Sound Isolation Projects
Noise Engineers regularly works on sound isolation projects. Generally, it involves reducing the noise between spaces or from the exterior to interior. Usually, we need to test and/or predict the noise passing between spaces.
Exterior to Interior Sound Isolation
In many cities there are building requirements for construction near airports and highways. We are required to look at the proposed construction and the noise exposure and predict the interior noise levels. Usually, the requirements are for a 24 hour average (LDN) noise level of 45 dBA inside. If the requirement is not met, we discuss options to improve the exterior construction. This could include include improving windows and door construction. Sometime wall and roof construction need improvements.
Room to Room Sound Isolation Testing
For existing partitions, many times we test the walls. We produce broad band (including all frequencies between 31 and 8,000 Hz) pink noise in the source room and we measure the noise in the source and receiving room. We measure the reverberation time in the receiving room (the echoiness) to normalize the measurement. Then we calculate the Sound Transmission Class (STC).
Speech privacy is a function of the noise level in the source room, construction of the path (wall, door, window), the absorption in the receiving room (less important than path construction), and the background noise level. If the noise level in the receiving room is very low, even low noise levels can be disturbing and/or over-heard. In some cases, a noise masking system is appropriate to increase the background noise level.
Room to Room Sound Isolation Predicting
We use a software program called INSUL to predict the STC of various partitions. It allows us to predict the impact of making improvements on a partition. In general, the lowest STC component of a partition should be addressed first. For example, if there is a wall and a window and the wall has a high STC and the window has a low STC, there is little impact on improving the STC of the wall and a significant impact on improving the STC of the window.
It is critical to know the path of the noise and the STC of the various components. This will help avoid spending resources to improve a component that is not contributing significantly to the noise level in the receiving space.
Impact Insulation Class (IIC)
IIC is a related descriptor of the impact noise transmitting from one unit to another through the floor-ceiling system. This structure borne transmission should not be confused with the air borne transmission that STC measures.