Dynaquad

Dynaquad, or DY, was a matrix 4-channel quadraphonic sound system developed by Dynaco in 1969.

The system originally had four speakers that were arranged in a diamond shape (centre-front, centre-left, centre-rear, centre-right). Originally (first available in 1969 with th Dynaco SCA-80Q amplifier [1]), it was used as 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 Stereo-4 system. As such it wasn't used initially used as an encoding method, and was limited only as a decoding solution.

Four channel record pioneers Vanguard Records started to use it as an encoding/decoding matrix in 1971.[2] The encoding was unusual in that, like Electrovoice's Stereo-4 system, it did not use 90° phase shifters. There were few albums released in the format, the most being by The Beach Boys.

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.[3][4] A lot of stereo material, recorded with a central, non-directional microphone (so-called kidney sensitivity diagram) placed in front of the orchestra, possessed suitable difference signals across the stereo signals. When taken across this passive speaker matrix for the rear channels, these produced a quasi-quadraphonic effect at low cost (the patent specifies the use of one fixed 10 ohm resistor and three variable 20 ohm resistors in a star arrangement). Especially for classical music, a fine impression of concert-hall ambiance is achieved with such a system.[2]

Dynaco sold this matrix circuit (Dynaco QD-1 Quadaptor, introduced in 1971[3][4])with a large and triple high-wattage potentiometer inside, for a sum equivalent to 70 euros (about 100 US dollars) or so in present-day currency.

Electronic amateurs could build this circuit much more cheaply – e.g., with a four-position switch (four steps in level of the rear sound from min. to max. level) using fixed resistors of, for example, 20, 10, 5 and 0 (short-circuit) 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. Note that the system requires more or less 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. (Lower impedance meant higher power output for these amplifiers, compensating for the lower efficiency of such designs.) The system worked best using a transistor-based stereo amplifier, low-efficiency front speakers, and high-efficiency, constant impedance rear speakers.

Encoding matrix

Dynaquad encoding Matrix[5] Left Front Right Front Left Back Right Back
Left Total 1.0 0.0 0.64 -0.36
Right Total 0.0 1.0 -0.36 0.64

Decoding matrix

Dynaquad decoding matrix Left Front Right Front Left Back Right Back
Left Total 1.0 0.0 1.0 -1.0
Right Total 0.0 1.0 -1.0 1.0

Dynaquad records[6]

References

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