KEF B110
A four-inch cone that punched far above its size, and ended up in some of the most respected monitors of the 1970s and '80s.
Overview
The B110 is a KEF drive unit, not a finished loudspeaker. It was a midrange and bass/midrange driver that KEF sold to builders and installed in its own systems. A "very fine" midrange unit by that name became the benchmark for KEF's own later drivers. When the company developed an improved polypropylene-cone midrange for a newer system, the documentation used the B110 as the reference point. The new driver was described as an improved version of it, with higher sensitivity and power handling.
The published parameters describe a compact, well-behaved unit. A driver-parameter table compiled from measurements by Prof. J. Robert Ashley of the University of Colorado lists the B110 with an advertised diameter of 5 inches, a free-air resonance of 31 Hz, a QTS of 0.39, a Vas of 27 liters, and an efficiency of 0.18 percent. A low QTS and modest Vas mean the driver is comfortable in vented enclosures, and 31 Hz is unusually low for a cone this size. The efficiency is the catch. 0.18 percent is not a high-sensitivity design, so it wants real amplifier power, not a few flea-watts. The same table says these are typical values and that individual drivers vary with manufacturing tolerances, so a pair from different production runs may not match as tightly as a modern buyer would like.
In at least one KEF system, a 4-inch (100 mm) polypropylene-cone midrange, the improved descendant of the B110, was run from 160 Hz up to a 3 kHz crossover. That covers more than four octaves. The documentation for that design flags the trade-off plainly: giving a driver that much bandwidth raises the possibility of intermodulation, with high-amplitude signals in the 150-300 Hz region modulating the upper midrange.
Builders who bought the B110 loose treated it as a component. One 1981 advertisement offered two B110 mids and two T27 tweeters, made in England and unused in their original containers, as a package for speaker-building projects. A British parts list from the early 1970s priced the B110 mid alongside the T15 and T27 high-frequency units and the B200 and B139 low-frequency drivers. Those were the parts of the DIY two- and three-way systems that were a staple of the hobby. You specified the driver by part number, mounted it in a cabinet you built or bought as a kit, and crossed it over with a network you chose.
The driver's most famous application came in KEF's own finished loudspeakers. In the Reference Series Model 107, Mix (1987, p.206) documented a swiveling head assembly housing the 4-inch B110 midrange and a 1-inch tweeter. The head rotated in the horizontal plane so the listener could aim it for optimum imaging. KEF put the B110 in the adjustable head of a monitoring-oriented design and trusted a four-inch cone to carry the midband. The same review noted the shift in studio practice toward alternate monitor speakers, which is the context in which the 107 was being judged.
Collectors chasing B110s today are usually restoring a KEF system that used them or sourcing a matched pair for a build. The published parameters are typical rather than guaranteed, so pairs should be checked rather than assumed matched. The low efficiency means modest amplifiers will run out of steam before the driver does. And because the B110 was sold both as a standalone component and installed in finished systems, the same part number can turn up in very different condition, from unused in original packaging to pulled from a decades-old cabinet. Confirm what you are getting before you buy.
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Related Models
- KEF B200 (1970)