loudspeaker for other uses see loudspeaker disambiguation loudspeaker for home use with three types of dynamic drivers midrange drivertweeterwoofers the hole below the lowest woofer is a port for a bass reflex system a loudspeaker or loudspeaker or speaker is an electroacoustic transducer the most widely used type of speaker in the 2010s is the dynamic speaker invented in 1925 by edward w kellogg and chester w rice the dynamic speaker operates on the same basic principle as a dynamic microphone but in reverse to produce sound from an electrical signal when an alternating current electrical audio signal is applied to its voice coil a coil of wire suspended in a circular gap between the poles of a permanent magnet the coil is forced to move rapidly back and forth due to faradays law of induction which causes a diaphragm usually conically shaped attached to the coil to move back and forth pushing on the air to create sound waves besides this most common method there are several alternative technologies that can be used to convert an electrical signal into sound the sound source eg a sound recording or a microphone must be amplified or strengthened with an audio power amplifier before the signal is sent to the speaker speakers are typically housed in a speaker enclosure or speaker cabinet which is often a rectangular or square box made of wood or sometimes plastic the enclosures materials and design play an important role in the quality of the sound where high fidelity reproduction of sound is required multiple loudspeaker transducers are often mounted in the same enclosure each reproducing a part of the audible frequency range picture at right in this case the individual speakers are referred to as drivers and the entire unit is called a loudspeaker drivers made for reproducing high audio frequencies are called tweeters those for middle frequencies are called midrange drivers and those for low frequencies are called woofers smaller loudspeakers are found in devices such as radios televisions portable audio players computers and electronic musical instruments larger loudspeaker systems are used for music sound reinforcement in theatres and concerts and in public address systems terminology the term loudspeaker may refer to individual transducers also known as drivers or to complete speaker systems consisting of an enclosure including one or more drivers to adequately reproduce a wide range of frequencies with even coverage most loudspeaker systems employ more than one driver particularly for higher sound pressure level or maximum accuracy individual drivers are used to reproduce different frequency ranges the drivers are named subwoofers for very low frequencies woofers low frequencies midrange speakers middle frequencies tweeters high frequencies and sometimes supertweeters optimized for the highest audible frequencies the terms for different speaker drivers differ depending on the application in twoway systems there is no midrange driver so the task of reproducing the midrange sounds falls upon the woofer and tweeter home stereos use the designation tweeter for the high frequency driver while professional concert systems may designate them as hf or highs when multiple drivers are used in a system a filter network called a crossover separates the incoming signal into different frequency ranges and routes them to the appropriate driver a loudspeaker system with n separate frequency bands is described as nway speakers a twoway system will have a woofer and a tweeter a threeway system employs a woofer a midrange and a tweeter loudspeaker driver of the type pictured are termed dynamic short for electrodynamic to distinguish them from earlier drivers ie moving iron speaker or speakers using piezoelectric or electrostatic systems or any of several other sorts history johann philipp reis installed an electric loudspeaker in his telephone in 1861 it was capable of reproducing clear tones but also could reproduce muffled speech after a few revisions alexander graham bell patented his first electric loudspeaker capable of reproducing intelligible speech as part of his telephone in 1876 which was followed in 1877 by an improved version from ernst siemens during this time thomas edison was issued a british patent for a system using compressed air as an amplifying mechanism for his early cylinder phonographs but he ultimately settled for the familiar metal horn driven by a membrane attached to the stylus in 1898 horace short patented a design for a loudspeaker driven by compressed air he then sold the rights to charles parsons who was issued several additional british patents before 1910 a few companies including the victor talking machine company and path produced record players using compressedair loudspeakers however these designs were significantly limited by their poor sound quality and their inability to reproduce sound at low volume variants of the system were used for public address applications and more recently other variations have been used to test spaceequipment resistance to the very loud sound and vibration levels that the launching of rockets produces the first experimental movingcoil also called dynamic loudspeaker was invented by oliver lodge in 1898 kellogg and rice in 1925 holding the large driver of the first movingcoil cone loudspeaker media all and maxwidth720px prototype movingcoil cone loudspeaker by kellogg and rice in 1925 with electromagnet pulled back showing voice coil attached to conethe first commercial version of the speaker sold with the rca radiola receiver had only a 6 inch cone in 1926 it sold for 250 equivalent to about 3000 today the movingcoil principle commonly used today in speakers was patented in 1924 by chester w rice and edward w kellogg the key difference between previous attempts and the patent by rice and kellogg is the adjustment of mechanical parameters so that the fundamental resonance of the moving system is below the frequency where the cones radiation impedance becomes uniform these first loudspeakers used electromagnets because large powerful permanent magnets were generally not available at a reasonable price the coil of an electromagnet called a field coil was energized by current through a second pair of connections to the driver this winding usually served a dual role acting also as a choke coil filtering the power supply of the amplifier that the loudspeaker was connected to ac ripple in the current was attenuated by the action of passing through the choke coil however ac line frequencies tended to modulate the audio signal going to the voice coil and added to the audible hum in 1930 jensen introduced the first commercial fixedmagnet loudspeaker however the large heavy iron magnets of the day were impractical and fieldcoil speakers remained predominant until the widespread availability of lightweight alnico magnets after world war ii in the 1930s loudspeaker manufacturers began to combine two and three bandpasses worth of drivers in order to increase frequency response and sound pressure level altec lansing introduced the 604 which became their most famous coaxial duplex driver in 1943 it incorporated a highfrequency horn that sent sound through the middle of a 15inch woofer for nearpointsource performance in 1954 edgar villchur developed the acoustic suspension principle of loudspeaker design in cambridge massachusetts this allowed for better bass response than previously from drivers mounted in smaller cabinets which was important during the transition to stereo recording and reproduction he and his partner henry kloss formed the acoustic research company to manufacture and market speaker systems using this principle subsequently continuous developments in enclosure design and materials led to significant audible improvements driver design dynamic loudspeakers cutaway view of a dynamic loudspeaker for the bass register magnetvoicecoilsuspensiondiaphragm cutaway view of a dynamic midrange speaker magnetcooler sometimes presentvoicecoilsuspensiondiaphragm cutaway view of a dynamic tweeter with acoustic lens and a domeshaped membrane magnetvoicecoildiaphragmsuspension the most common type of driver commonly called a dynamic loudspeaker uses a lightweight diaphragm or cone connected to a rigid basket or frame via a flexible suspension commonly called a spider that constrains a voice coil to move axially through a cylindrical magnetic gap when an electrical signal is applied to the voice coil a magnetic field is created by the electric current in the voice coil making it a variable electromagnet the coil and the drivers magnetic system interact generating a mechanical force that causes the coil and thus the attached cone to move back and forth accelerating and reproducing sound under the control of the applied electrical signal coming from the amplifier the following is a description of the individual components of this type of loudspeaker the diaphragm is usually manufactured with a cone or domeshaped profile a variety of different materials may be used but the most common are paper plastic and metal the ideal material would 1 be rigid to prevent uncontrolled cone motions 2 have low mass to minimize starting force requirements and energy storage issues 3 be well damped to reduce vibrations continuing after the signal has stopped with little or no audible ringing due to its resonance frequency as determined by its usage in practice all three of these criteria cannot be met simultaneously using existing materials thus driver design involves tradeoffs for example paper is light and typically well damped but is not stiff metal may be stiff and light but it usually has poor damping plastic can be light but typically the stiffer it is made the poorer the damping as a result many cones are made of some sort of composite material for example a cone might be made of cellulose paper into which some carbon fiber kevlar glass hemp or bamboo fibers have been added or it might use a honeycomb sandwich construction or a coating might be applied to it so as to provide additional stiffening or damping the chassis frame or basket is designed to be rigid avoiding deformation that could change critical alignments with the magnet gap perhaps causing the voice coil to rub against the sides of the gap chassis are typically cast from aluminum alloy or stamped from thin steel sheet though in some drivers with large magnets cast chassis are preferable as sheet metal can easily be warped in whenever the loudspeaker is subjected to rough handling other materials such as molded plastic and damped plastic compound baskets are becoming common especially for inexpensive lowmass drivers metallic chassis can play an important role in conducting heat away from the voice coil heating during operation changes resistance causes physical dimensional changes and if extreme may even demagnetize permanent magnets the suspension system keeps the coil centered in the gap and provides a restoring centering force that returns the cone to a neutral position after moving a typical suspension system consists of two parts the spider which connects the diaphragm or voice coil to the frame and provides the majority of the restoring force and the surround which helps center the coilcone assembly and allows free pistonic motion aligned with the magnetic gap the spider is usually made of a corrugated fabric disk impregnated with a stiffening resin the name comes from the shape of early suspensions which were two concentric rings of bakelite material joined by six or eight curved legs variations of this topology included the addition of a felt disc to provide a barrier to particles that might otherwise cause the voice coil to rub the german firm rulik still offers drivers with uncommon spiders made of wood the cone surround can be rubber or polyester foam or a ring of corrugated resin coated fabric it is attached to both the outer diaphragm circumference and to the frame these diverse surround materials their shape and treatment can dramatically affect the acoustic output of a driver each implementation having advantages and disadvantages polyester foam for example is lightweight and economical though usually leaking air to some degree but is degraded by exposure to ozone uv light humidity and elevated temperatures significantly limiting useful life with adequate performance the wire in a voice coil is usually made of copper though aluminumand rarely silvermay be used the advantage of aluminum is its light weight which reduces the moving mass compared to copper this raises the resonant frequency of the speaker and increases its efficiency a disadvantage of aluminum is that it is not easily soldered and so connections are instead often crimped together and sealed these connections must be made well or they may fail in an intense environment of mechanical vibration voicecoil wire cross sections can be circular rectangular or hexagonal giving varying amounts of wire volume coverage in the magnetic gap space the coil is oriented coaxially inside the gap it moves back and forth within a small circular volume a hole slot or groove in the magnetic structure the gap establishes a concentrated magnetic field between the two poles of a permanent magnet the outside of the gap being one pole and the center post called the pole piece being the other the pole piece and backplate are often a single piece called the poleplate or yoke modern driver magnets are almost always permanent and made of ceramic ferrite alnico or more recently rare earth such as neodymium and samarium cobalt electrodynamic drivers were often used in musical instrument amplifierspeaker cabinets well into the 1950s there were economic savings in those using tube amplifiers as the field coil could and usually did do double duty as a power supply choke a trend in design due to increases in transportation costs and a desire for smaller lighter devices as in many home theater multispeaker installations is the use of the last instead of heavier ferrite types very few manufacturers still produce electrodynamic loudspeakers with electrically powered field coils as was common in the earliest designs one of the last is a french firm when high fieldstrength permanent magnets became available after wwii alnico an alloy of aluminum nickel and cobalt became popular since it dispensed with the problems of fieldcoil drivers alnico was used almost exclusively until about 1980 despite the embarrassing problem of alnico magnets being partially degaussed ie demagnetized by accidental pops or clicks caused by loose connections especially if used with a highpower amplifier the damage can be reversed by recharging the magnet but this requires uncommon specialist equipment and knowledge after 1980 most but not quite all driver manufacturers switched from alnico to ferrite magnets which are made from a mix of ceramic clay and fine particles of barium or strontium ferrite although the energy per kilogram of these ceramic magnets is lower than alnico it is substantially less expensive allowing designers to use larger yet more economical magnets to achieve a given performance the size and type of magnet and details of the magnetic circuit differ depending on design goals for instance the shape of the pole piece affects the magnetic interaction between the voice coil and the magnetic field and is sometimes used to modify a drivers behavior a shorting ring or faraday loop may be included as a thin copper cap fitted over the pole tip or as a heavy ring situated within the magnetpole cavity the benefits of this complication is reduced impedance at high frequencies providing extended treble output reduced harmonic distortion and a reduction in the inductance modulation that typically accompanies large voice coil excursions on the other hand the copper cap requires a wider voicecoil gap with increased magnetic reluctance this reduces available flux requiring a larger magnet for equivalent performance driver designincluding the particular way two or more drivers are combined in an enclosure to make a speaker systemis both an art involving subjective perceptions of timbre and sound quality and a science involving measurements and experiments adjusting a design to improve performance is done using a combination of magnetic acoustic mechanical electrical and material science theory and tracked with high precision measurements and the observations of experienced listeners a few of the issues speaker and driver designers must confront are distortion radiation lobing phase effects offaxis response and crossover artifacts designers can use an anechoic chamber to ensure the speaker can be measured independently of room effects or any of several electronic techniques that to some extent substitute for such chambers some developers eschew anechoic chambers in favor of specific standardized room setups intended to simulate reallife listening conditions fabrication of finished loudspeaker systems has become segmented depending largely on price shipping costs and weight limitations highend speaker systems which are typically heavier and often larger than economic shipping allows outside local regions are usually made in their target market region and can cost 140000 or more per pair economical mass market speaker systems and drivers available for much lower costs may be manufactured in china or other lowcost manufacturing locations driver types a fourway high fidelity loudspeaker system each of the four drivers outputs a different frequency range the fifth aperture at the bottom is a bass reflex port individual electrodynamic drivers provide their best performance within a limited frequency range multiple drivers eg subwoofers woofers midrange drivers and tweeters are generally combined into a complete loudspeaker system to provide performance beyond that constraint the three most commonly used sound radiation systems are the cone dome and horn type drivers fullrange drivers fullrange speaker a fullrange driver is a speaker designed to be used alone to reproduce an audio channel without the help of other drivers and therefore must cover the entire audio frequency range these drivers are small typically 3 to 8 inches 76 to 203cm in diameter to permit reasonable high frequency response and carefully designed to give lowdistortion output at low frequencies though with reduced maximum output level fullrange or more accurately widerange drivers are most commonly heard in public address systems in televisions although some models are suitable for hifi listening small radios intercoms some computer speakers etc in hifi speaker systems the use of widerange drive units can avoid undesirable interactions between multiple drivers caused by noncoincident driver location or crossover network issues fans of widerange driver hifi speaker systems claim a coherence of sound due to the single source and a resulting lack of interference and likely also to the lack of crossover components detractors typically cite widerange drivers limited frequency response and modest output abilities most especially at low frequencies together with their requirement for large elaborate expensive enclosuressuch as transmission lines quarter wave resonators or hornsto approach optimum performance with the advent of neodymium drivers lowcost quarterwave transmission lines are made possible and are increasingly made availably commercially fullrange drivers often employ an additional cone called a whizzer a small light cone attached to the joint between the voice coil and the primary cone the whizzer cone extends the highfrequency response of the driver and broadens its high frequency directivity which would otherwise be greatly narrowed due to the outer diameter cone material failing to keep up with the central voice coil at higher frequencies the main cone in a whizzer design is manufactured so as to flex more in the outer diameter than in the center the result is that the main cone delivers low frequencies and the whizzer cone contributes most of the higher frequencies since the whizzer cone is smaller than the main diaphragm output dispersion at high frequencies is improved relative to an equivalent single larger diaphragm limitedrange drivers also used alone are typically found in computers toys and clock radios these drivers are less elaborate and less expensive than widerange drivers and they may be severely compromised to fit into very small mounting locations in these applications sound quality is a low priority the human ear is remarkably tolerant of poor sound quality and the distortion inherent in limitedrange drivers may enhance their output at high frequencies increasing clarity when listening to spoken word material subwoofer subwoofer a subwoofer is a woofer driver used only for the lowestpitched part of the audio spectrum typically below 200hz for consumer systems because the intended range of frequencies is limited subwoofer system design is usually simpler in many respects than for conventional loudspeakers often consisting of a single driver enclosed in a suitable box or enclosure since sound in this frequency range can easily bend around corners by diffraction the speaker aperture does not have to face the audience and subwoofers can be mounted in the bottom of the enclosure facing the floor this is eased by the limitations of human hearing at low frequencies such sounds cannot be located in space due to their large wavelengths compared to higher frequencies which produce differential effects in the ears due to shadowing by the head and diffraction around it both of which we rely upon for localization clues to accurately reproduce very low bass notes without unwanted resonances typically from cabinet panels subwoofer systems must be solidly constructed and properly braced to avoid unwanted sounds of cabinet vibrations as a result good subwoofers are typically quite heavy many subwoofer systems include integrated power amplifiers and electronic subsonic subfilters with additional controls relevant to lowfrequency reproduction eg a crossover knob and a phase switch these variants are known as active or powered subwoofers with the former including a power amplifier in contrast passive subwoofers require external amplification in typical installations subwoofers are physically separated from the rest of the speaker cabinets because of propagation delay their output may be somewhat out of phase from another subwoofer on another channel or slightly out of phase with the rest of the sound consequently a subwoofers power amp often has a phasedelay adjustment approximately 1 ms of delay is required for each additional foot of separation from the listener which may improve performance of the system as a whole at subwoofer frequencies and perhaps an octave or so above the crossover point however the influence of room resonances sometimes called standing waves is typically so large that such issues are secondary in practice subwoofers are widely used in large concert and midsized venue sound reinforcement systems subwoofer cabinets are often built with a bass reflex port ie a hole cut into the cabinet with a tube attached to it a design feature which if properly engineered improves bass performance and increases efficiency woofer woofer a woofer is a driver that reproduces low frequencies the driver works with the characteristics of the enclosure to produce suitable low frequencies see speaker enclosure for some of the design choices available indeed both are so closely connected that they must be considered together in use only at design time do the separate properties of enclosure and woofer matter individually some loudspeaker systems use a woofer for the lowest frequencies sometimes well enough that a subwoofer is not needed additionally some loudspeakers use the woofer to handle middle frequencies eliminating the midrange driver this can be accomplished with the selection of a tweeter that can work low enough that combined with a woofer that responds high enough the two drivers add coherently in the middle frequencies midrange driver midrange speaker a midrange speaker is a loudspeaker driver that reproduces a band of frequencies generally between 16khz otherwise known as the mid frequencies between the woofer and tweeter midrange driver diaphragms can be made of paper or composite materials and can be direct radiation drivers rather like smaller woofers or they can be compression drivers rather like some tweeter designs if the midrange driver is a direct radiator it can be mounted on the front baffle of a loudspeaker enclosure or if a compression driver mounted at the throat of a horn for added output level and control of radiation pattern tweeter exploded view of a dome tweeter tweeter a tweeter is a highfrequency driver that reproduces the highest frequencies in a speaker system a major problem in tweeter design is achieving wide angular sound coverage offaxis response since high frequency sound tends to leave the speaker in narrow beams softdome tweeters are widely found in home stereo systems and hornloaded compression drivers are common in professional sound reinforcement ribbon tweeters have gained popularity in recent years as the output power of some designs has been increased to levels useful for professional sound reinforcement and their output pattern is wide in the horizontal plane a pattern that has convenient applications in concert sound coaxial drivers a coaxial driver is a loudspeaker driver with two or several combined concentric drivers coaxial drivers have been produced by many companies such as altec tannoy pioneer kef seas bc speakers bms cabasse and genelec system design electronic symbol for a speaker crossover audio crossover a passive crossover biampedused in multidriver speaker systems the crossover is an assembly of filters that separate the input signal into different frequency ranges ie bands according to the requirements of each driver hence the drivers receive power only at their operating frequency the sound frequency range they were designed for thereby reducing distortion in the drivers and interference between them the ideal characteristics of a crossover may include perfect outofband attenuation at the output of each filter no amplitude variation ripple within each passband no phase delay between overlapping frequency bands to name just a few crossovers can be passive or active a passive crossover is an electronic circuit that uses a combination of one or more resistors inductors or nonpolar capacitors these components are combined to form a filter network and are most often placed between the full frequencyrange power amplifier and the loudspeaker drivers to divide the amplifiers signal into the necessary frequency bands before being delivered to the individual drivers passive crossover circuits need no external power beyond the audio signal itself but have some disadvantages they may require larger inductors and capacitors due to power handling requirements being driven by the amplifier limited component availability to optimize the crossovers characteristics at such power levels etc unlike active crossovers which include a builtin amplifier passive crossovers have an inherent attenuation within the passband typically leading to a reduction in damping factor before the voice coil some loudspeaker designs use a combination of passive and active crossover filtering such as a passive crossover between the mid and highfrequency drivers and an active crossover between the lowfrequency driver and the combined mid and high frequencies passive crossovers are commonly installed inside speaker boxes and are by far the most usual type of crossover for home and lowpower use in car audio systems passive crossovers may be in a separate box necessary to accommodate the size of the components used passive crossovers may be simple for loworder filtering or complex to allow steep slopes such as 18 or 24db per octave passive crossovers can also be designed to compensate for undesired characteristics of driver horn or enclosure resonances enclosures loudspeaker enclosure an unusual threeway speaker system the cabinet is narrow to raise the frequency where a diffraction effect called the baffle step occurs most loudspeaker systems consist of drivers mounted in an enclosure or cabinet the role of the enclosure is to prevent sound waves emanating from the back of a driver from interfering destructively with those from the front the sound waves emitted from the back are 180 out of phase with those emitted forward so without an enclosure they typically cause cancellations which significantly degrade the level and quality of sound at low frequencies the simplest driver mount is a flat panel ie baffle with the drivers mounted in holes in it however in this approach sound frequencies with a wavelength longer than the baffle dimensions are canceled out because the antiphase radiation from the rear of the cone interferes with the radiation from the front with an infinitely large panel this interference could be entirely prevented a sufficiently large sealed box can approach this behavior since panels of infinite dimensions are impossible most enclosures function by containing the rear radiation from the moving diaphragm a sealed enclosure prevents transmission of the sound emitted from the rear of the loudspeaker by confining the sound in a rigid and airtight box techniques used to reduce transmission of sound through the walls of the cabinet include thicker cabinet walls lossy wall material internal bracing curved cabinet wallsor more rarely viscoelastic materials eg mineralloaded bitumen or thin lead sheeting applied to the interior enclosure walls however a rigid enclosure reflects sound internally which can then be transmitted back through the loudspeaker diaphragmagain resulting in degradation of sound quality this can be reduced by internal absorption using absorptive materials often called damping such as glass wool wool or synthetic fiber batting within the enclosure the internal shape of the enclosure can also be designed to reduce this by reflecting sounds away from the loudspeaker diaphragm where they may then be absorbed other enclosure types alter the rear sound radiation so it can add constructively to the output from the front of the cone designs that do this including bass reflex passive radiator transmission line etc are often used to extend the effective lowfrequency response and increase lowfrequency output of the driver to make the transition between drivers as seamless as possible system designers have attempted to timealign or phase adjust the drivers by moving one or more driver mounting locations forward or back so that the acoustic center of each driver is in the same vertical plane this may also involve tilting the face speaker back providing a separate enclosure mounting for each driver or less commonly using electronic techniques to achieve the same effect these attempts have resulted in some unusual cabinet designs the speaker mounting scheme including cabinets can also cause diffraction resulting in peaks and dips in the frequency response the problem is usually greatest at higher frequencies where wavelengths are similar to or smaller than cabinet dimensions the effect can be minimized by rounding the front edges of the cabinet curving the cabinet itself using a smaller or narrower enclosure choosing a strategic driver arrangement using absorptive material around a driver or some combination of these and other schemes horn loudspeakers a threeway loudspeaker that uses horns in front of each of the three drivers a shallow horn for the tweeter a long straight horn for mid frequencies and a folded horn for the woofer horn loudspeaker horn loudspeakers are the oldest form of loudspeaker system the use of horns as voiceamplifying megaphones dates at least to the 17th century and horns were used in mechanical gramophones as early as 1857 horn loudspeakers use a shaped waveguide in front of or behind the driver to increase the directivity of the loudspeaker and to transform a small diameter high pressure condition at the driver cone surface to a large diameter low pressure condition at the mouth of the horn this improves the acousticelectromechanical impedance match between the driver and ambient air increasing efficiency and focusing the sound over a narrower area the size of the throat mouth the length of the horn as well as the area expansion rate along it must be carefully chosen to match the drive to properly provide this transforming function over a range of frequencies every horn performs poorly outside its acoustic limits at both high and low frequencies the length and crosssectional mouth area required to create a bass or subbass horn require a horn many feet long folded horns can reduce the total size but compel designers to make compromises and accept increased complication such as cost and construction some horn designs not only fold the low frequency horn but use the walls in a room corner as an extension of the horn mouth in the late 1940s horns whose mouths took up much of a room wall were not unknown amongst hifi fans room sized installations became much less acceptable when two or more were required a horn loaded speaker can have a sensitivity as high as 110db at 283 volts 1 watt at 8 ohms at 1 meter this is a hundredfold increase in output compared to a speaker rated at 90db sensitivity and is invaluable in applications where high sound levels are required or amplifier power is limited wiring connections twoway binding posts on a loudspeaker connected using banana plugs a 4ohm loudspeaker with two pairs of binding posts capable of accepting biwiring after the removal of two metal straps most home hifi loudspeakers use two wiring points to connect to the source of the signal for example to the audio amplifier or receiver to accept the wire connection the loudspeaker enclosure may have binding posts spring clips or a panelmount jack if the wires for a pair of speakers are not connected with respect to the proper electrical polarity the and connections on the speaker and amplifier should be connected to and to speaker cable is almost always marked so that one conductor of a pair can be distinguished from the other even if it has run under or behind things in its run from amplifier to speaker location the loudspeakers are said to be out of phase or more properly out of polarity with sound reinforcement system pa system and instrument amplifier speaker enclosures cables and some type of jack or connector are typically used lower and midpriced sound system and instrument speaker cabinets often use 14 speaker cable jacks higherpriced and higher powered sound system cabinets and instrument speaker cabinets often use speakon connectors speakon connectors are considered to be safer for high wattage amplifiers because the connector is designed so that human users cannot touch the connectors wireless speakers wireless speaker hp roar wireless speaker wireless speakers are very similar to traditional wired loudspeakers but they receive audio signals using radio frequency rf waves rather than over audio cables there is normally an amplifier integrated in the speakers cabinet because the rf waves alone are not enough to drive the speaker this integration of amplifier and loudspeaker is known as an active loudspeaker manufacturers of these loudspeakers design them to be as lightweight as possible while producing the maximum amount of audio output efficiency wireless speakers still need power so require a nearby ac power outlet or possibly batteries only the wire to the amplifier is eliminated specifications specifications label on a loudspeaker speaker specifications generally include speaker or driver type individual units only fullrange woofer tweeter or midrange size of individual drivers for cone drivers the quoted size is generally the outside diameter of the basket however it may less commonly also be the diameter of the cone surround measured apex to apex or the distance from the center of one mounting hole to its opposite voicecoil diameter may also be specified if the loudspeaker has a compression horn driver the diameter of the horn throat may be given rated power nominal or even continuous power and peak or maximum shortterm power a loudspeaker can handle ie maximum input power before destroying the loudspeaker it is never the sound output the loudspeaker produces a driver may be damaged at much less than its rated power if driven past its mechanical limits at lower frequencies in some jurisdictions power handling has a legal meaning allowing comparisons between loudspeakers under consideration elsewhere the variety of meanings for power handling capacity can be quite confusing impedance typically 4 ohms 8 etc baffle or enclosure type enclosed systems only sealed bass reflex etc number of drivers complete speaker systems only twoway threeway etc class of loudspeaker class 1 maximum spl 110119 db the type of loudspeaker used for reproducing a person speaking in a small space or for background music mainly used as fill speakers for class 2 or class 3 speakers typically small 4 or 5 woofers and dome tweeters class 2 maximum spl 120129 db the type of medium powercapable loudspeaker used for reinforcement in small to medium spaces or as fill speakers for class 3 or class 4 speakers typically 5 to 8 woofers and dome tweeters class 3 maximum spl 130139 db high powercapable loudspeakers used in main systems in small to medium spaces also used as fill speakers for class 4 speakers typically 65 to 12 woofers and 2 or 3 compression drivers for high frequencies class 4 maximum spl 140 db and higher very high powercapable loudspeakers used as mains in medium to large spaces or for fill speakers for these medium to large spaces 10 to 15 woofers and 3 compression drivers and optionally crossover frequencyies multidriver systems only the nominal frequency boundaries of the division between drivers frequency response the measured or specified output over a specified range of frequencies for a constant input level varied across those frequencies it sometimes includes a variance limit such as within 25db thielesmall parameters individual drivers only these include the drivers fs resonance frequency qts a drivers q more or less its damping factor at resonant frequency vas the equivalent air compliance volume of the driver etc sensitivity the sound pressure level produced by a loudspeaker in a nonreverberant environment often specified in db and measured at 1 meter with an input of 1 watt 283 rms volts into 8 typically at one or more specified frequencies manufacturers often use this rating in marketing material maximum sound pressure level the highest output the loudspeaker can manage short of damage or not exceeding a particular distortion level manufacturers often use this rating in marketing materialcommonly without reference to frequency range or distortion level electrical characteristics of dynamic loudspeakers electrical characteristics of dynamic loudspeakers the load that a driver presents to an amplifier consists of a complex electrical impedancea combination of resistance and both capacitive and inductive reactance which combines properties of the driver its mechanical motion the effects of crossover components if any are in the signal path between amplifier and driver and the effects of air loading on the driver as modified by the enclosure and its environment most amplifiers output specifications are given at a specific power into an ideal resistive load however a loudspeaker does not have a constant impedance across its frequency range instead the voice coil is inductive the driver has mechanical resonances the enclosure changes the drivers electrical and mechanical characteristics and a passive crossover between the drivers and the amplifier contributes its own variations the result is a load impedance that varies widely with frequency and usually a varying phase relationship between voltage and current as well also changing with frequency some amplifiers can cope with the variation better than others can to make sound a loudspeaker is driven by modulated electric current produced by an amplifier that pass through a speaker coil which then through inductance creates a magnetic field around the coil creating a magnetic field the electric current variations that pass through the speaker are thus converted to a varying magnetic field whose interaction with the drivers magnetic field moves the speaker diaphragm which thus forces the driver to produce air motion that is similar to the original signal from the amplifier electromechanical measurements examples of typical measurements are amplitude and phase characteristics vs frequency impulse response under one or more conditions eg square waves sine wave bursts etc directivity vs frequency eg horizontally vertically spherically etc harmonic and intermodulation distortion vs sound pressure level spl output using any of several test signals stored energy ie ringing at various frequencies impedance vs frequency and smallsignal vs largesignal performance most of these measurements require sophisticated and often expensive equipment to perform and also good judgment by the operator but the raw sound pressure level output is rather easier to report and so is often the only specified valuesometimes in misleadingly exact terms the sound pressure level spl a loudspeaker produces is measured in decibels dbspl efficiency vs sensitivity loudspeaker efficiency is defined as the sound power output divided by the electrical power input most loudspeakers are inefficient transducers only about 1 of the electrical energy sent by an amplifier to a typical home loudspeaker is converted to acoustic energy the remainder is converted to heat mostly in the voice coil and magnet assembly the main reason for this is the difficulty of achieving proper impedance matching between the acoustic impedance of the drive unit and the air it radiates into at low frequencies improving this match is the main purpose of speaker enclosure designs the efficiency of loudspeaker drivers varies with frequency as well for instance the output of a woofer driver decreases as the input frequency decreases because of the increasingly poor match between air and the driver driver ratings based on the spl for a given input are called sensitivity ratings and are notionally similar to efficiency sensitivity is usually defined as so many decibels at 1w electrical input measured at 1 meter except for headphones often at a single frequency the voltage used is often 283vrms which is 1watt into an 8 nominal speaker impedance approximately true for many speaker systems measurements taken with this reference are quoted as db with 283v 1m the sound pressure output is measured at or mathematically scaled to be equivalent to a measurement taken at one meter from the loudspeaker and onaxis directly in front of it under the condition that the loudspeaker is radiating into an infinitely large space and mounted on an infinite baffle clearly then sensitivity does not correlate precisely with efficiency as it also depends on the directivity of the driver being tested and the acoustic environment in front of the actual loudspeaker for example a cheerleaders horn produces more sound output in the direction it is pointed by concentrating sound waves from the cheerleader in one direction thus focusing them the horn also improves impedance matching between the voice and the air which produces more acoustic power for a given speaker power in some cases improved impedance matching via careful enclosure design lets the speaker produce more acoustic power typical home loudspeakers have sensitivities of about 85 to 95db for 1w 1man efficiency of 054 sound reinforcement and public address loudspeakers have sensitivities of perhaps 95 to 102db for 1w 1man efficiency of 410 rock concert stadium pa marine hailing etc speakers generally have higher sensitivities of 103 to 110db for 1w 1man efficiency of 1020 a driver with a higher maximum power rating cannot necessarily be driven to louder levels than a lowerrated one since sensitivity and power handling are largely independent properties in the examples that follow assume for simplicity that the drivers being compared have the same electrical impedance are operated at the same frequency within both drivers respective pass bands and that power compression and distortion are low for the first example a speaker 3db more sensitive than another produces double the sound power is 3db louder for the same power input thus a 100w driver a rated at 92db for 1w 1m sensitivity puts out twice as much acoustic power as a 200w driver b rated at 89db for 1w 1m when both are driven with 100w of input power in this particular example when driven at 100w speaker a produces the same spl or loudness as speaker b would produce with 200w input thus a 3db increase in sensitivity of the speaker means that it needs half the amplifier power to achieve a given spl this translates into a smaller less complex power amplifierand often to reduced overall system cost it is typically not possible to combine high efficiency especially at low frequencies with compact enclosure size and adequate low frequency response one can for the most part choose only two of the three parameters when designing a speaker system so for example if extended lowfrequency performance and small box size are important one must accept low efficiency listening environment room acoustics at jay pritzker pavilion a lares system is combined with a zoned sound reinforcement system both suspended on an overhead steel trellis to synthesize an indoor acoustic environment outdoors the interaction of a loudspeaker system with its environment is complex and is largely out of the loudspeaker designers control most listening rooms present a more or less reflective environment depending on size shape volume and furnishings this means the sound reaching a listeners ears consists not only of sound directly from the speaker system but also the same sound delayed by traveling to and from and being modified by one or more surfaces these reflected sound waves when added to the direct sound cause cancellation and addition at assorted frequencies eg from resonant room modes thus changing the timbre and character of the sound at the listeners ears the human brain is very sensitive to small variations including some of these and this is part of the reason why a loudspeaker system sounds different at different listening positions or in different rooms a significant factor in the sound of a loudspeaker system is the amount of absorption and diffusion present in the environment clapping ones hands in a typical empty room without draperies or carpet produces a zippy fluttery echo due both to a lack of absorption and to reverberation that is repeated echoes from flat reflective walls floor and ceiling the addition of hard surfaced furniture wall hangings shelving and even baroque plaster ceiling decoration changes the echoes primarily because of diffusion caused by reflective objects with shapes and surfaces having sizes on the order of the sound wavelengths this somewhat breaks up the simple reflections otherwise caused by bare flat surfaces and spreads the reflected energy of an incident wave over a larger angle on reflection placement in a typical rectangular listening room the hard parallel surfaces of the walls floor and ceiling cause primary acoustic resonance nodes in each of the three dimensions leftright updown and forwardbackward furthermore there are more complex resonance modes involving three four five and even all six boundary surfaces combining to create standing waves low frequencies excite these modes the most since long wavelengths are not much affected by furniture compositions or placement the mode spacing is critical especially in small and medium size rooms like recording studios home theaters and broadcast studios the proximity of the loudspeakers to room boundaries affects how strongly the resonances are excited as well as affecting the relative strength at each frequency the location of the listener is critical too as a position near a boundary can have a great effect on the perceived balance of frequencies this is because standing wave patterns are most easily heard in these locations and at lower frequencies below the schroeder frequency typically around 200300hz depending on room size directivity acousticians in studying the radiation of sound sources have developed some concepts important to understanding how loudspeakers are perceived the simplest possible radiating source is a point source sometimes called a simple source an ideal point source is an infinitesimally small point radiating sound it may be easier to imagine a tiny pulsating sphere uniformly increasing and decreasing in diameter sending out sound waves in all directions equally independent of frequency any object radiating sound including a loudspeaker system can be thought of as being composed of combinations of such simple point sources the radiation pattern of a combination of point sources is not the same as for a single source but depends on the distance and orientation between the sources the position relative to them from which the listener hears the combination and the frequency of the sound involved using geometry and calculus some simple combinations of sources are easily solved others are not one simple combination is two simple sources separated by a distance and vibrating out of phase one miniature sphere expanding while the other is contracting the pair is known as a doublet or dipole and the radiation of this combination is similar to that of a very small dynamic loudspeaker operating without a baffle the directivity of a dipole is a figure 8 shape with maximum output along a vector that connects the two sources and minimums to the sides when the observing point is equidistant from the two sources where the sum of the positive and negative waves cancel each other while most drivers are dipoles depending on the enclosure to which they are attached they may radiate as monopoles dipoles or bipoles if mounted on a finite baffle and these out of phase waves are allowed to interact dipole peaks and nulls in the frequency response result when the rear radiation is absorbed or trapped in a box the diaphragm becomes a monopole radiator bipolar speakers made by mounting inphase monopoles both moving out of or into the box in unison on opposite sides of a box are a method of approaching omnidirectional radiation patterns polar plots of a fourdriver industrial columnar public address loudspeaker taken at six frequencies note how the pattern is nearly omnidirectional at low frequencies converging to a wide fanshaped pattern at 1 khz then separating into lobes and getting weaker at higher frequencies in real life individual drivers are complex 3d shapes such as cones and domes and they are placed on a baffle for various reasons a mathematical expression for the directivity of a complex shape based on modeling combinations of point sources is usually not possible but in the far field the directivity of a loudspeaker with a circular diaphragm is close to that of a flat circular piston so it can be used as an illustrative simplification for discussion as a simple example of the mathematical physics involved consider the following the formula for far field directivity of a flat circular piston in an infinite baffle is p p 0 j 1 k a sin k a sin displaystyle ptheta frac p0j1kasin theta kasin theta where k a 2 a displaystyle kafrac 2pi alambda p 0 displaystyle p0 is the pressure on axis a displaystyle a is the piston radius displaystyle lambda is the wavelength ie c f speed of sound frequency displaystyle lambda frac cffrac textspeed of soundtextfrequency displaystyle theta is the angle off axis and j 1 displaystyle j1 is the bessel function of the first kind a planar source radiates sound uniformly for low frequencies wavelengths longer than the dimensions of the planar source and as frequency increases the sound from such a source focuses into an increasingly narrower angle the smaller the driver the higher the frequency where this narrowing of directivity occurs even if the diaphragm is not perfectly circular this effect occurs such that larger sources are more directive several loudspeaker designs approximate this behavior most are electrostatic or planar magnetic designs various manufacturers use different driver mounting arrangements to create a specific type of sound field in the space for which they are designed the resulting radiation patterns may be intended to more closely simulate the way sound is produced by real instruments or simply create a controlled energy distribution from the input signal some using this approach are called monitors as they are useful in checking the signal just recorded in a studio an example of the first is a room corner system with many small drivers on the surface of a 18 sphere a system design of this type was patented and produced commercially by professor amar bosethe 2201 later bose models have deliberately emphasized production of both direct and reflected sound by the loudspeaker itself regardless of its environment the designs are controversial in high fidelity circles but have proven commercially successful several other manufacturers designs follow similar principles directivity is an important issue because it affects the frequency balance of sound a listener hears and also the interaction of the speaker system with the room and its contents a very directive sometimes termed beamy speaker ie on an axis perpendicular to the speaker face may result in a reverberant field lacking in high frequencies giving the impression the speaker is deficient in treble even though it measures well on axis eg flat across the entire frequency range speakers with very wide or rapidly increasing directivity at high frequencies can give the impression that there is too much treble if the listener is on axis or too little if the listener is off axis this is part of the reason why onaxis frequency response measurement is not a complete characterization of the sound of a given loudspeaker other speaker designs while dynamic cone speakers remain the most popular choice many other speaker technologies exist with a diaphragm movingiron loudspeakers moving iron speaker moving iron speaker the moving iron speaker was the first type of speaker that was invented unlike the newer dynamic moving coil design a movingiron speaker uses a stationary coil to vibrate a magnetized piece of metal called the iron reed or armature the metal is either attached to the diaphragm or is the diaphragm itself this design was the original loudspeaker design dating back to the early telephone moving iron drivers are inefficient and can only produce a small band of sound they require large magnets and coils to increase force balanced armature drivers a type of moving iron driver use an armature that moves like a seesaw or diving board since they are not damped they are highly efficient but they also produce strong resonances they are still used today for high end earphones and hearing aids where small size and high efficiency are important piezoelectric speakers piezoelectric speaker see also piezo tweeter a piezoelectric buzzer the white ceramic piezoelectric material can be seen fixed to a metal diaphragm piezoelectric speakers are frequently used as beepers in watches and other electronic devices and are sometimes used as tweeters in lessexpensive speaker systems such as computer speakers and portable radios piezoelectric speakers have several advantages over conventional loudspeakers they are resistant to overloads that would normally destroy most high frequency drivers and they can be used without a crossover due to their electrical properties there are also disadvantages some amplifiers can oscillate when driving capacitive loads like most piezoelectrics which results in distortion or damage to the amplifier additionally their frequency response in most cases is inferior to that of other technologies this is why they are generally used in single frequency beeper or noncritical applications piezoelectric speakers can have extended high frequency output and this is useful in some specialized circumstances for instance sonar applications in which piezoelectric variants are used as both output devices generating underwater sound and as input devices acting as the sensing components of underwater microphones they have advantages in these applications not the least of which is simple and solid state construction that resists seawater better than a ribbon or cone based device would in 2013 kyocera introduced piezoelectric ultrathin mediumsize film speakers with only 1 millimeter of thickness and 7 grams of weight for their 55 oled televisions and they hope the speakers will also be used in pcs and tablets besides mediumsize there are also large and small sizes which can all produce relatively the same quality of sound and volume within 180 degrees the highly responsive speaker material provides better clarity than traditional tv speakers magnetostatic loudspeakers magnetostatic loudspeaker magnetostatic loudspeaker instead of a voice coil driving a speaker cone a magnetostatic speaker uses an array of metal strips bonded to a large film membrane the magnetic field produced by signal current flowing through the strips interacts with the field of permanent bar magnets mounted behind them the force produced moves the membrane and so the air in front of it typically these designs are less efficient than conventional movingcoil speakers magnetostrictive speakers magnetostrictive transducers based on magnetostriction have been predominantly used as sonar ultrasonic sound wave radiators but their use has spread also to audio speaker systems magnetostrictive speaker drivers have some special advantages they can provide greater force with smaller excursions than other technologies low excursion can avoid distortions from large excursion as in other designs the magnetizing coil is stationary and therefore more easily cooled they are robust because delicate suspensions and voice coils are not required magnetostrictive speaker modules have been produced by fostex electrostatic loudspeakers electrostatic loudspeaker schematic showing an electrostatic speakers construction and its connections the thickness of the diaphragm and grids has been exaggerated for the purpose of illustration electrostatic loudspeakers use a high voltage electric field rather than a magnetic field to drive a thin statically charged membrane because they are driven over the entire membrane surface rather than from a small voice coil they ordinarily provide a more linear and lowerdistortion motion than dynamic drivers they also have a relatively narrow dispersion pattern that can make for precise soundfield positioning however their optimum listening area is small and they are not very efficient speakers they have the disadvantage that the diaphragm excursion is severely limited because of practical construction limitationsthe further apart the stators are positioned the higher the voltage must be to achieve acceptable efficiency this increases the tendency for electrical arcs as well as increasing the speakers attraction of dust particles arcing remains a potential problem with current technologies especially when the panels are allowed to collect dust or dirt and are driven with high signal levels electrostatics are inherently dipole radiators and due to the thin flexible membrane are less suited for use in enclosures to reduce low frequency cancellation as with common cone drivers due to this and the low excursion capability full range electrostatic loudspeakers are large by nature and the bass rolls off at a frequency corresponding to a quarter wavelength of the narrowest panel dimension to reduce the size of commercial products they are sometimes used as a high frequency driver in combination with a conventional dynamic driver that handles the bass frequencies effectively electrostatics are usually driven through a stepup transformer that multiplies the voltage swings produced by the power amplifier this transformer also multiplies the capacitive load that is inherent in electrostatic transducers which means the effective impedance presented to the power amplifiers varies widely by frequency a speaker that is nominally 8 ohms may actually present a load of 1 ohm at higher frequencies which is challenging to some amplifier designs ribbon and planar magnetic loudspeakers a ribbon speaker consists of a thin metalfilm ribbon suspended in a magnetic field the electrical signal is applied to the ribbon which moves with it to create the sound the advantage of a ribbon driver is that the ribbon has very little mass thus it can accelerate very quickly yielding very good highfrequency response ribbon loudspeakers are often very fragilesome can be torn by a strong gust of air most ribbon tweeters emit sound in a dipole pattern a few have backings that limit the dipole radiation pattern above and below the ends of the more or less rectangular ribbon there is less audible output due to phase cancellation but the precise amount of directivity depends on ribbon length ribbon designs generally require exceptionally powerful magnets which makes them costly to manufacture ribbons have a very low resistance that most amplifiers cannot drive directly as a result a step down transformer is typically used to increase the current through the ribbon the amplifier sees a load that is the ribbons resistance times the transformer turns ratio squared the transformer must be carefully designed so that its frequency response and parasitic losses do not degrade the sound further increasing cost and complication relative to conventional designs planar magnetic speakers having printed or embedded conductors on a flat diaphragm are sometimes described as ribbons but are not truly ribbon speakers the term planar is generally reserved for speakers with roughly rectangular flat surfaces that radiate in a bipolar ie front and back manner planar magnetic speakers consist of a flexible membrane with a voice coil printed or mounted on it the current flowing through the coil interacts with the magnetic field of carefully placed magnets on either side of the diaphragm causing the membrane to vibrate more or less uniformly and without much bending or wrinkling the driving force covers a large percentage of the membrane surface and reduces resonance problems inherent in coildriven flat diaphragms bending wave loudspeakers bending wave transducers use a diaphragm that is intentionally flexible the rigidity of the material increases from the center to the outside short wavelengths radiate primarily from the inner area while longer waves reach the edge of the speaker to prevent reflections from the outside back into the center long waves are absorbed by a surrounding damper such transducers can cover a wide frequency range 80hz to 35000hz and have been promoted as being close to an ideal point sound source this uncommon approach is being taken by only a very few manufacturers in very different arrangements the ohm walsh loudspeakers use a unique driver designed by lincoln walsh who had been a radar development engineer in wwii he became interested in audio equipment design and his last project was a unique oneway speaker using a single driver the cone faced down into a sealed airtight enclosure rather than move backandforth as conventional speakers do the cone rippled and created sound in a manner known in rf electronics as a transmission line the new speaker created a cylindrical sound field lincoln walsh died before his speaker was released to the public the ohm acoustics firm has produced several loudspeaker models using the walsh driver design since then german physiks an audio equipment firm in germany also produces speakers using this approach the german firm manger has designed and produced a bending wave driver that at first glance appears conventional in fact the round panel attached to the voice coil bends in a carefully controlled way to produce full range sound josef w manger was awarded with the diesel medal for extraordinary developments and inventions by the german institute of inventions flat panel loudspeakers there have been many attempts to reduce the size of speaker systems or alternatively to make them less obvious one such attempt was the development of exciter transducer coils mounted to flat panels to act as sound sources most accurately called exciterpanel drivers heil air motion transducers air motion transformer in heils air motion transducer current through the membrane 2 causes it to move left and right in magnetic field 6 moving air in and out along directions 8 barriers 4 prevent air from moving in unintended directions oskar heil invented the air motion transducer in the 1960s in this approach a pleated diaphragm is mounted in a magnetic field and forced to close and open under control of a music signal air is forced from between the pleats in accordance with the imposed signal generating sound the drivers are less fragile than ribbons and considerably more efficient and able to produce higher absolute output levels than ribbon electrostatic or planar magnetic tweeter designs ess a california manufacturer licensed the design employed heil and produced a range of speaker systems using his tweeters during the 1970s and 1980s lafayette radio a large us retail store chain also sold speaker systems using such tweeters for a time there are several manufacturers of these drivers at least two in germanyone of which produces a range of highend professional speakers using tweeters and midrange drivers based on the technology and the drivers are increasingly used in professional audio martin logan produces several amt speakers in the us and goldenear technologies incorporates them in its entire speaker line transparent ionic conduction speaker in 2013 a research team introduced transparent ionic conduction speaker which a 2 layers transparent conductive gel and a layer of transparent rubber in between to make high voltage and high actuation work to reproduce good sound quality the speaker is suitable for robotics mobile computing and adaptive optics fields without a diaphragm plasma arc speakers plasma speaker plasma speaker plasma arc loudspeakers use electrical plasma as a radiating element since plasma has minimal mass but is charged and therefore can be manipulated by an electric field the result is a very linear output at frequencies far higher than the audible range problems of maintenance and reliability for this approach tend to make it unsuitable for mass market use in 1978 alan e hill of the air force weapons laboratory in albuquerque nm designed the plasmatronics hill type i a tweeter whose plasma was generated from helium gas produced by rf decomposition of air in an earlier generation of plasma tweeters made by the pioneering dukane corporation who produced the ionovac marketed as the ionofane in the uk during the 1950s currently there remain a few manufacturers in germany who use this design and a doityourself design has been published and has been available on the internet a less expensive variation on this theme is the use of a flame for the driver as flames contain ionized electrically charged gases thermoacoustic speakers in 2008 researchers of tsinghua university demonstrated a thermoacoustic loudspeaker of carbon nanotube thin film whose working mechanism is a thermoacoustic effect sound frequency electric currents are used to periodically heat the cnt and thus result in sound generation in the surrounding air the cnt thin film loudspeaker is transparent stretchable and flexible in 2013 researchers of tsinghua university further present a thermoacoustic earphone of carbon nanotube thin yarn and a thermoacoustic surfacemounted device they are both fully integrated devices and compatible with sibased semiconducting technology rotary woofers a rotary woofer is essentially a fan with blades that constantly change their pitch allowing them to easily push the air back and forth rotary woofers are able to efficiently reproduce infrasound frequencies which are difficult to impossible to achieve on a traditional speaker with a diaphragm they are often employed in movie theaters to recreate rumbling bass effects such as explosions new technologies digital speakers digital speaker digital speakers have been the subject of experiments performed by bell labs as far back as the 1920s the design is simple each bit controls a driver which is either fully on or off problems with this design have led manufacturers to abandon it as impractical for the present first for a reasonable number of bits required for adequate sound reproduction quality the physical size of a speaker system becomes very large secondly due to inherent analog digital conversion problems the effect of aliasing is unavoidable so that the audio output is reflected at equal amplitude in the frequency domain on the other side of the sampling frequency causing an unacceptably high level of ultrasonics to accompany the desired output no workable scheme has been found to adequately deal with this the term digital or digitalready is often used for marketing purposes on speakers or headphones but these systems are not digital in the sense described above rather they are conventional speakers that can be used with digital sound sources eg optical media mp3 players etc as can any conventional speaker association of loudspeaker manufacturing acoustics international alma audio power audiophile bandwidth extension directional sound dust cap echo cancellation electronics ferrofluidheat transfer guitar speaker headphones highend audio isobaric loudspeaker list of loudspeaker manufacturers loudspeaker acoustics long range acoustic devicelrad music centre parabolic loudspeaker phase plug planephones rotary woofer sound from ultrasound soundbar speaker driver speaker stands speaker wire speakerphone studio monitor super tweeter surround sound wikimedia commons has media related to loudspeaker category look up loudspeaker in wiktionary the free dictionary alma a forum for the global loudspeaker industry conversion of sensitivity to energy efficiency in percent for passive loudspeakers article on sensitivity and efficiency of loudspeakers speaker principles illustrated guide to loudspeaker design and practice vtemusic technologymusic technology mechanical electrical electronic and digital sound recording audio channel audio console mixing board binaural recording digital audio workstation daw effects unit equalizer headphones microphone microphone preamplifier monitor speaker multitrack recording music production music sequencer outboard gear recording media phonograph record magnetic tape compact cassette compact disc dat hard disk minidisc mp3 opus analog recording 8track cartridge amplifier cassette deck comparison of analog and digital recording experimental musical instrument phonograph player piano reeltoreel audio tape recording tape recorder playback transducers loudspeaker headphones monitor speaker pa system sound reinforcement system speaker enclosure subwoofer digital audio digital recording digital signal processing live music audio console bass amplifier effects unit foldback guitar amplifier keyboard amplifier pa system radio reverberation sound reinforcement system electronic music chiptune circuit bending drum machine electronic drums electronic musical instrument midi midi controller music workstation sampler sequencer sound module synthesizer theremin software digital audio editor digital audio workstation garageband protools scorewriter software effect processor software sampler software synthesizer professions audio engineer dj guitar technician mixing engineer monitor engineer piano tuner record producer rerecording mixer sound designer sound follower sound operator sound recording engineer tape op people and organizations audio engineering society goji electronics institute of broadcast sound lejaren hiller ircam max mathews musical electronics library professional lighting and sound association robert moog smpte steim related topics audiophile high fidelity home audio home cinema music store professional audio store new interfaces for musical expression nime vehicle audio authority control gnd 40347771 nara 10647904 ndl 00564759 