Open and Closed Pipes Sound Open Tube Instruments

Open and Closed Pipes Sound

Open Tube Instruments Many woodwind instruments consist of an air column enclosed inside of a hollow metal tube. These tubes metal may be more than a meter in length and often curve one or more times in order to conserve space. If the end of the tube is uncovered such that the air at the end of the tube can freely vibrate when the sound wave reaches it, then the end is referred to as an open end. If both ends of the tube are uncovered or open, the musical instrument is said to contain an open-end air column. A variety of instruments operate on the basis of open-end air columns such as • flute • trombone • saxophone • oboe.

Open Pipes • The first resonant frequency for an open pipe occurs at 1/2 of a wavelength for a wave. • The peaks of the wave will be placed at the ends of the tube, this will create the loudest sound.

The Third and Fourth Harmonics • The next resonant frequency will occur at one wavelength. At this point the peaks of the wave still occur at the open ends of the tube creating the loudest sound • The third frequency at which resonance occurs is at 1 1/4 wavelengths

Relationships for Open Pipes

Practice Problem The speed of sound waves in air is found to be 340 m/s. Determine the fundamental frequency (1 st harmonic) of an open-end air column which has a length of 67. 5 cm

Closed Pipes • The first resonant frequency for an open pipe occurs at 1/4 of a wavelength for a wave. • The peaks of the wave will be placed at the ends of the tube, this will create the loudest sound.

The Third and Fifth Harmonics • The next resonant frequency will occur at 3/4 wavelength. At this point the peaks of the wave still occur at the open ends of the tube creating the loudest sound • The third frequency at which resonance occurs is at 1 1/4 wavelengths

Relationships for Closed Pipes

Practice Problem The speed of sound waves in air is found to be 340 m/s. Determine the fundamental frequency (1 st harmonic) of a closed-end air column which has a length of 67. 5 cm.