No, sound waves from even-number vibration modes do not always cancel out due to destructive interference. The interference pattern depends on various factors such as the geometry of the sound source and the surrounding environment.
Destructive interference occurs when two sound waves of equal frequency and amplitude are out of phase with each other, meaning their peaks and troughs align in opposite directions. This can happen for any vibration mode, whether it is an even or odd mode.
In the case of a string or a pipe with open ends, the fundamental mode (first vibration mode) is odd, while the second vibration mode is even. When these modes are excited simultaneously, they can interfere constructively or destructively depending on the specific conditions. If the amplitudes, frequencies, and positions of the sources are carefully controlled, destructive interference can occur for either the odd or even modes.
However, it's important to note that the interference pattern is not solely determined by the even or odd nature of the vibration mode. The specific characteristics of the sound source and the surrounding environment play crucial roles in determining the interference pattern. Therefore, it is not accurate to make a general statement that sound waves from even-number vibration modes always cancel out due to destructive interference.