![]() ![]() To understand how diffraction occurs, let’s consider the example of light waves passing through a narrow slit. These secondary wavelets interfere with each other, resulting in the bending and spreading of the wave. According to this principle, every point on a wavefront acts as a source of secondary wavelets, which spread out in all directions. ![]() One of the key principles that explain diffraction is Huygens’ principle. Diffraction plays a crucial role in the field of physical optics, which focuses on the wave propagation and behavior of light. It is a result of wave interference and can be observed in various types of waves, including light waves, sound waves, and water waves. Definition of Diffractionĭiffraction refers to the bending or spreading of waves as they encounter an obstacle or pass through an opening. In this section, we will explore the definition of diffraction and delve into the explanation of how it occurs. It is a fundamental concept in the field of physics, particularly in the study of wave behavior and characteristics. This is used to test how good walls are at stopping sound getting from one room to another.Diffraction is a fascinating phenomenon that occurs when waves encounter an obstacle or pass through an opening. One place where acoustical engineers don’t want absorption is a special laboratory called a transmission suite. The listening room, Acoustical & Audio Engineering Laboratories, Salford University No absorbers An extreme example is shown in the listening room photo below. ![]() Consequently, design is all about locating the reflection points for first order reflections, and applying appropriate treatment there. By using sound diffusers, first order reflections are dispersed to be heard later by the listener, and by removing and delaying early reflections, diffusion and absorption can make a small music studio sound like a larger room. But specialist (=expensive!) diffusing surfaces can achieve greater diffusion in a more controlled manner. Some diffusion can be obtained by carefully placing book cases and other furniture in a room. The anechoic chamber at University of Salford where every wall is sound absorbing DiffusersĪcoustic Diffusers are used to disperse reflections spatially – to spread out reflected sound energy over a wide range of angles – as shown in the diagram above with the black path. The sound quality would be like listening outdoors, where only the direct sound from a source is heard (assuming soft ground and an absence of nearby buildings). It can be a tricky balance for an acoustic designer – too much absorption, and the room will sound dead. This absorption can be a specialist product such as those made of mineral wool, open cell foam, or recycled fibrous material like paper-waste, but absorption can also be provided by more commonplace object such as curtains, sofas or carpets. One solution to reflections is to apply absorption to the wall, which turns acoustic energy into heat – this is a kind of damping. There are two basic forms of acoustic treatment to deal with reflections: absorption and diffusion. These later reflections all blend in together, and cause reverberation. The higher-order the reflection, the further the wave has travelled and the later they arrive. Second order reflections are like shots played off two cushions, third order off three etc etc. You can imagine the waves bouncing around like balls on a pool table. In small rooms, first order reflections tend to be loud and arrive very soon after the direct sound. The diagram below shows a plan view of a small rectangular room, highlighting a first order (involving only one reflecting surface) reflection from the top wall in red. (Timbre is a French word which describes sound quality). These reflections can cause the sound to be coloured, or to put it another way, the timbre of the sound will change. The direct sound arriving at your ears directly from your hands is quickly followed by reflections from the walls, ceiling and floor. Try this experiment – go into a small bare room like a bathroom and make noise – a handclap will do. ![]() Hear the difference between a room with strong reflections and one with no reflections (anechoic chamber) ![]()
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