Magnepan

Technology

Magnepan has used several different technologies in constructing their magnetostatic speakers. All Magnepan speakers are based on flexible ferrite magnet strips (like refrigerator magnets), 0.060" (1.5 mm) thick, typically cut to either 1/4" (6 mm) wide (mid-bass) or 1/8" (3 mm) wide (tweeters) and more or less the length of the speaker. The magnets are glued to a piece of custom perforated 20-gauge (1 mm) steel sheet. The steel supports the magnets and also completes the magnetic circuit on the back of the magnets, resulting in about a 25% stronger magnetic field in front of the magnets. Mylar film, 0.0005" (12.5 μm) thick, is suspended in front of the magnet structure about 1/16" (1.6 mm) away from the magnets. Aluminum wires or film are then glued to the mylar. Only aluminum was used: copper has two-thirds the resistance of aluminum, which would make the speakers either much larger or much more difficult to drive. Very few amplifiers can handle 2.7-ohm speakers. Older Magnepans used aluminum magnet wire, thin 31 gauge (0.0089", 0.23 mm) for the tweeters and thicker 22 gauge (0.0253", 0.64 mm) for the mid-bass. The wire is glued to the mylar with 3M 77 spray adhesive, then sealed with 3M Fastbond 30NF (Magnepan used to use Milloxane to seal, but no more).

Newer Magnepans use 30 μm (0.0012") thick 1/8" (3 mm) wide aluminum tape instead of wire. When the aluminum tape is used instead of wires, Magnepan calls the speakers "Quasi-Ribbons". Using the aluminum tape spreads out the driving force on the mylar speaker diaphragm, resulting in noticeably lower distortion.

Magnepan ribbons are constructed with a strip of aluminum roughly 5 μm (0.0002") thick, 1/4" (6 mm) wide, 60" (1.5 m) long. The aluminum is corrugated – the pleats help keep the ribbon from flexing between the magnets. Before corrugating the ribbon it's more like 80" (2 m) long. The aluminum is suspended between two ferrite magnets, about 3⁄8 in × 1⁄2 in (9.5 mm × 12.7 mm) in cross-section. The magnets are attached to a 1/8" (3 mm) thick piece of formed and perforated steel, which both holds the magnets in place and also completes the magnetic circuit, resulting in about a 40% stronger magnetic field in the magnet gap.

The 20.7 and 30.7 speakers have magnet structures on both sides of the diaphragm, front and back. This push-pull design results in a more linear magnetic field and noticeably lower distortion in the midrange. It also results in much heavier speakers - about twice as heavy. All other models have magnets only at the back of the diaphragm.