A comparison of different expression devices in pipe organs
Jonas Braasch, Thomas D. Rossing · The Journal of the Acoustical Society of America · 2004
After the introduction of the orchestra crescendo at the end of the 18th century by the ‘‘Mannheim school,’’ the ability to play the organ expressively like an orchestra was one of the organ builders’ greatest concerns. Soon, both the wind swell and door swell came into fashion, and later another swell system, the crescendo wheel, was introduced. While both door swell and crescendo wheel can be successfully applied to all types of organ stops, the wind swell only works well with free reeds for tuning reasons. In this investigation, all three swell systems were measured on various instruments and compared to each other. In addition, two free-reed pipes were measured at the Northern Illinois University using a laser vibrometer. The crescendo wheel was found to be most effective, and for frequencies around 2 kHz the increase in sound-pressure level could be up to 50 dB between the softest and the loudest adjustment. The maximum dynamic range for the wind and the door swells is approximately 10 dB in the same frequency range. While the dynamic range is lower for the wind swell and the door swell, their advantage is the continuous variability.