Understanding Sound Propagation and how it travels in an environment is essential to designing quality acoustics treatments
Sounds very rarely have only one direct path from the source to the receiver (worker, resident, consumer or equipment). It can be reflected or absorbed and is affected by the size of objects in its path. Much of this we are not consciously aware of when receiving sound from a particular source. To say we can’t see sound may be an obvious statement but it does mean unless we are in a carefully designed and therefore a controlled environment, the awareness and prediction of Sound Propagation to a particular point is not straightforward.
- Sound reverberation in an enclosed space
Sounds may consist of a range of frequencies. Materials will absorb different frequencies in varying amounts and the size of an object will determine how it affects the propagation of a sound.
Objects impeding the propagation of sound waves can be thought of as a wave on the seashore. A large wave meeting a pebble has little or no effect on the passing of the wave. This represents lower frequencies, which have larger wavelengths, with a small object in its path.
On the other hand, a small wave meeting a large rock is reflected back and the remaining part of the wave loses energy as it travels around to the rear of the rock. This represents higher frequencies, which have smaller wavelengths, with a large object in its path.
A sound wave that is not absorbed will be reflected. Sound waves can also propagate through, across and or around the material or its surface. A sound may be reflected many times before reaching the receiver. This sound multipath can cause interference in the sound waves, altering the quality or characteristics of the sound at the receiver.
This interference can be visualised by ripples on water. A single water drop landing on water causes even waves/ripples to radiate outwards. When two drops land water the ripples collide causing an interference pattern. Below is a video illustrating a simple interference pattern. The more sources and the more complex the reflections the more complex the pattern.
In essence, the art of acoustics consultancy is to measure and then minimise the impact of interference through good design.
With all of these variables, it is important to either measure the actual sound impacting at a particular location or to measure sources such that these variables are minimised to a level of uncertainty that no longer impacts on the decisions regarding the Acoustical Design and any subsequent process such as Planning decisions.