Not all sound reaches us through loudspeakers, and the advent of the Sony Walkman has led many listeners back to headphone stereo. In this chapter, Ian Sinclair shows the very different type of problems and their solutions as applied to this alternative form of listening.
A Brief History
The history of modern headphones can be traced back to the distant first days of the telephone and telegraph. Then, headphone transducers for both telephone and radio worked on the same moving-iron principle—a crude technique compared to today’s sophistication, but one which served so well that they are still to be found in modern telephone receivers.
Moving-iron headphones suffered from a severely restricted frequency response by today’s standards, but they were ideal. These sensitive headphones could run directly from a “cat’s whisker” of wire judiciously placed on a chunk of galena crystal. Radio could not have become such a success so early in its development without them.
As “cat’s whiskers” bristled around the world, these sensitive headphones crackled to the sound of the early radio stations and headphones became as much a part of affluent living as the gramophone. But the invention of sensitive moving-iron loudspeakers was the thin end of the wedge for headphones. Although little more than a telephone earpiece with a horn or radiating cone tagged on (with developments like the balanced armature to increase sensitivity and reduce distortion), they freed individuals or even whole families from the inconvenience of having to sit immobile.
Later, in the 1930s, with the invention of the then revolutionary but insensitive moving-coil loudspeaker and the development of more powerful amplifiers to drive them, headphones were largely relegated to the world of communications, where they stayed until the mid- 1950s, when they underwent something of a revival.
Why the change? In a nutshell, stereo. Although stereo was developed in the thirties by Alan Blumlein, it was not to see commercial introduction, via the stereo microgroove record, until the 1950s. Hi-fi, as we now know it, had been developing even before the introduction of the LP, with the 78 rpm record as its source, but the introduction of the microgroove record and then stereo were definitely two large shots in the arm for this emergent science of more accurate sound reproduction. Stereo was also a major stimulus to headphones, and although it may seem an obvious thing now, it took an American Henry Koss to think of the idea of selling stereo headphones as “stereophones” and creating a whole new market for quality stereo headphone listening. Needless to say, Koss has not looked back since and neither has Sony since the introduction of its first Walkman personal cassette player. Ironic, perhaps, because stereo was originally developed by Alan Blumlein for loudspeaker reproduction!