Definitions for "Constructive interference"
The adding together of two or more waves to form a third wave that has a greater amplitude than either of the orginal waves. Image of total constructive interference. Image of constructive interference.
The strengthening of waves that occurs when two waves interact and in phase portions of each wave combine to create a wave with a higher intensity. (Basic Science/Sound/interference.htm)
Constructive interference occurs when two waves overlap such that they are in phase (the troughs and peaks of the two waves coincide). Note, for this to occur down the entire wave, the two waves must have the same wavelength. When constructive interference occurs, the amplitude of the resulting wave is the sum of the two waves. So, if the original two waves had the same amplitude, the resulting wave would have twice their amplitude.