SOUND TRANSMISSION MEASUREMENTS: THE STANDARD METHOD - COMMENTS ON ITS OBJECTIVITY AND A PROPOSAL TO IMPROVE ON

摘要

The quality of sound insulation in buildings is mostly expressed by the standardized level difference D_(nT) and its weighted equivalent D_(nT, w). The survey method is described and illustrated in the standard ISO 10052:2004. It is found that D_(nT), being a survey quantity, is too much a reflection from the sound reduction index, R, which has a completely different meaning and is conceived for laboratory measurements. The recommendation that one has to measure near the centre of the floor results from the condition to measure in the reverberant field. The fact to normalize for the reverberation in the receiving room is needed to make results comparable but the reference T_0 = 0, 5 s is in many cases unrealistic and moreover, reverberation in a room has nothing to do with the sound insulation of a separating structure. An alternative would be to use a hammer impact sound and calculate the result based on the transmission of the direct sound and the first reflections, and disregard all of the late reflections in the receiving room. The advantage would be that one is not bound to the centre of the room for recording the sound level and the result no longer would depend on the reverberation time in the room. The disadvantage of the method is that a broad band spectrum of a hammer impact is hard to produce and the reproducibility depends too much on the operator and his experience. However, digital measuring techniques based on Fourier transformation and making use of the impulse response function can successfully replace the hammer impact.