CHAPTER 4

The shape or configurations of the component compressions and rarefactions as they diffuse through a medium.

The dissipation of sound energy or weakening of wave trains as they travel through a medium.

The bending of wave fronts as they pass through media having unequal or varying density.

The spreading of wave fronts into areas behind or around physical barriers.  Stated the other way: the filling-in of area spaces behind physical barriers that are blocked and not in a straight shot from the sound source.

The periodic reinforcement and cancellation of two wave fronts with frequencies closer together than 20 Hz.

The periodic reinforcement and cancellation of two wave trains with frequencies further apart than 20 Hz may be perceived as a third tone whose frequency is the difference between frequencies of the original tones.

Subjective tones produced by the ear that are perceived as the sum of two external frequencies.  Summation tones, if heard at all, are heard best when they occur near the middle of the audible frequency spectrum.

Tones that do not exist in the environment, but by forcing parts of the ear into non-linear vibration, are created within the ear itself.

The perceived phenomenon of multiple echoes mixing with the primary sound.

The trapping of sound waves in fibrous or porous materials which weakens the wavefront by reflecting and diffusing sound energy.

Preventing sound waves from traveling through physical barriers.  This may be accomplished by various combinations of reflection, absorption, diffusion, or by creating a barrier that will not transmit vibration.