Science universe: Physics articles

speaker The term speaker is a diminution of loudspeaker . The full word is now so rarely used, some catalogs do not recognize it as a search term. This encyclopedia acknowledges contemporary usage by using speaker rather than loudspeaker . A fully assembled consumer product can be referred to as a “speaker,” but it also contains one or more individual components that are described as “speakers.” To resolve this ambiguity, referring to the components as drivers is helpful, but this practice can create more ambiguity because other types of components are also called “drivers.” The only real guide to the meaning of speaker is the context in which it is used. For the purposes of this entry, a speaker is a sound reproduction device , distinguished from a typical electromagnetic transducer by being larger and more powerful, with a more linear frequency response. A transducer may be used as a noise-creating device to provide an alert, informing the user of the status of a piece of equip...

headphone The term headphone is used here to include almost any device that fits into or over the ear for the purpose of sound reproduction. ( Hearing aids are not included.) Because headphones are used in pairs, the term is usually pluralized. The term phones is fairly common as a colloquial diminution of headphones but is not used here. An earphone used to be a single sound reproduction device designed for insertion into the ear, but has become rare. Pairs of earbuds are now common. Because this encyclopedia assigns more emphasis to electronic components than to consumer products, this entry provides only a superficial overview of fully assembled headphones, and deals more with the drivers inside them, their principles of operation, and the general topic of sound reproduction. What It Does A headphone converts fluctuations of an electric signal into pressure waves that the human ear perceives as sound. It can be used for reproduction of music for entertainment purposes, o...

audio indicator An audio indicator is defined here as a noise-creation device that generates a simple tone or series of tones. Unlike a transducer , which requires an external source of AC to determine its audio frequency, an indicator contains its own electronics and requires only a DC power supply. Either of these components is often described as a beeper or buzzer . While piezoelectric alerts formerly used crystals, only the more modern piezoelectric type that uses a ceramic wafer will be considered here. What It Does When DC power is applied to an audio indicator , in its simplest form it creates a continuous or intermittent tone of a fixed frequency. This is called an alert . Audio alerts are used in microwave ovens, washer/dryers, automobiles, gasoline pumps, security devices, toys, phones, and many other consumer products. They are often applied with touch pads, to provide audio confirmation that a tactile switch has been pressed. A few indicators are programmed to c...

transducer The term transducer is used here to describe a noise-creating device that is driven by external electronics. By comparison, an audio indicator (discussed in the next entry) contains its own internal electronics and only requires a DC power supply. Either of these components is often described as a beeper or buzzer . A speaker , more properly termed a loudspeaker , is an electromagnetic transducer but is seldom described in those terms. It has a separate entry in this encyclopedia and is defined here as a sound reproduction device that is larger and more powerful than a typical transducer and has a more linear frequency response. While piezoelectric transducers formerly used crystals, only the more modern piezo- electric type that uses a ceramic wafer will be considered here. Some transducers convert sound into electricity, but these are categorized as sensors , and will be discussed in Volume 3. The only transducers discussed in this entry are those that convert elec...