Audio Engineering

Loudspeaker Enclosures 707

diaphragm, a compression driver must never be driven with a program having frequencies
below its rated range and not driven without being attached to a suitable horn. Usually,
the diaphragm is pressed out of a plastic fi lm, or a phenolic resin-impregnated cloth or
other composite, or from very light, but stiff metal, usually aluminum or else titanium or
beryllium. Size ranges from about 6  (150 mm) for midrange down to 1 (25 mm) for high
treble and above.

24.1.1.3 Soft and Hard Dome Drivers

The equal-second most common type of speaker drive-unit is familiar enough. It has an
almost hemispherical diaphragm shaped like some compression drivers, but the dome is
forward (like a fried egg) and nearly always working into free air. This is used on its own,
instead of a small diameter cone, as a tweeter (hf drive-unit). The material can be any of
those used in cone or compression drivers.

24.1.1.4 Common Voice Coil

The three types of drive-units discussed so far all have similar voice coils. They may
range widely in weight, diameter (from 0.75719 up to 67150 mm), and power handling

Magnet phasing

plug assembly

Voice coil diaphragm

Back plate assembly

Figure 24.2 : Two types of hf compression drivers made by Emilar, widely used in PA systems

from the mid-1970s.