Chapter 4
Horns
No practical direct radiating loudspeaker can achieve high radiation efficiency at low frequencies. For example, a diaphragm with a diameter of 250 mm has a radiation efficiency of just 0.7% at 50 Hz when mounted in an infinite baffle, and half that when mounted in a cabinet. Sound power output is proportional to the product of the mean-squared diaphragm velocity and the radiation efficiency, so a low radiation efficiency means that a high diaphragm velocity is required to radiate a given sound power. The only way in which the radiation efficiency can be increased is to increase the size of the radiating area, but larger diaphragms have more mass (if rigidity is to be maintained) which means that greater input forces are required ...
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