Closed Flue Pipe Experiment
The wind instrument I will be researching in this experiment will be the pipe organ, commonly used in cathedrals and churches. Pipe organs produce sound by pushing pressurized air through a set of flue pipes. Flue pipes usually have a circular cross section and are mostly made of wood or metal. One pipe can only produce one pitch, so to produce a range of pitches an organ will have multiple sets of pipes called stops. Organs can have as little as 12 pipes to as many as 20,000.
All wind instruments rely on the vibration of air to produce sound. They all have some sort of pipe or tube in which standing air resonates and produces a fundamental frequency. This frequency of the sound produced is dependent on the length of the tube. In some instruments, the length of the tube can be modified to alter the frequency produced. However, this is impractical for other wind instruments such as the pipe organ, so they have multiple pipes for different notes.
Older pipe organs usually needed two people to operate them. One person to operate the bellows and one to play the notes. Now, modern organs have a turbine that provides constant air to the organ. A pipe organ works by blowing pressurized air into the pipe from the and into the foot of the pipe. At the top of the foot is a narrow slit, called a flue. The pressurized air is forced through this slit, deflects off the upper lip and out into the air. This action causes the standing air inside the main body of the pipe to resonate at a fundamental frequency.
The longer the pipe length, the lower the frequency.
In this experiment, I believe that the fundamental frequency of the pipe will be higher as the pipe length decreases. I think this is because a longer pipe has a larger surface area means the air molecules have more space to move around and will therefore perform fewer oscillations. The formula for fundamental frequency f0 is :...
References: Bush, D.E, 1962. The Organ: An Encyclopedia. 1st ed. UK: Taylor & Francis group.
David Howard, 2006. Acoustics and Psychoacoustics, Third Edition (Music Technology). 3 Edition. Focal Press.
Organ Project - Flue Pipes. 2012. Organ Project - Flue Pipes. [ONLINE] Available at: http://mikebanahan.com/Organproject/organ_flue_pipe.php. [Accessed 10 May 2012].
Organ Pipes, Acoustics. 2012. Organ Pipes, Acoustics. [ONLINE] Available at: http://www2.ibp.fraunhofer.de/akustik/ma/pipesound/index_e.html. [Accessed 10 May 2012].
Campbell, W. (2012), "Acoustic of Pipes", Lecture, Anglia Ruskin University, unpublished.
Graph showing pipe length against frequency
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