The damping of gypsum plaster board wooden stud cavity walls

Published test reports on the sound insulation of gypsum plaster board cavity stud walls with viscoelastic glue sandwiched between two layers of gypsum plaster board working as a constrained layer damper show large increases in sound insulation compared to the sound insulation of the same wall without the viscoelastic material. An increase in the sound insulation would be expected above the critical frequency of the gypsum plaster board panels and in the vicinity of the mass-air-mass resonant frequency due to the increased damping. However the test results show significant increases at other frequencies as well. A critical examination of the theory shows that the sound transmission via the air in the wall cavity is not expected to be greatly affected by the damping at these other frequencies. On the other hand, the sound transmission via the studs is affected at all frequencies by the damping. Hence it is not surprising that the published results are all for cavity stud walls. The sound insulation of two 16 mm thick gypsum plaster board sheets was measured. The sheets were mounted touching each other in three different configurations. These were without glue in between, bonded together with viscoelastic glue and spot bonded together with standard commercial glue. Surprisingly the elastic material compound gave better results even below the critical frequency, although the improvement became smaller and then disappeared as the frequency was decreased. A cavity stud wall with the second and third of the above configurations on each side of the studs was also tested. Again the viscoelastic glue performed better than the standard commercial glue, but the viscoelastic results were less than the original published results. Further published results were found which were in between the original published results and the experimental results obtained by the authors of this paper.