Coaxial loudspeaker

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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. [1] The design is favored for its compactness and behavior as an audio point source.

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Professional audio

The studio monitors over the window are a pair of UREI 813s, each of which has a horn driver for high frequencies (blue rectangle) and coaxial 15-inch coaxial driver beneath it and a plain 15-inch driver above. MCI equipped Studiod.jpg
The studio monitors over the window are a pair of UREI 813s, each of which has a horn driver for high frequencies (blue rectangle) and coaxial 15-inch coaxial driver beneath it and a plain 15-inch driver above.
Studio monitor loudspeaker from Tannoy (c. 1990) with a 12 inch (30 cm) bass driver having a second, independent 2-inch-driver for high frequencies in the center. The crossover frequency is 1.400 Hz. Tannoy Little Gold monitor - professional studio loudspeaker box.jpg
Studio monitor loudspeaker from Tannoy (c. 1990) with a 12 inch (30 cm) bass driver having a second, independent 2-inch-driver for high frequencies in the center. The crossover frequency is 1.400 Hz.

Coaxial loudspeakers in professional audio enable sound from two drivers to come from one source. This characteristic allows a wider field of listening to a synchronized summation of speaker drivers than loudspeaker enclosures containing physically separated drivers. As well, the pattern of response is symmetric around the axis of the loudspeaker. [2]

Since the 1943 introduction of the Altec Lansing Duplex 601 coaxial driver, recording studio monitors have often been coaxial loudspeaker designs. In 1945 the improved Altec 604 [3] was introduced, and it soon became the recording industry standard studio monitor in the U.S. [4] First shown in 1947 in England, the Tannoy Dual Concentric design assumed the same role across Europe from the 1950s onward. The Altec 604 combined a 15-inch (380 mm) woofer with a compression driver attached to a horn to carry the high frequencies. The Tannoy also used a 15-inch woofer and a compression driver for high frequencies, but differed in that the woofer itself served as the final horn flare for the high frequency driver. [5] Thus, its output pattern was radially symmetric, not just mirror-image symmetric as in the Altec. Both designs placed the high frequency driver behind the low frequency driver, and both were not initially time aligned. The high frequencies arrived at the listener's ear slightly later than the low frequencies.

One drawback of the design is the production line difficulty in mating the two drivers, and in replacing or reconing the woofer. Another drawback is that the low frequencies tend to modulate the high frequencies, causing greater intermodulation distortion. [6] The Tannoy style of coaxial, with the woofer forming part of the high frequency horn, had greater intermodulation distortion. Designs similar to the Altec 604 have further problems with diffraction of the low frequencies around the central horn, and with rearward emanations from the horn body reflected forward by the woofer out of time with direct sound. All of the problems with sound waves tend to increase with sound pressure level, causing significant shifts in tone as the loudspeaker changes volume. [7]

In the late 1970s, Bill Putnam of Universal Audio worked with Ed Long and his patented Time Alignment crossover design to fix the long-standing problem of the two bandpasses not being aligned in time at their crossover point. The Altec 604 was given this elaborate new crossover feature and incorporated into the UREI 813 studio monitor, which also had a second woofer physically separate from the coaxial pair. This design dominated recording studios of the 1980s, and time alignment became a feature of competing manufacturers. [5] In 1977, Bob Cavin of McCune Sound in San Francisco modified the Altec 604 for the McCune SM-4, a large proprietary stage wedge, using John Meyer's patented high-compliance compression driver diaphragm, a higher-power woofer, and processor-controlled bi-amplification with line-level all-pass time alignment. [8] [9] The McCune SM-4 was the first multi-angle stage monitor, and was used by many McCune clients such as the Playboy Jazz Festival and the Monterey Jazz Festival. In the 2000s, digital signal processing (DSP) was used by Fulcrum Acoustic to reduce some of the coaxial drawbacks such the diffraction of the woofer's upper range around the central horn, by filling in this "shadow" with low frequency sound from the compression driver, and by countering the out-of-time reflections bouncing off of the woofer. [7]

Coaxial loudspeakers have been used in stage monitors, giving musicians a more even sound field because of the single-source characteristic. As well, the enclosure may be made more compact. In the 1980s, Professional Audio Systems (PAS), using Time Alignment technology from Ed Long, sold the popular SW series of compact stage wedges, offered with a 12- or 15-inch woofer, and having a projecting high-frequency horn as in the 604. Other stage monitors using coaxial designs are made by Clair Brothers, L-Acoustics, Radian Audio Engineering, RCF, Beyma, dB Technologies, Fulcrum Acoustic, and Rat Sound in partnership with Eastern Acoustic Works. [10]

David Gunness and Fulcrum Acoustic have designed coaxial loudspeakers beginning in 2009, notably collaborating with PreSonus in 2013 to create the self-powered line of Sceptre S6 and S8 coaxial studio monitors, [11] and releasing Fulcrum's own FH15 full-range horn-loaded loudspeaker series in 2018. [12] All of the coaxial Fulcrum designs use digital signal processing to reduce distortion modes. Fulcrum's proprietary process is called Temporal Equalization (TQ). [13]

Home audio

Tannoy has produced coaxial loudspeakers, for the hi fidelity home consumer market since the early 1950s. Their "Dual Concentric" drivers early series included in order of introduction: Tannoy Blacks, Tannoy Reds, and Tannoy Golds. Jensen introduced several coaxial speakers in the 1950s including their highly regarded triaxial models. Several other manufacturers introduced coaxial speakers and drivers in the 1950s including University, however due to their higher cost most did not last in the consumer market. In 1988, KEF introduced an extension of the coaxial loudspeaker concept. Their Uni-Q driver is a coincident driver, where the two drivers share the same acoustic center and therefore are closer in time alignment. This was made possible by using the then newly affordable powerful yet small neodymium magnets for the tweeter making the whole tweeter assembly small enough, magnet included, to fit inside the woofer's voice coil. Other home audio speaker companies making coaxial speakers include TAD, Cabasse with their 4-way Concentric QC-55 Driver as seen in their flagship model - La Sphère, Hsu, Vandersteen, until recently Theil, and a budget speaker made a few years ago by Insignia.

Car audio

A car audio speaker with a coaxial tweeter in front of the woofer Infinity Reference 6022si 6.5inch car speaker top view.jpeg
A car audio speaker with a coaxial tweeter in front of the woofer

Coaxial speakers in automobiles are 2- or 3-way loudspeakers in which the tweeter, or the tweeter and a mid-range driver, are mounted in front of the woofer, partially obscuring it. The advantage of this design is the ability to use a smaller area, hence their popularity in car audio. The low frequency sound waves from the woofer are not reduced too much by the drivers in their path. Without time-alignment correction, the sound from the tweeter may arrive slightly before the sound from the woofer; this misalignment is not generally addressed in automobile sound systems.

This design was popularized in the 1970s with Electronic Industries, Inc. of South Holland, Illinois introducing the general concept in May 1973, [14] and Jensen Loudspeakers introducing a retail model the next month. [15] This was followed by designs from Sparkomatic, Clarion, Infinity and others.

Related Research Articles

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

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

Audio crossover Type of electronic filter circuitry

Audio crossovers are a type of electronic filter circuitry that splits an audio signal into two or more frequency ranges, so that the signals can be sent to loudspeaker drivers that are designed to operate within different frequency ranges. The crossover filters can be either active or passive. They are often described as two-way or three-way, which indicate, respectively, that the crossover splits a given signal into two frequency ranges or three frequency ranges. Crossovers are used in loudspeaker cabinets, power amplifiers in consumer electronics and pro audio and musical instrument amplifier products. For the latter two markets, crossovers are used in bass amplifiers, keyboard amplifiers, bass and keyboard speaker enclosures and sound reinforcement system equipment.

Tweeter

A tweeter or treble speaker is a special type of loudspeaker that is designed to produce high audio frequencies, typically deliver high frequencies 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).

A woofer or bass speaker is a technical term for a loudspeaker driver designed to produce low frequency sounds, typically from 50 Hz up to 1000 Hz. The name is from the onomatopoeic English word for a dog's bark, "woof". The most common design for a woofer is the electrodynamic driver, which typically uses a stiff paper cone, driven by a voice coil surrounded by a magnetic field.

Electrostatic loudspeaker Sound playback device

An electrostatic loudspeaker (ESL) is a loudspeaker design in which sound is generated by the force exerted on a membrane suspended in an electrostatic field.

Horn loudspeaker

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

Klipsch Audio Technologies is an American loudspeaker company based in Indianapolis, Indiana. Founded in Hope, Arkansas, in 1946 as 'Klipsch and Associates' by Paul W. Klipsch, the company produces loudspeaker drivers and enclosures, as well as complete loudspeakers for high-end, high-fidelity sound systems, public address applications, and personal computers.

JBL American audio hardware company

JBL is an American company that manufactures audio hardware, including loudspeakers and headphones. JBL serves the consumer home and professional market. The professional market includes studios, installed/tour/portable sound, cars, music production, DJ, cinema markets, etc. JBL is owned by Harman International, a subsidiary of Samsung Electronics.

Altec Lansing, Inc. is a U.S. audio electronics company founded in 1927. Their primary products are loudspeakers and associated audio electronics for professional, home, automotive and multimedia applications.

Powered speakers Loudspeaker that have built-in amplifiers

Powered speakers, also known as self-powered speakers and active speakers, are loudspeakers that have built-in amplifiers. Powered speakers are used in a range of settings, including in sound reinforcement systems, both for the main speakers facing the audience and the monitor speakers facing the performers; by DJs performing at dance events and raves; in private homes as part of hi-fi or home cinema audio systems and as computer speakers. They can be connected directly to a mixing console or other low-level audio signal source without the need for an external amplifier. Some active speakers designed for sound reinforcement system use have an onboard mixing console and microphone preamplifier, which enables microphones to be connected directly to the speaker.

Full-range speaker Type of loudspeaker

A full-range loudspeaker drive unit is defined as a driver which reproduces as much of the audible frequency range as possible, within the limitations imposed by the physical constraints of a specific design. The frequency range of these drivers is maximized through the use of a whizzer cone and other means. Most single driver systems, such as those in radios, or small computer speaker designs, cannot reproduce all of the audible frequencies or the entire audible audio range.

Acoustic Research

Acoustic Research was a Cambridge, Massachusetts-based company that manufactured high-end audio equipment. The brand is now owned by VOXX. Acoustic Research was known for the AR-3 series of speaker systems, which used the 12 in (300 mm) acoustic suspension woofer of the AR-1 with newly designed dome mid-range speaker and high-frequency drivers. AR's line of acoustic suspension speakers were the first loudspeakers with relatively flat response, extended bass, wide dispersion, small size, and reasonable cost.

Loudspeaker enclosure Acoustical component

A loudspeaker enclosure or loudspeaker cabinet is an enclosure in which speaker drivers and associated electronic hardware, such as crossover circuits and, in some cases, power amplifiers, are mounted. Enclosures may range in design from simple, homemade DIY rectangular particleboard boxes to very complex, expensive computer-designed hi-fi cabinets that incorporate composite materials, internal baffles, horns, bass reflex ports and acoustic insulation. Loudspeaker enclosures range in size from small "bookshelf" speaker cabinets with 4-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 monitor Speaker designed to reproduce sound accurately

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 of 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.

The Air Motion Transformer (AMT) is a type of electroacoustic transducer. Invented by noted physicist and scientist Dr. Oskar Heil (1908–1994), it operates on a different transduction principle from other loudspeaker designs, such as moving coil, planar magnetic or electrostatically driven loudspeakers, and should not be confused with planar or true ribbon loudspeakers. In contrast to a planar ribbon loudspeaker, the diaphragm of the AMT is of pleated shape similar to a bellows. The AMT moves air laterally in a perpendicular motion using a metal-etched folded sheet made of polyethylene terephthalate (PET) film. The circuit path embossed on the PET membrane, acts as the voice coil unit. The diaphragm is then housed between 4 stacks of steel pole-plate pieces positioned at 45° within a high-intensity, quadratic, opposing magnetic field. The air motion transformer with its sheet film equally exposed at 180° behaves as a dipole speaker, exciting front and rear sonic waves simultaneously.

Electrodynamic speaker driver An individual transducer that converts an electrical audio signal to sound waves

An electrodynamic speaker driver, often called simply a speaker driver when the type is implicit, is an individual transducer that converts an electrical audio signal to sound waves. While the term is sometimes used interchangeably with the term speaker (loudspeaker), it is usually applied to specialized transducers which reproduce only a portion of the audible frequency range. For high fidelity reproduction of sound, multiple loudspeakers are often mounted in the same enclosure, each reproducing a different part of the audible frequency range. 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 mid-range drivers, and those for low frequencies are called woofers, while those for very low bass range are subwoofers. Less common types of drivers are supertweeters and rotary woofers.

Loudspeaker time-alignment usually simply referred to as "time-alignment" or "Time-Align" is a term applied in loudspeaker systems which use multiple drivers to cover a wide audio range. It involves delaying the sound emanating from one or more drivers to correct the transient response, improve accuracy and, in non-coaxial drivers, improve the directivity or lobe tilting at the crossover frequencies. It employs adjusting the front-to back spacing of the individual drivers so that the sound output is truly simultaneous.

Altec Lansing Duplex Line of loudspeakers

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 Gunness American audio engineer

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.

Phase plug

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.

References

  1. ↑ Eiche, Jon F. (1990). Guide to Sound Systems for Worship. Recording and Audio Technology. Hal Leonard Corporation. p. 92. ISBN   0-7935-0029-X.
  2. ↑ Ballou, Glen (2005). Handbook for Sound Engineers. Focal Press, Gulf Professional Publishing. pp. 514–516. ISBN   0-240-80758-8.
  3. ↑ Audioheritage. Altec Duplex
  4. ↑ McGowan, Chris (November 15, 1980). "Sound Pioneers". Billboard. Nielsen Business Media. 92 (46): 42. ISSN   0006-2510.
  5. 1 2 Borwick, John (2001). Loudspeaker and headphone handbook (3 ed.). Focal Press. pp. 474–476. ISBN   0-240-51578-1.
  6. ↑ Dupont, Edward; Lipshitz, Stanley P. (September 2010). "Modeling the Intermodulation Distortion of a Coaxial Loudspeaker". Audio Engineering Society. Retrieved May 1, 2011.
  7. 1 2 "Building a Better Coax". Fulcrum Acoustic. 2009. Archived from the original on March 23, 2012. Retrieved May 1, 2011.
  8. ↑ Maloney, Pat (December 1980). "Time Alignment of Sound Reinforcement Equipment" (PDF). Recording Engineer Producer. p. 54.
  9. ↑ Harvey, Robert (August 1983). "The Venerable 604" (PDF). DB. p. 34.
  10. ↑ Frink, Mark (April 7, 2011). "Monitor Wedge Tips: Tools Of The Trade To Have A Successful Show". ProSoundWeb. Retrieved May 1, 2011.
  11. ↑ White, Paul (July 2014). "PreSonus Sceptre S6 & S8". Sound on Sound. Retrieved July 22, 2020.
  12. ↑ Staff (May 23, 2018). "Fulcrum Acoustic Announces FH15 Full-Range Coaxial Horn Product Line". Lighting and Sound (America). Retrieved July 22, 2020.
  13. ↑ Basnicki, Erica (March 25, 2013). "Dave Gunness: loudspeaker design comes full circle". Pro Sound News (Europe). Retrieved July 22, 2020.
  14. ↑ "Car Speakers Hi-Fi Emphasis—Display Vital". Billboard. Nielsen Business Media. 85 (21): 37. May 26, 1973. ISSN   0006-2510.
  15. ↑ "Car Stereo". Billboard. Nielsen Business Media. 85 (25): 68. June 23, 1973. ISSN   0006-2510.
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