In Germany, pipes are almost exclusively made of traditional so-called metal, a tin and leas alloy, whereas in the U.S. many pipes are manufactured of zinc by numerous organ organ building enterprises. In the long tradition of organ building zinc was also used for building pipes in this country from time to time. In applying zinc, however, organ builders were faced with the problem that pipes manufactured of zinc have a different sound than those made of organ metal. Voicers, who had to process the harder zinc pipes manually, had problems in copingwith this material. By the decision to use organ metal again the question had to be answered, whether zinc was a reasonable alternative, and how this material had to be assessed.
This problem was investigated at the Fraunhofer IBP by using current knowledge and up-to-date methods of organ acoustics. In a first step it was found out in cooperation with manufacturers and specialists of processing of zinc that the quality of zinc, which is available nowadays, is definitely higher. Therefore, the voicer has better opportunities to cope with this material. The question of sound, however, remains still unanswered, that is in how far the wall vibrations of a pipe are changed by using zinc, and what impact on the sound may occur.
In cooperation with Werkstätte für Orgelbau Mühleisen in Leonberg (organ building enterprise) various pairs of pipes made of organ metal and zinc were investigated with regard to vibrations and acoustics. The wall thickness of the experimental pipes made of zinc, designed and used in this project, amounted to approx. 90 percent of the standard organ metal pipes. The voicer participating in the project had to solve the problem of adjusting the pairs of pipes, which were made of various materials, to the same sound according to hearing.
The results of the vibro-acoustical experiments show clearly defined differences between the frequency-dependent wall vibrations of the flue organ pipes manufactured by the two materials. For an "intererence-free" vibration analysis three laser vibrometers were simultaneously used to achieve a 3-dimensional analysis of the pipes synchronously. Subsequent acoustical measurements, however, showed that the pipes can be voiced to the same sound. This is verified by the analysis of the stationary spectra as well as of the attack transients (attack of pipes). Simultaneous recording by a microphone array served as validation allowing the determination at a glance and representation of the complex sound field emitted by the organ pipe.
The research result is obvious: Zinc has advantages in some ways and is a real alternative as concerns the sound. Now, the question is to optimize the thickness of a material for practical use in a way that it is suitable for the sound as well as for the processing of the material. Then, the robust zinc pipes can be voiced by means of adequate tools without any problems.