Also known as “diffraction loss.” This is a term that has many meanings, depending on context, but in the pro audio/music world, refers to distortion in frequency response and stereo imaging resulting from sound diffracting off the edges of the speaker cabinet. More specifically, sound radiates from a speaker baffle in a hemispherical pattern (half space). Low frequencies, however, tend to radiate in more omnidirectional fashion (full space), resulting in up to 6dB loss in low frequencies, along with a series of response “ripples” or anomalies that result from the location of the speaker driver in relation to the baffle edges. Waveforms can also be distorted if they radiate from the edge of a speaker baffle, and reflections in the baffle can cause smearing and phase distortion.
Maufacturers deal with edge diffraction by reducing the level of the high-frequency driver relative to the low-frequency driver, by carefully placing the drivers within the baffle, and by rounding the edges of the cabinet, though this only reduces edge diffraction, it does not eliminate it.