The objective of this research is to obtain a correlation between air and sound leakages through slits. Audible sound, in the frequency range from 160 to 8000 Hz, is provided and sound pressure levels on both sides of the considered slit are detected by microphones, so that sound transmission losses can be obtained. Simultaneously, the air leakage through the slit under an inside-outside pressure difference of 50 Pa is also measured. Two different slits are used, one of which is rectangular of narrow width (0Â·05-1Â·00 mm), and the other is of the same section but with bent portions of the passage, as might be encountered in building constructions. The results show the correlation which represents graphically different curves for the source sound frequencies: ~ 2000 Hz is found favourable for the intended purpose.