Joseph A. D'Appolito is best known as the developer of the "D'Appolito Configuration" which was first described in his "A Geometric Approach to Eliminating Lobing Error in Multiway Loudspeakers". This configuration is recognized by loudspeakers which have two midrange

Mid-range speaker

A loudspeaker driver that produces the frequency range from approximately 300–5000 hertz is known as a mid-range.Midrange drivers are usually cone types or, less commonly, dome types, or compression horn drivers...

 or woofer

Woofer

Woofer is the term commonly used for a loudspeaker driver designed to produce low frequency sounds, typically from around 40 hertz up to about a kilohertz or higher. The name is from the onomatopoeic English word for a dog's bark, "woof"...

 drivers arranged vertically above and below the tweeter

Tweeter

A tweeter is a loudspeaker designed to produce high audio frequencies, typically from around 2,000 Hz to 20,000 Hz . Some tweeters can manage response up to 65 kHz...

 and implements the 3rd order (18dB/octave) crossover allowing the drivers to have similar horizontal dispersion, resulting in absence of any sudden change in directivity with frequency. The loudspeaker configuration is also known as a midwoofer-tweeter-midwoofer (MTM) configuration. D'Appolito is the author of "Testing Loudspeakers" and a contributing editor to AudioXpress magazine. He is also the owner of a consulting firm, Audio and Acoustics, Ltd. whose clients include Snell Acoustics; HECO/Recoton, GmbH and Usher Audio Technology.