amplitude antinode auditory effect auditory phenomenon crest de Broglie wave diffraction electromagnetic radiation electromagnetic wave frequency frequency band frequency spectrum guided wave in phase interference light longitudinal wave loudness mechanical wave node noise out of phase period periodic wave phone radio wave ray reinforcement resonance resonance frequency seismic wave shock wave sonance sound sound intensity level sound propagation speech sound surface wave tidal wave transverse wave trough ultrasound wave wave equation wave motion wave number wavelength