Epos ES 14 loudspeaker John Atkinson review

John Atkinson reviewed the Epos ES 14 in January 1995 (Vol.18 No.1):
In the ice-cream world, chocolate is the universal end of the line. Vanilla experiments that taste great but look foul, maple syrup flavors that are more maple than syrup, tutti-frutti that's too tutti—all are recycled as chocolate flavor, their visual sins permanently hidden from view. In the world of wood, the equivalent of chocolate ice cream is the ubiquitous "black ash" veneer. The original color and character of the wood are irrelevant: it all ends up stained black.

I was reminded of chocolate ice cream when I unpacked the loudspeakers I'm reviewing this month. Finished in chocolate—I mean, black ash veneer, the Epos is a two-way ported design from a designer who learned his speaker engineering at the British Broadcasting Corporation. The Epos ES 14 was designed by Robin Marshall after he'd left the government-controlled broadcasting organization; Robin had played a small role in the development of the BBC's classic LS3/5A design.

The ES 14 is also typically British in that it isn't time-coherent. In the December 1994 Stereophile, I reviewed two small two-way speakers from American designers—the Spica TC-60 and the Dunlavy Audio Labs SC-I—for which time coherency had been a major design goal. The fact that both speakers had superbly flat, uncolored midranges also revealed their designers' not forgetting the importance of the traditional frequency-response measurement. In the UK, however, while flat frequency response has always been a prime goal, for a speaker to be time-coherent has never been considered a necessary indicator of goodness.

Technology
The $1395/pair Epos ES 14 was last reviewed in Stereophile by Thomas J. Norton in 1988 and Sam Tellig in 1990, both of whom enthusiastically recommended it (footnote 1). As it was upgraded a couple of years back to allow for bi-wiring, I thought it worth taking a third listen and look.

The ES 14 is a reasonably large stand-mounted loudspeaker with a handsome aspect ratio. Though the top two-thirds of its front baffle is made from ½" MDF, the front plates of the drive-units are square/rectangular castings that occupy the full baffle width. When each is fixed in position with four Allen-head bolts, which screw into captive T-nuts, the result is a strong metal/wood sandwich. In addition, because the driver front plates are rabbeted, the result is a flush acoustic environment for the drive-units, optimizing their dispersion. The rest of the cabinet appears to be made from ¾" MDF, veneered on the inside surfaces as well as the outer ones, while bracing is provided by a horizontal aluminum rod that holds the sidewalls under tension. Urethane foam partly fills the inner cavity.

Both of the 14's drive-units are manufactured by Epos. Prominent on the front baffle is a 1" aluminum-dome tweeter, protected from prying two-year-old fingers by a wire mesh and mounted vertically in-line above a plastic-cone woofer. Rather than a dustcap, the latter features a stationary "phase plug" attached to the magnet pole-piece. The woofer is also unusual in that it uses a 17mm-long magnet gap and a 5mm coil, as opposed to the normal system in which a coil perhaps 12-14mm long works in a 6mm gap. This gives superior linearity/lower distortion because the coil is always driven by a more nearly constant magnetic field. In addition, the fact that the coil is totally enclosed by a large amount of steel endows the drive-unit with good thermal stability, leading to good power handling and dynamic range capability.

The downside—there's always a downside—is that it makes for an expensive woofer. The magnet has to be physically much larger and heavier than normal for the same amount of drive, which is proportional to the magnetic flux multiplied by the length of the coil. The woofer uses an inverted half-roll surround and is reflex-loaded via a large port on the speaker's rear, 2.7" (70mm) in diameter and about 8" long. The port can be filled with a cylinder of polyurethane foam to convert the ES 14's bass alignment to an overdamped sealed-box, if room acoustics or personal taste make that a desirable choice.

There isn't a grille. The crossover is also unusual in that there almost isn't one! The woofer is connected directly to the input terminals; the tweeter has a series capacitor—a 2.4µF non-polarized electrolytic type—stuck to its magnet, and that's it. Robin Marshall believes in using a minimal crossover to maximize dynamic range and retrieval of detail. He also states that if you can spread the transition between the two drive-units over a larger part of the bandwidth than normal by using gentle-slope crossover filters, you can achieve a controlled off-axis dispersion across the band. However, this means that the bass driver has to be designed to have a natural roll-out slope to complement the tweeter's first-order high-pass action. And that's not something speaker designers who buy off-the-shelf parts have the luxury of doing.

Internal wiring is good-quality multistrand, and the drive-unit joints are soldered. Electrical connection is via two pairs of 4mm sockets that take banana plugs—optimally, the British spring-loaded ones. All in all, the ES 14 is very well engineered for what is a relatively affordable loudspeaker.



Footnote 1: Stereophile, Vol.11 No.6, p.117, and Vol.13 No.1, p.73, respectively.
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