Coaxial speakers

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.

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, and Jensen Loudspeakers introducing a retail model the next month. This was followed by designs from Sparkomatic, Clarion, Infinity and others.

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.

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 was introduced, and it soon became the recording industry standard studio monitor in the U.S. 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. 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.

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