Signposts of Sound

By Prof. Unnikrishnan Panickar

The Early Years

From the tinfoil cylinder of Edison to the multi-bit digital gizmos of today, the long road to 'audio nirvana' is peppered with landmarks and milestones marking man’s never-ending quest for 'fidelity' in the reproduction of 'canned sound'.

Nobody at the Scientific American office on that fateful morning back in 1877 thought the spoken words emerging forth from the diminutive horn of the phonograph device lacked any fidelity. But, for good or for bad, the human mind is programmed with built-in avarice, and like little Oliver Twist at the workhouse, keeps asking "I want some more". And as technology slowly marched ahead, and as material science became less of an esoteric black art, man's ingenuity, that Divine spark of creativity, forged ever new technological pieces to try and complete the jigsaw puzzle of fidelity. The 'audio avenue' has been one long road of inventions and innovations, revolutionary and evolutionary concepts and ideas, peppered with signposts that point to the spirited chase after the Holy Grail of Fidelity.

The early days of the phonograph witnessed increasing fidelity, thanks to the larger and better horns and their 'mechanical advantage'. Till the 1920s, the acoustic devices with their increasingly sophisticated horns and diaphragm mechanisms ruled the roost.

However, the foundations were being laid for the major inventions of the as yet unborn 'electrical era'. Johann Philipp Reis installed an electric loudspeaker in his telephone in 1861. It was capable of reproducing pure tones, but it could also reproduce speech. Alexander Graham Bell patented his first electric loudspeaker (capable of reproducing intelligible speech) as part of his telephone in 1876. In Germany a revolutionary and much improved design was thought up and patented by Ernst Siemens in 1877, which was to provide much of the inspiration for researchers on the other side of the Atlantic in the beginnings of the next century. Indeed credit should go to Siemens for being the first to perfect the design of the dynamic or moving coil transducer, with a circular coil of wire in a magnetic field that carried the audio signal, and supported so that it could move axially. Later in 1898 Sir Oliver Lodge, the English scientist, received the second patent for an improved loudspeaker.

The 'Electric Era'

All that was before the reproduction of music was 'electrified'. The second quarter of the 20'th century is generally acknowledged as the beginning of the 'electrical era' with the introduction of the vacuum tube amplifier, the powered loudspeaker and the microphone. Bell Laboratories and General Electric of the US were the key players in the field and this resulted in a 'quantum leap' in fidelity.

In the 1920s Bell Laboratories set itself the task of developing an 'electrical music playback instrument'. It was the practice in those days for research labs to acquire models of prototypes of the previous decades. Bell Labs and General Electric both had models of the 'babies' of Siemens and Lodge. E C Wente at the Bell Labs was instrumental in perfecting a 'condenser' microphone and later the moving coil loudspeaker.
However, two young researchers at GE --Chester W. Rice and Edward W. Kellogg-- were pursuing independently a similar goal. Though patents were granted to the two teams independently, the invention of Rice and Kellogg took the limelight with a practical system. Advanced for its day, the Rice-Kellogg dynamic loudspeaker included 'modern' touches such as a rubber 'surround' around the edge of the paper cone, a conical paper diaphragm attached to a coil of wire that was energized by a large (electro)magnet. They were the first to lay out many of the basic tenets of loudspeaker design, such as detailing the importance of the baffle in preventing the 'circulation' of the sound from the speaker's forward and backward motion. Rice and Kellogg also discussed the need for more powerful amplifiers to provide adequate headroom required for quality reproduction.

It is a testimony to the vision of pioneers like Siemens and Lodge and the inventive genius of researchers like Wente, Rice and Kellogg that the system they perfected has lasted virtually unchanged for very nearly a century, and right into the 'digital age', and looks like it is here to stay.

Other Exotica

That the electro-dynamic or the moving coil loudspeaker had virtually 'taken over' the world of audio does not automatically mean that there were no other competent or comparable transducer designs. In fact, the much-touted 'modern' electrostatic speaker happens to have a lineage older than its more popular cousin, the electrodynamic.
Though the concept of electrostatic speakers has been theorized since the discovery of electricity, a practical implementation was demonstrated only towards the end of the 19th C. At the Paris Electrical Exhibition of 1881, Professor Amos Dolbear exhibited a complete electrostatic telephone system. What is interesting about this fact is that it pre-dates by some 30 years any attempts to convert electrical energy into sound by alternative means, thus establishing the pre-eminence of the technology. Electrostatic speakers continued to be made during the 1920's and 1930's mainly in Germany. Notable were the loudspeaker and headphones designed by Eugen Reisz (famous for the 'marble block' Reisz microphone), [1] and the 'differential' ESL exhibited at the 1927 Berlin Radio Exhibition by Hans Vogt, [2] with a design topology that has remained virtually unchanged till the present. In the 1930s, there was a British design marketed under the name of 'Primustatic' that delighted radio listeners with its 'touch of naturalsness', its clear mid and high frequencies.

On the other side of the Atlantic, at the Bell Labs, E C Wente had unprecedented success with his 'condenser' microphone, essentially an electrostatic device, which was easily a hundred times more sensitive than conventional microphones. The Wente microphone and his 'light valve' system of sound-on-film went on to 'electrify' the movie industry. But it is unfortunate that Wente did not turn his expertise on electrostatics to the design of a speaker. Rather, he collaborated with Thuras in 1926 to patent a speaker of the moving coil type that met the requirements of quality, efficiency and power handling.

It is equally interesting to note that Rice and Kellogg, the masters of the moving coil/cone speaker, were intrigued by the great sounding electrostatic speaker initially. In fact Kellogg did file a patent in 1929 for an electrostatic speaker composed of many small sections able to radiate sound without magnets or cones or baffles. (Cited later by Peter Walker of Quad as one of the sources for his inspiration for designing an advanced ESL, the other being the work of Hans Vogt.) It can only be surmised that they too had turned away from the demonstrably higher fidelity of the ESL to the 'inferior' electrodynamic only because of the many pitfalls and problems that were in the way of realising a commercially successful product with current technology and materials.

For the next 20 years the only electrostatic devices available were condenser microphones, which attained a rare pefection and fidelity, with names like Neumann being synonymous with truly high fidelity. The ESL faded away from the scene since large, thin diaphragms could not be fabricated with any reliability using the materials available then, and their theory had not been worked out properly. The 'dangerous' high voltages required, the difficulty of matching them to the amplifiers (which even today remains a problem), their sheer size and unreliable operation particularly in humid atmospheres, all made them unpopular despite their superior fidelity. No wonder the rugged and compact cones were able to occupy centre stage for long.

It will be the 1950s before the ESL put in another appearance consequent on two events. The first was the publication of Prof. F. V. Hunt's seminal book "Electroacoustics"(1954), which provided the solution to the theoretical design of ESLs. A year later DuPont patented a new material called Mylar, which in every way was the answer to the prayers for a suitable diaphragm material.

Peter Walker, a little known British pro audio salesman and engineer, has been dreaming about the ESL for long. In 1956 finally his design was ready and thus was launched the Quad ESL-57. Legendary is perhaps the only word to describe this remarkable speaker as it reigned supreme and remained in production, virtually unchanged, for all of 28 years. A tribute indeed to the genius and the vision of its maker. What lifted the Quad-57 above even the best of the era was not its 'outstanding' technical specs. Rather, it lacked the many colourations and distortions that came as a 'bonus' with virtually all the reproducers of the period. To borrow Quad's own blurb, it was "the closest approach to the original", and audiphiles and critics, not to speak of music lovers in their droves the world over, were only too happy to concur.

It was 1981 before Peter Walker was ready to introduce the world to a 'quantum jump' in concept and performance with the first major re-design of his loudspeaker--the ESL-63. A radically different ESL concept with the diaphragm divided up into annular rings, with each ring fed by a calibrated sequential delay line, thus mimicking the radiation pattern of a theoretical point source located about a foot behind the panel. This meant that the ESL-63 behaved in a predictable fashion and it was free from the shifting radiation patterns (with frequency) that was the bane of all conventional speakers. What made ESL-63 an unmatched speaker was the synergy of speed and accuracy of the electrostatic flat panel, the 'un-boxy' sound of the dipole radiator, the coherence and 'continuity' offered by a single full-range driver and, of course, the solid imaging and 'sound-staging' of the ideal point source. No wonder the ESL-63 found a place even in the references of competitors, and for long it has remained the 'standard' against which other loudspeakers were judged, electrostatic or not.

Surely the time was ripe for the ESL. Improvements in programme material, programme sources and better recording techniques were all 'conspiring' to show up the many shortcomings of the 'cheap and cheerful' cones. As the main hurdles to the production of an ESL had been overcome, many got onto the bandwaggon and today we have an array of ESL makers, each claiming to offer the ultimate in fidelity. But sadly the laws of Physics remain immutable and the ESL, as we know it today, cannot hope to span the entire audible range.

It is but a small step from the electrostatic planar to the electrodynamic planar loudspeaker. In all likelihood many must have toyed with the idea, though they must have been kept from fruition by the unavailability of powerful magnets. In the mid 20th C, all that changed and powerful ferrite and ceramic magnets became available. One of the first practical and commercially successful magnetic planar speakers was the brainchild of Jim Winey -- the Magneplanar launched in the early seventies. The best of the magnetic planars are often rated on a par with the ESL, though like the ESL their physical limitations are something that cannot be wished away. A close relation is the ribbbon loudspeaker, which are often used as tweeters or supertweeters. But rarely do you find a full-range ribbon loudspeaker.

An overview of loudspeaker technology cannot overlook the 'ancient' bending wave loudspeaker. Bending wave transducers use a diaphragm that is intentionally flexible, with the high frequencies radiating primarily from the central area, while longer waves reach the edges of the diaphragm. The BWL has the potential to cover the entire audible spectrum and have been promoted as being close to an ideal point sound source. It is intriguing that though the technology has existed for nearly a century, we see only rare working examples.

Even in our  'digital era', we have to tread the known and  familiar pathways, filled with reflections and reverberations and what not, in our never ending quest for fidelity. It has been a long and tortuous route, but nonetheless a pleasing and satisfying trip in many ways.


[1] The 'marble block' Reisz microphone was used by the first German radio station broadcasting from Vox House on Potsdamer Platz in 1923, and later by the BBC. As a matter of fact, the Reisz mic was the brainchild of his employee Georg Neumann, who later achieved fame as the motive force behind the successful Neumann brand.

[2] Vogt was one of the 'tri' that patented the Tri-Ergon sound-on-film system in 1919; the others were Josef Engl and Joseph Massolle. Later the rights to the Tri-Ergon system were purchased by the Fox Corporation of the U S.