Bowers & Wilkins PV1 manual Problem, Pressure Vessel Concept

The Problem

The holy grail of subwoofer design is deep and clean bass from a near-invisible box. The immediate problem that arises is that reduced box size both curtails bass extension and increases pressure on the enclosure wall and driver diaphragm.

Many small subwoofers are unable to reproduce sufficiently extended bass and suffer from considerable cabinet coloration, often resulting in bass that is uneven and dissociated from the midrange and treble.

Some existing designs have tried to address this problem by using complex, rugged drive units and very large amplifiers in small boxes, but have neglected to give sufficient consideration to the design of the enclosure. Typically, the huge backpressures and mechanical reaction forces generated by the heavy driver tend to deform the cabinet walls, which then resonate and distort the sound, particularly in relation to pitch definition.

Bracing the cabinet extensively certainly helps but to satisfactorily solve the problem, you have to change the design approach.

Pressure Vessel Concept

It is often the case that effective solutions to problems in one scientific discipline may be derived from work done in another. An example of that within B&W is the derivation of our dimpled Flowport design from the aerodynamics of a golf ball.

The Pressure Vessel takes its inspiration from deep-sea diving bells. Their characteristic curved form resists the pressure differences on each side of the walls to a much greater degree than flatter panels, however well braced they may be.

The trick is to change the way forces are distributed in the structure, from bending (i.e. at right angles to the panel) to being in the plane of the panel. After all, it's much harder to squash or stretch a panel along its length or width than to bend it.