Dynaquad, or DY, was a matrix decoder 4-channel quadraphonic sound system developed by Dynaco in 1969. The system originally had four speakers that were arranged in a diamond shape. Originally, it was used as a derived four channel "decoding" system, where the back channels played ambient sounds recovered from standard stereo sounds. It is based on the Hafler circuit, along with the ElectrovoiceStereo-4 system. As such it wasn't used initially used as an encoding method. Four channel record pioneers Vanguard Records started to use it as an encoding/decoding matrix in 1971. The encoding was unusual in that, like the Stereo-4 system, it did not use 90° phase shifters. There were few albums released in the format. A much simpler form of the Dynaco patent keeps the four speakers in their normal left and right plus front and rear positions. The left and right rear speakers are connected to the two-channel stereo amplifier via a passive matrix circuit, while the front ones stay directly connected to the amplifier. A lot of stereo material, recorded with a central, non-directional microphone placed in front of the orchestra, possessed suitable phase difference stereo signals. When taken from this passive speaker matrix for the rear channels, they produced a quasi-quadraphonic effect at low cost. Especially for classical music, a fine impression of concert-hall ambiance is achieved with such a system. Dynaco sold this matrix circuit with a large and triple high-wattage potentiometer inside, for a sum equivalent to 70 euros or so in present-day currency. Electronic amateurs could build the circuit much more cheaply – e.g., with a four-position switch using fixed resistors of, for example, 20, 10, 5 and 0 ohms. Because, in practice, only the highest level was of any use, a more basic set-up with only the fixed 10 ohm resistor at close-to-zero cost is possible. The system requires relatively flat impedance curves for the rear speakers to work properly, which was often the case in the tube-amplifier days. Tube amplifiers had a constant impedance over a wide range, and worked best with high-efficiency speakers. Later on, when transistor amplifiers were used, speakers tended to lose that design feature. The system worked best using a transistor-based stereo amplifier, low-efficiency front speakers, and high-efficiency, constant impedance rear speakers.
During 2016, recording engineer Stephen W Desper in several online forum posts publicly refuted the common rumour that a number of Beach Boys recordings had been mixed and released in Dynaquad or any other four channel matrix. He confirmed that he had developed a two channelvirtual surround matrix that had only been partially realised by the record companyon the Beach Boys releases.
