![]() Smooth walls have a tendency to direct sound waves in a specific direction. In auditoriums and concert halls, reverberations occasionally occur and lead to the displeasing garbling of a sound.īut reflection of sound waves in auditoriums and concert halls do not always lead to displeasing results, especially if the reflections are designed right. Perhaps you have observed reverberations when talking in an empty room, when honking the horn while driving through a highway tunnel or underpass, or when singing in the shower. This is why reverberations are common in rooms with dimensions of approximately 17 meters or less. Since sound waves travel at about 340 m/s at room temperature, it will take approximately 0.1 s for a sound to travel the length of a 17 meter room and back, thus causing a reverberation ( recall from Lesson 2, t = d/v = (34 m)/(340 m/s) = 0.1 s). The reception of multiple reflections off of walls and ceilings within 0.1 seconds of each other causes reverberations - the prolonging of a sound. If a reflected sound wave reaches the ear within 0.1 seconds of the initial sound, then it seems to the person that the sound is prolonged. Why the magical 17 meters? The effect of a particular sound wave upon the brain endures for more than a tiny fraction of a second the human brain keeps a sound in memory for up to 0.1 seconds. A reverberation often occurs in a small room with height, width, and length dimensions of approximately 17 meters or less. Reflection of sound waves off of surfaces can lead to one of two phenomena - an echo or a reverberation. This gives the room more pleasing acoustic properties. These materials are more similar to air than concrete and thus have a greater ability to absorb sound. Walls and ceilings of concert halls are made softer materials such as fiberglass and acoustic tiles. A hard material such as concrete is as dissimilar as can be to the air through which the sound moves subsequently, most of the sound wave is reflected by the walls and little is absorbed. For this reason, acoustically minded builders of auditoriums and concert halls avoid the use of hard, smooth materials in the construction of their inside halls. As discussed in the previous part of Lesson 3, the amount of reflection is dependent upon the dissimilarity of the two media. When a wave reaches the boundary between one medium another medium, a portion of the wave undergoes reflection and a portion of the wave undergoes transmission across the boundary. In this part of Lesson 3, we will investigate behaviors that have already been discussed in a previous unit and apply them towards the reflection, diffraction, and refraction of sound waves. Possible behaviors include reflection off the obstacle, diffraction around the obstacle, and transmission (accompanied by refraction) into the obstacle or new medium. Rather, a sound wave will undergo certain behaviors when it encounters the end of the medium or an obstacle. The most amount of diffraction happens when the wavelength is a similar size to the gap.Like any wave, a sound wave doesn't just stop when it reaches the end of the medium or when it encounters an obstacle in its path. ![]() (a picture would help to explain this)ĭiffraction: Waves spread out as they enter an aperture (gap). As it slows down it changes direction, meaning that the angle that it is travelling at changes - the angle becomes closer to the normal. Refraction: When light travels from air into another material (such as glass) at any angle other than normal (perpendicular), it slows down. Remember that in reflection the angle of incidence (this is the angle that the initial wave makes from the normal), is the same as the angle of reflection (the angle that the reflected wave makes from the normal). ![]() Reflection: This is when a wave hits a surface (e.g light hitting a mirror) and is bounced back. On the diagram it is useful to mark on a line for 'normal', this is a straight line that is perpendicular (makes a 90 degree angle) with a surface. It can also be helpful to draw diagrams of each to help you to remember the difference. These are all properties of waves and their definitions are useful to remember for exams.
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