Compression Drivers and Horns

Compression drivers and horns carry the top end of almost every PA because the pair converts amplifier power into sound far more efficiently than a direct radiator, and the horn controls where that sound goes. B&C rate their DE250 and DE82TN at 108.5 and 106.5 dB, against 93.5 dB for the WM1850/8 sub driver.

The compression driver

A light diaphragm (titanium, aluminium or polymer) is driven by a voice coil as in any speaker. Instead of radiating into open air, it works into a shallow chamber closed by a phase plug: a block with shaped channels that lead to a small exit. Because the diaphragm area is larger than the channel area feeding the throat, the diaphragm sees a much higher acoustic load and couples to the air more efficiently. The ratio of those areas is the compression ratio. The phase plug's other job is to equalise path lengths from different parts of the diaphragm to the throat, so they arrive in phase at high frequencies.

1" vs 1.4" exits: published data

The larger coil and diaphragm buy nearly double the power handling and a crossover an octave lower, at a small cost in sensitivity. Driver exit and horn throat must match in diameter and bolt pattern.

What the horn does

• Loading. The horn flares from the small, high-pressure throat to a large mouth, matching the driver's acoustic impedance to open air. This raises efficiency above the horn's cut-off frequency, which is set largely by mouth size and flare rate.
• Directivity. The horn's walls set the coverage angle, quoted as horizontal × vertical (for example 90° × 40°), so energy goes to the audience and less to walls and ceiling.
• Pattern control frequency. A horn holds its pattern only down to a frequency set by its mouth dimensions; below that it widens. Big horns control lower.

The same loading principle applies at the bottom end in scoops and folded horns. See horn loading explained.

Protection

Diaphragm excursion rises steeply below the driver's intended range. Always high-pass at or above the maker's recommended crossover, ideally with a steep slope, and put a limiter on the HF channel. Power ratings for compression drivers are only valid with the specified filter in place. A cracked diaphragm or a driver that drops out on loud passages is the usual result of ignoring this; see compression driver cutting out and crossover basics.

Sources: B&C Speakers published data for the DE250 and DE82TN (8 Ω), checked October 2026; Wavemark WM1850/8 spec sheet. Horn and compression principles: L. L. Beranek, Acoustics.