First ISCA ITRW on Auditory Quality of Systems

April 23-25, 2003
Akademie Mont-Cenis, Germany

On the Acoustical Quality of Free-Reed Organ Pipes

Jonas Braasch

Institut für Kommunikationsakustik, Ruhr-Universität Bochum, Germany

Free-reed organ pipes were introduced at the end of the 18th century and soon became popular across Europe, especially in Germany and Switzerland. As opposed to striking-reed pipes (bound- or beating-reed pipes) the reed in free-reed pipes does not beat against the shallot, an orifice in the reed, when it is played. Instead it swings freely through a perforated rectangular plate of brass, like in reed organs or accordions. Stops with free-reed pipes were often termed Clarinet, Cor anglais, Bassoon or Aeoline. They were appreciated for having a "mellow, round and agreeable sound" (Lehr, 1912), whereas the sound of striking-reed pipes was often considered to be somewhat "hard, rattling, clanking in sound and having most of the time something nasal" (Hackel and Topp, 1993). In the 1920’s, free-reed pipes were abandoned with the beginning of the "Orgelbewegung", a German movement trying to restore the ideal of the organ sound during the age of Bach. The promoters of this movement considered free-reed pipes as being "too mellow", "pappy" and "sluggish" (Adelung, 1955; Ellerhorst, 1936; Mahrenholz, 1968). Nowadays, free-reed pipes have gained popularity again and are considered frequently when building new organs.

To investigate how the verbal descriptions are related to physical properties of free-reed pipes, the attack transients and stationary sounds of three free-reed organ stops were previously measured throughout the whole frequency range of the stop and compared to the measurements of striking-reed stops and flue stops (Braasch and Ahrens, 2000). As the results show, the attack transients of free-reed pipes differ in a number of parameters, e.g, the rise time of free-reed pipes is shorter than the rise time of striking-reed pipes, but in the same order of the rise time of the diapason pipes. A psychoacoustical test was conducted, revealing that parameters other than rise time, namely different initial delays of the partials and the presence of the chiff in case of the diapason pipe, lead to the perception of a longer attack duration of the free-reed pipe compared to the diapason pipe.

In contrast to striking-reed pipes and flue pipes, free-reed pipes display a shift in the fundamental frequency during the attack phase. This shift is typically an upward movement from the initial frequency to the final frequency. This upward movement probably leads to the typical sound of free-reed instruments and contributes most likely to the negative judgments that were often made about these stops, especially, when the pipes were not carefully tuned.

Another reason why free-reed pipes fell out of fashion is due to their frequency stability with changes in room temperature. Typically, they fall out of tune with the flue pipes every time the temperature changes in the church. A few historic free-reed organ pipes, however, were built differently and these pipes detune with changes in temperature in a more similar way to flue pipes.

Full Paper

Bibliographic reference.  Braasch, Jonas (2003): "On the acoustical quality of free-reed organ pipes", In AQS-2003, 109-116.