BISA Module provides different absorption characteristics for its alternative perforation ratios. T1 can be used where absorption is necessary on wall surfaces and to provide optimunn reverberation desired for a room. T4 can be used where absorption is necessary on wall surfaces and to provide optimum reverberation desired for a room. T6 can be used where medium absorption is demanded for low frequency range, especially suited for electroacoustic sound reinforcement with music material of dominant low-frequency energy content in such rooms.