Digital Sound & Music: Concepts, Applications, & Science, Chapter 4, last updated 6/25/2013
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Figure 4.14 Angle of incidence equals angle of reflection
Figure 4.15 Sound radiating from source and reflecting off flat wall, as seen from above
In a special case, if the wavefront were to approach a concave curved solid surface, it
would be reflected back to converge at one point in the room, the location of that point
depending on the angle of the curve. This is how whispering rooms are constructed, such that
two people whispering in the room can hear each other perfectly if they're positioned at the
sound’s focal points, even though the focal points may be at the far opposite ends of the room. A
person positioned elsewhere in the room cannot hear their whispers at all. A common shape
found with whispering rooms is an ellipse, as seen in Figure 4.16. The shape and curve of these
walls cause any and all sound emanating from one focal point to reflect directly to the other.
Figure 4.16 Sound reflects directly between focal points in a whispering room
FOCAL POINT
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