The Satellite 21-225 system, consisting of a pair of A21-2 speakers and a single A225-1 sub, represents true 3-way stereo reproduction. The crossover frequencies between the units are perfectly aligned and form a flat frequency response from 30Hz up to 20KHz. The Satellite 21-252 system comes with all the technologies of the single units (CPR and AOI), but provides an increased frequency range and SPL. The big advantage of the A21-225 system is that it delivers the dynamic performance and quality of sound of much larger systems, but takes up a minimum of space. Protecting your investment over time, the Satellite A21-225 system can be used as the basis of a PSI Audio 5.1 surround sound system.