B&W Pressure Vessel Prototype - Bowers & Wilkins PV1 Brochure & Specs

To illustrate this, there are two analogies that we can
apply. The first is the soap bubble. An undisturbed bubble
assumes a spherical shape because the pressure
difference inside and out is perfectly balanced by the only
force the bubble can sustain - surface tension that is
entirely in the curved plane of the skin.
The second important analogy is found in the architecture
of Antonio Gaudi. For our subwoofer, not only do we have
to consider pressure changes in the enclosed volume of
air, we must also deal with mechanical reaction forces
generated in the magnet system of the driver and
transmitted to the enclosure walls via the driver's chassis.
The delicate and almost skeletal structure of the temple of
the Sagrada Familia in Barcelona was derived from a
novel simulation of the structure using string and weights.
Tension in the string of the inverted structure is analogous
to compression in the arches and pillars. The string
naturally assumes a shape where the only force is tension
along its length. It cannot support any other. There are
therefore no bending forces. The resulting arches and
pillars built following these natural forms suffer only
compression along their length, so they are very strong yet
slender compared to traditional designs.
B&W Pressure Vessel prototype
The principle of restricting forces to compression or
tension in the plane of a structure was applied to a
subwoofer enclosure in order to minimise sound radiation
caused by flexing of its walls.
Early prototypes used a single drive unit mounted in a
large spherical enclosure. This worked very well at ultra
low frequencies, as the conditions approached those of
the static analogies discussed above. However, as the
frequency increased, it was found that internal pressure
changes due to movement of the driver diaphragm did not
transmit instantaneously throughout the whole of the
internal volume. Neither were the mechanical reaction
forces from the driver chassis transmitted instantaneously
throughout the structure of the enclosure.
Gaudi's inverse force model.
Support pillars in the temple of the Sagrada Familia,
Barcelona