Напольная акустика — Magnepan Magnepan 20.7

The 20.7 is a single-panel loudspeaker from Magnepan, the Minnesota manufacturer of Magneplanar planar-magnetic speakers. It is a three-way, full-range dipole with no conventional box, combining a true ribbon tweeter with quasi-ribbon midrange and bass panels in one tall, thin frame. It replaced the earlier 20.1 and introduced 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 uses a true ribbon tweeter, a quasi-ribbon midrange and a quasi-ribbon bass panel. Frequency response is 25Hz to 40kHz, sensitivity is 86dB at 500Hz for 2.83V and impedance is 4 ohms. Each panel is 737mm wide, 2,006mm tall and 52mm deep, and weighs about 28kg. Frames are offered 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, which means the whole diaphragm is driven across its surface rather than at a single voice coil. The ribbon tweeter is an ultra-thin aluminium foil about 1.5m long and 6mm wide, which Magnepan says is 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 conductors bonded to them, suspended between rows of magnets on both sides in the midrange and driven by opposing magnets in the bass. Such low moving mass lets the diaphragms follow signal changes quickly. Because the panels radiate equally front and back with opposite polarity, they form a dipole, whose output cancels to the sides; this reduces the sidewall reflections and uneven room-mode excitation typical of box speakers. Without a cabinet, there are no box resonances to control, part of why Magnepan can build such a large speaker at a lower cost than comparably ambitious box designs. The tweeter can be placed on the outside for a wider listening area, or on the inside for a more focused central seat, and Magnepan specifies that the tweeter should never be closer to the listener than the bass section.

Pairing

As a fairly inefficient panel, the 20.7 needs substantial amplifier power with good current delivery. As a dipole, it needs generous space behind it for the rear wave, typically well out from the front wall, and toe-in toward the listener, making it best suited to medium and large rooms.

Alternatives

Magnepan's own 3.7i is a smaller three-way panel sharing the same ribbon tweeter, for medium-sized rooms.