Speakers

Speakers use a vibrating membrane or diaphragm to produce sound in response to an electric, digital, or wireless signal. They include an integral or external amplifier, drivers, and a crossover circuit that divides an audio signal into specific bands. There are three basic types of speaker drivers: woofers, tweeters, and midrange devices. Woofers, the largest drivers, are designed to produce low frequency sounds. Tweeters are much smaller than woofers and are designed to produce higher frequencies. Speakers are often housed in a case, chassis or enclosure made from wood, metal, plastic, or composite materials. Sealed speaker enclosures or acoustic suspension enclosures prevent air from escaping so that the internal air pressure is constantly changing. Other enclosure designs redirect the inward pressure outward, using it to supplement the forward sound wave. In these bass reflex speakers, the backward motion of the diaphragm pushes sound waves out of the port in order to boost the overall sound level. 

Performance specifications for speakers include sound pressure level, nominal input power, input impedance, frequency response, speaker size, and speaker weight. Sound pressure level (SPL) is a rating which corresponds to a maximum or nominal amount at a specific frequency within the dynamic range. SPL is usually measured in decibels (dB) or with the A-weighted value. Nominal input power is the typical design power that speakers require. Input impedance is matched to the output impedance of the driving amplifier for the most efficient and accurate sound replication. Frequency response or dynamic range is the range of frequencies over which speakers operate while meeting performance specifications. Speaker size is measured in English design units such as inches (in) or metric design units such as centimeters (cm). For round or square speakers, the speaker size is the diameter or width. For rectangular or oval speakers, the speaker size is the shorter dimension. Speaker weight is measured in grams (g) and includes the weight of the speaker’s enclosure or any attached features. 

There are many applications for speakers. Active noise cancellation devices identify noise frequencies and produce offsetting sound signals that are 180º out of phase. Dynamic receivers are compact speaker/receiver combinations that are suitable for earphones, cell phones, hearing aids, and other designs where space is at a premium. Some speakers are used in aerospace, automotive, telephone, security, paging and other voice communication applications. Others are used in headsets or helmets, consumer electronics or gaming, or public address systems. Professional-grade audio speakers are designed for recording studios or television and radio broadcast facilities and equipment. Fire proof and waterproof speakers are also available.

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