First, the range from 100Hz to 20kHz by Woofer, tweeter and crossover handled. Most of the vendors are the bass and tweeter speakers in the same box, which is relatively simple and economical way. Second, from 20Hz to 100Hz by a special subwoofer processing, usually on has its own amplifier. But to create a shaking, moving spirits effect, it is absolutely indispensable, for example, when you hear a helicopter from the front and then, “boom” is heard flying overhead, if you will quickly head down, trying to find a place to hide that subwoofer at play. Because of the low frequency belongs isotropic, so surround sound system only needs a subwoofer would be enough. Since the distance between high-woofer, affecting projection and produce high-frequency jet lag, which means that low frequency does not arrive to your ears at the same time, it is also different corners so that your family has a different frequency response, and therefore will not be able to enjoy a seamless sound. Third, another problem is the phase distortion, both said that when the original audio and video or sound recordings and hear different, phase distortion changes the harmonic structure of the sound, and it is accurate harmonic we need to identify instruments timbre. Method to solve these problems is to treble and bass unit placed in the same axis, both the tweeter in the middle woofer, dual coaxial speaker unit becomes (Dual Concentric), so all frequencies are cast from the same location out of time and space differences disappeared.