Flue Organ Pipes Research Articles

Sounding Mechanism of a Flue Organ Pipe-A Multi-Sensor Measurement Approach.

This work presents an approach that integrates the results of measuring, analyzing, and modeling air flow phenomena driven by pressurized air in a flue organ pipe. The investigation concerns a Bourdon organ pipe. Measurements are performed in an anechoic chamber using the Cartesian robot equipped with a 3D acoustic vector sensor (AVS) that acquires both acoustic pressure and air particle velocity. Also, a high-speed camera is employed to observe the jet coming out from the windway. For that purpose, the steam resulting from dry ice and hot water is used. A numerical simulation of the sounding mechanism of a pipe of the same geometry is based on measuring the pressure signal and the intensity field around the mouth employing an intensity probe and visualizing and observing the motion of the air jet, which represents the excitation mechanism of the system. The ParaVIEW software serves for the simulation and visualization of the air jet. Then, the results obtained from measurements and simulations are compared and discussed. Also, some future directions discussing the application of a machine-learning approach to the area of pipe organ air flow investigation are contained in the Conclusions section.

Measuring the behavior of the acoustic standing wave exiting a flue organ pipe: Is the decay sinusoidal or exponential?

Correctly predicting the playing frequencies of a musical instrument is dependent on the length of the resonator with the addition of an end correction. There are multiple theories describing this end correction, perhaps the simplest being that the end correction of a pipe is a physical extension of the sinusoidal pressure standing wave inside the pipe. However, recent optical imaging of the flow in a flue organ pipe found an unexpected exponential decay of pressure just outside of the pipe. This work looks to validate those findings acoustically. A flue organ pipe was played at the 1st, 5th, and 7th harmonics and the pressure just inside and immediately outside the end of the pipe played was measured using a zero-degree PU Match Microflown sound intensity probe. These measurements were fit to both exponential and sinusoidal curves and compared to the optical images. While an exponential trend is in fact apparent in some cases, the goodness-of-fit appears to be dependent on which harmonic is sounding. Future work includes exploration of a potential transitional region, assessing the impact of altered pipe geometry (both cross-sectional shape and size), and investigating potential sensor interference by using other measurement equipment.

Numerical study on role of foot of a flue organ pipe: relative phases in oscillations among pipe, foot and jet

Recent numerical studies showed that the foot of flue organ pipes closed at one end acts as a Helmholtz resonator and influences the acoustic oscillation in the pipe. Namely, the relative phase of oscillations between the pipe and foot changes depending on the resonance frequency of the foot. This fact can be explained by the theory of forced harmonic oscillators, in which the pipe works as a force driving the foot. However, in the damping-controlled regime, in which the resonance frequency of the foot, fH, is nearly equal to the frequency of acoustic oscillation, fa, the amplitude of the acoustic oscillation is smaller than those in the mass-controlled regime fH < fa and the stiffness-controlled regime fH > fa, even though the pressure oscillation in the foot lags behind that in the pipe by π/2. In this paper, to investigate this problem and to explore the role of the foot in detail, using a three-dimensional model of a closed flue organ pipe, we numerically investigate the relative phases among the pressure oscillation in the pipe, that in the foot and the jet velocity. We conclude that total balance among them is crucial for sustaining acoustic and fluid oscillations in the sound generation process. The oscillating jet drives the pipe with appropriate timing to sustain the acoustic oscillation for the stiffness-controlled and mass-controlled regimes. In contrast, the jet inefficiently drives the pipe with inappropriate timing for the damping-controlled regime.

Revisiting the Open-End Reflection Coefficient and Turbulent Losses in an Organ Pipe with Low Mach Number Flowipe with low Mach number flow

The reflection coefficient of the open end belongs among the essential parameters in the physical description of a flue organ pipe. It leads directly to practical topics such as the pipe scaling. In this article, sound propagation is investigated inside an organ pipe with the most intense mean flow that is achievable under musically relevant conditions. A theoretical model is tested against the experimental data to obtain a suitable formula for the reflection coefficient when a non-negligible flow through the open end is considered. The velocity profile is examined by means of particle image velocimetry. A fully developed turbulent profile is found and interactions of the acoustic boundary layer with the turbulent internal flow are discussed. A higher value of the end correction than expected from the classical result of Levine and Schwinger is found, but this feature shall be associated with the pipe wall thickness rather than the mean flow effects.

Investigation of the Sound Source Regions in Open and Closed Organ Pipes

The airflow in the mouth of an open and closed flue organ pipe of corresponding geometrical proportions is studied. The phase locked particle image velocimetry with subsequent analysis by the biorthogonal decomposition is employed in order to compare the flow mechanisms and related features. The most significant differences lie in the mean velocity distribution and rapidity of the jet lateral motion. Remarks on the pressure estimation from PIV data and its importance for the aeroacoustic source terms are made and a specific example is discussed.

On a Robust Descriptor of the Flue Organ Pipe Transient

The initial transient of an organ pipe is known to be of great influence to the perceived sound quality. At the same time, the unsteady process of the tone onset is essentially nonlinear and lacks exact repeatability, so the search for a robust descriptor is in place. Initial transients were recorded using an adjustable flue organ pipe. The blowing pressure and cut-up height were varied. Prony’s method was employed to analyze the results. Utilizing the Principal Component Analysis (PCA) on the standardized exponential model coefficients, it was shown that the transients are well described by just one scalar parameter. Its value is predominantly dependent on the number of important Prony’s components taking part in the transient process (i.e., the overall complexity of the transient signal). A strong correlation was found between the PCA component and the Strouhal number inverse.

Resonance phenomena in dielectric media: A review and comparison of acoustic and electromagnetic modes

The theory and application of resonances and vibrational modes are part of the foundation of science. In this contribution, examples of acoustical resonators are highlighted, and compared to electromagnetic modes. As an example from architecture, we describe the phenomenon of whispering galleries; such modes are nowadays known in dielectric and optical resonators. A specimen of a semicircular whispering bench in Park Sanssouci in Potsdam is acoustically investigated and demonstrated to show low losses for sound propagation. A special acoustical bug is discussed which was used for the espionage of the U.S. ambassador in Moscow. The Sovyets could interrogate this passive device by radio waves. Its working principle was based on the electromagnetic resonance of the cavity that the sound-sensitive membrane was part of. The underlying relation between excitation and resonance is compared to the sound production in flue organ pipes. A stopped flue organ pipe was investigated using a piezoelectric film sensor inside the pipe body. The results show that even-numbered modes, which are usually suppressed in the radiated sound of a stopped pipe, are still present in the vibrations inside the resonator.

End behavior of the acoustic standing wave in a flue organ pipe

The acoustic standing wave in a transparent flue organ pipe has been imaged using high-speed transmission electronic speckle pattern interferometry. Spectral filtering of the interferograms at the acoustic resonance frequency of the gas inside the pipe results in an image showing the sinusoidal pressure dependence inside the pipe as well as the expected extension of the standing wave beyond the pipe end. However, the image also reveals anomalous and unexplained behavior as the standing wave transitions from inside to outside the pipe.

Imaging standing waves in the resonator of a flue organ pipe

The acoustic standing wave inside a transparent flue organ pipe has been imaged using transmission electronic speckle pattern interferometry (TESPI). Optically imaging acoustic standing waves in a pipe requires sensing the pressure-induced change in index of refraction of the air, and imaging this change in index has been accomplished in the past using a variety of methods. However, the presence of the flowing air that is responsible for creating the sound of an organ pipe masks the optical effects attributable to the standing wave. We demonstrate that the optical effects of the standing wave can be separated from those of the flow by spectrally filtering high-speed TESPI images at acoustic frequencies. The resulting images show both expected and unexpected details of the standing wave inside an organ pipe. [Work supported by NSF through Grant No. PHY–2109932.]

The effect of resonator shape on air flow in flue organ pipes

The effect of changing the shape of the resonator of a flue organ pipe was studied in a replica of an organ pipe that was printed using transparent media. The pipe was designed so that the rectangular resonator could be replaced by a cylindrical one of the same cross sectional area, and the airflow in the pipe was imaged using high-speed transmission electronic speckle pattern interferometry. The resulting images reveal that there is a fundamental difference in the flow when the resonator shape is altered. Differences in the airflow and sound attributable to the shape of the resonator will be discussed.

Transients in wind instruments modeled with the Navier-Stokes equations

Transient components make an important contribution to the “color” of a musical tone. While such transients can be observed in experiments, realistic modeling can be very challenging. We describe a modeling study of initial transients in the tone produced by a recorder using Navier-Stokes-based simulations. We have studied how the harmonic content of a recorder tone during the attack portion of the tone depends on a variety of factors including the labium position, the presence of chamfers at the exit of the windway, and the initial dynamics of the blowing pressure. While our results are obtained for a realistic model of the recorder, they should also be applicable to similar instruments such as flue organ pipes. [Work supported by NSF Grant PHY1513273.]Transient components make an important contribution to the “color” of a musical tone. While such transients can be observed in experiments, realistic modeling can be very challenging. We describe a modeling study of initial transients in the tone produced by a recorder using Navier-Stokes-based simulations. We have studied how the harmonic content of a recorder tone during the attack portion of the tone depends on a variety of factors including the labium position, the presence of chamfers at the exit of the windway, and the initial dynamics of the blowing pressure. While our results are obtained for a realistic model of the recorder, they should also be applicable to similar instruments such as flue organ pipes. [Work supported by NSF Grant PHY1513273.]

Role of the foot chamber in the sounding mechanism of a flue organ pipe

Role of the foot chamber in the sounding mechanism of a flue organ pipe

Minimum Energy Method (MEM) microphone array back-propagation for measuring musical wind instruments sound hole radiation

Using a 128 microphone array, the sound source distribution of musical wind instruments from their blowing and finger holes are measured. The Japanese \emph{shakuhachi} flute, the Chinese \emph{dizi} transverse flute, the Balinese \emph{suling} bamboo flute and flue organ pipes are investigated. The sound radiation is measured by a rectangular microphone array in the near field, and back-propagated onto the flute radiation plane using the Minimum Energy Method (MEM). Here, the radiation is assumed to be composed of as many sound sources as there are microphones, where the source positions can be chosen arbitrarily in space. Using a regularization parameter $\alpha$ the virtual sound sources, which are monopoles for $\alpha = 0$ are narrowed for higher $\alpha$. Calculating the reconstruction energy on the radiation plane while using different $\alpha$, this energy becomes minimal for the correct $\alpha$. The ill-posedness of the solved Fredholm integral at the presence of measurement noise is met by easing $\alpha$ slightly, therefore stabilizing the solution in a robust way. This is especially necessary for problems like musical wind instruments, where the sound sources are the air itself and often a precise sound source position cannot be known in advance. The flutes show complex radiation behavior and sometimes even a coupling of the sound field between finger holes outside the flute. Coupling between organ pipes can also lead to synchronization between the pipes.

Numerical study of the influence of the mouth-flue-foot geometry on sounding mechanism of an “air-jet” instrument model

The geometry of flue and foot influences the stability of jet oscillation, which products aerodynamic sound as the sound source of “air-jet instruments. Thus, we numerically study the influence of mouth-flue-foot geometry on the stability of jet oscillation with compressible LES. We introduce a 2D flue organ pipe model terminated with a closed end. We investigate the influence of the length of the flue, the existence of chamfers at the flue exit and the volume of the foot. As a result, eliminating the chamfer makes the jet oscillation unstable, while adding the chamfer stabilizes the jet oscillation and sound generation. A long flue makes the jet motion stable and robust, so that it spends a long time to reach a stable oscillation and cannot response quickly to the change of the air supply. Thus a relatively short flue with the chamfers is suitable for a performance. This result qualitatively agrees with the experimental result reported by Segoufin et al.. We also found that the existence of foot stabilizes the sound oscillation in the pipe: the pressure oscillation in the foot synchronizes with that in the pipe with a phase delay, but eliminating the foot rather makes the sound oscillation unstable.

Acoustic energy generation of “air-jet” instruments: Energy transfer between jet oscillation and acoustic field

In this talk, we discuss how to estimate the acoustic energy generation of “air-jet” instruments with numerical simulation. To attack this problem, we use Howe’s energy corollary, with which we can estimate energy transfer between unsteady flow, i.e., oscillating jet and acoustic field. To calculate Howe’s formula, we need solenoidal velocity of the flow and its vorticity together with acoustic particle velocity separated from the whole velocity of compressible fluid. Recently, a method, which allows us to approximately calculate Howe’s formula, was developed in experiments by Bamberger and Yoshikawa et al., and it can be applied for the numerical calculation. We apply the method for the numerical calculation of a flue organ pipe model. We also introduce a toy model of the oscillating jet to investigate the mechanism of sound generation from the oscillating jet in detail. The acoustic energy is mainly generated in the downstream of the oscillating jet near the edge of the mouth opening, but it is consumed in the upstream near the flue exit to synchronize the jet motion with it. Our results are in good agreement with the experimental result by Yoshikawa et al. as well as Howe’s theoretical prediction.

Particle Image Velocimetry and Proper Orthogonal Decomposition Applied to Aerodynamic Sound Source Region Visualization in Organ Flue Pipe

AbstractThe paper presents experimental results of the visualization of the nonlinear aeroacoustic sound generation phenomena occurring in organ flue pipe. The phase-locked particle image velocimetry technique is applied to visualize the mixed velocity field in the transparent organ flue pipe model made from Plexiglas. Presented measurements were done using synchronization to the tone generated by the pipe itself sup- plied by controlled air flow with seeding particles. The time series of raw velocity field distribution images show nonlinear sound generation mechanisms: the large amplitude of deflection of the mean flue jet and vortex shedding in the region of pipe mouth. Proper Orthogonal Decomposition (POD) was then applied to the experimental data to separately visualize the mean mass flow, pulsating jet mass flow with vortices and also sound waves near the generation region as well as inside and outside of the pipe. The resulting POD spatial and temporal modes were used to approximate the acoustic velocity field behaviour at the pipe fundamental frequency. The temporal modes shapes are in a good agreement with the microphone pressure signal shape registered from a distance. Obtained decomposed spatial modes give interesting insight into sound generating region of the organ pipe and the transition area towards the pure acoustic field inside the resonance pipe. They can give qualitative and quantitative data to verify existing sound generation models used in Computational Fluid Dynamics (CFD) and Computational Aero-Acoustics (CAA).

Aeroacoustics of the panpipes

The generic term “flute-like instruments” includes a wide variety of instruments whose sound production is ensured by the coupling of an air jet with an acoustic resonator. Within the family, different kinds of resonator (for instance Helmholtz resonator, open-open, or open-closed tube), may be used with different kind of air supply systems such as the ones found in the recorder, the flue organ pipe, or the shakuhachi. It is common to extent the results obtained on one of the member of the family to the whole family. However, when an accurate description of the sound production mechanisms is required, small discrepancies may arise due to the wide variability in the geometries or in the air supply systems. Among other, a closed-end flute may have a different behavior than an open-open flute since the recirculation of air flow within the pipe may alter the hydrodynamics of the jet, and thus the auto-oscillation process. While most of the studies on flute-like instruments have focused on open pipes (organ pipes and recorder), the panpipes (a representative closed-end flute) has only received little attention. We present experimental data, including flow visualization and pressure signal measurement gathered on a closed pipe. A model of the flow in the pipe allows to interpret the data and compare the behavior of a closed pipe blown with a turbulent jet with that of an open pipe blown with a laminar jet.

Aerodynamical sounding mechanism in flue instruments: Acceleration unbalance between the jet vortex layers

According to particle image velocimetry (PIV) measurement applied to the sound production in organ flue pipes and flutes, the vortex shedding at the pipe edge proposed by Howe (1975) are not observed but the formation of the vortex layer is clearly observed along both sides of the jet flow. This has been confirmed in various sounding conditions with different blowing pressures and resulting pitches. The acceleration unbalance is generated from an incomplete cancelation of the aeroacoustical source term (ω×U) between both sides of the jet, where U is the jet velocity and ω (= rotU) the vorticity. In addition, the vortex layer is essentially unstable because it is formed along the inflection point of the lateral jet-velocity profile. Therefore, the acceleration unbalance and inflection instability of the vortex layer activates the jet wavy motion to reinforce the inward or outward acoustic velocity u at the pipe mouth. Phase relations between acoustic quantities approve conventional acoustical models based on the volume-flow drive and momentum drive. Since ω×U can also activate the jet movement in edge-tone generation, the vortex-layer formation may be regarded as the fluid-dynamical mechanism common to the edge-tone generation and the pipe-tone generation.

Effective techniques and crucial problems of numerical study on flue instruments

In the last several decades, there have been many important proposals for study on flue instruments from theoretical and experimental points of view. Analyses based on aerodynamic sound theory are crucial for understanding the sounding mechanism of flue instruments. According to the growth of computer power and the improvement of numerical schemes, numerical simulations based on fluid dynamics now become important tools for the study of aerodynamics sound. In this talk, we will discuss accuracy, efficiency, and reliability of numerical calculations with large-eddy-simulation (LES) of compressible flow and we will show to what extent LES can reproduce the fluid and acoustic behavior of flue instruments observed experimentally. Furthermore, we will consider how to calculate the important theoretical formulae of aerodynamics sound theory, e.g., Lighthill’s quadrupole, Powell-Howe vortex sound source, Howe’s formula that allows us to estimate the energy transfer between the acoustic field and the hydro-dynamic field. Actually, those quantities given by the theoretical formulae play an important role in the analyses of sounding mechanisms of flue instruments. M. Miyamoto et al., “Numerical study on acoustic oscillations of 2D and 3D flue organ pipe like instruments with compressible LES,” Acta Acustica (accepted for publication).

Flute-like musical instruments: A toy model investigated through numerical continuation

Self-sustained musical instruments (bowed string, woodwind and brass instruments) can be modelled by nonlinear lumped dynamical systems. Among these instruments, flutes and flue organ pipes present the particularity to be modelled as a delay dynamical system. In this paper, such a system, a toy model of flute-like instruments, is studied using numerical continuation. Equilibrium and periodic solutions are explored with respect to the blowing pressure, with focus on amplitude and frequency evolutions along the different solution branches, as well as “jumps” between periodic solution branches. The influence of a second model parameter (namely the inharmonicity) on the behaviour of the system is addressed. It is shown that harmonicity plays a key role in the presence of hysteresis or quasiperiodic regime. Throughout the paper, experimental results on a real instrument are presented to illustrate various phenomena, and allow some qualitative comparisons with numerical results.