» Organ Pipe 22-1 (0575)

Immagini

DESCRIPTION

Exhibit 575 is a wood organ pipe of square cross section, with a flaut type mouthpiece, constructed by Albert Marloye (1795-1874), a maker of acoustic instruments in Paris. The air introduced through the mouthpiece is compressed in a small chamber 'C' (see design:1) and exits in the form of a thin laminar flow through the narrow slit 'F' where it encounters the sharpened lip 'L', that defines the flow way to the outside. The vibration of L are thus transmitted to the column of air in the inside of the pipe. The other end of the pipe is open and in direct contact with the external air, thus forming an antinode. Between the two openings, there is one node as in design-2a.

If L is the length of the pipe and $Formula: [\lambda_1 ]$ is the wave length of the produced sound, than:

Equazione: [n = \frac{V}{\lambda_1} = \frac{V}{2L}]

where n is the frequency of the fundamental note and V is the velocity of sound.

The successive possible vibrational mode is illustrated in design-2b. Here the same length of the pipe contains three antinodes instead of two, therefore the length of the pipe corresponds to $Formula: [\lambda_2]$ , the new wavelength. then:

that is;

Equazione: [n_2 = \frac{V}{\lambda_2} = \frac{2V}{L} = 2n]

The next successive harmonic occurs when the pipe contains four antinodes as illustrated in design 2-c and therefore the pipe length corresponds to $Formula: [{3\over 2} \lambda_3]$ , where $Formula: [\lambda_3]$ is the new wavelength.

Quindi

Equazione: [ L = \frac{3}{2} \lambda_2 ]

Cioè

Quindi

Equazione: [n_3 = \frac{V}{\lambda_3} = 3\frac{V}{L} = 3n ]

This relation shows that an open pipe emits harmonic notes of freqency n, 2n, 3n, 4n, etc. When air vibrates in an open pipe all harmonic notes are produced, while a closed pipe emits only odd notes.

For major details, see references ref. ^[1] e ref. ^[2].

ISCRIZIONI

Su un lato è inciso "MARLOYE ET C¶
A PARIS"
Su un lato é inciso: "22"

BIBLIOGRAPHY

[1] Oreste Murani,"Trattato Elementare di FISICA", Volume Primo, § 345, pag. 493
[2] A brief guide to the Pipe Organ: URL [ http://www.nazard.co.uk/organ.html ]
[3] Paolo Brenni, "The triumph of experimental acoustics: Albert Marloye (1795--1874) and Rudolph Koenig (1832--1901)", Bulletin of the Scientific Instrument Society, no. 44.

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