Coaxial loudspeaker

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.

[6] The Tannoy style of coaxial, with the woofer forming part of the high frequency horn, had greater intermodulation distortion.

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.

[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.

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.

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.

[13] In 2015, Fluid Audio launched the FX8 studio monitor, featuring a coaxial design with the tweeter mounted directly in front of the woofer on a fixed post.

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.