The effects of centrifugal blowers, control valves, attenuating devices and reservoir resonance on organ pipe flutter

• Main Author: Taylor, Alan
• Published: University of Salford 2019
• Online Access: https://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.766383

The aim of this research is to investigate the noticeable organ pipe flutter that may, under certain conditions, exist on a sounding organ pipe. The effectiveness of a pipe organ wind system is notoriously difficult to predict. For many years pipe organ builders have been aware of organ pipe flutter and several have tried to address the problem with little success. For pureness of tone it is important that the wind system is perfectly steady and without any imperfections that may cause organ pipe flutter. A survey of 83 UK pipe organs, was conducted by 8 organ tuners, confirms that 57% of the pipe organs surveyed had organ pipe flutter. Organ pipe flutter is particularly noticeable when tuning pipework or playing single notes. During this condition there is "no flow" in the duct connecting the blower to the reservoir. Using a specially constructed test apparatus, built from pipe organ components, this research examines the conditions necessary to produce organ pipe flutter, and how organ pipe flutter may be eliminated. Employing a microphone to measure a sounding test organ pipe and an accelerometer to measure the vibration of a reservoir top, various pipe organ wind system elements are examined and correlated with the excitation and attenuation of the reservoir top vibration and organ pipe flutter. The reservoir acts as a mass spring system. For weighted wind systems the mechanical mass, which may exceed 100kgs, is the dominant factor. For sprung reservoir wind systems, the mass is approximately 25% of that for a weighted system and is less dominant. Results indicate that under certain conditions, the blower excites the reservoir at its natural resonant frequency with sufficient amplitude to cause unwanted amplitude modulation on a sounding organ pipe. Results are systematically presented for weighted and sprung reservoir wind systems, organ blowers and the effects of blade frequencies, reservoir control valves, and attenuating devices inserted between the blower and the reservoir, to determine their effect on reservoir top vibration and the development of organ pipe flutter. With this knowledge, the pipe organ builder will be able to build pipe organs with improved wind systems and flutter free pipework.