Composite Diaphragm: Rent Com Inc: Audio Visual, Video, Projection, Presentation Rental AV Equipment

Composite Diaphragm

A large diaphragm is essential for a 4-inch midrange driver capable of producing 100 acoustic watts. The diaphragm of an M4 is a full 6.65" (16.89 cm) in diameter and has an effective piston area of about 40 in2 (258 cm2). This is due in part to the use of the outer suspension as part of the piston. The phase plug throat area of 8 square inches with this 40 square inch (258 cm2) diaphragm results in a compression ratio of about 5:1. The M4's maximum diaphragm excursion is +/- 0.1 inches (2.54 mm), rivaling that of some woofers.

The response of all diaphragms begins to break-up at some high frequency. This is the point where the diaphragm is no longer acting like a piston. The design goal of the M4 was to extend high-frequency response to beyond 2000Hz. This was accomplished by the development of a sandwich diaphragm with 2.0 mil aluminum "skins" and a rigid, low-density foam core. To further reduce breakup, the outer edge of the diaphragm is rolled, greatly increasing it's stiffness.

The result is a lightweight, stiff diaphragm that maintains a smooth frequency response to about 2200Hz.