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. [1]
The narrow part of the horn next to the driver is called the "throat" and the large part farthest away from the driver is called the "mouth". [1] The angular coverage (radiation pattern) of the horn is determined by the shape and flare of the mouth. A major problem of horn speakers is that the radiation pattern varies with frequency; high frequency sound tends to be emitted in narrow beams with poor off-axis performance. [2] Significant improvements have been made, beginning with the "constant directivity" horn invented in 1975 by Don Keele.
The main advantage of horn loudspeakers is they are more efficient; they can typically produce approximately 10 times [3] : p.30 (10 dB) [4] [5] [6] more sound power than a cone speaker from a given amplifier output. Therefore, horns are widely used in public address systems, megaphones, and sound systems for large venues like theaters, auditoriums, and sports stadiums. Their disadvantage is that their frequency response is more uneven because of resonance peaks, and horns have a cutoff frequency below which their response drops off. (The cutoff frequency corresponds to the wavelength equal to the circumference of the horn mouth. [7] ) To achieve adequate response at bass frequencies horn speakers must be very large and cumbersome, so they are more often used for midrange and high frequencies. The first practical loudspeakers, introduced around the turn of the 20th century, were horn speakers. Due to the development in recent decades of cone loudspeakers which sometimes have a flatter frequency response, and the availability of inexpensive amplifier power, the use of horn speakers in high fidelity audio systems over the last decades has declined.
An acoustic horn converts large pressure variations with a small displacement area into a low pressure variation with a large displacement area and vice versa. It does this through the gradual, often exponential increase of the cross sectional area of the horn. The small cross-sectional area of the throat restricts the passage of air thus presenting a high acoustic impedance to the driver. This allows the driver to develop a high pressure for a given displacement. Therefore, the sound waves at the throat are of high pressure and low displacement. The tapered shape of the horn allows the sound waves to gradually decompress and increase in displacement until they reach the mouth where they are of a low pressure but large displacement. [8]
The physics (and mathematics) of horn operation were developed for many years, reaching considerable sophistication before WWII. The most well known early horn loudspeakers were those on mechanical phonographs, where the record moved a heavy metal needle that excited vibrations in a small metal diaphragm that acted as the driver for a horn. A famous example was the horn through which Nipper the RCA dog heard "His Master's Voice". The horn improves the loading and thus gets a better "coupling" of energy from the diaphragm into the air, and the pressure variations therefore get smaller as the volume expands and the sound travels up the horn. This kind of mechanical impedance matching was absolutely necessary in the days of pre-electrical sound reproduction in order to achieve a usable sound level. [9]
The megaphone, a simple cone made of paper or other flexible material, is the oldest and simplest acoustic horn, used prior to loudspeakers as a passive acoustic amplifier for mechanical phonographs and for the human voice; it is still used by cheerleaders and lifeguards. Because the conic section shape describes a portion of a perfect sphere of radiated sound, cones have no phase or amplitude distortion of the wavefront. [2] The small megaphones used in phonographs and as loudhailers were not long enough to reproduce the low frequencies in music; they had a high cutoff frequency which attenuated the bottom two octaves of the sound spectrum, giving the megaphone a characteristic tinny sound. [2]
The exponential horn has an acoustic loading property that allows the speaker driver to remain evenly balanced in output level over its frequency range. The benefits of the design were first published by C.R. Hanna and J. Slepian in 1924 for the American Institute of Electrical Engineers (AIEE). [11] A major drawback is that the exponential horn allows for a narrowing of the radiation pattern as frequency increases, making for high frequency 'beaming' on axis and dull sound off axis. [2] Another concern is that a throat of small diameter is needed for high efficiency at high frequencies but a larger throat is best for low frequencies. A common solution is to use two or more horns, each with the appropriate throat size, mouth size and flare rate for best performance in a selected frequency range, with sufficient overlap between the frequency ranges to provide a smooth transition between horns. Another solution tried in the late 1930s by Harry F. Olson of RCA was to use multiple exponential flare rates, either by connecting increasingly larger horns in series or by subdividing the interior of a single horn. [12] Exponential horns continue to be used by some designers, and in some applications. [13]
A number of symmetrical, narrow dispersion, usually exponential horns can be combined in an array driven by a single driver to produce multicell horns. Patented in 1936 by Edward C. Wente of Western Electric, [14] multicell horns have been used in loudspeakers since 1933 to address the problem of directivity at higher frequencies, and they provide excellent low frequency loading. Their directional control begins to beam both vertically and horizontally in the middle of their target frequency range, narrowing further at high frequencies [2] with level changes as great as 10 dB between lobes. [15] Multicell horns are complex and difficult to fabricate and thus have a higher associated expense. They persisted in public address applications for many years because, even with their faults, they sounded very good, and still do with competent design. [16] The revolutionary coaxial driver, the Altec Lansing Duplex 601 and 604, used a multicell horn for its high frequency component from 1943 to 1998. [17]
Radial horns have two surfaces based on an exponential flare rate, and two straight walls that determine the output pattern. The radial horn exhibits some of the beaming of the exponential horn. [2] Altec sectoral horns were radial horns with vanes placed in the mouth of the horn for the stated purpose of pattern control. For ease in mounting to loudspeaker cabinets, flat front radial horns have been used, for instance by Community in their SQ 90 high-frequency horn. [18] JBL's diffraction or "Smith" horn was a variation on the radial design, using a very small vertical dimension at the mouth as a method of avoiding the mid-range horizontal beaming of radial horns that have a larger vertical dimension at the mouth.
The diffraction horn has been popular in monitor designs and for near-field public address applications which benefit from its wide horizontal dispersion pattern. [15] Counterintuitively, the narrow vertical dimension provided for an expansive vertical output pattern approaching 90° for frequencies of a wavelength equal to the narrow vertical dimension. [16] A very small version of the diffraction horn was designed in 1991 into the JBL model 2405H Ultra-High Frequency Transducer, yielding a 90° x 35° output pattern at 20 kHz. [19]
The tractrix horn is very similar in many respects to the exponential horn and has gained adherents among DIY horn enthusiasts, audiophile consumers, and some manufacturers. [20] It uses a curve formula derived by assuming that a tangent to any point on the horn's inner curve will reach the central axis of the horn with a line segment of set length. At the mouth, the tangent line segment becomes perpendicular to the axis and describes the radius of the mouth. This horn concept was studied by Paul G.A.H. Voigt in the mid-1920s and patented in 1927. [21] The size of the tractrix horn is generated by specifying the desired low frequency "cutoff" or limit which will determine the mouth diameter. [20] Two incremental improvements over the exponential horn include slightly better support for low frequency extension and a somewhat broader high-frequency coverage pattern. [20]
In May 1975, [22] to address problems of beamwidth changing at different frequencies, D. Broadus "Don" Keele, Jr. of Electro-Voice introduced a hybrid horn with an exponential expansion rate near the throat followed by a conical expansion section and ending with a rapidly flaring flange at the mouth. [23] The flange at the mouth solved some remaining problems with lobing at higher frequencies. [16] Don Keele specified in one version of his design a wider horizontal flare for pattern control appropriate to public address purposes. Keele's paper [24] set forth the relationships between mouth size, frequency and coverage angle, providing a basis for many future developments of horn design. [16] One problem found with constant directivity horns is that the horizontal coverage pattern cannot be narrowed without making the vertical coverage pattern too small to be useful. [2]
Subsequent to Keele's work and using his principles, Clifford A. Henricksen and Mark S. Ureda of Altec designed a strikingly different hybrid horn displaying constant directivity traits, the horizontal diffraction or "Mantaray" horn. [25] [26] The Mantaray horn separates desired vertical coverage pattern from horizontal, making it possible to design horns for a variety of coverage patterns. The Mantaray shape starts with a vertically oriented JBL-style diffraction horn, leading into a conical waveguide (earliest designs), or a square or rectangular horn with four planar sides. [27] For midrange beaming control, the outer mouth is expanded further with a short, flared flange in the Keele style, or with added planar sides of a greater flare angle. Low frequency efficiency is not as pronounced as the constant directivity design. [25] Unlike previous designs, the apparent apex, [28] which is the focal point of pattern dispersion, is not the same for every frequency, making for an ellipsoidal wavefront rather than spherical. Because of this, the Mantaray can only be arrayed satisfactorily in one plane (rather than multiple planes). Its abrupt breaks in flare rate causes diffraction, reflection and distortion components. [2]
By 1980, Keele was at JBL where he took both his and Altec's designs a step further. He mated a JBL-style diffraction horn to a secondary horn consisting of exponentially curved sides derived by using two radial formulas. This resulted in a hybrid constant directivity horn that was free from the distortion components associated with abrupt angle changes. [25] The market responded well to the design in products such as the JBL model 4430 studio monitor with its 100° × 100° model 2344 Bi-Radial high frequency horn often called "butt-cheeks". [30] The Bi-Radial design had problems with apparent apex and arrayability in the same manner as the Mantaray. [2]
Ramsa, the professional audio division of Panasonic Corporation, introduced a twin Bessel constant directivity horn shortly after the Mantaray appeared. The design was very similar to the Mantaray and the Bi-Radial but it used a dual series Bessel expansion formula to determine the flare rate of the secondary horn section. [31]
Most popular constant directivity horns (also known as CD horns) suffer from non-spherical wavefronts, limitations in arrayability, and distortion at high sound pressure levels as well as reflections and distortions related to the transition from diffraction slot to secondary horn. [2] They tend toward a narrowing of dispersion pattern at the higher frequencies whose wavelengths approach the width of the throat or the width of the diffraction slot. [15]
Because the CD horn's high frequencies are more spread out over its coverage pattern, they appear attenuated relative to other horns. The CD horn requires an equalization boost of approximately 6 dB per octave [32] with a filter knee centered between 2 and 4 kHz [33] (depending on horn design) in order to sound neutral and balanced. Most manufacturers of active electronic audio crossovers responded to this requirement by adding an optional CD EQ boost filter or high frequency shelf filter. For instance, such circuitry was provided via internal jumper links by BSS in their FDS-310 [34] crossover and by Rane in their AC 22S [35] and AC 23B [36] crossovers. Rane allowed for greater front panel control of two bandpasses ("hi-mid" and "high") using CD horn equalization including sweepable frequency range on their AC 24 crossover. [37] Further refinements of the filtering process are available in DSP-based crossovers.
Firstly published in December 2019 in a Voice Coil article [38] and then at the 148th AES Convention [39] in June 2020, Dario Cinanni presented a new horns family.
The HCD algorithm, already used by SpeakerLAB Horn.ell.a [40] software from 2006, transforms any expansion (exponential, hyperbolic sine, hyperbolic cosine, catenoidal, tractrix, spherical, or a new expansion) horn into a constant directivity horn.
The HCD permits to maintain the same acoustic load of the original expansion. HCD algorithm reduces reflections if compared to a CD horn, or in general to a multiflare horn, providing low distortion at high sound pressure levels.
Similar to the Radial horn HCD offers a constant directivity on one plane, to be specific a progressive constant directivity on the plane along the horn mouth major axis. The progression depends on the selected mouth-ratio. While on the plane along the mouth minor axis we will have an equivalent directivity contour of a circular mouth horn (using the same expansion).
In 1996, Ralph D. Heinz of Renkus-Heinz received a patent for a multiple entry horn which incorporated multiple drivers for two bandpasses, high and mid, whose sound waves all exited into a single horn but at differing distances depending on the bandpass. It was marketed as the "CoEntrant" horn. [41] The mid- and high-frequency drivers in the Renkus-Heinz ST/STX product line both exited through a "Complex Conic" waveguide. [42] In the late 1990s, Thomas J. "Tom" Danley of Sound Physics Labs began working on a three-way multiple entry horn, bringing the SPL-td1 to market in 2000. [43] The design used seven drivers, with one high frequency driver at the horn's throat, four mid-frequency drivers near the throat and two low frequency drivers ported closer to the horn mouth. In 2001, Tom Danley began developing the "Unity" horn for Yorkville Sound, patenting the improvement in 2002. [44] Following the 2003 release of Yorkville's Unity line, [45] Danley formed Danley Sound Labs and developed a significant improvement over the SPL-td1 called the "Synergy" horn, yielding substantially better phase and magnitude response along with smoother polar pattern. The synergy horn design delivered greater power output from a smaller loudspeaker enclosure. [46] Because the design retains pattern control through its crossover regions and over a large range of its total bandwidth, and because the acoustic center of the design is near the rear of the enclosure, it is more easily combined in arrays for public address applications. [47]
The term "waveguide" is used to describe horns with low acoustic loading, such as conic, quadratic, oblate spheroidal or elliptic cylindrical horns. These are designed more to control the radiation pattern rather than to gain efficiency via improved acoustic loading. All horns have some pattern control, and all waveguides provide a degree of acoustic loading, so the difference between a waveguide and a horn is a matter of judgement. [48]
In 1999, Charlie Hughes of Peavey Electronics filed for a patent on a hybrid horn he called Quadratic-Throat Waveguide. [49] The horn was basically a simple conic section but its throat was curved in a circular arc to match the desired throat size for proper mating to the speaker driver. Instead of increasing the horn mouth size with a flare to control midrange beaming, a relatively thin layer of foam covering the mouth edge was found to suit the same end. The QT waveguide, when compared to popular CD horns, produced about 3-4 dB lower levels of second harmonic distortion across all frequencies, and an average of 9 dB lower levels of the more annoying third harmonic distortion. Being without a diffraction slot, the QT waveguide was free from problems with apparent apex, making it arrayable as needed for public address purposes. [2]
Oblate spheroid waveguide (OSWG) horn designs improve directivity pattern control above 1 kHz, provide a lower frequency of directivity to better match the mid-range driver, and, as claimed by inventor Dr. Earl Geddes, mitigate higher order modes, a form of phase and amplitude distortion. The practical limitation of horn length is explicitly not addressed by the theory of OSWG. [50]
Horn loudspeakers are used in many audio applications. The drivers in horn loudspeakers can be very small, even for bass frequencies where conventional loudspeakers would need to be very large for equivalent performance. Horn loudspeakers can be designed to reproduce a wide range of frequencies using a single, small driver; to some extent these can be designed without requiring a crossover.
Horn loudspeakers can also be used to provide the very high sound pressure levels needed for sound reinforcement and public address applications, although in these high sound pressure applications, high fidelity is sometimes compromised for the sake of the necessary efficiency, and also for the controlled dispersion characteristics which are generally required in most large volume spaces. "Gunness Focusing", a new method of counteracting some of the horn distortions, especially in the time domain, was pioneered by Dave Gunness while he was with Eastern Acoustic Works (EAW). EAW horn-loaded loudspeakers that have been processed with this proprietary system show reduced compression driver diaphragm/phase plug time-smear distortion while retaining high output power and controlled dispersion. [51] [52] [53] [54] [55]
Concert venues often use large arrays of horn loudspeakers for high-volume bass reproduction ("bass bins" or subwoofers), in order to provide bass that concertgoers can not only hear but feel. Combining multiple horn loudspeakers in an array affords the same benefits as having a single horn with a greater mouth area: the low frequency cut-off extends lower as the horn mouth gets larger, and the array has the greater output power of multiple drivers.
Commercial cinema theaters often use horn-loaded loudspeakers for pattern control and increased sensitivity needed to fill a large room.
Consumer audio employs horn loudspeakers for controlled directivity (to limit audio reflections from room surfaces such as walls, floor, and ceiling) and for greater speaker sensitivity.
Horn loudspeakers can provide very high efficiencies, making them a good match for very low-powered amplifiers, such as single-ended triode amps or other tube amplifiers. After WWII, some early hi-fi fans went so far as to build low frequency horns whose mouths took up much of a wall of the listening room. The throats were sometimes outside on the lawn, or in the basement. With the coming of stereo in the 1960s, this approach was rarely seen. Many loudspeaker buyers and do-it-yourself loudspeaker fans sought smaller designs for aesthetic reasons.
Some audiophiles use horn loudspeakers for audio reproduction, while others eschew horn systems for their harmonic resonances, finding in them an unpleasant form of distortion. Since there are a variety of horn designs (of differing length, material, and taper), as well as different drivers, it is, to some extent, impossible to give such blanket characterizations to horn loudspeakers. Audiophiles using low power amplifiers, sometimes in the 5 to 25 watt range, may find the high efficiency of horn loudspeakers an especially attractive feature. Conversely, the high sensitivity can also make any background noise present at the amplifier outputs noticeably worse.
Film soundtracks have great dynamic range where peak levels are 20 dB greater than average levels. The high sensitivity of horn loudspeakers aids in achieving movie theater sound levels at the listening position with typical ~100 watts-per-channel receiver/amplifiers used in home cinema. [56]
A subwoofer is a loudspeaker designed to reproduce low-pitched audio frequencies, known as bass and sub-bass, that are lower in frequency than those which can be (optimally) generated by a woofer. The typical frequency range that is covered by 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. Thus, one or more subwoofers are important for high-quality sound reproduction as they are responsible for the lowest two to three octaves of the ten octaves that are audible. This very low-frequency (VLF) range reproduces the natural fundamental tones of the bass drum, electric bass, double bass, grand piano, contrabassoon, tuba, in addition to thunder, gunshots, explosions, etc.
A loudspeaker is an electroacoustic transducer that converts an electrical audio signal into a corresponding sound. A speaker system, also often simply referred to as a speaker or 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; 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.
A tweeter or treble speaker is a special type of loudspeaker that is designed to produce high audio frequencies, typically up to 100 kHz. The name is derived from the high pitched sounds made by some birds (tweets), especially in contrast to the low woofs made by many dogs, after which low-frequency drivers are named (woofers).
JBL is an American audio equipment manufacturer headquartered in Los Angeles, California, United States. JBL serves the customer home and professional market. The professional market includes studios, installed/tour/portable sound, music production, DJ, cinema markets. The home market includes high-end home amplification/speakers/headphones as well as high-end car audio. JBL is owned by Harman International, itself a subsidiary of Samsung Electronics.
A horn antenna or microwave horn is an antenna that consists of a flaring metal waveguide shaped like a horn to direct radio waves in a beam. Horns are widely used as antennas at UHF and microwave frequencies, above 300 MHz. They are used as feed antennas for larger antenna structures such as parabolic antennas, as standard calibration antennas to measure the gain of other antennas, and as directive antennas for such devices as radar guns, automatic door openers, and microwave radiometers. Their advantages are moderate directivity, broad bandwidth, low losses, and simple construction and adjustment.
Altec Lansing, Inc. is an American audio electronics company founded in 1927. Their primary products are loudspeakers and associated audio electronics for professional, home, automotive and multimedia applications.
A bass reflex system is a type of loudspeaker enclosure that uses a port (hole) or vent cut into the cabinet and a section of tubing or pipe affixed to the port. This port enables the sound from the rear side of the diaphragm to increase the efficiency of the system at low frequencies as compared to a typical sealed- or closed-box loudspeaker or an infinite baffle mounting.
An acoustic horn or waveguide is a tapered sound guide designed to provide an acoustic impedance match between a sound source and free air. This has the effect of maximizing the efficiency with which sound waves from the particular source are transferred to the air. Conversely, a horn can be used at the receiving end to optimize the transfer of sound from the air to a receiver.
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-inch (10 cm) 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-inch (46 cm) or even 21-inch (53 cm) speakers in huge enclosures which are designed for use in stadium concert sound reinforcement systems for rock music concerts.
Studio monitors are loudspeakers in speaker enclosures specifically designed for professional audio production applications, such as recording studios, filmmaking, television studios, radio studios and project or home studios, where accurate audio reproduction is crucial. Among audio engineers, the term monitor implies that the speaker is designed to produce relatively flat (linear) phase and frequency responses. In other words, it exhibits minimal emphasis or de-emphasis of particular frequencies, the loudspeaker gives an accurate reproduction of the tonal qualities of the source audio, and there will be no relative phase shift of particular frequencies—meaning no distortion in sound-stage perspective for stereo recordings. Beyond stereo sound-stage requirements, a linear phase response helps impulse response remain true to source without encountering "smearing". An unqualified reference to a monitor often refers to a near-field design. This is a speaker small enough to sit on a stand or desk in proximity to the listener, so that most of the sound that the listener hears is coming directly from the speaker, rather than reflecting off walls and ceilings. Monitor speakers may include more than one type of driver or, for monitoring low-frequency sounds, such as bass drum, additional subwoofer cabinets may be used.
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.
A coaxial loudspeaker is a loudspeaker system in which the individual driver units radiate sound from the same point or axis. Two general types exist: one is a compact design using two or three speaker drivers, usually in car audio, and the other is a two-way high-power design for professional audio, also known as single-source or dual-concentric loudspeakers. The design is favored for its compactness and behavior as an audio point source.
DUPLEX was the trade name given by Altec Lansing to its line of coaxial loudspeakers, beginning with the first model 601 in 1943. However, the name was most commonly associated with the subsequent model 604 which was a seminal loudspeaker that became a milestone in loudspeaker development. Well over a dozen different models carried the Duplex name over a near 50-year period. The vast majority consisted of a high frequency (HF) compression driver mounted to the back of a large diameter paper cone low frequency (LF) driver. However, there were also a few models with small diameter LF cones and direct radiator tweeters.
David W. Gunness is an American audio engineer, electrical engineer and inventor. He is known for his work on loudspeaker design, especially high-output professional horn loudspeakers for public address, studio, theater, nightclub, concert and touring uses.
Cliff Henricksen is a musician, inventor and audio technologist. He is self-taught as a musician with a graduate degree in mechanical engineering at Massachusetts Institute of Technology (MIT). Throughout his career Cliff has found innovative ways to apply engineering basics to electro acoustics and to audio technology as it applies to music and in particular to live music performance. He has invented and engineered a wide variety of technologies and products well known in the world of professional audio. Today he balances work in audio and work as a performing musician.
In a loudspeaker, a phase plug, phasing plug or acoustical transformer is a mechanical interface between a speaker driver and the audience. The phase plug extends high frequency response because it guides waves outward toward the listener rather than allowing them to interact destructively near the driver.
Charles Emory Hughes II is an American inventor and audio engineer. He is known for his work on loudspeaker design, and the measurement of professional audio sound systems. Hughes first worked for Peavey Electronics designing loudspeakers and horns where he was granted a patent for the Quadratic-Throat Waveguide horn used in concert loudspeakers. He worked for Altec Lansing for two years as chief engineer for the pro audio division and was granted two more patents. In 2021, Hughes was hired by Biamp as principal engineer.
D. Broadus Keele Jr., also known simply as Don Keele or D. B. Keele Jr., is an American audio engineer and inventor who has helped shape and influence the professional and consumer loudspeaker industries since the early seventies. He is one of the developers of the constant directivity horn design with several patents of Bi-radial horns from companies like JBL, and Electrovoice.
Monitor Audio is a British company that specialises in designing and manufacturing loudspeakers and sound systems.
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.