Acoustic waveguide
Other examples include the rear passage in a transmission-line loudspeaker enclosure, the ear canal, and a stethoscope.Its length is typically around a quarter of the wavelength which is intended to be guided, but the dimensions of its cross section are smaller than this.A load that matches the characteristic impedance (defined below) will completely absorb the wave and the energy associated with it.Where a transmission line of finite length is mismatched at both ends, there is the potential for a wave to bounce back and forth many times until it is absorbed.When this resonance effect is combined with some sort of active feedback mechanism and power input, it is possible to set up an oscillation which can be used to generate periodic acoustic signals such as musical notes (e.g. in an organ pipe).