With respect to percussion sounds, the characterization of the isolation provided by the horizontal compartmentation elements is performed, in the frequency domain, by obtaining a radiation spectrum.
The impact sound insulation index – is determined by comparing the referred aspect with the conventional reference description in standard EN ISO 717-2. For this purpose, this description is overlaid on the curve in question, so that the average value of the unfavorable deviation (as shown in the figure), calculated by dividing the sum of the deviations in this same direction (unfavorable) by the total number of frequency bands, considered in the test, must be as high as possible, but without exceeding the value of 2 dB. The sound insulation index corresponds to the ordinate value of the conventional reference description for the frequency of 500 Hz, and is expressed in dB.