The TTS28-A is a reference, high output, 2 x 18" bass reflex subwoofer module ideal for touring applications. With the digital switching amplifiers, neodymium woofers and well designed structure, it is one of the smallest and lightest double 18" systems available. A unique feature is the semi charged horn design which at low frequencies around 40 Hz operates as a conventional bass reflex cabinet. However at slightly higher frequencies in the 80 to 100 Hz area, the system operates as a semi charged horn loaded design which provides around 3 to 4 dB more efficiency.