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Teach Yourself Electricity and Electronics Third Edition Book
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Teach Yourself Electricity and Electronics Third Edition Book

  • contained within the headset. There are portable cassette tape players and CD playersthat allow private hi-fi listening via headsets. The sound quality from these systems canbe excellent. The most important factor is the quality of the headset.A headphone radio should never be worn while driving a car or truck, while ridinga bicycle or motorcycle, or while jogging in traffic. The music obscures external soundsand increases the risk of an accident. If you want to walk or jog while wearing a head-set, do it someplace where cars never go. Don’t even think about getting behind thewheel of a motor vehicle with a headset on.Another form of portable hi-fi set is popularly known as a boom box. It can pro-duce several watts of audio output, and delivers the sound to a pair of speakers builtinto the box. A typical boom box is about 8 in high by 18 in wide by 6 in deep. It in-cludes an AM/FM radio and a cassette tape player; some also have CD players. Thesystem gets its name from the amazingly loud bass acoustic energy peaks its speak-ers can deliver.Quadraphonic soundQuadraphonic sound refers to four-channel audio recording and reproduction. It isalso called quad stereo or four-channel stereo.A conventional stereophonic circuit splits sound into two channels, the left channeland the right channel. In a quad stereo system, both of these channels are separatedinto front and rear components. In a true quadraphonic system, each of the four chan-nels is independent of the other three. This is not the case in all so-called quadraphonicsystems. Although true quad sound needs four tracks on a recording, some systems usetwo tracks and combine the left and right channels in phase quadrature (90 degrees outof phase) to obtain the front and rear signals.Figure 31-8 shows the ideal placement of the speakers with respect to the lis-tener in a quadraphonic sound system. The speakers should be level with the lis-tener, equidistant from the listener, and separated by angles of 90 degrees from thelistener’s point of view. If the listener is facing north, the left front speaker is to thenorthwest, the right front speaker is to the northeast, the left rear speaker is to thesouthwest, and the right rear speaker is to the southeast. This provides optimum bal-ance, and also facilitates the greatest possible left-to-right and front-to-rear contrastin the perceived sounds.It is possible to add two more channels to quad sound, placing a fifth channel abovethe listener and a sixth channel below. These might be called “zenith” and “nadir” chan-nels, respectively, and the system called hexaphonic sound. The main problem withthis scheme is that the optimum placement of the listener is critical and rather bizarre.The ideal arrangement would require that the user sit or lie suspended in the exact spa-tial center of a perfectly cubical room. However, some audiophiles might put up withthat to enjoy the effects.Recorded MediaAudio music recordings are available in three traditional forms: vinyl disk, compactdisk, and magnetic tape. A fourth scheme, digital audio computer files, is not dis-cussed here; this technology falls into the category of personal computing.Recorded media597