The size of an object being larger than the wavelength of a sound wave is an important consideration in the field of acoustics and has several implications. Here are a few reasons why this condition is often preferred:
Diffraction: When a sound wave encounters an obstacle or passes through an opening, it undergoes diffraction. Diffraction is the bending and spreading of waves around obstacles or edges. If the size of the object is comparable to or smaller than the wavelength of the sound wave, significant diffraction occurs, resulting in the wave bending around the object and spreading out. This can lead to changes in the wave's direction and the formation of secondary waves, causing complications in accurately predicting the sound field.
Scattering: When sound encounters an object, some of it gets scattered in various directions. Scattering of sound waves occurs when the size of the object is comparable to or larger than the wavelength. If the object is much larger than the wavelength, scattering effects are typically more predictable and easier to model. In contrast, if the object is similar in size or smaller than the wavelength, scattering becomes more complex, with multiple scattering events occurring, making it difficult to analyze and interpret the resulting sound field.
Geometrical Acoustics: Geometrical acoustics is an approximation used to analyze sound propagation in environments where the wavelength of the sound is much smaller than the dimensions of the objects and the room. This approximation assumes that sound travels in straight lines and that reflections and diffraction can be neglected. If the object is larger than the wavelength, the geometrical acoustics approximation is generally valid and simplifies the analysis of the sound field.
Resonance and Standing Waves: In certain scenarios, sound waves can create resonances and standing waves within an enclosed space or around objects. Resonances occur when the dimensions of the object or the room allow for the constructive interference of sound waves at specific frequencies. If the object's size is much larger than the wavelength, it is more likely to support resonances and standing waves, which can have important implications in architectural acoustics and musical instrument design.
It's important to note that these considerations are general guidelines, and there can be exceptions depending on the specific context and application. In some cases, studying the interaction of sound waves with objects smaller than the wavelength can be of interest, such as in microacoustics or certain specialized experiments. However, in many practical situations, having the size of the object larger than the wavelength allows for simpler and more accurate analysis of the sound field.