Floorstanding loudspeakers — Pbn Audio M2!5

Designer Peter B. Noerbaek founded PBN Audio, which had been in business for 27 years by 2019, and the M2!5 is one of its two-way floorstanders. It combines two large bass drivers with a compression driver on a waveguide, and its price at that time was USD 30,000 per pair.

Key specs that matter

Two 15 inch woofers cover the low range, while everything above the crossover point is handled by a single compression driver with a dual diaphragm, loaded by a waveguide. The two sections meet at 900 Hz. Sensitivity is 95 dB measured with 2.83 V at 1 m, and the rated frequency response is 25 Hz to 20 kHz held to plus or minus 2 dB. Nominal impedance is 4 ohm, with a minimum of 3.5 ohm and a maximum of 9 ohm across the range. Each cabinet stands 53 inches tall, 18 inches wide and 23 inches deep, and weighs 280 lbs.

Engineering and use context

PBN specifies the woofers with low-loss magnetic structures and a symmetrical field geometry around the voice coil. The crossover is a fifth-order network, and PBN states that it produces acoustic slopes of 30 dB per octave, so the woofers and the compression driver share very little of the band around 900 Hz. It uses five hand-wound inductors and twelve metallized polypropylene capacitors rated for 400 V DC. The network is charge coupled, meaning that three 9 V batteries in series hold a 27 V bias on the capacitors so they never sit at zero volts while the signal swings through them. The front baffle is a faceplate of layered MDF 1.75 inches thick, and behind it the cabinet is divided into internal chambers that PBN describes as engineered for accurate measured performance. The cabinet is reinforced internally against vibration, stands on steel spike feet and is finished in custom hardwood veneers made to order. The low crossover point means the compression driver works across most of the midrange band and the treble. Given the weight of each cabinet, positioning in the room needs two people at least.

Pairing

With such high sensitivity, even a low-powered tube or Class A amplifier can drive the M2!5 to high levels. The impedance dips only slightly below the nominal figure, so any amplifier rated for continuous operation into 4 ohm is a suitable match, whether valve or solid-state.

Alternatives

PBN Audio's MR!777 is a larger floorstanding model of the brand, built with two 18 inch woofers, two 12 inch midrange drivers and a 6 inch ribbon.