Descriptor of the position through a single cycle of a sound wave, i.e. 0° might be the starting point where the pressure is zero. The peak rises at 90°, back to zero at 180°, negative maximum amplitude at 270° and back to zero at 360° (see diagram, below).</p>
<p>If two identical sound waves arrive at the same location at the same time and are exactly 180° out of phase, the waves will cancel each other out. Similarly, if the two waves are in phase they will reinforce each other creating a wave of double the amplitude. </p>
<p>The most likely scenario in practice involving waves of multiple frequencies is partial reinforcement or cancellation. I.e. two interacting sound waves are typically non-identical and likely to be ‘out of phase’. The resultant interaction causes reinforcement and cancellation at differing frequencies, thus producing an uneven tonal response.