The influence of thermal-hygrometric properties of air on the tune of pipe-organs

Abstract

Pipes of pipe-organ dynamically change their tune during the year due to environmental conditions, sometimes consistently, making these instruments hard to be played. Because thermal-hygrometric properties of air change through the seasons, this study investigates the influence of air temperature and relative humidity on pipes' tune by monitoring a real pipe organ during a year. Normalized frequency was introduced to analyze and compare notes and logs of different extents with each other, and a variation within 7% was reported. Absolute Humidity parameter was introduced to gather temperature and relative humidity under a single parameter, allowing the evaluation of the contribution of the relative humidity to the frequency changes. Fitting models and their equations were extracted, and normalized residuals were estimated. The same analyses were performed on a small pipe organ at a laboratory scale to confirm the reliability of those models. A comparison between standard equations for calculating the resonance frequency of pipes and the introduced models is also discussed. Finally, the slight influence of humidity on the sounding frequency was confirmed. K/coefficients were introduced to align the results of the longitudinal resonance frequency equation for cylindrical cavities from literature with the resulting model by comparing the temperature influence.