Altavoz parabólico

Un altavoz parabólico es un altavoz que busca enfocar su sonido en ondas planas coherentes , ya sea reflejando la salida de sonido de un transductor hacia un reflector parabólico dirigido al público objetivo, o bien apilando transductores en una superficie parabólica. El haz de sonido resultante viaja más lejos, con menor disipación en el aire, que los altavoces de bocina , y puede enfocarse más que los altavoces de arreglo lineal , lo que permite enviar el sonido a objetivos de público aislados. ^{[ 1 ]} El altavoz parabólico se ha utilizado para propósitos tan diversos como dirigir el sonido a objetivos lejanos en centros de artes escénicas y estadios , para pruebas industriales, para escucha íntima en exposiciones de museos y como arma sónica .

Un altavoz parabólico puede enviar el sonido más lejos que los diseños de altavoces tradicionales. Las ondas focalizadas de un altavoz parabólico tienden a disiparse en el aire a aproximadamente 3 dB SPL por cada duplicación de la distancia, en lugar de los 6 dB habituales de los altavoces convencionales. ^{[ 2 ]}  

El primer uso de un reflector parabólico para dirigir energía sonora como arma fue el Luftkanone , diseñado por el ejército alemán durante la Segunda Guerra Mundial . Su propósito era emitir un pulso concentrado de energía sónica dirigido desde tierra hacia aeronaves en vuelo y derribarlas. El sistema para crear una onda de choque de energía sónica se basaba en la combustión de metano y oxígeno , con un rango de frecuencia de 800 a 1500 pulsos por segundo. El reflector parabólico tenía 3,2 metros (10,5 pies) de diámetro. ^{[ 5 ]} Fracasó como arma, principalmente porque su alcance no era suficiente. 

Modern sonic weapons such as the Long Range Acoustic Device (LRAD) rely on multiple loudspeaker drivers for increased sound power, and may array them in a flat plane rather than on a parabolic surface. Such weapons do not use parabolic reflectors which necessarily limit the number of drivers—a large area of drivers aimed at the reflector would occlude the parabolic dish.

Since 1986, parabolic loudspeakers have been designed to give museum exhibits a very focused sound field so that each exhibit can send sound to just one or two museum-goers^[1] without having too much interference and an increase in background noise. A typical installation involves one parabolic dish hanging above the area where people would be standing—sound is directed straight down. Some designs use a dual-focus dish to expand the sound field slightly beyond an ideal plane wave, while others incorporate dual drivers and amplifiers in a hemispheric dome to achieve a degree of stereophonic sound at the listener.^[6] Further uses for this kind of loudspeaker include video games and computer kiosks at trade shows and video arcades.^[7]

In 1997, Meyer Sound Laboratories produced the SB-1, a 54-inch (1,370 mm) parabolic reflector loudspeaker intended for public address and as a supplement to conventional horn-loaded sound reinforcement systems, for "spotlight" long-throw applications.^[8] Its frequency response was 500–15,000 Hz; the region below 500 Hz was to be covered by other loudspeaker types. The sound wave output was not perfectly planar—it spread out at a narrow 10° angle and at 300 feet (91 m), the area of coverage was a circle 53 feet (16 m) in diameter, with 110 dB SPL reported at that distance by an independent critic.^[1] The SB-1 was designed to direct 100 dB SPL 500 feet (152 m), or 116 dB SPL 420 feet (128 m), depending on atmospheric conditions, and eliminate the need for delay speakers.^[2][9]

In 2002, Meyer Sound produced the SB-2, a bi-amplified loudspeaker which uses a parabolic dish as the front face of the enclosure. Slightly smaller than the SB-1, the SB-2 uses 28 4-inch (102 mm) drivers arrayed on the surface of the parabola combined with a coaxial horn with a 2-inch (51 mm) throat and a 4-inch (102 mm)voice coil. Similar to the SB-1, the SB-2 preserves pattern control from 500 Hz up to 16 kHz, with a 20° angle of dispersion, complemented by more widely dispersed low frequency sound down to 130 Hz. The loudspeaker was designed for permanent installation in high-ceilinged buildings such as exhibition centers and airports.^[4]

A parabolic loudspeaker can be used to test the sound-damping characteristics of materials used for soundproofing. A parabolic loudspeaker is aimed at the material under test, and a parabolic microphone is used to pick up the sound detected on the other side of the material. The difference between the emitted sound and the picked up sound is analyzed to determine the sound-damping qualities of the material. The narrow directionality of the parabolic loudspeaker and microphone aid in reducing the amount of stray sound that could skew test results.^[10]

The Holophones loudspeaker system was designed in 1999 by composer Michelangelo Lupone and realized at CRM – Centro Ricerche Musicali in Rome, in order to realize a specific sound spatialization defined as "wavefront sculpture".^[11] The parabolic reflector of the Holophones system emits plane waves.^[12][13] Each unit of the Holophones system consists of a parabolic dish with a limited band loudspeaker at its focal point, with controllable radiation angle. The dynamic controls for sculpturing the wavefront are managed by a computer.^[14]

• USpatent 3997023,Stanley F. White,"Loudspeaker with improved surround",issued 1976-12-14 
• USpatent 5821470,Stanley F. White,"Loudspeaker with improved surround",issued 1976-12-14 
• Solicitud estadounidense 20,070,201,711  . John D. Meyer , Perrin Meyer, Roger Schwenke, Alejandro Antonio García Rubio: Sistema de altavoces y método para producir un campo sonoro sintetizado controlable.

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