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Horn DriversHorns require compression drivers. These transducers produce high pressure but little displacement. The diaphragm therefore moves very little, which results in less distortion than a conventional radiating driver. Horn drivers need high magnet strengths to produce the high pressure. Ordinary radiating drivers do not usually meet the requirements of a compression driver, so you cannot just horn load a normal cone speaker. Cone drivers that will work usually have a Qts of between 0.2 and 0.3 and large magnetic fluxes. For example, the Lowther full range driver has a Qts of 0.247 and so is suitable for horn loading (as well as direct radiating). Compression drivers are produced by JBL, Pioneer TAD, Onken, GOTO, and others, including Altec. Bass horn drivers that have been recommended and used include the Electro-Voice EVM 12L, a driver with a Qts of 0.232 and an Fs of 55 Hz. For horn loading, you want a driver with a low Qts and a higher (relatively) Fs. Dividing Fs by Qts, we want greater than or equal to 120. The EVM 12L comes in at 237 (see Bruce Edgar's article "The Show Horn" in Speaker Builder, 2/1990). The JBL Prosound division have a driver for bass applications along with some theory on horns at Technical Notes. Other good horn theory resides in scientific papers and magazine articles, see the References section. Top
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