Alternative reference curves for evaluation of the impact sound insulation between dwellings

Abstract

A survey of the sound insulation between modern Swedish dwellings was made by the National Testing Institute in 1983. This survey, which comprised measurements and interviews with tenants in eight housing areas, brought up the old subject of discussion about how to measure and evaluate the impact sound insulation of floors. A good correlation was revealed between the mean impact sound index (determined by ISO 140 and 717) and the corresponding subjective mean score of each housing area and party construction, but there were also indications about how to improve the method of deriving the impact sound index. Therefore, some more party floors have been investigated and an analysis has been made whether or not there are more effective reference values than the curve standardized by ISO 717/2. Including the new floors, a total of 22 different party constructions have been investigated, comprising 160 impact sound pressure level measurements and 464 scores obtained by interviews with 398 tenants. Both timer joist and concrete floors with soft and hard floorings are represented. The data was processed by a computer program to determine new impact sound indices with optional reference curves and to perform a linear regression analysis between the pairs of subjective and objective results. By testing various alternatives it was found that a flat reference curve, as independently suggested by Fasold and by Olynyk and Northwood, or the use of a C-weighting network, as in the Japanese standard, were much better alternatives than the ISO method. It was also found that an even better choice was a straight curve with a positive slope of 1 dB per 1/3-octave band starting at 50 Hz and terminating at 1000 Hz. This alternative gave a correlation coefficient as high as 87%. The concordant experiences suggest that the dispute about the method of determining the impact sound insulation can be easily solved by keeping the standardized tapping machine as the sound source and merely introducing a new reference curve for dwellings.