The Bose Acoustimass 5 bass module uses two 5.25″ (13.3 cm) woofers, in a triple band-pass enclosure (also called 8th order bandpass).
Bass Module dimensions: 35.5 x 48 x 19.1 cm
User manual: Bose Acoustimass 5 Series II User Guide
In the gallery below, you can find photos of the see-thru Acoustimass 5. The transparent plexiglass enclosures are a very high quality build from Bose for showcase.