Parabolic loudspeaker
Encyclopedia
A parabolic loudspeaker is a loudspeaker
which seeks to focus its sound in coherent plane wave
s either by reflecting sound output from a speaker driver
to a parabolic reflector
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 loudspeakers, and can be sent to isolated audience targets, unlike line array
loudspeakers. The parabolic loudspeaker has been used for such diverse purposes as directing sound at faraway targets in performing arts center
s and stadia
, for industrial testing, for intimate listening at museum exhibits, and as a sonic weapon.
per doubling of distance, rather than the usual 6 dB of conventional loudspeakers.
, 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 lowest desired wavelength, so to obtain directional control of frequencies down to 20 Hz
, the dish would have to be over 50 feet (15 m) 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
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
material placed, such that no sound is reflected directly at the speaker driver.
, 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.
. 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
of sonic energy relied on the combustion of methane
and oxygen
, with a frequency range of 800–1500 pulses per second. The parabolic reflector was 3.2 metres (10.5 ft) in diameter. It failed as a weapon, primarily because its range was not sufficient.
Modern sonic weapons such 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.
dome to achieve a degree of stereophonic sound
at the listener. Further uses for this kind of loudspeaker include video games and computer kiosks at trade shows
and video arcade
s.
produced the SB-1, a 54 inches (1,371.6 mm) parabolic reflector loudspeaker intended for public address
and as a supplement to conventional horn-loaded sound reinforcement system
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 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. 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 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
. Slightly smaller than the SB-1, the SB-2 uses 28 4 inches (102 mm) drivers arrayed on the surface of the parabola combined with a coaxial horn
with a 2 inches (51 mm) throat and a 4 inches (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 airport
s.
. 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.
, in order to realize a specific sound spatialization
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.
, Perrin Meyer, Roger Schwenke, Alejandro Antonio Garcia Rubio: Loudspeaker system and method for producing a controllable synthesized sound field
Loudspeaker
A loudspeaker is an electroacoustic transducer that produces sound in response to an electrical audio signal input. Non-electrical loudspeakers were developed as accessories to telephone systems, but electronic amplification by vacuum tube made loudspeakers more generally useful...
which seeks to focus its sound in coherent plane wave
Plane wave
In the physics of wave propagation, a plane wave is a constant-frequency wave whose wavefronts are infinite parallel planes of constant peak-to-peak amplitude normal to the phase velocity vector....
s either by reflecting sound output from a speaker driver
Speaker driver
A speaker driver is an individual transducer that converts electrical energy to sound waves, typically as part of a loudspeaker, television, or other electronics device. Sometimes the transducer is itself referred to as a speaker, particularly when a single one is mounted in an enclosure or as...
to a parabolic reflector
Parabolic reflector
A parabolic reflector is a reflective device used to collect or project energy such as light, sound, or radio waves. Its shape is that of a circular paraboloid, that is, the surface generated by a parabola revolving around its axis...
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 loudspeakers, and can be sent to isolated audience targets, unlike line array
Line array
A line array is a loudspeaker system that is made up of a number of loudspeaker elements coupled together in a line segment to create a near-line source of sound...
loudspeakers. The parabolic loudspeaker has been used for such diverse purposes as directing sound at faraway targets in performing arts center
Performing arts center
Performing arts center, often abbreviated 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....
s and stadia
Stadium
A modern stadium is a place or venue for outdoor sports, concerts, or other events and consists of a field or stage either partly or completely surrounded by a structure designed to allow spectators to stand or sit and view the event.)Pausanias noted that for about half a century the only event...
, for industrial testing, for intimate listening at museum exhibits, and as a sonic weapon.
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 SPLDecibel
The decibel is a logarithmic unit that indicates the ratio of a physical quantity relative to a specified or implied reference level. A ratio in decibels is ten times the logarithm to base 10 of the ratio of two power quantities...
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 parabolaParabola
In mathematics, the parabola is a conic section, the intersection of a right circular conical surface and a plane parallel to a generating straight line of that surface...
, 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 lowest desired wavelength, so to obtain directional control of frequencies down to 20 Hz
Hertz
The hertz is the SI unit of frequency defined as the number of cycles per second of a periodic phenomenon. One of its most common uses is the description of the sine wave, particularly those used in radio and audio applications....
, the dish would have to be over 50 feet (15 m) 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
Audio signal processing, sometimes referred to as audio processing, is the intentional alteration of auditory signals, or sound. As audio signals may be electronically represented in either digital or analog format, signal processing may occur in either domain...
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
In physics, damping is any effect that tends to reduce the amplitude of oscillations in an oscillatory system, particularly the harmonic oscillator.In mechanics, friction is one such damping effect...
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 steeringBeam steering
Beam steering is about changing the direction of the main lobe of a radiation pattern.In radio systems, beam steering may be accomplished by switching antenna elements or by changing the relative phases of the RF signals driving the elements.In optical systems, beam steering may be accomplished by...
, 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 IIWorld War II
World War II, or the Second World War , was a global conflict lasting from 1939 to 1945, involving most of the world's nations—including all of the great powers—eventually forming two opposing military alliances: the Allies and the Axis...
. 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
Shock wave
A shock wave is a type of propagating disturbance. Like an ordinary wave, it carries energy and can propagate through a medium or in some cases in the absence of a material medium, through a field such as the electromagnetic field...
of sonic energy relied on the combustion of methane
Methane
Methane is a chemical compound with the chemical formula . It is the simplest alkane, the principal component of natural gas, and probably the most abundant organic compound on earth. The relative abundance of methane makes it an attractive fuel...
and oxygen
Oxygen
Oxygen is the element with atomic number 8 and represented by the symbol O. Its name derives from the Greek roots ὀξύς and -γενής , because at the time of naming, it was mistakenly thought that all acids required oxygen in their composition...
, with a frequency range of 800–1500 pulses per second. The parabolic reflector was 3.2 metres (10.5 ft) in diameter. It failed as a weapon, primarily because its range was not sufficient.
Modern sonic weapons such the Long Range Acoustic Device
Long range acoustic device
The Long Range Acoustic Device is a distance hailing device and non-lethal crowd control weapon developed by LRAD Corporation to send messages, warnings, and harmful, pain inducing tones over longer distances than normal loudspeakers....
(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.
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 hemisphericSphere
A sphere is a perfectly round geometrical object in three-dimensional space, such as the shape of a round ball. Like a circle in two dimensions, a perfect sphere is completely symmetrical around its center, with all points on the surface lying the same distance r from the center point...
dome to achieve a degree of stereophonic sound
Stereophonic sound
The term Stereophonic, commonly called stereo, sound refers to any method of sound reproduction in which an attempt is made to create an illusion of directionality and audible perspective...
at the listener. Further uses for this kind of loudspeaker include video games and computer kiosks at trade shows
Trade fair
A trade fair is an exhibition organized so that companies in a specific industry can showcase and demonstrate their latest products, service, study activities of rivals and examine recent market trends and opportunities...
and video arcade
Video arcade
An amusement arcade or video arcade is a venue where people play arcade games such as video games, pinball machines, electro-mechanical games, redemption games, merchandisers , or coin-operated billiards or air hockey tables...
s.
Public address
In 1997, Meyer Sound LaboratoriesMeyer 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 reinforcement, fixed installation, and sound...
produced the SB-1, a 54 inches (1,371.6 mm) parabolic reflector loudspeaker intended for public address
Public address
A public address system is an electronic amplification system with a mixer, amplifier and loudspeakers, used to reinforce a sound source, e.g., a person giving a speech, a DJ playing prerecorded music, and distributing the sound throughout a venue or building.Simple PA systems are often used in...
and as a supplement to conventional horn-loaded sound reinforcement system
Sound reinforcement system
A sound reinforcement system is the combination of microphones, signal processors, amplifiers, and loudspeakers that makes live or pre-recorded sounds louder and may also distribute those sounds to a larger or more distant audience...
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 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. 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 so eliminate the need for delay speakers.
In 2002, Meyer Sound produced the SB-2, a bi-amplified
Bi-amping
Bi-amping is the practice of using two audio amplifier channels to power a loudspeaker with multiple drivers.-Description:Bi-amping is the act of using a single loud-speaker system, that is one channel of a speaker pair, with one channel handling only low frequency information and the other channel...
loudspeaker which uses a parabolic dish as the front face of the enclosure
Loudspeaker enclosure
A loudspeaker enclosure is a purpose-engineered cabinet in which speaker drivers and associated electronic hardware, such as crossover circuits and amplifiers, are mounted...
. Slightly smaller than the SB-1, the SB-2 uses 28 4 inches (102 mm) drivers arrayed on the surface of the parabola combined with a coaxial horn
Horn (acoustic)
A horn is a tapered sound guide designed to provide an acoustic impedance match between a sound source and free air. This has the effect of maximizing the efficiency with which sound waves from the particular source are transferred to the air...
with a 2 inches (51 mm) throat and a 4 inches (102 mm) voice coil
Voice coil
A voice coil 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...
. 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 airport
Airport
An airport is a location where aircraft such as fixed-wing aircraft, helicopters, and blimps take off and land. Aircraft may be stored or maintained at an airport...
s.
Industrial testing
A parabolic loudspeaker can be used to test the sound-damping characteristics of materials used for soundproofingSoundproofing
Soundproofing is any means of reducing the sound pressure with respect to a specified sound source and receptor. There are several basic approaches to reducing sound: increasing the distance between source and receiver, using noise barriers to reflect or absorb the energy of the sound waves, using...
. A parabolic loudspeaker is aimed at the material under test, and a parabolic microphone
Parabolic microphone
A parabolic microphone is a microphone that uses a parabolic reflector to collect and focus sound waves onto a receiver, in much the same way that a parabolic antenna does with radio waves...
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 Holophones loudspeaker system was designed in 1999 by composer Michelangelo Lupone and realized at CRM – Centro Ricerche Musicali in RomeRome
Rome is the capital of Italy and the country's largest and most populated city and comune, with over 2.7 million residents in . The city is located in the central-western portion of the Italian Peninsula, on the Tiber River within the Lazio region of Italy.Rome's history spans two and a half...
, in order to realize a specific sound spatialization
Spatial music
Spatial music, music in space, or space music uses the localization of sounds in physical space as a compositional element in music, in sound art, and in sound editing for audio recordings, film, and video...
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.
Patents
. John D. MeyerJohn Meyer (audio engineer)
John Meyer is a pioneer in the sound reinforcement industry. In 1979 he founded founded Meyer Sound Laboratories with his wife, Helen Meyer.John Meyer grew up in Berkeley, California. His earliest involvement with audio was in the late 50s hanging out at the local radio station KPFA...
, Perrin Meyer, Roger Schwenke, Alejandro Antonio Garcia Rubio: Loudspeaker system and method for producing a controllable synthesized sound field