Abstract
All of the single-number indices currently used to assess the sound insulation of walls use one-third octave band sound transmission loss data in the frequency range 125 to 4,000 Hz. Forty-two walls were measured over the range 50 to 5,000 Hz. None of the existing indices correlated well with the calculated 50- to 4,000-Hz loudness reduction using the International Organisation for Standardisation method. A new proposed rating, the outdoor-indoor transmission class (OITC), which is based on A-weighted sound reduction in the range 80 to 5,000 Hz, shows significant improvement over other methods. Typically, both the loudness reduction and OITC give lower numbers than sound transmission class for wall constructions.