Plasma speaker
Encyclopedia
Plasma speakers are a form of loudspeaker
which varies air pressure via a high-energy electrical plasma
instead of a solid diaphram
. Connected to the output of an audio amplifier
, plasma speakers vary the size of a plasma glow discharge, corona discharge
or electric arc
which then acts as a massless radiating element, creating the compression waves in air that listeners perceive as sound
. The technique is an evolution of William Duddell
's "singing arc" of 1900, and an innovation related to ion thruster
spacecraft propulsion.
The effect takes advantage of two unique principles. Firstly, ionization
of gases causes their electrical resistance
to drop significantly, making them extremely efficient conductors
. And conductors can vibrate sympathetically with magnetic field
s.
Secondly, the involved plasma, itself a field of ion
s, has a relatively negligible mass. Thus as current frequency varies, more-resistant air remains mechanically coupled with and is driven by vibration of the more conductive and essentially-massless plasma, radiating a potentially ideal reproduction of the sound source.
Conventional loudspeaker transducer
designs use input electrical frequencies to vibrate a significant mass: This driver
is coupled to a stiff plastic composite speaker-cone- a diaphram which pushes air at respective frequencies. But the inertia
inherent in its mass resists acceleration
- and all changes in cone position. Additionally, speaker-cones will eventually suffer tensile fatigue
from the repeated shaking of sonic vibration.
Thus conventional speaker output, or the fidelity
of the device, is distorted by physical limitations inherent in its design. These distortions have long been the limiting factor in commercial reproduction of strong high frequencies. To a lesser extent square wave
characteristics are also problematic; the reproduction of square waves most stress a speaker-cone.
In a plasma speaker, as member of the family of massless speakers, these limitations do not exist. The low-inertia driver has exceptional transient response over other designs. The result is an even, linear
output accurate even at extreme frequencies beyond any audible range. Such speakers are notable for accuracy and clarity- but not tremendous power: Plasmas composed of tiny particles are unable to move large volumes of air. So these designs are more effective as tweeters.
and oxygen
. In an intense electrical field these gases can produce reactive by-products, and in closed rooms these can reach a hazardous level.
Plasmatronics
produced a commercial plasma speaker that used a helium
tank to provide the ionization gas. In 1978 Alan E. Hill of the Air Force Weapons Laboratory in Albuquerque, NM, designed the Plasmatronics Hill Type I, a commercial helium-plasma tweeter. This avoided the ozone
and nitrous oxide
produced by Radio frequency
decomposition of air in an earlier generation of plasma tweeters. Theirs is also the only design relying on the quieter glow discharge mode instead of the more common arc
and corona discharge
s. But The operator of such speakers requires a continuous supply of ionizable helium.
In the 1950s, the pioneering DuKane Corporation produced the air-ionizing Ionovac, marketed in the UK as the Ionofane. Currently there remain manufacturers in Germany who use this design, as well as a do-it-yourself design available on the Internet.
Flame also contains ionized gases; A less expensive variation on this theme is the flame speaker which uses a flame for the driver. Some designs dating to the 1950s use combustion of natural gas or candles to produce a plasma through which current is then passed. These combustion designs do not require high voltages to generate a plasma field.
Despite offering an aspect of ideal sound-reproduction, plasma speaker designs tend not to be used in practical musical systems nor any performing instruments. Due to investment costs, limits in frequency range, and the many practical considerations in safely maintaining any air-coupled plasma, they remain experiments and curiosities.
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 varies air pressure via a high-energy electrical plasma
Plasma (physics)
In physics and chemistry, plasma is a state of matter similar to gas in which a certain portion of the particles are ionized. Heating a gas may ionize its molecules or atoms , thus turning it into a plasma, which contains charged particles: positive ions and negative electrons or ions...
instead of a solid diaphram
Diaphragm (acoustics)
In the field of acoustics, a diaphragm is a transducer intended to faithfully inter-convert mechanical motion and sound. It is commonly constructed of a thin membrane or sheet of various materials. The varying air pressure of the sound waves imparts vibrations onto the diaphragm which can then be...
. Connected to the output of an audio amplifier
Audio amplifier
An audio amplifier is an electronic amplifier that amplifies low-power audio signals to a level suitable for driving loudspeakers and is the final stage in a typical audio playback chain.The preceding stages in such a chain are low power audio amplifiers which perform tasks like pre-amplification,...
, plasma speakers vary the size of a plasma glow discharge, corona discharge
Corona discharge
In electricity, a corona discharge is an electrical discharge brought on by the ionization of a fluid surrounding a conductor that is electrically energized...
or electric arc
Electric arc
An electric arc is an electrical breakdown of a gas which produces an ongoing plasma discharge, resulting from a current flowing through normally nonconductive media such as air. A synonym is arc discharge. An arc discharge is characterized by a lower voltage than a glow discharge, and relies on...
which then acts as a massless radiating element, creating the compression waves in air that listeners perceive as sound
Sound
Sound is a mechanical wave that is an oscillation of pressure transmitted through a solid, liquid, or gas, composed of frequencies within the range of hearing and of a level sufficiently strong to be heard, or the sensation stimulated in organs of hearing by such vibrations.-Propagation of...
. The technique is an evolution of William Duddell
William Duddell
William Du Bois Duddell was a British electro-physicist and electrical engineer. He was privately educated in the UK and France and rose quickly through the prestigious City & Guilds Schools via scholarships...
's "singing arc" of 1900, and an innovation related to ion thruster
Ion thruster
An ion thruster is a form of electric propulsion used for spacecraft propulsion that creates thrust by accelerating ions. Ion thrusters are categorized by how they accelerate the ions, using either electrostatic or electromagnetic force. Electrostatic ion thrusters use the Coulomb force and...
spacecraft propulsion.
The effect takes advantage of two unique principles. Firstly, ionization
Ionization
Ionization is the process of converting an atom or molecule into an ion by adding or removing charged particles such as electrons or other ions. This is often confused with dissociation. A substance may dissociate without necessarily producing ions. As an example, the molecules of table sugar...
of gases causes their electrical resistance
Electrical resistance
The electrical resistance of an electrical element is the opposition to the passage of an electric current through that element; the inverse quantity is electrical conductance, the ease at which an electric current passes. Electrical resistance shares some conceptual parallels with the mechanical...
to drop significantly, making them extremely efficient conductors
Electrical conductor
In physics and electrical engineering, a conductor is a material which contains movable electric charges. In metallic conductors such as copper or aluminum, the movable charged particles are electrons...
. And conductors can vibrate sympathetically with magnetic field
Magnetic field
A magnetic field is a mathematical description of the magnetic influence of electric currents and magnetic materials. The magnetic field at any given point is specified by both a direction and a magnitude ; as such it is a vector field.Technically, a magnetic field is a pseudo vector;...
s.
Secondly, the involved plasma, itself a field of ion
Ion
An ion is an atom or molecule in which the total number of electrons is not equal to the total number of protons, giving it a net positive or negative electrical charge. The name was given by physicist Michael Faraday for the substances that allow a current to pass between electrodes in a...
s, has a relatively negligible mass. Thus as current frequency varies, more-resistant air remains mechanically coupled with and is driven by vibration of the more conductive and essentially-massless plasma, radiating a potentially ideal reproduction of the sound source.
Conventional loudspeaker transducer
Transducer
A transducer is a device that converts one type of energy to another. Energy types include electrical, mechanical, electromagnetic , chemical, acoustic or thermal energy. While the term transducer commonly implies the use of a sensor/detector, any device which converts energy can be considered a...
designs use input electrical frequencies to vibrate a significant mass: This driver
Transducer
A transducer is a device that converts one type of energy to another. Energy types include electrical, mechanical, electromagnetic , chemical, acoustic or thermal energy. While the term transducer commonly implies the use of a sensor/detector, any device which converts energy can be considered a...
is coupled to a stiff plastic composite speaker-cone- a diaphram which pushes air at respective frequencies. But the inertia
Inertia
Inertia is the resistance of any physical object to a change in its state of motion or rest, or the tendency of an object to resist any change in its motion. It is proportional to an object's mass. The principle of inertia is one of the fundamental principles of classical physics which are used to...
inherent in its mass resists acceleration
Acceleration
In physics, acceleration is the rate of change of velocity with time. In one dimension, acceleration is the rate at which something speeds up or slows down. However, since velocity is a vector, acceleration describes the rate of change of both the magnitude and the direction of velocity. ...
- and all changes in cone position. Additionally, speaker-cones will eventually suffer tensile fatigue
Fatigue (material)
'In materials science, fatigue is the progressive and localized structural damage that occurs when a material is subjected to cyclic loading. The nominal maximum stress values are less than the ultimate tensile stress limit, and may be below the yield stress limit of the material.Fatigue occurs...
from the repeated shaking of sonic vibration.
Thus conventional speaker output, or the fidelity
Fidelity
"Fidelity" is the quality of being faithful or loyal. Its original meaning regarded duty to a lord or a king, in a broader sense than the related concept of fealty. Both derive from the Latin word fidēlis, meaning "faithful or loyal"....
of the device, is distorted by physical limitations inherent in its design. These distortions have long been the limiting factor in commercial reproduction of strong high frequencies. To a lesser extent square wave
Square wave
A square wave is a kind of non-sinusoidal waveform, most typically encountered in electronics and signal processing. An ideal square wave alternates regularly and instantaneously between two levels...
characteristics are also problematic; the reproduction of square waves most stress a speaker-cone.
In a plasma speaker, as member of the family of massless speakers, these limitations do not exist. The low-inertia driver has exceptional transient response over other designs. The result is an even, linear
Linear amplifier
A linear amplifier is an electronic circuit whose output is proportional to its input, but capable of delivering more power into a load. The term usually refers to a type of radio-frequency power amplifier, some of which have output power measured in kilowatts, and are used in amateur radio...
output accurate even at extreme frequencies beyond any audible range. Such speakers are notable for accuracy and clarity- but not tremendous power: Plasmas composed of tiny particles are unable to move large volumes of air. So these designs are more effective as tweeters.
Practical considerations
Early plasma-speaker designs ionized ambient air containing the gases nitrogenNitrogen
Nitrogen is a chemical element that has the symbol N, atomic number of 7 and atomic mass 14.00674 u. Elemental nitrogen is a colorless, odorless, tasteless, and mostly inert diatomic gas at standard conditions, constituting 78.08% by volume of Earth's atmosphere...
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...
. In an intense electrical field these gases can produce reactive by-products, and in closed rooms these can reach a hazardous level.
Plasmatronics
Plasmatronics
Plasmatronics was a company, founded by former Air Force Weapons Laboratory scientist Dr. Alan E. Hill, which produced a plasma speaker design...
produced a commercial plasma speaker that used a helium
Helium
Helium is the chemical element with atomic number 2 and an atomic weight of 4.002602, which is represented by the symbol He. It is a colorless, odorless, tasteless, non-toxic, inert, monatomic gas that heads the noble gas group in the periodic table...
tank to provide the ionization gas. In 1978 Alan E. Hill of the Air Force Weapons Laboratory in Albuquerque, NM, designed the Plasmatronics Hill Type I, a commercial helium-plasma tweeter. This avoided the ozone
Ozone
Ozone , or trioxygen, is a triatomic molecule, consisting of three oxygen atoms. It is an allotrope of oxygen that is much less stable than the diatomic allotrope...
and nitrous oxide
Nitrous oxide
Nitrous oxide, commonly known as laughing gas or sweet air, is a chemical compound with the formula . It is an oxide of nitrogen. At room temperature, it is a colorless non-flammable gas, with a slightly sweet odor and taste. It is used in surgery and dentistry for its anesthetic and analgesic...
produced by Radio frequency
Radio frequency
Radio frequency is a rate of oscillation in the range of about 3 kHz to 300 GHz, which corresponds to the frequency of radio waves, and the alternating currents which carry radio signals...
decomposition of air in an earlier generation of plasma tweeters. Theirs is also the only design relying on the quieter glow discharge mode instead of the more common arc
Electric arc
An electric arc is an electrical breakdown of a gas which produces an ongoing plasma discharge, resulting from a current flowing through normally nonconductive media such as air. A synonym is arc discharge. An arc discharge is characterized by a lower voltage than a glow discharge, and relies on...
and corona discharge
Corona discharge
In electricity, a corona discharge is an electrical discharge brought on by the ionization of a fluid surrounding a conductor that is electrically energized...
s. But The operator of such speakers requires a continuous supply of ionizable helium.
In the 1950s, the pioneering DuKane Corporation produced the air-ionizing Ionovac, marketed in the UK as the Ionofane. Currently there remain manufacturers in Germany who use this design, as well as a do-it-yourself design available on the Internet.
Flame also contains ionized gases; A less expensive variation on this theme is the flame speaker which uses a flame for the driver. Some designs dating to the 1950s use combustion of natural gas or candles to produce a plasma through which current is then passed. These combustion designs do not require high voltages to generate a plasma field.
Despite offering an aspect of ideal sound-reproduction, plasma speaker designs tend not to be used in practical musical systems nor any performing instruments. Due to investment costs, limits in frequency range, and the many practical considerations in safely maintaining any air-coupled plasma, they remain experiments and curiosities.
External links
- The Art of Speaker Design
- A loudspeaker with a plasma ion tweeter
- An attempt at a working DIY plasma loudspeaker
- William Du Bois Duddell and the "Singing Arc"
- The Plasma Speaker Homepage
- History
- May 1968 Popular Electronics "Flame Amplification"
- "HVwiki, plasma speaker" Guide de réalisation d'un Plasma Speaker (ClubElek)