The impact of temperature and humidity variations on the resulting frequencies of metal flue pipes in pipe-organs: An analytical model

Abstract

Pipe organs are probably the biggest existing instruments. Apart from positive organs that wheels can move, pipe organs remain in the same place where they have been installed and become parts of the buildings architecture that host them. Churches are the main venues for these instruments due to their important role in the liturgy. Unfortunately, these buildings, usually characterized by huge volumes, are hardly air-conditioned except during events, and temperature and humidity variations affect the pipes' sound. An analytical model has been developed for metal flue pipes to analyse the entity of the emitted-frequency variations. Temperature and humidity affect the dimensions of the pipe as well as air density and sound’s velocity. The model involved plane wave mode and air-jet analysis dynamics depending on the temperature and humidity of the flowed air. Thermo-viscous effect of air flowing into the pipe is also considered. Results have been compared to the spectral analysis of a metal flue pipe of an existing pipe organ located inside a church. Conclusions gather the differences between the results and explain the open opportunities for this research.