Waves can be combined
together such that, at a given location and time, they may cause either constructive effects,
in which the amplitude is strengthened, or
destructive effects in which the amplitude is reduced. A remarkable
property of waves is that they can pass through one another without being
disturbed. While they are passing through, the resulting acoustic pressure is
always just the sum of the acoustic pressures of each individual wave at
that moment and location.
The following example shows two wave
pulses travelling in opposite directions. See for yourself that the
resulting displacement is the sum of the individual wave displacements.