Quadraphonic

Quadraphonic, or quadraphonic sound, is a four-channel audio reproduction system that places four loudspeakers around the listener, typically forming a square around the listening position (front-left, front-right, rear-left, rear-right). The aim is to reproduce a more immersive sound field than conventional stereo.

In consumer use, four-channel sound was achieved either by matrix-encoded formats that derived four channels from two-channel sources, or by discrete four-channel carriers. The two popular matrix formats were SQ (Stereo Quadraphonic) and QS (Quadraphonic Sound). SQ encoded the four channels in two channels using phase and amplitude relationships and required a compatible decoder. QS similarly encoded four channels into two, but with a different matrix and decoding approach. A true four-channel system, CD-4 (Quadradisc), carried all four channels discretely on vinyl using a high-frequency subcarrier around 45 kHz, requiring a special phono cartridge and demodulator.

Quadraphonic products were introduced in the early 1970s and achieved cultural visibility through albums and hardware; however, the format competition, higher equipment costs, and uneven compatibility limited adoption. The market largely collapsed by the late 1970s, though the concept influenced later multichannel standards.

In modern times, quadraphonic is mainly of historical interest but contributed to the development of surround sound. In cinema, four-channel sound evolved into more advanced multichannel formats such as Dolby Digital and DTS, while home enthusiasts sometimes recreate quad setups for archival releases or specialized audio systems.