GB/T 19889.4-2005 "Acoustics—Measurement of sound insulation in buildings and of building elements—Part 4: Field measurements of airborne sound insulation between rooms" specifies field methods for measuring the airborne sound insulation performance between two adjacent rooms in existing buildings. It is primarily applicable for evaluating the overall sound insulation performance of interior walls, floors, and doors under actual diffuse sound field conditions. This method also provides the airborne sound insulation index as a function of frequency and allows for converting measured data into a single rating index according to the "Standard for Sound Insulation Evaluation of Buildings." This facilitates the comparison of the actual sound insulation performance of rooms or verification of their compliance with specified sound insulation requirements.