Полочная акустика — PMC MB2S

The MB2S is a passive monitor with three frequency bands, made by PMC, the British maker of loudspeakers built around its Advanced Transmission Line bass loading. PMC designed it for mid-sized control rooms, where it can be soffit mounted in the front wall or placed on custom studio stands made for it, and states that it reaches higher SPL without the distortion and loss of definition usually tied to a cabinet of its size. It also forms the upper part of the MB2S XBD system.

Key specs that matter

Every MB2S cabinet houses four transducers. Two 310 mm PMC Radial woofers handle the bass, a 75 mm PMC fabric dome covers the midrange and a 27 mm PMC fabric soft dome looks after the treble. The crossover points sit at 380 Hz and 3.8 kHz. Frequency response is 20 Hz to 25 kHz, sensitivity is 91 dB at 1 W and 1 m, and PMC recommends amplifiers delivering 200 to 800 W. The cabinet is 380 mm wide and 535 mm deep, and each speaker weighs 49 kg.

Engineering and use context

Below the lower crossover point the two woofers are loaded by ATL, the transmission line technology PMC uses across its range. Instead of venting the rear output of the bass units through a port or trapping it in a sealed box, ATL guides that energy along a long internal path divided into three sections and uses it to extend the low frequencies more efficiently. The Radial woofer is built to allow very large controlled excursions, and it avoids the effects of power compression because heat leaves through a cast alloy exo-skeleton and a new rear-vented magnet. The midrange unit is the PMC 75, a soft dome that PMC describes as taking the limits of soft dome design and construction to their conclusion. PMC positions the design for tracking and mixing music, for mastering and for post production work, in stereo as well as surround layouts, and in the XBD version both the main and bass cabinets use three-section lines.

Pairing

As a passive design, the MB2S relies on outboard amplification, from a single stereo unit or from a pair of monoblocks, within the recommended power window. For rooms that need more low-frequency headroom, PMC offers the MB2S XBD, which adds a second precision 12 inch Radial driver in an external XBD cabinet under the monitor and gives 3 dB more headroom in the bass range, a configuration intended for larger rooms and surround systems while keeping the same transducers above.

Alternatives

PMC also lists the twenty5.21i as a passive bookshelf model in its twenty5i series of hi-fi loudspeakers.