Fulop Augusztinovicz

Vibro‐acoustical modal analysis: Reciprocity, model symmetry, and model validity

For low‐frequency applications, a modal approach can be useful to describe vibro‐acoustical coupling. Based on combined vibrational/acoustical frequency response function measurements, either with respect to acoustical or structural excitation, modal vibro‐acoustical analysis can be carried out. This paper presents a consolidation of the theory behind the vibro‐acoustical modal model. The model formulation is shown to be a nonsymmetrical formulation. It is shown that this is not contradictory to the well‐known vibro‐acoustical reciprocity principle. The implications of the nonsymmetry for the modal model are discussed. It is pointed out which variables must be measured and what kind of scaling must be used in order to end up with a consistent modal formulation. The theory is illustrated and verified by measurements on an experimental vibro‐acoustical system, consisting of a rigid cavity with one flexible wall.

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.

Application and extension of acoustic holography techniques for tire noise investigations

Acoustic holography (AH) is a powerful measurement tool for the investigation of complex sound radiation problems. Enabling detailed source investigations based on noncontact measurements, it is especially useful for the investigation of rotating noise sources such as automotive tires. Nevertheless, conventional AH techniques are burdened by the constraint that the source is assumed to be planar. Based on a detailed measurement series which was performed on a laboratory roller bench, the radiation of a test tire was investigated by means of AH. It was found that even though valuable information could be obtained, the most important forward and backward radiation of the tire is difficult to tackle in this way. Another approach of the radiation analysis is offered by developing an inverse BEM method. Different implementations of the method have been worked out and tested, based mainly on the sysnoise and matlab software packages. The technique is applied to experimental tire mock‐ups as well as to real‐life...

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.

Acoustic modal analysis

The phenomena, related to the existence of acoustic modes, were already known in the ancient world and our ancestors, though instinctively, have even exploited some of the acoustic effects [1]. The first treatments of scientific character of the field date back to the 19thcentury [2,3] while the basics of the modal theory of room acoustics were developed in the first half of this century [4–7]. Nevertheless, a revival of the acoustic modal theory and its experimental aspects seems to be worthwhile for a couple of reasons.

Time domain simulations of a novel lingual organ pipe construction

In a traditional pipe organ, the dynamic range of both labial (flue) and lingual (reed) pipe ranks are strictly limited as each rank is tuned and voiced to a nominal windchest pressure. Changing this pressure not only affects the amplitude of the radiated sound but both the pitch and the timbre of the pipes. A new pipe construction with a blown open free tongue was proposed recently to overcome this limitation. Prototype pipes of the new construction were built and measurements were carried out on them at different blowing pressures. It was found that the new construction provides a pleasing stability of the pitch and a broad range of playable amplitudes; however, the timbre of the pipes changes significantly with the blowing pressure. To improve the design in the latter aspect, a physical model of the pipes needs to be established first. In this contribution the sound generation of the experimental pipes is simulated by time domain computations. The resonator and its interaction with the vibration of the...

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.

The physics and sound design of flue organ pipes

Sound design methods for flue organ pipes can be developed for the practical application in organ building due to the high performance of modern computers and the advanced level of the scientific research on flue organ pipe acoustics. The research of Neville Fletcher and the team around him has contributed in a high extent to the scientific understanding of the behaviour of flue organ pipes. By extending this knowledge sound design methods and dimensioning software for different special flue organ pipes have been developed in the frames of European research projects. As examples the following topics will be mentioned: -the development of optimal scaling and a software for designing the depth and width of wooden organ pipes without changing the sound character; -the development of optimal scaling, design and software of chimney flutes by means of appropriate laboratory experiments and computer simulations.

A parametric study on the isolation of ground‐borne noise and vibrations in a building using a coupled numerical model

Underground traffic induced vibrations and noise in buildings are a major environmental concern in urban areas. To quantify these vibrations a numerical prediction model has been developed and validated. A coupled FE‐BE model is used to compute the incident ground vibrations due to the passage of a train in the tunnel. A dynamic soil‐structure interaction model is used to determine the vibration levels of the building. The soil‐structure interaction problem is solved by means of a 3D boundary element method for the soil coupled to a 3D finite element method for the structural part. An acoustic 3D spectral finite element method is used to predict the acoustic response. The coupled numerical model is used to quantify the efficiency of vibration and noise mitigation measures at different stages of the vibration propagation chain. Vibration isolation with a floating slab track is modeled on the source side, base isolation is incorporated in the structure model, and a box‐within‐box arrangement is considered for the isolation of re‐radiated noise in the buildings rooms. The insertion gain of the three methods is compared using the model of a multi‐story portal frame office building subjected to ground‐borne vibrations from an underground railway line.

Effects of filtering of room impulse responses on room acoustics parameters by using different filter structures

Room acoustic evaluation is usually based on post‐processing of measured room impulse responses (RIRs), and this often requires some kind of filtering, for instance to derive fractional octave band parameters of a room. In this paper it is shown that the considerable variance of room acoustic parameters of almost any hall is partly caused by the filtering method and the filter properties used in the course of post‐processing. The paper proposes new qualification methods and parameters for determining the quality of FIR filter banks, taking their use for acoustic evaluation into account. It suggests practical considerations for the design as well, and shows the analysis and comparison of effects of various filter properties ‐‐ such as filter types and topology structures ‐‐ on some room acoustics parameters. By using the suggested methods, it is possible to derive more accurate and reliable results in room acoustic evaluation.