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THIS guide has already run through most of its pages but many things still remain to be said to clarify some of the obscurities that have arisen in audio and high fidelity. The fundamental approach to high fidelity is through an understanding of audio circuits, but you cannot stop at circuits because there is much more to audio than that. However, the biggest region of confusion exists in the matter of circuit choice and the components most closely associated with circuits, which we have covered. It has been impossible to cover, in this one guide, the range of additional factors such as, for example, the various mechanical features. A whole guide could be devoted--and probably will be to them: the drive for phonograph and tape systems, the properties of tone-arm and tape-transport mechanisms; different constructions and their relative merits; various approaches to correct pick up tracking on the phonograph; more data about the relative advantages of different transducer types for microphones and pick ups, as well as speakers. Then, different ways of constructing tape heads, various circuits for bias oscillators in the case of tape recorders and the question of mixing circuits for recording and choice of the best circuits for tuner design. But in this guide we have attempted to cover the things most basic to audio. In conclusion, however, we should include a few words about tidying up what we have; putting it all together, so to speak, and getting rid of the bits and pieces that might be lying around the living room to annoy "the other half." Much of this part of the story is esthetic rather than a matter of audio performance. At the same time, however, it is necessary to give some consideration to the performance aspect. What we have said in the preceding sections should help considerably in making many of these decisions. For example, the section on speaker distribution will help you determine how you want to arrange them to suit your home. Deciding this will help you make the necessary choice between a music comer or a music wall to house your equipment (or maybe you will prefer to use a combination, putting the speaker in a comer and having matching cabinetry for the control part that can be placed somewhere along the wall). Whichever you decide on, from the viewpoint of acoustic performance, you can find a suitable cabinet to house your equipment properly. Alternatively, if you prefer to buy a complete package system which fulfills these requirements, we have shown what to look for. A number of cabinetmakers are in business just to provide cabinets for components. In this way you can buy components made by specialists in each section of the art and fit them into a cabinet of your own choice that will fit in with the decor of your home. In deciding how to mount the equipment in the cabinetry, do not overlook some details about possible performance, from the electrical aspect as well as the acoustic. Avoid possible hum transfer, for example, between various sources of hum such as the power transformer of the main amplifier or the preamplifier and the pickup and its wiring. Usually the motor board of a turntable is laid out so that the normal position for mounting the pickup will not pick up too much hum from the motor. This is a feature that needs attention and usually has received it from the motor-board designer. But this care is lost if you mount the power transformer of a tuner, preamplifier or power amplifier immediately underneath where the pickup is going to be. A little careful thought here will avoid some tedious hum elimination later. Then consider possibilities of acoustic feedback from the speakers. It's very nice to get these wonderful low frequencies but they are rather apt to shake the walls and floors of houses and this can result in transmission of vibration back to the pickup or the tubes in the tuner and result in an acoustic feedback effect. Don't have any part of the system that works at low levels, like the pick up, the front end of the preamplifier or a tuner, too close to high level sound sources so that direct acoustic feedback can take place. At the same time watch out for mechanical feedback through floors, walls and cabinet housing. Select a method of mounting that provides good absorption of this feedback. Some turntable mountings in custom-built cabinets provide for the motor board to be suspended on foam rubber or equivalent absorptive material. This is a good precaution against acoustic feedback. Even though acoustic feedback may not be evident without such precautions, they can result in much cleaner reproduction. This is because the first effect due to acoustic feedback is not al ways a definite howl or vibration. It may result in distortion due to interference with the proper functioning of the low-level circuit or of the pickup. For example, the vibration may tend to lift the stylus out of the groove a little. Another thing to watch is the position of controls and the lengths of leads that may be involved. Connections between a preamplifier and power amplifier can be as long as you wish, if the preamplifier output has a cathode follower to make it low impedance. But some preamplifiers provide for remote control of the volume and tone control facilities. If this is done by bringing out high-impedance leads to a small remote panel, excessive lead lengths can result in the loss of high frequencies and possibly pickup of hum. It is better, if not convenient to place the pre amplifier in a position where the controls are readily accessible, to use a mechanical method of making them remote, such as a shaft extension. In conclusion we hope that we have not left any readers behind anywhere in this guide. 1 do not use "we" here in an editorial sense. While it has been my objective, as author, to make the material in this guide comprehensible to the widest possible audience, the publishers have given every cooperation possible to further this objective. I would like to take this opportunity of extending acknowledgment of this effort in helping to minimize any obscurities I may have left. Audio has become an extremely complex art (or should it be science?!). It started by being just the sound section of a radio transmitter or a receiver. But modern high fidelity imposes much more rigorous requirements, as this guide will have made evident. In sensory units one does not immediately get the impression of something very critical or difficult of achievement. For example, a frequency range (or should it be pitch range?) of 10 octaves and a loudness range of 120 decibels (I suppose 12 bels would be nearer what one would think of in sense units) does not seem so fantastic but, when you stop to realize that, in the acoustic realm, 20 Hz to 20,000 corresponds to wavelengths from 50 feet to 1 /20th of a foot, and the intensity range represents a power ratio of 1 followed by 12 zeroes, it seems as though we do have a problem. On top of this tremendous frequency and dynamic range, our binaural hearing capacity is capable of discriminating, not only between the frequency and intensity of different tones, but also the way in which different waves are radiated. We begin to realize that we have gotten ourselves into a very complex thing. |
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