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Impact of Wall Impedance Phase Angle on Indoor Sound Field and Reverberation Parameters Derived from Room Impulse Response

Meissner Mirosław, Zieliński Tomasz

Archives of Acoustics

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2022

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Vol. 47, No. 3

343--353

EN

Accurate definition of boundary conditions is of crucial importance for room acoustic predictions because the wall impedance phase angle can affect the sound field in rooms and acoustic parameters applied to assess a room reverberation. In this paper, the issue was investigated theoretically using the convolution integral and a modal representation of the room impulse response for complex-valued boundary conditions. Theoretical considerations have been accompanied with numerical simulations carried out for a rectangular room. The case of zero phase angle, which is often assumed in room acoustic simulations, was taken as a reference, and differences in the sound pressure level and decay times were determined in relation to this case. Calculation results have shown that a slight deviation of the phase angle with respect to the phase equal to zero can cause a perceptual difference in the sound pressure level. This effect was found to be due to a change in modal frequencies as a result of an increase or decrease in the phase angle. Simulations have demonstrated that surface distributions of decay times are highly irregular, while a much greater range of the early decay time compared to the reverberation time range indicates that a decay curve is nonlinear. It was also found that a difference between the decay times predicted for the complex impedance and real impedance is especially clearly audible for the largest impedance phase angles because it corresponds approximately to 4 just noticeable differences for the reverberation metrics.

2

Application of high-density sound absorbing materials for improving low-frequency spectral flatness in room response

Meissner Mirosław

Vibrations in Physical Systems

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2021

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Vol. 32, nr 1

art. no. 2021111

EN

A room impulse response obtained for complex-valued boundary conditions on wall surfaces was used to determine the frequency response of arbitrary shaped room. Based on theoretical findings, a numerical procedure was developed to test the effectiveness of a high-density sound absorbing material in improving low-frequency spectral flatness. The impedance of absorbing material was determined using the two-parameter Komatsu model. The simulation results have shown that the smoothing effect of the frequency response becomes apparent when the thickness of absorbing material is large enough. This is because as the material thickness increases, the sound absorption tends to increase at lower frequencies.

3

Prediction of low-frequency sound field in rooms with complex-valued boundary conditions on walls

Meissner Mirosław

Vibrations in Physical Systems

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2019

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Vol. 30, nr 1

art. no. 2019127

EN

A modal representation of a room impulse response has been used to formulate expressions for low-frequency sound field in rooms of arbitrary shape. Based on theoretical results, a simulation program has been developed to predict a sound pressure distribution and a room transfer function for rectangular enclosure having walls covered by a material of complex impedance. Calculation results have shown that changes in the wall reactance entail a substantial modification of a sound pressure distribution. Furthermore, an influence of wall reactance on the room transfer function was investigated and it was discovered that a change in a reactance sign causes a shift in frequencies of modal vibrations excited in the room.

4

A Novel Method for Determining Optimum Dimension Ratios for Small Rectangular Rooms

Meissner M.

Archives of Acoustics

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2018

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Vol. 43, No. 2

217--225

EN

A new method for determining optimum dimension ratios for small rectangular rooms has been presented. In a theoretical model, an exact description of the room impulse response was used. Based on the impulse response, a frequency response of a room was calculated to find changes in the sound pressure level over the frequency range 20-200 Hz. These changes depend on the source and receiver positions, thus, a new metric equivalent to an average frequency response was introduced to quantify the overall sound pressure variation within the room for a selected source position. A numerical procedure was employed to seek a minimum value of the deviation of the sound pressure level response from a smooth fitted response determined by the quadratic polynomial regression. The most smooth frequency responses were obtained when the source was located at one of the eight corners of a room. Thus, to find the best possible dimension ratios, in the numerical procedure the optimal source position was assumed. Calculation results have shown that optimum dimension ratios depend on the room volume and the sound damping inside a room, and for small and medium volumes these ratios are roughly 1 : 1.48 : 2.12, 1 : 1.4 : 1.89 and 1 : 1.2 : 1.45. When the room volume was suitably large, the ratio 1 : 1.2 : 1.44 was found to be the best one.

5

Prediction of Reverberant Properties of Enclosures via a Method Employing a Modal Representation of the Room Impulse Response

Meissner M.

Archives of Acoustics

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2016

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Vol. 41, No. 1

27--41

EN

A theoretical method has been presented to describe sound decay in enclosures and simulate the room impulse response (RIR) employed for prediction of the indoor reverberation characteristics. The method was based on a solution of wave equation with the form of a series whose time-decaying components represent responses of acoustic modes to an impulse sound source. For small sound absorption on room walls this solution was found by means of the method of variation of parameters. A decay function was computed via the time-reverse integration of the squared RIR. Computer simulations carried out for a rectangular enclosure have proved that the RIR function reproduces the structure of a sound field in the initial stage of sound decay sufficiently well. They have also shown that band-limitedness of the RIR has evident influence on the shape of the decay function and predicted decay times.

6

Modelling of Green function in a rectangular room based upon the geometrical-filtration model

Marczuk R., Majkut L.

Archives of Acoustics

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2006

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Vol. 31, No. 2

213-230

EN

Significant problem in room acoustic is evaluating an acoustic quality of projected and modernized rooms. Estimation of room impulse response giving posibility to evaluate the subjective and objective room acoustic properties and hence to run the room simulation tests (the sound sources configuration, the room planning) in order to reach optimal solutions, which meet the given criterion. To this end it is necessary to work out an impulse response calculating algorithm for a digital room model. The Green's function is the solution of wave equation then give consideration to source and receiver positions. For inhomogenous wave equation with function $delta(x-y)?(t-T) as excitation, Green's function corresponds to the impulse response of linear system described by this equation. This paper presents a Green function (impulse response) approximation method based on combined room acoustics model. Sound propagation paths are calculated using geometrical acoustics model (image sources method) while events like reflection from bounding walls, air absorption and delay between events are modeled as digital filters. Results of room impulse response approximation model are compared with analytical solution for rectangular room.

7

Oprogramowanie systemowe stanowiska komputerowego do pomiaru odpowiedzi impulsowej obiektu

Mężyk J.

Mechanika / Akademia Górniczo-Hutnicza im. St. Staszica

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2004

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T. 23, z. 1

63-16

PL

Dostrzegając braki na rynku oprogramowania autor niniejszej pracy stworzył aplikację, która, dzięki swoim parametrom, ma szansę stać się bardzo użytecznym narzędziem do wyznaczania odpowiedzi impulsowej pomieszczeń o dużym czasie pogłosu. W artykule przedsta- wiono właściwości sekwencji MLS (Maximum Length Sequence) oraz zasady ich wykorzystania przy pomiarze odpowiedzi impulsowych obiektów. Opisano także wspomnianą wyżej aplikację IRRecorder.

EN

When the author of this work realized deficiencies in the software market, he created an application, which, thanks to its parameters, has a chance to become a very useful tool for measuring impulse responses of rooms with very long reverberation times. In this article, properties of MLS (Maximum Length Sequence) signals and rules of its usage for impulse response measurement arę shown. It also describes the application IRRecorder mentioned above.