Quadraphonic sound

Quadraphonic sound refers to 4-channel audio recording and reproduction.  It is called as quad stereo or 4-channel stereo.A conventional stereophonic circuit splits the sound into 2 channels, left channel and right channel. In a quad stereo system, both of these channels can be separated into front and rear components.  In a true quadraphonic system, each of the 4 channels is independent of the other 3. This is not the case in all so called quadraphonic systems. Although true quad sound requires 4 tracks on a recording, some systems use 2 tracks and combine the left and right channels in phase quadrature (90° out of phase) to obtain front and rear signals.

Figure given to us shows the ideal placement of speakers with respect to listener in a quadraphonic sound system. The speakers must be level with the listener, equidistant from listener, and separated by angles of 90° from listener’s point of view. If listener is facing north, the left front speaker is to northwest, right front speaker is to northeast, left rear speaker is to southwest, and right rear speaker is to southeast. This provides optimum balance, and facilitates the greatest possible left to right and front to rear contrast in perceived sounds.

It is possible to add 2 more channels to quad sound, placing a 5th channel above the listener and a 6th channel below. These might be called as zenith and nadir channels, respectively, and system is called as hexaphonic sound. The main problem with this scheme is that optimum placement of listener is critical and rather than bizarre. The ideal arrangement would require that the user sit or lie suspended in the exact spatial center of a perfectly cubical room. But, some audiophiles might put up with that to enjoy effects.