Definition: A D'appolito array is a speaker design pioneered by Dr. Joseph D'appolito in the early 1980s. A D'appolito array consists of a single tweeter with two midrange drivers arranged above and below the tweeter in a vertical alignment. The benefit of a D'appolito array is reduced interference between the tweeter and midrange drivers, which produces very smooth phase response. The design is also referred to as M-T-M (midrange-tweeter-midrange) although not all speakers with this driver alignment are D'appolito arrays. A true D'appolito array requires a very accurate crossover to achieve the desired results.
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A D'Appolito speaker array produces very smooth phase response in the midrange and higher frequencies.