Digital Sound & Music: Concepts, Applications, & Science, Chapter 4, last updated 6/25/2013
Figure 4.12 Graphs of A, B, and C-weighting functions
(Figure derived from a program by Jeff Tacket, posted at the MATLAB Central File Exchange)
4.1.7 The Interaction of Sound with its Environment
Sometimes it's convenient to simplify our understanding of sound by considering how it behaves
when there is nothing in the environment to impede it. An environment with no physical
influences to absorb, reflect, diffract, refract, reverberate, resonate, or diffuse sound is called a
free field. A free field is an idealization of real world conditions that facilitates our analysis of
how sound behaves. Sound in a free field can be pictured as radiating out from a point source,
diminishing in intensity as it gets farther from the source. A free field is partially illustrated in
Figure 4.18. In this figure, sound is radiating out from a loudspeaker, with the colors indicating
highest to lowest intensity sound in the order red, orange, yellow, green, and blue. The area in
front of the loudspeaker might be considered a free field. However, because the loudspeaker
partially blocks the sound from going behind itself, the sound is lower in amplitude there. You
can see that there is some sound behind the loudspeaker, resulting from reflection and diffraction.
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