EWPAA Structural Plywood and LVL Design Manual - Engineered ...

For a truck noise of 70dBA - Solid Block WallDue to transmission:By diffraction:Adding:Noise received70 – 35 = 35dba70 – 12 = 58dBA58 – 35 = 23dBA> 10 so +0.= 58dBATimber WallDue to transmissionBy diffraction:Adding70 – 21 = 49dBA70 – 12 = 58dBA58 – 49 = 9dBA so + 0.5= 58.5dBARounding could go either way. Going down:Noise received= 58dBAHence, no additional benefits are gained by using a material having a higher acoustic performance than25mm thick timber.14.9 Noise in BuildingsIdentifying potential noise sources at the design stage of a building is imperative since remedial work can bevery costly and inconvenient to the client.Noise in buildings can be categorised into two types:airbornestructure bornefrom within from voices, TV’s and radios, from outside from traffic, weather, etc.from vibrating machines, impact from footsteps from people walking or running,moving furniture, etc.Materials providing adequate insulation against airborne sound may not be so effective against impact.This is particularly so if the Mass Law is invoked to improve transmission loss.14.10 Timber Stud Cavity Walls – Airborne NoiseThe Mass Law shows by doubling the mass/m 2 of a single skin wall contributes to a 6dB increase in TL.That is, a 10mm thick panel increased to 20mm thick gives an additional 6dB noise reduction. However, iffurther 6dB increases are required it can be seen taking the Mass Law approach soon becomes impractical.If instead of doubling the thickness of the single skin, another identical single skin wall panel is locatedbeside the first one, but sufficiently separated to render them acoustically independent. This system wouldnot result in just a 6dB gain but rather it would double the TL of the first panel.Again, the practicalities of the cavity stud wall construction shown in FIGURE 14.5(a) dictates the sheathingmaterial must be relatively close together. This results in the gain in TL not even approaching that of theidealised case due to resonances within the cavity.228