ABSTRACT
An acoustic model suitable for the characterization of tuning slots of labial organ pipes is presented in this paper. Since the tuning slot arrangement is similar (but not identical) to that of toneholes in woodwind instruments, the adaptability of the well-established tonehole model for the specific problem is examined. A numerical model utilizing the finite element (FE) and perfectly matched layer techniques is set up for the simulation of tuning slots with design parameters varying over a wide range. Analytical tonehole models and the proposed numerical tuning slot model are both combined with analytical one-dimensional waveguide models to predict the acoustic behavior of tuning slot pipes. Comparison to measurements carried out on experimental pipes proves that the hybrid waveguide/FE model can predict the most important properties of the tuning slot pipe with good accuracy. The finite element method (FEM) also overcomes the limitations of traditional tonehole models relying on the equivalent T-circuit approximation. By means of the FE model the eigenfrequency-structure and its impact on the character of the sound can be foretold in the design phase, by which a more efficient scaling of tuning slot pipes can be achieved.
ABSTRACT
The effect of tuning slots on the sound characteristics of labial organ pipes is investigated in this paper by means of laboratory experiments. Besides changing the pitch of the pipe, the tuning slot also plays an important role in forming the timbre. The objectives of this contribution are to document the influence of tuning slots built with different geometries on the pipe sound and to validate the observed tendencies by means of reproducible experiments. It is found that the measured steady state sound spectra show unique characteristics, typical only for tuning slot organ pipes. By separately adjusting the geometrical parameters of the tuning slots on experimental pipes, the impact of each scaling parameter on the steady state spectrum is determined. It is shown that the scaling procedures used currently in organ building practice do not provide sufficient control over the sound characteristics, leaving the capabilities provided by the tuning slot unexploited. Subjective comparison made by organ builders of sound recordings of various setups confirms that the observed sound quality of tuning slot pipes is strongly dependent on the scaling of the slot.
