Magnetic Assembly: Rent Com Inc: Audio Visual, Video, Projection, Presentation Rental AV Equipment

Magnetic Assembly

A unique feature of M4's magnetic assembly is its position relative to the diaphragm and phase plug. On a conventional mid/high-frequency compression driver, the magnetic assembly is in front of the diaphragm and phase plug. Forcing the sound through the narrow opening in the pole piece contributes to throat distortion. In addition, this opening actually behaves like a short horn section whose flare is only randomly matched to the primary horn. On the M4, the magnet is behind the diaphragm and phase plug.

This placement avoids both the distortion and horn mismatch problems and allows the M4's throat size and other parameters to be selected without regard to the size of the opening in the pole piece.

A survey of commercially available ferrite magnets shows that a 9.6 in O.D. (24.3 cm), 1.2 in (1.27 cm) thick ferrite magnet (approximately 5.2 kg) could be used to supply a 4.5 in (11.4 cm) diameter, 0.24 in (6.1 mm) high and 0.055 in (1.4 mm) wide airgap with 17.2 kilogauss. This approaches the highest flux density possible from a commercially available magnet, using good magnetic engineering practice. The final magnet design (patented) is shown below. The thick top and bottom plates reduce fringing and make this extremely powerful magnet structure a manageable weight of approximately 30 pounds.