Melodeon (organ) - Acoustics

Acoustics

The acoustical effects described below are a result of the free-reed mechanism. Therefore, they are essentially identical for the Western and Indian harmoniums and the reed organ. In 1875, Hermann von Helmholtz published his seminal book, On the Sensations of Tone, in which he used the harmonium extensively to test different tuning systems:

"Among musical instruments, the harmonium, on account of its uniformly sustained tone, the piercing character of its quality of tone, and its tolerably distinct combinational tones, is particularly sensitive to inaccuracies of intonation. And as its vibrators also admit of a delicate and durable tuning, it appeared to me peculiarly suitable for experiments on a more perfect system of tones."

Using two manuals and two differently tuned stop sets, he was able to simultaneously compare Pythagorean to just and to equal-tempered tunings and observe the degrees of inharmonicity inherent to the different temperaments. He subdivided the octave to 28 tones, to be able to perform modulations of 12 minor and 17 major keys in just intonation without going into harsh dissonance that is present with the standard octave division in this tuning. This arrangement was difficult to play on. Additional modified or novel instruments were used for experimental and educational purposes. Notably, Bosanquet's Generalized keyboard, constructed in 1873 for use with a 53-tone scale. In practice, that harmonium was constructed with 84 keys, for convenience of fingering. Another famous reed organ that was evaluated was built by Poole.

Lord Rayleigh also used the harmonium to devise a method for indirectly measuring frequency accurately, using approximated known equal temperament intervals and their overtone beats. The harmonium had the advantage of providing clear overtones that enabled the reliable counting of beats by two listeners, one per note. However, Rayleigh acknowledged that maintaining constant pressure in the bellows is difficult and fluctuation of the pitch occurs rather frequently as a result.

Read more about this topic:  Melodeon (organ)