In the past, organ builders used many tree species for the production of wooden organ pipes, and the thicknesses of the pipe walls were also different. From the point of view of the sound of wooden organ pipes, it appears that the type of wood, as well as the thickness of the pipe wall, affect the resulting organ sound. Therefore, this research focused on how the wood species and the thickness of the pipe’s wall affect the sound of the organ. Two wood species were selected for our experiment: maple wood, representing hardwood; and spruce wood, representing softwood. The physical and acoustic characteristics (PACHs)—density (ρ), dynamic modulus of elasticity along the wood grain (E_L), specific modulus (E_sp), speed of sound along the grain (c_L), resonant frequency (f_r), acoustic constant (A), logarithmic decrement (ϑ), loss coefficient (η), acoustic conversion efficiency (ACE) and sound quality factor (Q)—were determined. Subsequently, the boards were used for making the back wall of the experimental wooden organ pipe with a replaceable back wall. The boards used for the back wall had an initial thickness of 7 mm. The boards were gradually thinned in 1 mm decrements to a final thickness of 1 mm. For each board thickness, the frequency spectrum was recorded at four different air pressures in the windchest, namely, 588 Pa, 716 Pa, 814 Pa and 941 Pa. The results of the experiment showed that at a given back wall thickness, the fundamental tone frequency increases with increasing air pressure. The decrease in the back wall thickness was manifested by a decrease in the fundamental frequency. With increasing air pressure, the intensity of higher harmonic frequencies also increased.

In the history of the pipe organ, we can observe different pitch standards, which are connected to the musical aesthetics of the time or the intentions of the builder. These differences are often noted based on provenance, meaning the origin or location where the organ was made. Each historical period had its own aesthetic and technical requirements, which were reflected in the tuning and pitch of the organ. The retuning of organs occurred mainly at the turn of the 19th and 20th centuries, with a change in the intonation of these instruments. In the territory of Slovakia, this change primarily involved a shift from the original pitch of approximately 412 Hz to 440 Hz. This change, of course, affected mainly older instruments and was part of a broader process known as the romanticization of organs. This process marked a departure from the original sound ideal of the Baroque period and a transition to the romantic sound ideal. Study examines the limitations of tuning height for wooden closed organ pipes, specifically the Copula stop, which has undergone significant retuning and intonation adjustments in the past. By using a gradual retuning method, the research analyses the sound’s frequency spectrum to determine the optimal tuning range. The results show that significant changes in tuning height can lead to substantial degradation in sound quality. The research emphasizes that ill-considered restorative modifications to the air column length of these or- gan pipes lead to undesirable and permanent changes in the instrument’s sound character- istics.