For 65 years, stereo sound has been widely used and remains in demand all over the world, which cannot be said about the quad sound, which never caught on. This result came as a surprise to absolutely all of its developers and manufacturers. And there are reasons for this.
The recorded fact of the very first application of the stereo effect in sound dates back to 1881. In Paris, special booths were equipped at the electrical exhibition. Visitors could listen to the opera with headphones in stereo. Specialists installed two powerful microphones in the opera building. The sound was broadcast using two telephone lines to the headphones separately. Eyewitnesses who attended the event were amazed at these opportunities. Unfortunately, the recording was not possible.
1. From stereo to quad
At the beginning of the twentieth century, various experiments were carried out on a regular basis in the field of stereo sound recording. But the technologies used were not only very complex, but also expensive.
Interestingly, the tape recorder turned out to be the first mass-produced stereo equipment. It was invented much later after the advent of the turntable with gramophone records. Stereo tape recorders were first produced by RCA from America in 1955. In 1958, three more years later, the production of stereo phonograph records and, accordingly, turntables was launched.
For almost ten years that followed, mono and stereo existed in parallel and did not even compete. Mono was considered budget-class equipment and was available to everyone. The stereo was of a higher quality, and hence the price. People with higher incomes could afford it.
By the end of the sixties of the last century, a number of manufacturers came to the conclusion that it was time to start producing another type of device - one that would reproduce quad sound. The reason for this decision was not too good quality equipment, but the desire to make a certain profit. The creators decided that if the stereo found its consumer, albeit not immediately, then the situation with the quad will be similar. But you can earn more on this new product.
Quad recording requires four channels. They are also in stereo tape recorders - two in one direction and two in the other direction. By and large, you need to slightly alter a regular stereo tape recorder to make it a quad.
Well, since there was no room for two additional channels, the creators went for a trick. JVC (Japan) and RCA (USA) have developed the CD-4 standard, which is quite an interesting solution. Its principle lies in the fact that a frequency band of 20 Hz-40 kHz is recorded on each of the channels of the plate. The band is divided into two front stereo channels with a frequency of 20 Hz-15 kHz. With the help of the module, the rear channels (also stereo) were transferred to the band with a frequency of 18 kHz to 45 kHz. This is FM-PM-SSBFM modulation type.
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Naturally, absolutely all manufacturers wanted to make money, so they enthusiastically began to develop and release new improved models of amplifiers of this type.
The Soviet radio industry also did not stand aside. The first samples of "Phoenix-002-Quadro" (a player improved to a certain level), Electronica TDK-3 "KVADRA" (headphones), "Jupiter-Quadro" (almost the same, but modified tape recorders and amplifiers) appeared in the Union.
2. What is the reason for the lack of demand
If for a short period of time the serial production of the amplifier was carried out, then all other developments were postponed until there was a demand for this type of sound in the Soviet Union. But he never appeared in our country.
In other countries, the situation was no better. Even super-expensive ads didn't do the trick. There was no excitement with sales. It can be assumed that the problem was that with a low listening effect, the price of the equipment was too high.
The bottom line is that we have about ten years of promotion, many high-end equipment models, colossal costs and abandonment of the standard. Dolby Digital 5.1 (another standard) did not fix the situation either. Home theaters were interesting at the time of release, but they were gradually forgotten.
For developments that may be more in demand, read the article: Smart metal and needle-free injection: 7 nanotechnologies that are shaping the future.