Floorstanding loudspeakers — PMC MB2S XBD

The MB2S XBD is a twin-cabinet passive monitor from PMC, the British Professional Monitor Company founded in 1991 by Peter Thomas of the BBC and Adrian Loader. It builds on the MB2S studio monitor by adding a second XBD bass cabinet with another 12-inch driver, and it is used for music recording, mastering and post-production in stereo or surround, including at Studio Hilversum in the Netherlands. The main and XBD boxes may sit one above the other or next to each other.

Key specs that matter

The MB2S XBD is a three-way design with two 310mm (12-inch) PMC Radial bass drivers, a 75mm PMC fabric soft-dome midrange and a 27mm twin-chamber fabric soft-dome tweeter with ferrofluid cooling. Crossover points are 380Hz and 3.8kHz, and the passive crossovers are 32-element, fourth-order networks. Frequency response is 20Hz to 25kHz, sensitivity is 91dB at 1W/1m and nominal impedance is 4 ohms, with 250 to 900W recommended. Each of the two cabinets has its own 3m effective ATL line, and peak SPL reaches 124dB at 1m. Three pairs of 4mm sockets allow tri-wiring or tri-amping, with suggested amplifier powers of 120W for HF, 120W for MF and 600W for each bass section. The stacked system measures 1,740 x 380 x 535mm and weighs 88kg per channel, in Neo Black.

Engineering and use context

PMC's Advanced Transmission Line (ATL) loads each bass driver with a long, folded, damped channel rather than a sealed box or simple port. The line absorbs the driver's rear output at higher frequencies while at the lowest frequencies its output emerges from the terminal in phase with the front of the cone, reinforcing bass without the resonant overhang of a small reflex port. Each MB2S cabinet has a 3m line folded inside, and the XBD cabinet repeats the arrangement with a second driver, adding 3dB of low-frequency headroom below 380Hz so larger rooms can be driven to higher levels. In surround systems, that extra headroom can handle the .1 effects channel without separate subwoofers. The Radial bass driver is designed for large, controlled excursion and resists power compression through cooling by its cast alloy exoskeleton and rear-vented magnet. The 75mm soft-dome midrange covers a wide band from 380Hz to 3.8kHz, carrying most of the vocal range on a single driver with no crossover point inside it. The fourth-order crossovers sit in external enclosures that can be mounted on the rear of the XBD cabinet, isolating them from cabinet vibration.

Pairing

As a low-impedance passive system, the MB2S XBD needs powerful amplification, ideally tri-amped with the largest amplifiers on the bass sections. It suits medium to large control rooms, soffit-mounted or on stands.

Alternatives

PMC's own MB2 XBD SE is the domestic version with 93dB sensitivity, SONOLEX tweeter and wood finishes.