Floorstanding loudspeakers — Magnepan Magnepan 3.7i

The Magnepan 3.7i is a three-way planar-magnetic dipole loudspeaker made in White Bear Lake, Minnesota. It grew out of the 3.7, which replaced the 3.6 and carried the full-ribbon approach of the smaller 1.7 up the range, a process Magnepan called trickle-up technology. Its three planar sections are a true ribbon at the top and Mylar-based quasi-ribbon midrange and bass units. The i version gathers a set of smaller refinements that Magnepan released as an update rather than waiting for a new model, and owners of the 3.7 were offered a factory upgrade to the new specification.

Key specs that matter

A single frame holds the ribbon treble unit and separate quasi-ribbon midrange and bass areas. Frequency response is 35Hz to 40kHz, sensitivity is 86dB at 500Hz for 2.83V and impedance is 4 ohms. Each panel measures about 61 x 180 x 4cm, and a pair weighs about 54kg. The standard finish is black aluminium trim with black cloth.

Engineering and use context

The true ribbon tweeter is the same type as in the Magnepan 20.7, a very thin aluminium foil. The foil is the diaphragm and the conductor at once, and it moves in a magnetic field along its entire length. The midrange and bass use quasi-ribbon construction, in which a light plastic diaphragm carries bonded conductors and is driven across its whole area by arrays of magnets. Every driver is planar and very low in moving mass, so the three sections behave alike and are easier to integrate across the crossover points. There is no box. Each panel radiates from both faces in opposite phase, forming a dipole with little output to the sides and fewer sidewall reflections than a conventional speaker. The 3.7i comes in mirror-image pairs so the tweeter can be placed on the outer or inner edge. According to Magnepan, outer tweeters give the widest listening area, while inner tweeters favour a single central seat, and the ribbon edge should never be nearer the listener than the bass panel. The factory X Upgrade option replaces the coils with air-core types, adds heavier solid-copper wiring and soldered connections throughout, and gold-plates the terminals.

Pairing

The 3.7i needs plenty of amplifier power and current, either solid-state or a high-power valve design. Being a dipole, it has to stand clear of the front wall, and it suits medium-sized rooms.

Alternatives

The Magnepan 20.7 is a larger panel with the same ribbon tweeter and a midrange driver of lower moving mass.