Anything involved in the process of the transfer of a SIGNAL from acoustic to electrical form, or vice versa or just the modification of the electrical form of an acoustical signal, goes in the field of the Electroacoustics.
An adjective describing any process involving the transfer of a SIGNAL from acoustic to electrical form, or vice versa. Most commonly, TRANSDUCERs such as the MICROPHONE or LOUDSPEAKER are examples of this process. Compare: AUDIO.
Although the term most precisely refers to a signal transfer from electrical to acoustic form or vice versa, it also is often used more loosely to refer to any process for the electronic generation and/or manipulation of sound signals, including techniques of SOUND SYNTHESIS for the electronic or digital generation of such signals. When the purpose of such manipulation is artistic, the result is commonly called electroacoustic music.
A large number of sounds commonly heard in the contemporary environment are electroacoustic in origin, ranging from HUMs and flat line sounds (see STATIONARY SOUND), through electrically driven devices, to the electroacoustic reproduction of sound via the TAPE RECORDER, phonograph record or compact disc, radio, television, telephone, film track, etc. As a result, it is now often claimed that the most universal acoustic instrument is the LOUDSPEAKER.
Electrification of sounds previously powered by other means will change their character, including waveform, timbre, duration, intensity and envelope characteristics. For instance, the ability to SWITCH an electronic siren on and off abruptly produces a faster and more startling ATTACK, a brief DECAY (contrasting sharply with the prolonged decay of mechanical sirens), higher intensities, and patterns of modulation, called the 'wail' and 'yelp' modes, that were previously impossible to obtain. See also: DISAPPEARING SOUND.
Each stage of an electroacoustic communication chain introduces a certain distortion, as well as NOISE, into the system. For instance, the DIRECTIVITY and FREQUENCY RESPONSE patterns of microphones and loudspeakers influence the way in which a sound is recorded or reproduced. The limited DYNAMIC RANGE of electroacoustic systems, compared to that of the ear or the original sound or environment, requires techniques of signal compression (note the further use of this technique in radio as described under COMPRESSION). Compare: FIDELITY.
More subtly, the split between the original sound and its electroacoustic reproduction, which has been termed SCHIZOPHONIA, changes the way in which the sound will be heard by the listener. Sounds may appear in unusual or inappropriate settings (e.g. orchestral music in elevators) and may thereby contribute to SOUND POLLUTION; sounds may be exact repetitions more often than they are unique occurrences; sounds may occur at intensities, durations, densities and speeds never before experienced, as well as in succession or simultaneity with other sounds to an arbitrary degree of complexity. All of these new possibilities can change a listener's habits or modes of listening, particularly through frequent exposure; some changes may dull, others stimulate, listening attitudes and abilities.
There are three characteristic processes involved in electroacoustics, perhaps the most basic of which is the process of "transduction", that is, the conversion of acoustic energy to an equivalent electrical signal, and vice versa. Secondly, there are electrical devices which modify and manipulate such signals, and thirdly, devices which store and/or retrieve these signals. The actual devices involved are considered in a separate section of this document. In addition, digital recording and playback converts the audio signal to digital form and vice versa.
In addition, the field of electronic and computer music substitutes signal generation (sound synthesis) for the initial process of transduction from an original acoustic source. Here we present the terms which describe the essential characteristics of all of the electroacoustic transfer processes mentioned.
See also: DIFFUSION, ELECTRONIC MUSIC, MOOZAK, MUSIQUE CONCRETE, SOUND OBJECT, STEREOPHONIC.
Now that you know a little more of how the human hearing and speech systems work, you are ready to learn how electrical systems convert acoustical sound to electrical sound or how they convert electrical sound to acoustical sound. A good example of this is a sound system in an auditorium. When you speak into a microphone, it converts your acoustical sound into electrical sound, then that sound is converted from electrical back to acoustical at the loud speaker.
In this module you will explore sound from the perspective of the electrical engineer. You will learn about electricity, amplifiers, electronic circuits, microphones, loudspeakers, and the role each of them play with sound.
You will also learn about electronic recording systems and how they record sound, and last but not least we will look at what components are necessary for building a Hi-Fi stereo system for your home. There is even an exercise where you can design your dream system.
You interact with electricity everyday, but do you have an understanding of how it works and the principles involved? One of the of the most important tools you will use to understand electricity is Ohms Law. Named after George Simon Ohm who discovered it, Ohms Law describes the relationship between voltage, current, and resistance. To be more precise; "current is directly proportional to voltage and inversely proportional to resistance." This law can be a big help to you in everyday life. Using it you can determine how much current a household appliance will use and if using it will overload a circuit.
In this chapter you will learn about Ohms Law and how to apply it. You will also learn about AC current, and the role that capacitors and inductors play with it. You will also learn about electrical resonance, diodes, transformers, and power transformers.
This chapter builds upon the electrical principles you learned in chapter 18. Your home stereo system uses these principles to deliver the sound it does.
A filter is used to get rid of unwanted sound or certain frequencies. An amplifier takes a small amount of power and uses it to control a large amount of power. An oscillator is an electrical circuit that is unstable and causes it to produce electrical waves. An example of this is a audio generator that can be tuned to produce sound at a certain frequency. Electronic keyboards are full of oscillators.
In this chapter you will learn about filters, amplifiers, and oscillators and how they function. You will learn the basic electronic theory and formulas for them.
Filters
high-pass
band-pass
band-reject
notch
cutoff frequency
Amplifiers
Transistors
PNP & NPN
Voltage gain
Current gain
Voltage amplifier
Power amplifier
Distortion in Amplifiers
Feedback
Operational Amplifiers
Oscillators
Function generators
Microphones take sound waves and convert them to electrical signals. These signals can then be modified and amplified before being presented to loudspeakers which turn the signals back in to acoustic waves we can hear. Loudspeakers convert electrical signals into sound waves. Between the microphone and loudspeakers is usually an amplifier. We use this type of a set-up when we want to amplify sound waves.
In reality there is no way to amplify sound waves, or add energy to them. To do this we must convert the sound waves to electrical signals and them amplify them and convert them back to sound waves again.
In this chapter you will learn the characteristics of various types of microphones as well as concepts of amplifiers and AM/FM tuners.
Loudspeakers are a major componant in any audio system. They convert electrical signals into sound we can hear.
In this chapter you will learn about several types of loudspeakers and the principles by which they work. You will also learn about loudspeaker enclosures and the effect they have on the sound you hear.
The mechanical recording of sound was invented by Thomas Edison in 1877. His
idea for it's possibility came while he was trying to invent a better way to
record telegraph messages on some form of paper or foil. He noticed when he used
the foil that it would create a indentation as the needle moved back and forth.
This caused him to wonder if he could have sound waves cause a needle to make
different levels of indentation in correlation with the frequency. These
indentations would be a "recording" that could be played back. It worked, and
thus was born the Edison phonograph.
Vinyl records, popular until CDs came along, used these very same principles for
recording and playback. The only difference is that the needle on modern record
players move horizontally instead of vertically as they did in Edison's
phonograph.
Everyone who loves listening to music, wants to be able to fill their listening room, or their car with high quality sound, especially when listening to CDs.
In this chapter, we will look at the various components that make up a high fidelity sound system. Although some of them (i.e. record player) are not used as much anymore, they will help you learn important principles that can assist you when purchasing your components for your system.
Disc recording
Dynamic range
Phonograph pickups
Stereophonic discs
Magnetic tape recording
Tape speed and frequency response
Bias and equalization
Tape noise
Multiple tracks
Digital tape recording
Everyone who loves listening to music, wants to be able to fill their listening room, or their car with high quality sound, especially when listening to CDs.
In this chapter, we will look at the various components that make up a high fidelity sound system. Although some of them (i.e. record player) are not used as much anymore, they will help you learn important principles that can assist you when purchasing your components for your system.