The “Weighted sound redution index”, Rw, described in ISO 717-1 standard, is considered a fundamental parameter for the comparison in laboratory of different building systems. This index considers a 1/3 octave band frequency range, between 100 Hz and 3150 Hz, which may not be sufficient for a satisfactory description of the behavior at low and high frequency. To consider the behavior, extended in frequency with respect to normalized noise spectra (pink noise and traffic noise), spectrum adaptation terms C and Ctr were introduced. The draft standard ISO/DIS 16717-1, a brand new version of the standard in use, considers three indices, Rliving, Rspeech and Rtraffic replacing the “old” concept of weighted index. This work presents the possibility to measure, in laboratory, sound reduction index below 100 Hz with current measurement standards. Physical aspects, measurement tecniques and CE marking problems and implications were considered. A comparison between ISO 717-1 and ISO/DIS 16717-1 with many measurements carried out in the Acoustic Laboratory of the Department of Industrial Engineering at the University of Padova, was also made.