Flue Instruments Research Articles

Study of "half-integer" harmonics in recorder tones and some speculations about their origin.

The musical notes produced by recorders and other flue instruments consist primarily of spectral components with frequencies given approximately by nf1, where n is an integer and f1 is the fundamental frequency. However, the real tones of these instruments contain other spectral components that have been observed and discussed by a number of authors. We report a study of spectral components in the tones produced by recorders that are odd half-integer multiples of f1, i.e., spectral components with frequencies n±12f1. Our results, obtained through a combination of experimental and simulation studies of soprano recorders, suggest that these components are associated with the air flow in the vicinity of the window region and the labium edge. We also show that these half-harmonics can be suppressed by modifications of the instrument that alter the pattern of air flow in those regions. Speculations concerning the importance of the half-harmonics and the degree to which they are perceptible by a listener are briefly discussed.

Numerical simulation of an acoustically excited plane jet in an incompressible framework and comparison with experimental data.

This paper is concerned with the interaction of a two-dimensional plane jet with transverse plane acoustic waves, which occur, for example, in flue instruments in the vicinity of the nozzle exit. The acoustic excitation is modeled with fluctuating boundary conditions within the framework of an incompressible simulation. This method can be easily implemented in commercial CFD software. The simulations are compared with well-documented measurement data from other authors. It is shown that the model can predict not only the growth rate but also the amplitude of the perturbation, thus it captures the key features of the jet behavior in the receptive and in the linear growth region.

Theoretical Estimation of the Acoustic Energy Generation and Absorption Caused by Jet Oscillation

We investigate the energy transfer between the fluid field and acoustic field caused by a jet driven by an acoustic particle velocity field across it, which is the key to understanding the aerodynamic sound generation of flue instruments, such as the recorder, flute, and organ pipe. Howe’s energy corollary allows us to estimate the energy transfer between these two fields. For simplicity, we consider the situation such that a free jet is driven by a uniform acoustic particle velocity field across it. We improve the semi-empirical model of the oscillating jet, i.e., exponentially growing jet model, which has been studied in the field of musical acoustics, and introduce a polynomially growing jet model so as to apply Howe’s formula to it. It is found that the relative phase between the acoustic oscillation and jet oscillation, which changes with the distance from the flue exit, determines the quantity of the energy transfer between the two fields. The acoustic energy is mainly generated in the downstream ar...

Interaction between compressible fluid and sound in a flue instrument

In order to study the generation of (aerodynamic) sound in flue instruments, we numerically apply Howeʼs energy corollary for a two-dimensional model of a flue instrument. Howeʼs energy corollary enables us to estimate the energy transfer between the fluid flow and acoustic field. To implement it, separating the acoustic field from the fluid flow is needed. However the complete method to numerically achieve it has not been established yet. In this work, we develop an approximate method, which has been recently proposed in their experimental studies by Yoshikawa et al (2012 J. Sound Vib. 331 2558–77) and others, and we apply it to the simulation of the model instrument. We first calculate fluid flow and acoustic oscillation simultaneously by a compressible fluid solver. Next referring to the information on the acoustic oscillation obtained we set up a pressure source on an acoustic solver and reproduce almost the same acoustic oscillation with it. Combining those results, we are able to calculate Howeʼs energy corollary. The numerical result shows that the aerodynamic sound is generated from the oscillating jet rather than the vortices shed by the collision of it with the edge of the mouth opening, namely vortex shedding.

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).

Numerical analysis of the interaction between fluid flow and acoustic field at the mouth-opening of a flue instrument

The fluid-sound interaction is the key to understanding the sounding mechanism of flue instruments. The formula introduced by Howe allows us to estimate the energy transfer between acoustic field and hydro-dynamic field. For calculation of Howe’s formula, it is necessary to divide acoustic fields from fluid, but we do not have any established method to do it, yet. Recently, several authors developed approximate methods to evaluate Howe’s formula and applied to experiments of cavity noise, flue instruments and so on. In this talk, we introduce a numerical method to calculate Howe’s formula, which is similar to those above. Our model is a small flue-organ like instrument with an end-stop. We use compressible large-eddy simulation (LES), which is able to reproduce the fluid flow and acoustic field, simultaneously. First, fluid flow and acoustic oscillation excited in the pipe by a jet-injection from the flue are reproduced by LES. Next, an acoustic field is reproduced by LES without the jet-injection but with driving at the far end, pressure driving, particle velocity driving or oscillating wall driving (like a loudspeaker). Combining those results allows us to calculate Howe’s formula and to estimate the fluid-sound interactions.

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.

Aeroacoustics of Musical Instruments

We are interested in the quality of sound produced by musical instruments and their playability. In wind instruments, a hydrodynamic source of sound is coupled to an acoustic resonator. Linear acoustics can predict the pitch of an instrument. This can significantly reduce the trial-and-error process in the design of a new instrument. We consider deviations from the linear acoustic behavior and the fluid mechanics of the sound production. Real-time numerical solution of the nonlinear physical models is used for sound synthesis in so-called virtual instruments. Although reasonable analytical models are available for reeds, lips, and vocal folds, the complex behavior of flue instruments escapes a simple universal description. Furthermore, to predict the playability of real instruments and help phoneticians or surgeons analyze voice quality, we need more complex models.

Aerodynamics of flue organ pipe voicing

The objective of this paper is to investigate the possibility of giving useful interpretations of flueorgan pipe voicing practices in terms of the aerodynamical and aeroacoustical behaviour of the pipes. Anoverview is first given of the current state of the knowledge on sound generation in flue instruments. Afteran introduction into the limited literature on voicing an scheme is presented as a possible framework toclassify and characterize various voicing approaches. Use is made of dimensionless analysis to quantifythe specific properties of voicing methods in terms of aerodynamic parameters rather than geometric data.It is concluded that such an analysis might be a useful tool to be able to better document and understandhistoric instruments and their genesis in order to better conserve them.

Influence of the geometrical parameters in flue instruments on the vorticity modulation near the separation points of the jet

In the making of the recorder, great care is given to the shape of the chamfers at the exit of the channel. Makers insist on the need of sharp chamfers, for a good tone quality. Recorders made with rounded chamfers present a noisy sound. On the other hand, in the flute, the channel is made by the lips of the musician, defining a rounder geometry. Previous work show that variations of the geometry of the exit of the channel has little influence on the velocity profile of the jet and on the position of the separation points. Thus, variations of the geometry are expected to affect mainly the interaction between the air jet and the acoustic field. The paper will present measurements together with direct Navier Stokes calculations for different geometrical configurations of a jet emerging in a transverse oscillating velocity field. We investigate the modulation of the vorticity of the jet shear layers by the acoustical field, in the vicinity of the separation points, in an attempt to develop a model that allows to predict the influence of the geometry.

Vortex sound of the flute and its interpretation

The flute as an example of flue instruments is investigated for its properties of the jet‐labium interaction at 1kHz. The jet and the externally excited acoustic flow in the embouchure especially near the labium is recorded with endoscopic Particle‐Image‐Velocimetry. Extracting the vorticity the data allows us to calculate the vortex sound according to M. How (1975) . The far field acoustic power of the flute is measured as well and compared with the vortex sound power, which matches in sign and magnitude up to a factor 2 for different sound levels. The non‐trivial interpretation of the sound production is based on the near cancellation of the two vortex layers of the jet along its path except near the labium. In order to gain insight of the interplay of the different ingredients of the vortex sound power the coriolis force, the acoustic field and their phase relation are determined. Scaling of laws for these quantities as a function of the jet velocity/pressure of the standing wave are deduced and compar...

Simplified models of flue instruments: influence of mouth geometry on the sound source.

Flue instruments such as the recorder flute and the transverse flute have different mouth geometries and acoustical response. The effect of the mouth geometry is studied by considering the aeroacoustical response of a simple whistle. The labium of a transverse flute has a large edge angle (60 degrees) compared to that of a recorder flute (15 degrees). Furthermore, the ratio W/h of the mouth width W to the jet thickness h can be varied in the transverse flute (lips of the musician) while it is fixed to a value W/h approximately 4 in a recorder flute. A systematic experimental study of the steady oscillation behavior has been carried out. Results of acoustical pressure measurements and flow visualization are presented. The sharp edge of the recorder provides a sound source which is rich in harmonics at the cost of stability. The larger angle of the labium of the flute seems to be motivated by a better stability of the oscillations for thick jets but could also be motivated by a reduction of broadband turbulence noise. We propose two simplified sound source models which could be used for sound synthesis: a jet-drive model for W/h>2 and a discrete-vortex model for W/h<2.

Sound production in flue instruments: A review

The introduction of computer implementation of numerical methods, 40 years ago, has opened the way towards quantitative modeling of the sound production in flue instruments. This has induced a first wave of new research initiated in the late 1960s by the precursor work of Bechert, Cremer, Ising and Coltman. The breakthrough of real-time sound synthesis in the last decade has allowed the judgment of models on the basis of the sound which they produce. With this breakthrough ‘‘verbal’’ modeling such as the controversy between Helmholtz and Rayleigh about the nature of the sound source at the labium (volume source or dipole) is now a historical curiosity. However, it has became clear that lumped models as used in sound synthesis will remain semi-empirical caricatures. It has appeared that direct numerical simulation of the details of the flow including the effect of turbulence is still impossible. One observes, therefore, a shift back towards experimental studies such as that of jet response to acoustical excitation, the effect of nicks, the effect of chamfers, the influence of materials, Coanda effect induced by turbulence, etc. A review of these recent studies will be presented.

Time‐domain simulation of an organ flue pipe.

Due to the difficulty in treating jet behavior, a general agreement on the sound production of flue instruments has not yet been obtained. This paper discusses three jet deflection models proposed by several authors by means of the time‐domain approach. Simulations of an organ flue pipe where the blowing pressure is changed as a parameter are carried out. These models in common provide oscillations in the fundamental pipe resonance mode and in the higher modes (overblows). They also provide the underblow regimes of oscillation when the blowing pressure is lower. Differences among the models appear in the number of the underblow regimes and in the levels of harmonics of oscillations. Transition among the oscillation modes would also be a clue to compare the models. The results should be compared with an experiment of the artificial blowing of a pipe in the wide range of blowing pressure, which is in progress.