Floorstanding loudspeakers — Magnepan Magnepan 20.7

The Magnepan 20.7 is a three-way, full-range dipole loudspeaker from the Minnesota company that makes Magneplanar planar-magnetic speakers. There is no conventional box. A true ribbon tweeter and quasi-ribbon midrange and bass panels share one tall, thin frame. The 20.7 replaced the earlier 20.1 and brought a newly designed quasi-ribbon midrange with roughly half the moving mass of the midrange panel in the Magnepan 3.7.

Key specs that matter

The 20.7 is rated from 25Hz to 40kHz. Sensitivity is 86dB at 500Hz for 2.83V, and nominal impedance is 4 ohms. Each panel is 737mm wide, 2,006mm tall and 52mm deep and weighs about 28kg. Frames come in natural oak, black, and silver or black matt aluminium, with white, dark grey or black cloth.

Engineering and use context

All three drivers are planar, so the force acts over the entire area of each diaphragm instead of at one voice coil. The ribbon tweeter is an ultra-thin aluminium foil about 1.5m long and 6mm wide, which Magnepan describes as one tenth the thickness of a human hair. The foil itself is the conductor, suspended in a magnetic field. The quasi-ribbon midrange and bass drivers use very light Mylar diaphragms with bonded conductors. In the midrange the diaphragm hangs between rows of magnets on both sides, while the bass panel is driven by opposing magnets. The panels radiate equally to the front and rear with opposite polarity, which makes the 20.7 a dipole whose output cancels to the sides. This reduces sidewall reflections and the uneven excitation of room modes typical of box speakers. With no cabinet there are no box resonances to control, which is part of why Magnepan can build a speaker this large at a lower cost than comparably ambitious box designs. The tweeter can sit on the outer edge for a wider listening area or on the inner edge for a more focused central seat, and Magnepan specifies that it should never be closer to the listener than the bass section.

Pairing

With fairly low efficiency, the 20.7 wants an amplifier with plenty of power and strong current output. As a dipole it also needs generous free space behind it for the rear wave, typically well out from the front wall, which makes it a speaker for medium and large rooms.

Alternatives

The Magnepan 3.7i is a smaller three-way panel with the same type of ribbon tweeter, intended for medium-sized rooms.