Tannoy Revolution XT 8F Loudspeaker

Virtuoso Performer

Equipment report
Tannoy Revolution XT 8F
Tannoy Revolution XT 8F Loudspeaker

It’s no secret that Tannoy is one of the oldest and most prestigious audio brands in the world. Having been in the public arena for decades, Tannoy has become synonymous with public address in the UK, the phrase “over the Tannoy” being commonly used to describe a PA announcement. The company’s Scottish factory is located near Glasgow where it’s been based for the past 35 years. Tannoy is also a major player in the U.S., predominantly for its commercial beam-steering, touring, and stadium speakers. Its impact on the high-end scene is primarily due to its Dual Concentric driver that approximates a point-source radiator. The majority of Tannoy loudspeakers, including all of the high-end residential, Prestige traditional, and most pro-audio/touring models, are made in Scotland. However, in order to attain affordable price points, entry-level residential loudspeakers (Mercury, Revolution, and Precision lines) are manufactured in China. These days, the paradigm of “designed in the West and manufactured in the East” applies to any product with mass-market aspirations, including the Hewlett-Packard laptop computer I’m using to write this review.

The Revolution XT line represents a significant overhaul of the Revolution series. The trapezoidal cabinet shape has been retained, but the internals feature sweeping changes. The top-of-the-line 8F, as well as the smaller 6F, are both floorstanders with integrated spiked bases (aka plinths). The numerical designation refers to the driver diameter, and in both cases the design can be best characterized as a two-and-a-half-way. In the 8F, the coaxial woofer is allowed to work into the bass while being augmented below 250Hz by an 8-inch woofer, with the crossover network being a second-order low-pass. The coaxial tweeter and woofer are crossed over at 1.8kHz using asymmetrical networks: first-order high-pass for the tweeter and second-order low-pass for the woofer.

The woofers are loaded by two chambers connected via an internal port. The lower chamber is smaller in volume, and vents to the exterior through a downward-firing port at the bottom of the cabinet. This type of dual-chamber bass-reflex alignment was described as early as 1961 by George Augspurger in an article in Electronics World, but has seen little commercial application since then. In contrast with a conventional bass reflex, which is tuned to a single frequency, the dual-chamber design is tuned to two frequencies typically an octave apart. As a consequence, compared to a conventional bass reflex, the double bass reflex is able to control woofer excursion over a wider range, well into the deeper low end. This was evident in the impedance magnitude plot that showed well-damped woofer resonance peaks. The impedance minimum in the upper bass clocks in at about 3 ohms while the maximum is about 40 ohms in the upper midrange.

The star attraction is of course the new coaxial driver, said to be a fresh interpretation of Tannoy’s point-source drive-unit philosophy—and a major milestone in more than 65 years of the company’s audio research and development. If you think that there’s a bit of hubris embedded in such a pronouncement, think again. My own listening tests and measurements have convinced me that it is indeed a major success. There was a time when speaker designers saturated a front baffle with multiple drivers giving little consideration to the resultant acoustical interference effects. And before Siegfried Linkwitz in the mid-1970s, crossover design was purely an electrical engineering exercise with no accounting for path length differences between individual acoustic centers. Published frequency-response specifications for these multiway speakers seemed to be based on a single mike position where the drivers integrated reasonably well. Move the mike a few inches, and the integration would collapse, resulting in severe response dips.

I’ve been a longtime fan of coaxials; functionally they perform as wide-range drivers and can be thought of as improved versions of 1930s twin-cone, full-range transducers such as the Lowther range. The first coaxial design, the Duplex 601, was unveiled in the early 1940s by Altec Lansing. An improved version, the Altec 604, was introduced circa 1945 and quickly became the standard studio monitor in the U.S. Then Tannoy’s Dual Concentric design arrived a couple of years later and was to become the leading studio monitor in the UK and throughout Europe. Both designs used high-frequency waveguides, but the unique aspect of the Tannoy was that the woofer cone provided the final horn flare for the tweeter.

The ideal of a point-source coaxial driver where the acoustic centers of the tweeter and woofer are nearly spatially coincident has been difficult to execute in practice without some serious side effects. The tweeter typically sits on the woofer magnet’s pole piece. Cavity resonances and the horn loading provided by the waveguide and woofer cone can color the response in the transition region between the two drivers—a “cupped hands” coloration being a common descriptor of previous Tannoy coaxials. In the new driver, a single magnet, dubbed the Omnimagnet by the marketing folks, powers both the tweeter and the woofer, improving time alignment and phase coherence. The tweeter diaphragm is one inch in diameter and is formed of polyetherimide, also known as PEI, a high-performance thermoplastic whose characteristics include high strength and rigidity at elevated temperatures. This is no ordinary dome; it is actually donut-shaped, a torus if you insist on a more precise geometrical description, and is coupled to a rocket-nosed (ogive-shaped) phase plug. The phase plug is enclosed by a waveguide that is brought further forward into the woofer cone. The waveguide is designed with an aggressive flare rate that results in a shallower profile to improve high-frequency dispersion through the mouth of the bass driver.

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