Stereophony – a series of perspectives Richard Hallum, M. Mus. Tech (merit) 1 Part 1: What exactly IS stereo? Stereophonic sound reproduction is not simply twice mono [1]. A second mono channel can be advantageous to provide increased coverage or even to give some arbitrary impression of difference (a second loudspeaker could, for example, be equalized differently). However, the point of adding a second channel is to specifically create an artificial soundstage between the two loudspeakers. While this definition can now be taken for granted, it is interesting and informative to look at the origins of stereo. The early days The idea of reproducing spatial sound goes back some 135 years. This was the time when the electrical age of the industrial revolution was born, and an event was held in Paris to show developments in electrical technology. This was one of several large electrical exhibitions that were held in the 1880s and 1890s. The “International Exposition of Electricity”, held in 1881, showcased such things as electric lighting with Edison and others presenting their incandescent lightbulbs. One of the exhibits was a ‘stereo telephone’. By 1881 Alexander Graham Bell had a working model of his telephone but it was the Frenchman Clément Ader whose invention was displayed [2]. Perhaps the British Government’s decision not to waste public money sponsoring the event was the reason. Each night music was performed at the Grande Opera and people could listen for a few minutes on telephones about two kilometers away at the Palais de Industrie, where the exposition was being held. An array of ten carbon microphones was placed along the width of the stage. Each of these was wired to eight listening stations at the far end. One might think that since the telephone was still in its infancy that for members of the public to simply hear the performance would have sufficed, but Ader added the experience of ‘stereo’. Each person listening held two earpieces, one for each ear. Each earpiece presented the performance from a separate location on the stage (e.g. microphones 1 & 6, 2 & 7, and so on) thus enabling the listener to gauge the lateral position of the performer. Luckily, the experiment was successful, and ‘stereo’ was born 2 . Several years after the Paris expo of 1881 the invention was used commercially in France and England. 3 The telephone and its required network was developed, as was electric power distribution, but the next milestone for stereo was not to come until 50 years later. 1 Senior Tutor, Music & Audio Institute of New Zealand 2 An attempt to connect another theatre to the exhibition failed, due to interference from the footlights. 3 In France from 1890 to 1932 as the Théâtrophone, and in England from 1895 to 1925 as the Electrophone.