Back to Basics Audio is a thorough, yet approachable handbook on audio electronics theory and equipment. The first part of the book discusses electrical and audio principles. Those principles form a basis for understanding the operation of equipment and systems, covered in the second section. Finally, the author addresses planning and installation of a home audio system.
Notes on home theater systems, speaker placement and calibration
System planning, diagram analysis, and signal processing
Easy introduction to practical audio, acoustics, and electrical theory
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Audio is Acoustic, Mechanical, and Electric. Sound, or wave-motion in air, is sensed, processed, and reproduced by electro-mechanical and electronic devices. It wasn’t always electric, but that’s the medium we use to do almost everything, and do it better.
Sound is transient, it’s gone as soon as it happens, but it can be examined and its equipment tested, largely with continuous tones, or in the steady state. More details of the nature of sound are given in Chapter 4, but as a necessary background to the technology of audio, the briefest account of electricity and its associated parts occupies most of this chapter.
ELECTRONICS AND ELECTRICITY
All matter is made up of identical Neutrons, Protons, and Electrons. In various combinations they form atoms; the basic clusters that form the elements. In turn, one or more atoms make up a molecule, the smallest functional form of an element or compound. The atomic weight of a stable element is determined by the number of negative charge electrons circling the nucleus of its atom, which in turn is made of an equivalent number of positive charge protons, plus various numbers of neutrons.
Electrical conductors have loosely bonded electrons in their atoms. Electrons are able to flow from atom to atom in conductors, and since they have a negative charge, convention says that positive current flows in the opposite direction to electron flow. Electrons flow from negative to positive in conductive media because unlike charges attract, so current flows from positive to negative. Poor conductors have closely bonded electrons, making flow difficult. They have high resistance.
All the use we make of electronics is based on working with the outer electron shell of atoms. We can make electrons pass from atom to atom. By heating conductors we can make them incandescent; photon emission is an indication of super-excited electrons. In fluorescent, carbon and xenon arc, and neon lamps, we see a demonstration of plasma; conducting, ionized gas; the fourth state of matter. Maser and laser technology, including semi-laser devices like LEDs (light emitting diodes), proves the connection between excitation of electrons by one form of energy, and production of microwaves or coherent light (single frequency or narrow band photon emission) by the electrons thus stimulated.
Nucleonics, on the other hand, is concerned with mobilizing the neutrons and protons that form atomic nuclei, in order to release energy. Nuclear engineering is beyond the reach of most people because it’s expensive and difficult to handle.
Electronics, understood and thoroughly exploited, is easy to get into, and safe as a box of matches.
AN ELECTRICAL CIRCUIT
1. When the switch in the circuit of Fig. 1.1 is open, voltage is present across the battery and therefore across the switch. But no current flows.
Fig. 1.1 An electric circuit.
2. When the switch is closed, current flows through the (lamp) load, limited by the combined resistance of the load, the source, the conductors, and the switch.
3. Work (Watts) done in the load equals electrical pressure (Volts) times current (Amps). A small proportion is wasted in heating the other resistive components, including the battery.
4. The current (flow) at any point in the circuit is the same at any other point (in a simple circuit that does not branch).
5. Electricity requires a complete circuit for current to flow.
ELECTRICAL PRINCIPLES
Volts, Amps (amperes) and Ohms are inter-related quantities, and refer to the physical properties of Electricity. Without an easily acquired understanding of these three basics, very little progress can be made in any application. A working knowledge is given in the following few pages, containing nothing more complex than simple equations.
Voltage is Electrical Pressure. Just as water in a tank exerts physical pressure on the pipe it supplies, so a voltage source exerts electrical pressure, or a potential difference, at the parts of a circuit to which it is connected. Voltage is also referred to as Electromotive Force, or EMF.
VOLT : The unit of ELECTRICAL PRESSURE
Symbol : V
Amperes denote Electric Current Flow. When pressure is released, water in a pipe flows. The flow rate could be expressed in liters per minute. A fundamental observation is that the flow rate is the same at any point in the pipe, assuming it does not branch. Three liters per minute at one end guarantees three liters per minute at the other. Electric current flow is the same.
AMP : The unit of ELECTRIC CURRENT FLOW
Symbol : I
Ohms are units of Electrical Resistance (to current flow). Again consider the water pipe. If it is rough inside, or narrow, it could be said to have high resistance. Even if it is perfectly smooth, it will have some resistance. Resistance is also a feature of Electrical Conductors.
The degree of resistance depends on the material and cross section area of the conductor, at normal temperatures.
OHM : The unit of ELECTRICAL RESISTANCE
Symbol : R
OHM’S LAW
Current flow is the operative factor in an electric circuit. Voltage makes it happen. Resistance retards it. This all works by good fortune, since without resistance, the simple act of switching on a light would initiate enormous currents, and other means would have to be found to limit the flow. Resistance is like friction, without which we would all need spiked shoes to stand erect.
Volts and amps are related by the equation:
AMPS EQUALS VOLTS DIVIDED BY OHMS
This is the basis of Ohm’s Law.
Current flow is directly related to Voltage, but inversely to Resistance. More Volts, more Amps, but more Ohms, less Amps.
USING OHM’S LAW
The equation can be converted to determine any one quantity, given the other two, by the rules of simple equations:
A figure can cross the equals sign provided it also crosses the divide line.
