Technical considerations

Chapter Technical considerations

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

  • If the listener moves a few feet, the antinodes will no longer be observed at 700 Hzand its harmonics. The frequency might change; the effect might diminish or even seemto disappear altogether. As produced by the set of baffles, the antinode for 700 Hz andits harmonics might well be confined to a single, small spot in the room.One of the most important considerations in acoustical design is the avoidance, tothe greatest extent possible, of significant nodes and antinodes at any frequency withinthe range of human hearing. The perfect acoustic chamber delivers sound effectively toall members of the listening audience, without favoring any particular regions of theroom or frequencies of the sound.Technical ConsiderationsHigh-fidelity, or hi-fi, audio systems can be found in most homes, in many cars andtrucks, in businesses, and even in government offices. They range in size from tiny“headphone radios” that operate from one AAA cell to huge, multicomponent sys-tems that consume thousands of watts and provide the sound for musical concerts inauditoriums and stadiums. However big or small the system, it must have certaincharacteristics to truly earn the label “hi-fi.”LinearityLinearity is the extent to which the output waveform of an amplifier is a faithful re-production of the input waveform. In hi-fi equipment, all the amplifiers must be aslinear as the state of the art allows.If you connect a dual-trace oscilloscope (one that lets you observe two waveformsat the same time) to the input and output terminals of a good hi-fi audio amplifier, theoutput waveform will appear as a vertically magnified duplicate of the input waveform.If you adjust the vertical gain control of the oscilloscope so the two waveforms have thesame peak-to-peak displacement on the screen, the input and output waveforms willlook identical. When the input signal is applied to the horizontal scope input and theoutput signal is applied to the vertical scope input, the display will be a straight line.Figures 31-2 and 31-3 illustrate the principle of linearity. The graph and waveformsin Fig. 31-2 show the characteristics of a linear circuit. The graph of the instantaneousoutput versus the instantaneous input is a straight line. When the input is a sine wave,the output is also a sine wave. Figure 31-3 shows what takes place in a hypothetical non-linear circuit. The instantaneous output-versus-input function is not a straight line.Therefore, the output waveform is not a faithful reproduction of the input, and distor-tion occurs. In this case, as the input increases, the output-to-input ratio (amplifica-tion factor, or gain) decreases, as indicated by the decreasing slope of the curve. Athigh input levels, the circuit doesn’t amplify as much as it does at low input levels, whichflattens the peaks of the output wave. This happens with all amplifiers if the input sig-nal amplitude is great enough. In some radio-frequency circuits this is all right; in hi-fiaudio systems, it is not.Linear amplifiers are designed to work with input signals up to a certain peak (max-imum instantaneous) amplitude. If the peak input exceeds this level, the amplifier willbecome nonlinear, and distortion will result. In a hi-fi system equipped with VU or Technical considerations587