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The idea of omnidirectional loudspeakers is not new. The earliest one that we are aware of is the American Eico HSF-2, from 1958. It was designed by the prolific American audio engineer, Stewart Hegeman, who also designed the Harmon-Kardon Citation II amplifier and the original Dynaco tuner. The Eico HSF-2 used a vertically firing 8.5-inch woofer, with a diffuser mounted directly over the cone to defect the sound waves outwards. The back of the woofer was coupled to a slot loaded conical horn, a technique that was invented and later patented by Hegeman. The tweeter was mounted directly above the woofer. Unusually this had a cone shaped rather like a lily flower. This was apparently done to give the tweeter a wider frequency response. Set inside the tweeter cone was a plug that deflected its radiation outwards. In an article for the magazine Radio Electronics, Hegeman said that two of his objectives in designing the HSF-2 were: To create a loudspeaker with an omnidirectional radiation pattern, to avoid the beaming of the mid-range and high frequencies that occurs with conventional loudspeakers, which he said caused, “unpleasantness and lack of naturalness in reproduction caused by the loss of the spatial characteristics typical of live sound”. To create a loudspeaker that was phase linear, thereby accurately preserving the phase relationships of all the individual tones that make up the complex musical signal.
This was quite a complex design and it took Hegeman three pages in the article in Radio Electronics to summarise. The complexity was also reflected in the price, which in 1958 was $139.95.
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