A universal problem
Sound energy does not remain in the room where it is produced, but propagates throughout the building by any available path, intruding into other rooms as noise. Each country has its own standards of sound insulation in buildings, but it is measured in the same way all over the world. The noise levels in the two rooms under investigation are measured and subtracted, and the level difference is corrected for the influence of the reverberation time and background noise level in the receiving room. The measurements and calculations are made in 1/1- or 1/3-octave bands and averaged over a number of positions in the rooms. Finally a single-number index is calculated by averaging over all the frequency bands.
Laboratory versus field measurements
For checking constructions such as windows, floors and walls, laboratories use test suites consisting of two adjoining rooms. The test sample is mounted in a test opening between the two rooms. The two rooms are designed to eliminate the influence of flanking transmission (sound that propagates through any path other than the test opening) and background noise. This ensures that results truly reflect the sound reduction of the sample.
When checking sound insulation in actual buildings (field or in situ situations), the results are often influenced by flanking transmission. To indicate this, results are often identified by adding a prime (like in 'R'). In field measurements, the consultant may have trouble accessing the site, have time constraints, or have to deal with background noise. In these situations, ease of use and fast, accurate measurements are vital.
Impact sound level
Impact sound, such as the noise made by footsteps, is simulated by using a standardised tapping machine. The level of impact sound insulation can then be measured.