This neglects the effect of absorption in the plenum space itself, which results in additional attenuation. Each system must be at least as good as the calculated value, and one or both must be somewhat better. Quantitatively, the sum of the two requirements should be about 6 db better than the sum of values obtained by the independent calculations. If adequate design information is lacking another approach is to require that the contractor or supplier construct a sample pair of rooms, where the actual performance can be determined. Such a step is very useful in any case, because it ensures that the performances of the individual components are not invalidated by an assembly problem.
Doors Doors constitute a serious weakness in a good wall.
A more typical installation, with stops on three sides but no gaskets, is about STC-20. The result for the combined wall and door should be adjusted as for wall and ceiling. Other weaknesses in a partition, such as holes or cracks, may also be studied in the same way. Originally published March 1964.