Practical formulas for quantifying the uncertainty of airborne sound insulation measurements caused by the diffuse field assumption

In the conventional approach for experimental airborne sound insulation assessment, as standardized in ISO 10140-2, it is (implicitly) assumed that the sound fields in the source and receiver rooms are diffuse.A diffuse field is by definition a random field: it represents a conceptual ensemble of rooms with the same volume and total absorption, but otherwise any possible arrangement of boundaries and objects that scatter incoming sound waves.Adopting a diffuse sound field model in the assessment procedure therefore inherently introduces uncertainty on the resulting ratings, such as the weighted sound reduction index and the spectrum adaptation terms from ISO 717-1.When determining such quantities in one particular transmission suite, this uncertainty is important below the highest Schroeder frequency of both rooms.In this work, closed-form expressions are presented for quantifying the uncertainty on experimentally determined sound reduction indices and related single-number ratings that is due to the diffuse field assumption when measurements are carried out in one particular transmission suite.They are numerically validated and their practical use is demonstrated in applications.They can be easily incorporated into overall uncertainty assessment procedures such as the detailed uncertainty budget analysis of ISO 12999-1.