The heart of the Heil air-motion transformer is a featherweight pleated Teflon diaphragm bonded with conductive aluminum strips. The diaphragm is suspended within a massive magnet structure. Its steel conductor plates concentrate an intense magnetic field around the diaphragm.
When a signal passes through the diaphragm's foil strips, the bellows-like motion of the pleats squeezes air out at five fimes the speed of the vibrating diaphragm itself. This virtual "instant acceleration" distinguishes the Heil from all other loudspeakers.
Polar response curves at a wide range of frequencies reveal a broad horizontal dispersion pattern through-out the audible spectrum. The ability of the Heil air-motion transformer to disperse even the highest frequencies over a large area assures full stereo imaging anywhere in the listening environment.
The superior response of the Heil air-motion transformer is revealed in its relatively flat impedance. The entire system's frequency response curve shows a typically broad, linear bandwidth. This exceptional efficiency at all frequencies permits the amplifier to deliver necessary power at ultrasonic frequencies.
A pair of drawings illustrates the movements of the Heil's pleats and the corresponding musical sine wave signals. In Figure 4A, the front facing pleats contract as the sine wave rises, forcing the air out under pressure. Meanwhile, the pleats opening towards the rear draw air in. When the sine wave reverses, as shown in Figure 4B, the pleats contract in the opposite direction.
The "squeezing" action of the heil diaphragm's pleats viewed in detail from above. As the pleat walls (A) squeeze together, they force a large amount of air to accelerate under pressure through a narrow opening (B). The folds are 5.3 times as deep as they are wide, resulting in a 430 percent increase in air velocity.