In organ pipes the contained volume of air is caused to vibrate.
The following materials have been used for organ pipes:
Metals: lead, tin, copper, and brass are the most common metals used. The lead and tin are usually alloyed to produce what is termed "common metal" (where it has spots on cooling). Rarely antimony is added for a hardening effect.
Tuning slides are normally made of coke tin sheet, but aluminum has been used also. Some aluminum pipes have been made but these seem to be mostly experimental and have not been adopted by mainstream builders.
Woods: sugar pine (Pinus labertiana), western white pine (Pinus monticola), spruce (Pinus glabra), and redwood (Sequoia sempervirens) are the most common woods used. Hot horse hide glue is used to hold them together!
Cardboard, PVC-Polyvinyl chloride and several forms of cardboard have also been used by amateurs and a few builders playing with a different material.
"In organ pipes, of a certain calibre, very sensitive waves occur at intervals; as according to the character of the sound evolved; but on a combination of resonators composed of brass tubes of more than nine in number, a wave of sound, induced by certain chords passing over them, produces high vortex action of the air enclosed in them. The vibration of tuning forks induces alternate condition of the air that surrounds them, if in open atmosphere; but quite a different action presents itself when the forks are exercised in resonating tubes, set to thirds of the mass chord they represent. Then high vortex action is the instant result. Vibrators cannot be set promiscuously in tubes, and get such results, any more than a musician can render a musical composition on the violin before tuning it." [Appendix I]
Musical sounds are usually caused in the ear by certain vibrations of the surrounding air, which originate from solid bodies in a state of vibration from some force exerted upon them. Vibrations of the air require to attain a certain rate of speed before they become audible to the human ear; and they require to have certain ratios of rate of rapidity in order to constitute that beautiful host of sounds which constitutes the music of mankind. These musical vibrations may arise in the air from a vibrating organ pipe, or a vibrating tuning fork, or a bell, or a sounding glass, or a strand of wire or gut-string, or other rhythmically vibrating body; but to explain and define the nature of a musical vibration from the action upon it of an elastic string is to explain and define it for all. But before defining what a vibration of a string is, let us hear what others have said about it. Charles Child Spencer, Treatise on Music, p. 6, says- "It is customary in calculating the ratios of vibration of musical strings, and which answer to the waves of the atmosphere, to reckon by double vibrations, so that instead of saying there are 32 single vibrations in the lowest sound, C, writers on this branch of music say there are 16 double vibrations in this sound. This method of calculation, therefore, gives 256 vibrations for the fourth Octave C." Playfair, in his Outlines of Natural Philosophy, p. 282, says- "It is usual to reckon the vibrations of a string different from those of a pendulum; the passage from the highest point on one side to the highest point on the other is reckoned a vibration of a pendulum; the passage from the farthest distance on one side to the farthest distance on the other and back again to its first position, is the accounted a vibration of a musical string. It is properly a double vibration." Holden, in his Rational System of Music, says- "Mr. Emerson reckons the complete vibration the time in which a sounding string moves from one side to [Scientific Basis and Build of Music, page 22]
5.2 - Vortex Motions in Resonators
air column resonance
Figure 6.17 - Areas and Volumes - Relations and Proportions
Table 12.02 - Length Area and Volume Math