field. The vibrations of air molecules, of course, constitute sound, and these vibrations are radiated from an acoustical chamber into the room.
Air molecules in their natural state are not susceptible to electrical attraction or repulsion because they are neutral in charge. The molecules in the acoustical chamber are therefore changed to positive ions, by inducing molecular collisions which knock off orbital electrons and destroy the balance of charge in each molecule. Thermal agitation starts the collision and ionization process, and once there are charged particles in the chamber ionization can be completed by an alternating electrostatic field, super-audible in frequency. The input audio signal is superimposed on the ultra-sonic field as a modulating voltage.
This new device is being worked on with a view towards commercial production by the French speaker company Audax, and rights have been acquired by firms in various countries, including the United States. Results from experimental models are currently being given rave reviews by periodicals like TSF et TV (“Qui n’a jamais entendu un haut-parleur ionique Audax 1952, n’a jamais entendu la verite musicale”), but the project is still in the developmental stage.
The practicality of the basic principle, however, has been demonstrated. The generation of imitative sound, which had been considered an inherently mechanical function, may thus be freed from the trammels of diaphragms and elastic suspensions, and one more distorting influence in musical reproduction will have been removed.
— EDGAR M. VILLCHUR