A parabolic loudspeaker is a

loudspeaker A loudspeaker (commonly referred to as a speaker or speaker driver) is an electroacoustic transducer that converts an electrical audio signal into a corresponding sound. A ''speaker system'', also often simply referred to as a "speaker" or ...

which seeks to focus its sound in coherent

plane wave In physics, a plane wave is a special case of wave or field: a physical quantity whose value, at any moment, is constant through any plane that is perpendicular to a fixed direction in space. For any position \vec x in space and any time t, ...

s either by reflecting sound output from a

speaker driver An electrodynamic speaker driver, often called simply a speaker driver when the type is implicit, is an individual transducer that converts an electrical audio signal to sound waves. While the term is sometimes used interchangeably with the ...

to a

parabolic reflector A parabolic (or paraboloid or paraboloidal) reflector (or dish or mirror) is a reflective surface used to collect or project energy such as light, sound, or radio waves. Its shape is part of a circular paraboloid, that is, the surface genera ...

aimed at the target audience, or by arraying drivers on a parabolic surface. The resulting beam of sound travels farther, with less dissipation in air, than

horn loudspeaker A horn loudspeaker is a loudspeaker or loudspeaker element which uses an acoustic horn to increase the overall efficiency of the driving element(s). A common form ''(right)'' consists of a compression driver which produces sound waves with a small ...

s, and can be more focused than line array loudspeakers allowing sound to be sent to isolated audience targets.Borgerson, Bruce
"Technology Showcase: Focused Loudspeaker Systems."
AVInstall, November 1, 2005. Retrieved on August 25, 2009. The parabolic loudspeaker has been used for such diverse purposes as directing sound at faraway targets in

performing arts center Performing arts center/centre (see spelling differences), often abbreviated as PAC, is used to refer to: * A multi-use performance space that is intended for use by various types of the performing arts, including dance, music and theatre. :The ...

s and stadia, for industrial testing, for intimate listening at museum exhibits, and as a

sonic weapon Sonic and ultrasonic weapons (USW) are weapons of various types that use sound to injure or incapacitate an opponent. Some sonic weapons make a focused beam of sound or of ultrasound; others produce an area field of sound. military and police ...

Technology

A parabolic loudspeaker can send sound farther than traditional loudspeaker designs. The focused waves of a parabolic loudspeaker tend to dissipate in air at about 3

dB SPL Sound pressure or acoustic pressure is the local pressure deviation from the ambient (average or equilibrium) atmospheric pressure, caused by a sound wave. In air, sound pressure can be measured using a microphone, and in water with a hydrophone ...

per doubling of distance, rather than the usual 6 dB of conventional loudspeakers.

Parabolic reflector

In a parabolic reflecting loudspeaker, one or more speaker drivers are mounted at the focal point of a

parabola In mathematics, a parabola is a plane curve which is mirror-symmetrical and is approximately U-shaped. It fits several superficially different mathematical descriptions, which can all be proved to define exactly the same curves. One descri ...

, pointing away from the audience, toward the parabolic surface. The sound is bounced off the parabolic dish and leaves the dish focused in plane waves. The lowest frequency that can be directed into a narrow beam is dependent on the size of the parabolic dish. A parabolic reflector type of loudspeaker must have a diameter twice that of the wavelength of the lowest desired frequency, so to obtain directional control of frequencies down to 20 Hz, the dish would have to be over wide. Limitations of parabolic reflector loudspeakers include the fact that they are comparatively large and bulky, and that they have a fixed beam width with no ability to broaden or narrow the coverage pattern without changing the curvature of the dish. Their beam width is wider for low frequencies than it is for high frequencies, so at the periphery of the coverage pattern there is a region of sound coverage that doesn't receive the full strength of the high frequencies. In addition, some frequencies are reflected more efficiently than others, so the frequency response is uneven unless

audio signal processing Audio signal processing is a subfield of signal processing that is concerned with the electronic manipulation of audio signals. Audio signals are electronic representations of sound waves— longitudinal waves which travel through air, consist ...

correction is applied before the signal reaches the amplifier. The presence and placement of the speaker driver prevents the center of the parabolic dish from reflecting sound outward, as that sound would reflect back into the speaker driver itself. In some loudspeaker designs, a hole is cut at the center of the parabolic dish, or

damping Damping is an influence within or upon an oscillatory system that has the effect of reducing or preventing its oscillation. In physical systems, damping is produced by processes that dissipate the energy stored in the oscillation. Examples i ...

material placed, such that no sound is reflected directly at the speaker driver.

Parabolic source

A loudspeaker can be constructed with multiple speaker drivers arrayed on the surface of a parabolic dish. This type of loudspeaker does not reflect sound—it aims sound directly at the audience. As in non-parabolic arrays of drivers, the signal going to each of the multiple drivers can be digitally delayed relative to its neighbors to achieve

beam steering Beam steering is a technique for changing the direction of the main lobe of a radiation pattern. In radio and radar systems, beam steering may be accomplished by switching the antenna elements or by changing the relative phases of the RF sign ...

, and thus to adjust the aiming point or coverage pattern of the parabolic array without physically changing its position or curvature. The expense of a multiple driver loudspeaker is typically higher than a reflector-type parabolic dish due to the increased number of speaker driver components and amplifier channels.

Sonic weapon

The first use of a parabolic reflector in directing sound energy as a weapon was the ''Luftkanone'' designed by the German military during

World War II World War II or the Second World War, often abbreviated as WWII or WW2, was a world war that lasted from 1939 to 1945. It involved the World War II by country, vast majority of the world's countries—including all of the great power ...

. Its purpose was to emit a focused pulse of sonic energy directed from the ground to aircraft overhead, and to knock the aircraft out of the sky. The system for creating a

shock wave In physics, a shock wave (also spelled shockwave), or shock, is a type of propagating disturbance that moves faster than the local speed of sound in the medium. Like an ordinary wave, a shock wave carries energy and can propagate through a me ...

of sonic energy relied on the combustion of

methane Methane ( , ) is a chemical compound with the chemical formula (one carbon atom bonded to four hydrogen atoms). It is a group-14 hydride, the simplest alkane, and the main constituent of natural gas. The relative abundance of methane ...

and

oxygen Oxygen is the chemical element with the symbol O and atomic number 8. It is a member of the chalcogen group in the periodic table, a highly reactive nonmetal, and an oxidizing agent that readily forms oxides with most elements ...

, with a frequency range of 800–1500 pulses per second. The parabolic reflector was in diameter. It failed as a weapon, primarily because its range was not sufficient. Modern sonic weapons such the

Long Range Acoustic Device A long-range acoustic device (LRAD) is an acoustic hailing device (AHD), sound cannon and sonic weapon developed by Genasys. It has been used as a method of crowd control, which has caused permanent hearing damage, having an extremely high ...

(LRAD) rely on multiple loudspeaker drivers for increased

sound power Sound power or acoustic power is the rate at which sound energy is emitted, reflected, transmitted or received, per unit time. It is defined as "through a surface, the product of the sound pressure, and the component of the particle velocity, at ...

, 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.

Museum exhibits

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 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 Stereophonic sound, or more commonly stereo, is a method of sound reproduction that recreates a multi-directional, 3-dimensional audible perspective. This is usually achieved by using two independent audio channels through a configuration ...

at the listener. Further uses for this kind of loudspeaker include video games and computer kiosks at

trade shows A trade fair, also known as trade show, trade exhibition, or trade exposition, is an exhibition organized so that companies in a specific industry can showcase and demonstrate their latest products and services, meet with industry partners and cu ...

and

video arcade An amusement arcade (often referred to as a video arcade, amusements or simply arcade) is a venue where people play arcade games, including arcade video games, pinball machines, electro-mechanical games, redemption games, merchandisers (such a ...

Public address

In 1997,

Meyer Sound Laboratories Meyer Sound Laboratories is an American company based in Berkeley, California that manufactures self-powered loudspeakers, multichannel audio show control systems, electroacoustic architecture, and audio analysis tools for the professional sound ...

produced the SB-1, a parabolic reflector loudspeaker intended for

public address A public address system (or PA system) is an electronic system comprising microphones, amplifiers, loudspeakers, and related equipment. It increases the apparent volume (loudness) of a human voice, musical instrument, or other acoustic sound sou ...

and as a supplement to conventional horn-loaded

sound reinforcement system A sound reinforcement system is the combination of microphones, signal processors, amplifiers, and loudspeakers in enclosures all controlled by a mixing console that makes live or pre-recorded sounds louder and may also distribute those sou ...

s, for "spotlight" long-throw applications. 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 such that at , the area of coverage was a circle in diameter, with 110 dB SPL reported at that distance by an independent critic. The SB-1 was designed to direct 100 dB SPL , or 116 dB SPL , depending on atmospheric conditions, and so eliminate the need for delay speakers. In 2002, Meyer Sound produced the SB-2, a bi-amplified loudspeaker which uses a parabolic dish as the front face of the

enclosure Enclosure or Inclosure is a term, used in English landownership, that refers to the appropriation of "waste" or " common land" enclosing it and by doing so depriving commoners of their rights of access and privilege. Agreements to enclose land ...

. Slightly smaller than the SB-1, the SB-2 uses 28 drivers arrayed on the surface of the parabola combined with a coaxial horn with a throat and a

voice coil A voice coil (consisting of a former, collar, and winding) is the coil of wire attached to the apex of a loudspeaker cone. It provides the motive force to the cone by the reaction of a magnetic field to the current passing through it. The te ...

. 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 center A convention center (American English; or conference centre in British English) is a large building that is designed to hold a convention, where individuals and groups gather to promote and share common interests. Convention centers typica ...

s and

airport An airport is an aerodrome with extended facilities, mostly for commercial air transport. Airports usually consists of a landing area, which comprises an aerially accessible open space including at least one operationally active surfa ...

s.Meyer Sound
SB-2: Parabolic Wide-Range Sound Beam. (Datasheet.)
Retrieved on August 18, 2009.

Industrial testing

A parabolic loudspeaker can be used to test the sound-damping characteristics of materials used for

soundproofing Soundproofing is any means of impeding sound propagation. There are several basic approaches to reducing sound: increasing the distance between source and receiver, decoupling, using noise barriers to reflect or absorb the energy of the sound w ...

. A parabolic loudspeaker is aimed at the material under test, and a

parabolic microphone A parabolic microphone is a microphone that uses a parabolic reflector to collect and focus sound waves onto a transducer, in much the same way that a parabolic antenna (e.g. satellite dish) does with radio waves. Though they lack high fidel ...

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.

Sound sculpture

The loudspeaker system was designed in 1999 by composer Michelangelo Lupone and realized at CRM – Centro Ricerche Musicali in

Rome , established_title = Founded , established_date = 753 BC , founder = King Romulus ( legendary) , image_map = Map of comune of Rome (metropolitan city of Capital Rome, region Lazio, Italy).svg , map_caption ...

, in order to realize a specific sound

spatialization Spatialization (or spatialisation) is the spatial forms that social activities and material things, phenomena or processes take on in geography, sociology, urban planning and cultural studies. Generally the term refers to an overall sense of soc ...

defined as "wavefront sculpture". The parabolic reflector of the Holophones system emits plane waves. 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.CRM - Centro Ricerche Musicali
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Patents

* * *. John D. Meyer, Perrin Meyer, Roger Schwenke, Alejandro Antonio Garcia Rubio: Loudspeaker system and method for producing a controllable synthesized sound field

References

{{reflist Loudspeaker technology