B&W John Bowers Silver Signature loudspeaker

In recent years, computer modeling, finite-element analysis, and laser interferometry have brought about a huge increase in our knowledge about what makes the moving-coil loudspeaker drive-unit work. Nevertheless, it has remained fundamentally unchanged since it was invented by Rice and Kellogg more than 60 years ago. That doesn't mean that it hasn't been refined considerably; in this review I examine the performance of a design whose drive-unit technology has been taken to the limit of what is currently possible, the B&W Silver Signature.

To celebrate its 25th anniversary in 1991, the English manufacturer B&W launched a most unconventional loudspeaker. The John Bowers Silver Signature is a modest-sized two-way design, named in tribute to the company's founder, who passed away at the end of 1987. It's initially hard to see why a pair should cost $8000, as the speaker looks like a taller, more ornate version of the $1600/pair B&W Matrix 805 that was favorably reviewed by Larry Greenhill in Stereophile just over a year ago (footnote 1). It even uses the same "Matrix" construction, whereby an internal honeycomb of perforated dividing panels both minimizes cabinet vibrational modes and pushes up the frequency of those that remain so that they will be less subjectively intrusive.

Under the skin, however, they are very different loudspeakers. The name gives it away: other than the anodized aluminum tweeter diaphragm, every metal part in the Silver Signature is silver, from the drive-unit voice-coils to the crossover inductors and capacitors, and from the binding posts to the ornamental crosses providing the drive-units with a moderate degree of protection from prying fingers.

The drive-units are both exclusive to the Silver Signature, and were developed with the aid of laser interferometry at B&W's Steyning Research Center, nestling in the shadow of the Sussex Downs. The tweeter is derived from that used in the Matrix 801 loudspeaker, but lacks the "phasing" ring in the front of the dome. It is mounted in a silver, bullet-shaped, wide-dispersion housing sitting atop the woofer enclosure. This is mounted slightly to one side of the vertical center line, to stagger in frequency the diffraction effects from the cabinet edges, and there is a slight profiling of the cabinet top plate immediately in front of it to minimize reflections. The tweeter looks like nothing so much as a silver bicycle horn, attractively retro in a Raymond Lowy-like way.

The woofer has a nominal 7" diameter and is constructed on a diecast chassis. It features an almost straight-sided cone fashioned from woven Kevlar, with a hard, bullet-shaped dust cap. The 2.25"-diameter, 5"-deep reflex port is mounted on the baffle below the woofer and is said to be designed to give a fourth-order, "quasi-Butterworth" bass alignment. Its silver trim ring is flared to minimize wind noise, while its inner reach is lined with foam. Twin sets of silver binding posts on the rear panel allow the drive-units to be connected to the remote crossover via a supplied cable with four conductors, each fabricated from two Teflon-insulated, 0.7mm (0.028") silver conductors.

The crossover is housed in a separate enclosure to keep it away from both vibration and the drive-units' magnetic fields. A fixed 24", silver-conductor, Teflon-dielectric cable runs to the amplifier output terminals; silver binding posts (footnote 2) with knurled knobs allow the supplied 10' four-conductor silver cables to connect the crossover to the speakers themselves. The components are attached to the MDF base of the crossover enclosure. The high-pass filter for the tweeter is a third-order (electrical) type consisting of two series 3.3µF capacitors, with a ferrite-cored inductor connecting their common connection to ground. The drive-unit terminals are marked so as to drive the tweeter in inverse polarity.

The low-pass filter for the positive-polarity woofer uses a series transformer-core inductor in the positive leg, with a network of a 3.3µF capacitor and an air-cored inductor across the drive-unit terminals. All the capacitors and coils are made with silver foils and windings; all the wiring is Teflon-insulated, solid-core silver.

Footnote 1: Vol.16 No.4, April 1993, p.225.

Footnote 2: As received, the cables and the crossover came tied up with rubber bands. The sulphur in these bands had caused the silver binding posts to tarnish. Though the damage was cosmetic, the metal contact surfaces not being affected, I found this oversight surprising from a company I usually associate with attention to detail.

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