Experimental investigation of dynamic lingual organ pipes with blown open tongue.

This paper presents the experimental examination of an alternative lingual organ pipe construction that uses a free tongue which, in contrast with traditional lingual organ pipes, operates in a blown open manner. A possible advantage of the construction is that it can enable changing the windchest pressure and thus, achieving an extended dynamic range while keeping a constant pitch. Three experimental pipes with diverse resonator shapes are investigated in various setups. The three pipes also demonstrate the variety of timbres obtainable by different configurations of tongues and resonators. The analysis of the measurement results shows that the pipes exhibit a very good stability of the fundamental frequency and can have a dynamic range of 15 dB. At the same time, the timbre of the sound is found to change significantly as the windchest pressure is increased. Experiments performed with damping the resonator reveal the working principle of the tongue-resonator coupling in the alternative construction. Several sound recordings are presented as multimedia file attachments enabling the subjective comparison of the pipe sounds.

Simulation of mallet percussion instruments by a coupled modal vibroacoustic finite element model.

A three-dimensional coupled vibroacoustic finite element model for physics-based simulations of the sound generation by mallet percussion instruments in the time domain is discussed in the present paper. The mechanical model takes the orthotropic material properties of the wooden sound bars and the nonlinear nature of the interaction force between the mallet head and the sound bar into account while the acoustical model considers radiation into an unbounded domain. A direct coupling of the sound bars, acoustical cavity resonators, and the excitation by a mallet is considered with exploiting the modal basis to reduce the number of degrees of freedom of the system. Both the mechanical and acoustical models are validated by comparing them to measurements performed on an Orff xylophone. A case study shows the capabilities of the coupled model, including the analysis of the energy balance, the effect of tuning the resonator, and the excitation of the torsional modes of the sound bar.

Examination of the reflection properties of sloping terminations to organ pipes.

The sound characteristics of both labial and lingual organ pipes are affected to a great extent by the reflection properties of the resonators. In this paper, the reflection properties of sloped pipe terminations are examined and the possible applications in organ building practice are investigated. Sloped shallots of reed organ pipes with different termination angles are of particular interest in this study. For the examination of the reflection properties two different approaches are applied. Sound pulse reflection measurements on model geometries provide experimental data in the time domain, while finite element simulations yield reflection coefficients in the frequency domain. These two remarkably different approaches are shown to provide consistent results for all examined geometries. Laboratory measurements performed on experimental labial pipes and "Trompete" (trumpet) shallots demonstrate some of the effects of sloped terminations on the sound of organ pipes and validate the applicability of the results obtained by the model measurements and simulations.

A finite element model of the tuning slot of labial organ pipes.

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.

Acoustic behavior of tuning slots of labial organ pipes.

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.

Sound design of chimney pipes by optimization of their resonators.

An optimization method, based on an acoustic waveguide model of chimney and resonator, was developed and tested by laboratory measurements of experimental chimney pipes. The dimensions of the chimney pipes are modified by the optimization algorithm until the specified fundamental frequency is achieved, and a predetermined harmonic partial overlaps with an eigenfrequency of the pipe. The experimental pipes were dimensioned by the optimization method for four different scenarios and were built by an organ builder. The measurements show excellent agreement between the measured sound spectra and calculated input admittances. The developed optimization method can be used for sound design of chimney pipes.

The influence of pipe organ reed curvature on tone quality.

Although organ flue pipes have been widely studied, the same claim cannot be made for pipe organ reed stops. Given certain design constraints, such as the type of reed stop being voiced and the desired tone quality, the reed voicer must use consummate skill to curve the reed tongue so as to produce the best and most stable tone as well as to guarantee that each pipe blends with its neighbors. The amount and type of curve given to a reed tongue influences not only the harmonic structure of the steady-state sound but also the attack. There are two fundamentally different types of curvature that can be given to a reed tongue, the trompette (chorus reed) curve (which gives a bright sound) and the smooth-toned curve employed for clarinet pipes. This study investigated the effect of reed curvature on the vibration and tone (as assessed by professionals) on reed tongues of both types. Two F2 (8'F, 87.3 Hz) pipes (a trompette and a clarinet) were constructed and voiced with differently curved tongues to produce a variety of tones. The vibration of the reed tongue was measured under typical conditions by laser vibrometer; the pressure waves in the boot and in the shallot were measured by means of one-quarter inch microphones, and the pipe's sound was recorded at the egress. By performing various measurements simultaneously, phase differences were also determined, the extreme sensitivity of tone to reed curvature was demonstrated, and a recently proposed theory of reed vibration was shown to be more accurate than the standard model.

Roughness of organ pipe sound due to frequency comb.

In the sound spectrum of flue organ pipes in addition to the usual harmonic partials, sometimes a series of equidistant but not harmonic lines can be found. This phenomenon has been observed in the recorded sound of pipes from different pipe ranks. The second set of spectral lines is similar to "frequency combs" used in optics for accurate measurement of optical frequencies. Analysis of measured sound spectra with and without frequency comb and simulations are presented and discussed in the paper. The appearance of frequency combs in the sound spectrum is explained by a model that assumes the presence of a mouth tone in addition to the pipe sound. Mouth tone bursts are generated when the oscillating air jet passes the upper lip. The burst repetition frequency is locked to the fundamental frequency of the pipe and the bursts are coherent with a pulse-to-pulse phase shift. The phase shift explains the observed frequency offset of the frequency comb to the harmonic frequencies. The simulations also show that weak and fluctuating mouth tones cannot generate frequency comb due to a lack of coherence.

Experimental jet velocity and edge tone investigations on a foot model of an organ pipe.

In order to investigate the physical processes involved in the build-up of the sound signal in a labial organ pipe a pipe foot model has been developed. The main important parameters, such as positions of the lower and upper lips, the wind pressure in the pipe foot, and the width of the flue, can be adjusted by means of this model. Moreover, different types of languids and pipe bodies (resonators) can be attached to the model. For the reason of corresponding to a real metal organ pipe these parts of the model are made of a typical alloy used in organ building. The reproducibility of measurements is provided by the micrometer screws applied for the adjustments. Flow and edge tone measurements are carried out with the help of this model. Velocity measurements with different flue widths show that the exit velocity of the jet corresponds to the Bernoulli-velocity and is asymmetrically contracted. At larger distances (>5 mm) the velocity distribution can be described by a Gauss-function having linearly increasing width. A mathematical relation of the centerline velocity as a function of the cut-up height L is found. The results of edge tone measurements show differences between previous studies and the present one. No frequency stages (and hysteresis phenomena) are found within the investigated pressure and cut-up range; the frequency modes of the edge tone coexist. The measured frequencies can be described by theoretical models.

Reed vibration in lingual organ pipes without the resonators.

Vibrations of plucked and blown reeds of lingual organ pipes without the resonators have been investigated. Three rather surprising phenomena are observed: the frequency of the reed plucked by hand is shifted upwards for large-amplitude plucking, the blown frequency is significantly higher than the plucked one, and peaks halfway between the harmonics of the fundamental frequency appear in the spectrum of the reed velocity. The dependence of the plucked frequency on the length of the reed reveals that the vibrating length at small vibrations is 3 mm shorter than the apparent free length. The frequency shift for large-amplitude plucking is explained by the periodic change of the vibrating length during the oscillation. Reed vibrations of the blown pipe can be described by a physical model based on the assumption of air flow between the reed and the shallot. Aerodynamic effects may generate and sustain the oscillation of the reed without acoustic feedback. The appearance of subharmonics is explained by taking into account the periodic modulation of the stress in the reed material by the sound field. Therefore, a parametric instability appears in the differential equation of vibration, leading to the appearance of subharmonics.