in that the maximum displacement amplitude in which the reed can vibrate is limited by fluctuations in damping forces, so that the resultant sound pressure is rather constant. Additionally, there is a threshold pumping pressure, below which the reed vibration is minimal. Within those two thresholds, there is an exponential growth and decay in time of reed amplitudes . Repertory The harmonium was considered by Curt Sachs to be an important instrument for music of Romanticism (1750s-1900), which "vibrated between two poles of expression" and "required the overwhelming power and strong accents of wind instruments". Harmonium compositions are available by European and American composers of classical music. It was also used often in the folk music of the Appalachians and South of the United States. Harmoniums played a significant part in the new rise of Nordic folk music, especially in Finland. In the late 1970s, a harmonium could be found in most schools where the bands met, and it became natural for the bands to include a harmonium in their setup. A typical folk band then—particularly in Western Finland—consisted of violin(s), double bass and harmonium. There was a practical limitation that prevented playing harmonium and accordion in the same band: harmoniums were tuned to 438 Hz, while accordions were tuned to 442 Hz. Some key harmonium players in the new rise of Nordic folk have been Timo Alakotila and Milla Viljamaa. In the Netherlands, the introduction of the harmonium triggered a boom in religious house music. Its organ-like sound quality allowed Reformed families to sing psalms and hymns at home. A lot of new hymns were composed expressly for voice and harmonium, notably those by Johannes de Heer. Western classical The harmonium repertoire includes many pieces written originally for the church organ, which may be played on a harmonium as well, because they have a small enough range and use fewer stops. For example, Bach's Fantasia in C major for organ BWV 570 is suitable for a four-octave harmonium. Other examples include: Alban Berg. Altenberg Lieder William Bergsma. Dances from a New England Album, 1856 for orchestra. It includes parts for melodeon (movements I-III) and harmonium (movement IV). William Bolcom. Songs of Innocence and of Experience for orchestra, choirs, and soloists, includes parts for melodeon, harmonica, and harmonium. Anton Bruckner. Symphony no. 7, an arrangement for chamber ensemble, prepared in 1921 by students and associates of Arnold Schoenberg for the