Parabolic loudspeaker

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A parabolic loudspeaker is a loudspeaker which seeks to focus its sound in coherent plane waves 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 more focused than line array loudspeakers allowing sound to be sent to isolated audience targets. [1] The parabolic loudspeaker has been used for such diverse purposes as directing sound at faraway targets in performing arts centers and stadia, for industrial testing, for intimate listening at museum exhibits, and as a sonic weapon.

Contents

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 per doubling of distance, rather than the usual 6 dB of conventional loudspeakers. [2]

Parabolic reflector

In a parabolic reflecting loudspeaker, one or more speaker drivers are mounted at the focal point of a parabola, pointing away from the audience, toward the parabolic surface. [1] 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. [2] [ failed verification ] A parabolic reflector type of loudspeaker must have a diameter twice that of the wavelength of the lowest desired frequency,[ citation needed ] so to obtain directional control of frequencies down to 20  Hz, the dish would have to be over 113 feet (34 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. [3] 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. [1] 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.

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. [4] 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, and thus to adjust the aiming point or coverage pattern of the parabolic array without physically changing its position or curvature. [1]

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. [1]

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. 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. [5] 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.

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 [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]

Public address

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 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. [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 so 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]

Industrial testing

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]

Sound sculpture

Two units of a Holophones system Olofoni3.jpg
Two units of a Holophones system

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]

Patents

See also

Related Research Articles

Cassegrain antenna Type of parabolic antenna with a convex secondary reflector

In telecommunications and radar, a Cassegrain antenna is a parabolic antenna in which the feed antenna is mounted at or behind the surface of the concave main parabolic reflector dish and is aimed at a smaller convex secondary reflector suspended in front of the primary reflector. The beam of radio waves from the feed illuminates the secondary reflector, which reflects it back to the main reflector dish, which reflects it forward again to form the desired beam. The Cassegrain design is widely used in parabolic antennas, particularly in large antennas such as those in satellite ground stations, radio telescopes, and communication satellites.

Subwoofer Loudspeaker designed to reproduce low-pitched audio frequencies

A subwoofer is a loudspeaker designed to reproduce low-pitched audio frequencies known as bass and sub-bass, lower in frequency than those which can be (optimally) generated by a woofer. The typical frequency range for a subwoofer is about 20–200 Hz for consumer products, below 100 Hz for professional live sound, and below 80 Hz in THX-certified systems. Subwoofers are never used alone, as they are intended to augment the low-frequency range of loudspeakers that cover the higher frequency bands. While the term "subwoofer" technically only refers to the speaker driver, in common parlance, the term often refers to a subwoofer driver mounted in a speaker enclosure (cabinet), often with a built-in amplifier.

Loudspeaker Electroacoustic transducer that converts an electrical audio signal into a corresponding sound

A loudspeaker is an electroacoustic transducer, that is, a device that converts an electrical audio signal into a corresponding sound. A speaker system, also often simply referred to as a "speaker" or "loudspeaker", comprises one or more such speaker drivers, an enclosure, and electrical connections possibly including a crossover network. The speaker driver can be viewed as a linear motor attached to a diaphragm which couples that motor's movement to motion of air, that is, sound. An audio signal, typically from a microphone, recording, or radio broadcast, is amplified electronically to a power level capable of driving that motor in order to reproduce the sound corresponding to the original unamplified electronic signal. This is thus the opposite function to the microphone, and indeed the dynamic speaker driver, by far the most common type, is a linear motor in the same basic configuration as the dynamic microphone which uses such a motor in reverse, as a generator

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 does with radio waves. Though they lack high fidelity, parabolic microphones have great sensitivity to sounds in one direction, along the axis of the dish, and can pick up distant sounds. Typical uses of this microphone include nature sound recording such as recording bird calls, field audio for sports broadcasting, and eavesdropping on conversations, for example in espionage and law enforcement. Parabolic microphones were used in many parts of the world as early as World War II, especially by the Japanese.

Parabolic reflector Reflector that has the shape of a paraboloid

A parabolicreflector 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 generated by a parabola revolving around its axis. The parabolic reflector transforms an incoming plane wave travelling along the axis into a spherical wave converging toward the focus. Conversely, a spherical wave generated by a point source placed in the focus is reflected into a plane wave propagating as a collimated beam along the axis.

Parabolic antenna

A parabolic antenna is an antenna that uses a parabolic reflector, a curved surface with the cross-sectional shape of a parabola, to direct the radio waves. The most common form is shaped like a dish and is popularly called a dish antenna or parabolic dish. The main advantage of a parabolic antenna is that it has high directivity. It functions similarly to a searchlight or flashlight reflector to direct the radio waves in a narrow beam, or receive radio waves from one particular direction only. Parabolic antennas have some of the highest gains, meaning that they can produce the narrowest beamwidths, of any antenna type. In order to achieve narrow beamwidths, the parabolic reflector must be much larger than the wavelength of the radio waves used, so parabolic antennas are used in the high frequency part of the radio spectrum, at UHF and microwave (SHF) frequencies, at which the wavelengths are small enough that conveniently-sized reflectors can be used.

Directional antenna Radio antenna which has greater performance in specific alignments

A directional antenna or beam antenna is an antenna which radiates or receives greater power in specific directions allowing increased performance and reduced interference from unwanted sources. Directional antennas provide increased performance over dipole antennas—or omnidirectional antennas in general—when greater concentration of radiation in a certain direction is desired.

Directional Sound refers to the notion of using various devices to create fields of sound which spread less than most (small) traditional loudspeakers. Several techniques are available to accomplish this, and each has its benefits and drawbacks. Ultimately, choosing a directional sound device depends greatly on the environment in which it is deployed as well as the content that will be reproduced. Keeping these factors in mind will yield the best results through any evaluation of directional sound technologies.

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 metal diaphragm vibrated by an electromagnet, attached to a horn, a flaring duct to conduct the sound waves to the open air. Another type is a woofer driver mounted in a loudspeaker enclosure which is divided by internal partitions to form a zigzag flaring duct which functions as a horn; this type is called a folded horn speaker. The horn serves to improve the coupling efficiency between the speaker driver and the air. The horn can be thought of as an "acoustic transformer" that provides impedance matching between the relatively dense diaphragm material and the less-dense air. The result is greater acoustic output power from a given driver.

Acoustic mirror

An acoustic mirror is a passive device used to reflect and focus (concentrate) sound waves. Parabolic acoustic mirrors are widely used in parabolic microphones to pick up sound from great distances, employed in surveillance and reporting of outdoor sporting events. Pairs of large parabolic acoustic mirrors which function as "whisper galleries" are displayed in science museums to demonstrate sound focusing.

Loudspeaker enclosure Acoustical component

A loudspeaker enclosure or loudspeaker cabinet is an enclosure in which speaker drivers and associated electronic hardware, such as crossover circuits and, in some cases, power amplifiers, are mounted. Enclosures may range in design from simple, homemade DIY rectangular particleboard boxes to very complex, expensive computer-designed hi-fi cabinets that incorporate composite materials, internal baffles, horns, bass reflex ports and acoustic insulation. Loudspeaker enclosures range in size from small "bookshelf" speaker cabinets with 4" woofers and small tweeters designed for listening to music with a hi-fi system in a private home to huge, heavy subwoofer enclosures with multiple 18" or even 21" speakers in huge enclosures which are designed for use in stadium concert sound reinforcement systems for rock music concerts.

Corner reflector antenna

A corner reflector antenna is a type of directional antenna used at VHF and UHF frequencies. It was invented by John D. Kraus in 1938. It consists of a dipole driven element mounted in front of two flat rectangular reflecting screens joined at an angle, usually 90°. Corner reflectors have moderate gain of 10-15 dB, high front-to-back ratio of 20-30 dB, and wide bandwidth.

Loudspeaker measurement

Loudspeaker measurement is the practice of determining the behaviour of loudspeakers by measuring various aspects of performance. This measurement is especially important because loudspeakers, being transducers, have a higher level of distortion than other audio system components used in playback or sound reinforcement.

Wind profiler

A wind profiler is a type of weather observing equipment that uses radar or sound waves (SODAR) to detect the wind speed and direction at various elevations above the ground. Readings are made at each kilometer above sea level, up to the extent of the troposphere. Above this level there is inadequate water vapor present to produce a radar "bounce." The data synthesized from wind direction and speed is very useful to meteorological forecasting and timely reporting for flight planning. A twelve-hour history of data is available through NOAA websites.

Sodar meteorological instrument

Sodar, or in full sonic detection and ranging, is a meteorological instrument used as a wind profiler to measure the scattering of sound waves by atmospheric turbulence. SODAR systems are used to measure wind speed at various heights above the ground, and the thermodynamic structure of the lower layer of the atmosphere.

Sound from ultrasound is the name given here to the generation of audible sound from modulated ultrasound without using an active receiver. This happens when the modulated ultrasound passes through a nonlinear medium which acts, intentionally or unintentionally, as a demodulator.

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 recording industries.

Line array

A line array is a loudspeaker system that is made up of a number of usually identical loudspeaker elements mounted in a line and fed in phase, to create a near-line source of sound. The distance between adjacent drivers is close enough that they constructively interfere with each other to send sound waves farther than traditional horn-loaded loudspeakers, and with a more evenly distributed sound output pattern.

In radio systems, many different antenna types are used with specialized properties for particular applications. Antennas can be classified in various ways. The list below groups together antennas under common operating principles, following the way antennas are classified in many engineering textbooks.

Thomas J. Danley is an American audio engineer, electrical engineer and inventor, the holder of multiple patents for audio transducers, especially high-linearity, high-output professional horn loudspeaker systems. Danley first gained notice in the 1980s with his novel servomotor-driven subwoofer systems used to reproduce very low frequencies in concert tours and theme parks. In 2000 he advanced the implementation of multiple-entry horns in 2000 with several designs led by the SPL-td1, a seven-driver loudspeaker. In 2005, he started a new company, Danley Sound Labs, through which he patented further technologies and produced a wide variety of loudspeaker models based on these technologies.

References

  1. 1 2 3 4 5 6 7 Borgerson, Bruce. "Technology Showcase: Focused Loudspeaker Systems." AVInstall, November 1, 2005. Retrieved on August 25, 2009.
  2. 1 2 3 "SB-1 Q&A" (PDF). Meyer Sound. Archived from the original (PDF) on 2016-08-20.
  3. ↑ Meyer, John; Meyer, Perrin; Schwenke, Roger; Rubio, Alejandro Antonio Garcia. Loudspeaker system and method for producing a controlled synthesized sound field. June 26, 2008. Retrieved on August 25, 2009.
  4. 1 2 Meyer Sound. SB-2: Parabolic Wide-Range Sound Beam. (Datasheet.) Retrieved on August 18, 2009.
  5. ↑ Altmann, Jürgen. "Acoustic Weapons—A Prospective Assessment: Sources, Propagation, and Effects of Strong Sound" Experimentelle Physik III. Universität Dortmund, Dortmund, Germany
  6. ↑ Brown Innovations. The Localizer's hemispheric dome. How It Works. Archived 2009-05-25 at the Wayback Machine Retrieved on August 18, 2009.
  7. ↑ Museum Tools: Secret Sound. Archived 2006-05-11 at the Wayback Machine Retrieved on August 18, 2009.
  8. ↑ Sound & Video Contractor, November 1998. Rod Sintow and Stan Hutto, "Pushing the Envelope of Stadium Audio". Hosted at Meyer Sound Laboratories. Retrieved on August 18, 2009.
  9. ↑ Meyer Sound. SB-1 Parabolic Sound Beam. (Datasheet.) Retrieved on August 18, 2009.
  10. ↑ McElroy, D. L.; Joseph F. Kimpflen. Insulation materials, testing, and applications, Issue 1030, p. 324. ASTM International, 1990. ISBN   0-8031-1278-5
  11. ↑ HiArt Semestral Magazine of Information of the High Artistic and Musical Formation – Music and Mutation – Lupone, Michelangelo – Gangemi Editore – April–October 2008 – ISBN   978-88-492-1422-2
  12. ↑ Acustica Musicale e Architettonica – Spazializzazione del Suono – Lupone, Michelangelo – UTET – ISBN   88-7750-941-4
  13. ↑ Studio di un Radiatore Acustico ad Elevata Direttività – Mariorenzi, Luca – Università degli Studi Roma3, Facoltà di Ingegneria Elettronica
  14. ↑ CRM - Centro Ricerche Musicali
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