| Loudspeaker is a device for efficient sound transmission into surrounding space (air, water etc media), structurally containing one or more drivers & if required, acoustic design & additional electrical facilities (filters, transformers, regulators, etc.) .
Loudspeaker's head is a passive electro acoustic converter, designed to convert electrical signals (usually audio frequency) into acoustic signals.
Acoustic design is a design element, ensuring efficient emission of sound (acoustic screen, box, horn etc).
Electromagnetic heads (abbreviated as "loudspeaker"), sometimes even the loudspeakers are referred to as, are most commonly used in loudspeakers.
Functionally, telephones (earphones) are similar to loudspeakers, but, unlike loudspeakers, telephones are not designed for sound transmission into open space. Loudspeaker, designed as closed body of arbitrary shape (usually box, cube) is speaker system or (incorrectly) speakers.
Classification of loudspeakers:
Loudspeaker types depending on the sound emission method:
Dynamic loudspeakers;
Electrostatic loudspeakers;
Capacitor loudspeakers;
Electret loudspeakers;
Piezoelectric loudspeakers;
Electromagnetic loudspeakers
Ionophone;
Loudspeakers on the base of special type speakers (magneplanar, isodynamic, ribbon, orthodynamic, Heil emitters)
Functional types of loudspeakers:
Acoustic speaker system - speaker, designed for use as functional unit in consumer electronic equipment & has high-performance sound reproduction characteristics; Main article - Acoustic speaker System;
Subscriber loudspeaker - loudspeaker, designed to transmit LF wire broadcasting channels, Main article - subscriber radio unit;
Concert loudspeaker - has large volume, coupled with high-quality sound transmission;
Loudspeakers for warning systems & playback applications (loudspeakers of these systems are similar with respect to application, but somewhat different from other in respect to volume & sound quality);
Wall-mounted loudspeakers;
Ceiling loudspeakers;
Panel loudspeakers;
Outdoor loudspeaker - has more output, usually horn loudspeaker variant, in colloquial language "Bell";
Special speakers to work in extreme conditions - shock-proof, blast-proof & underwater;
Other special types of loudspeakers:
Loudspeakers for different purposes:
Acoustic speaker system;
Subscriber loudspeaker;
Outdoor speakers
Classification on other characteristics:
Single-band loudspeaker - loudspeaker, driver of which operates in same frequency band;
Multi-band loudspeaker - loudspeaker, whose drivers operate in two or more different frequency bands;
Cone loudspeakers;
Horn loudspeakers - loudspeaker, acoustic design of which is rigid horn;
Direct transmission loudspeaker
History of loudspeaker:
In 1876, Alexander Graham Bell patented the first electrodynamic driver (capsule) as one of the components of his telephone. In 1878, design was improvised by Werner von Siemens. In 1881, Nikola Tesla announced invention of similar device but could not patent it.At the same time, Thomas Edison received British patent for system, which used compressed air as sound amplification mechanism in his early cylinder phonographs (see Siren (acoustics) & eventually fitted usual metal horn, air vibrations in which were caused by membrane, tied to a stylus. In 1898, H. Short patented design of dynamic loudspeaker, driven by compressed air, and then sold the rights to Charles Parsons, who got several British patents in early 1910. Several companies, including Victor Talking Machine Company and Pathe (Pathe) manufactured record players, which used loudspeakers, driven by compressed air. However, such devices (indirect emission loudspeakers) have found only limited use owing to poor sound quality & inability of reproducing low volume sounds. Varieties of similar systems were used in sound amplifying facilities (for large areas, stadiums etc) & much less frequently - other versions - which are used in industry in vibration testing facilities, for example, for testing space equipment on resistance to low frequency vibrations, produced during launching of rockets.
Modern design of driver with a moving coil was developed in 1898 by Oliver Lodge. Principle was patented in 1924 by Chester W. Rice & Edward W. Kellogg.
First loudspeakers with electromagnets were very huge in size & powerful permanent magnets - very difficult to procure because of being costly. Coil of electromagnet, which is being called a field, is magnetized by current, passing along the other coil of loudspeaker (actuating coil). Such connection has dual role, because it performs filtration of voltage, supplied to amplifier, to which the given acoustic speaker system is connected. Passing along the coil, AC ripple is amplified; however, AC frequencies tend to modulate audio signal, supplied onto voice coil & adding with audible noise of switched-on sound reproducing device.
Before 1950s, quality of sound reproducing speaker systems was very poor. Continuous improvement in design of enclosures and materials resulted in significant improvement in the sound reproduction quality. The following are the most significant improvements: improvement of frame, invention of high-technology adhesives, modernization in manufacturing technology of permanent magnets, improved measurement techniques & finally the design and analysis of components using computer. |
