The DI Series feature Definitive Technology's most advanced technologies such as BDSS drivers and pivoting Pure Aluminum dome tweeters for spectacular audio performance far beyond traditional flush-mount speakers. Definitives exclusive Balanced Dual Surround System (BDSS) driver technology permits these new flush mounts to deliver more bass output and dynamic range than larger drivers. For example, the 4-1/2" driver-based model has the bass and dynamics of a 5-1/4" traditional speaker, while the 5-1/4" performs like a traditional 6-1/2". Pure Aluminum dome tweeter featuring a specially shaped housing that avoids the diffraction distortions of traditional post mounted tweeters, and a sophisticated adjustable crossover network, the DI Series delivers the kind of lifelike sonic performance and broad even dispersion that you've come to expect from Definitive Technology.