This standard specifies the method for calculating a single-number rating for the airborne sound insulation of building facades and facade elements. It involves comparing measured one-third octave band sound insulation data with a standard reference curve to derive the weighted standardized level difference (D2m,nT,w). The code also defines spectrum adaptation terms (C and Ctr) to evaluate performance against specific noise sources like traffic.
Rating of sound insulation in buildings and building elements, Part 1: Airborne sound insulation in buildings and of interior building elements
Quick Reference Values
Evaluation frequency range100 Hz to 3150 Hz
Number of one-third octave bands for evaluation16 bands
Maximum unfavorable deviation at any single frequency8.0 dB
Maximum sum of unfavorable deviations over all frequencies32.0 dB
Key Formulas
D_2m,nT,w = Value of the shifted reference curve at 500 Hz
C = L_A,spectrum1 - L_A,Rw — Spectrum adaptation term for pink noise
C_tr = L_A,spectrum2 - L_A,Rw — Spectrum adaptation term for traffic noise
Practical Notes
The single-number rating D2m,nT,w is useful for comparison, but the spectrum adaptation term Ctr is critical for facades exposed to traffic noise, which is low-frequency dominated.
This code is only for 'rating' measured data. The actual measurement procedure is detailed in IS 9901 (Part 5): Field measurements of airborne sound insulation of facade elements.
A facade can meet the D2m,nT,w criteria but still have a significant acoustic weakness at a specific frequency, as an 8 dB unfavorable deviation is permitted at one frequency.