The article focuses on the determination of the acoustic properties (sound transmission loss, sound absorption and transmission coefficient under acoustic plane wave excitation) of membrane-type of specimens by means of a combination of incident plane wave sound pressure and membrane surface displacement information, measuring the sound pressure with a microphone and the membrane displacement by means of a laser Doppler vibrometer. An overview of known measurement methods and the theoretical background of the proposed so-called mobility-based method (MM) is presented. The proposed method was compared with the conventional methods for sound transmission loss and absorption measurement in the impedance tube, both numerically and experimentally. Finite element model (FEM) simulation results of two single layer membrane samples of different shape configurations were compared, amongst which six different variations of the backing wall termination. Four different approaches to determine the sound transmission loss and two methods to determine sound absorption properties of the membranes were compared. Subsequently, the proposed method was tested in a laboratory environment. The proposed MM method can be possibly used to measure the vibro-acoustic properties of building parts in situ.
Pre-test pro hodnocení kvality zvuku čerpacích palivových jednotek
This article is focused on the psychoacoustic evaluation of the sound produced by the fuel supply modules - common automotive products installed in the fuel tanks of automobiles with combustion engines, producing typical sound. It contains evaluation of several psychoacoustic metrics and description of the performed pre-test as a first part of more complex psychoacoustic experiment. This experiment will lead to the development of psychoacoustic model for objective evaluation of the fuel supply module sound, that could be used in product development processes in future.
In this paper, the psychoacoustic quantity of sharpness is discussed and three models which can objectively evaluate it. The motivation for this research is to compare several methods of sharpness evaluation and find the differences as it is difficult to say which is the best. The models that were proposed by Fastl, the German standard and the method from Musical Acoustics Research Centre (MARC) in Prague were tested for this paper. Different sounds including bandpass noise, traffic, speech and non-sinusoidal wave forms were tested on each model in MATLAB. Narrowband noises rose in sharpness at a faster rate than broadband noises. The MARC method returned higher values of sharpness than the Fastl method throughout while the German standard gave the highest sharpness at high frequency bands. The MARC method appeared to give results closer to the standard.Comparisons were made between the algorithms and variations discussed so that we can gain a deeper insight into psychoacoustics and sound quality.
Expectations of the acoustic environment in the national library of technology - Case study
The function of libraries has changed considerably in recent decades. This article presents the case study of the acoustic properties of the National Library of Technology (NTK), built in 2009, visited by more than 2000 users daily. From the acoustic point of view, these are coupled spaces, with horizontally structured spaces, which allow for dividing the space into zones according to the function of use. Through their openness, the individual floors can partially be viewed as open-space offices. Moreover, all floors are connected by a common central atrium, which is the cause of the mentioned acoustic coupling. Undesirable and annoying noise is one of the fundamental problems of these spaces. This article deals with the relationship between the number of visitors, noise in a given space and its acoustic parameters and the impact of these parameters on acoustic comfort, which is a compromise between RT, STI and noise. (C) 2020 Elsevier Ltd. All rights reserved.
Chemical and vibratory signals used in alarm communication in the termite Reticulitermes flavipes (Rhinotermitidae)
Termites have evolved diverse defence strategies to protect themselves against predators, including a complex alarm communication system based on vibroacoustic and/or chemical signals. In reaction to alarm signals, workers and other vulnerable castes flee away while soldiers, the specialized colony defenders, actively move toward the alarm source. In this study, we investigated the nature of alarm communication in the pest Reticulitermes flavipes. We found that workers and soldiers of R. flavipes respond to various danger stimuli using both vibroacoustic and chemical alarm signals. Among the danger stimuli, the blow of air triggered the strongest response, followed by crushed soldier head and light flash. The crushed soldier heads, which implied the alarm pheromone release, had the longest-lasting effect on the group behaviour, while the responses to other stimuli decreased quickly. We also found evidence of a positive feedback, as the release of alarm pheromones increased the vibratory communication among workers and soldiers. Our study demonstrates that alarm modalities are differentially expressed between castes, and that the response varies according to the nature of stimuli.
The influence of thermal insulation selection on a facade sound insulation property – theoretical case study
Impact of the external thermal insulation composite system (ETICS) on the sound
reduction index improvement is widely discussed topic. ETICSs are already several
years commonly used to reduce buildings thermal loses. However, its application
can negatively influence facades sound insulation properties. In the high frequency
range an additional thermal insulating layer improves the sound insulation
property. However, in the low frequency range the sound insulation spectra rather
often decrease. This decrease is caused by a mass - spring - mass resonance of the
ETICS system. Location and the depth of resonance dip depend on the ETICS
Several prediction models and measurement-based case studies were published
already. In this contribution, an analytical model is used to predict the sound
reduction index, using a measured dynamic stiffness of the ETICS system. A number
of different thermal insulating layers are analysed having similar thermal properties
but different material dynamic stiffnesses and loss factors. The comparison of
theoretically predicted sound insulation spectra and the impact of the dynamic
stiffness measurement technique are presented.
Near Field Acoustical Holography (NAH) is a practical tool for noise source identification and sound field visualization. Statistically Optimized Near Field Acoustical Holography (SONAH) is developed in recent years due to its patch reconstruction ability, enabling smaller measurement aperture and shorter measurement time. In this paper, SONAH is adopted to localize the spherical sound sources positions. Firstly, three spherical sound sources are placed at the baffled source plane. Then, the sound pressure at the holographic plane is synthesized using the spherical sound sources propagation formula. After that, the synthesized pressure data are used as input to SONAH to localize all sources positions. Truncated singular value decomposition (TSVD) regularization is utilized in the SONAH reconstruction process to stabilize the solution. The SONAH reconstruction results are compared with the synthesized pressure very close to the source plane using the same spherical sound sources propagation formula. The comparison demonstrates accurate localization capability of SONAH algorithm. In addition, the difference between the reconstruction pressure amplitude by SONAH and the synthesized pressure by the spherical sound sources propagation formula is also discussed in this study.
Piezoelectric line moment actuator for active radiation control from light-weight structures
This article outlines the design of a piezoelectric line moment actuator used for active structural acoustic control. Actuators produce a dynamic bending moment that appears in the controlled structure resulting from the inertial forces when the attached piezoelectric stripe actuators start to oscillate. The article provides a detailed theoretical analysis necessary for the practical realization of these actuators, including considerations concerning their placement, a crucial factor in the overall system performance. Approximate formulas describing the dependency of the moment amplitude on the frequency and the required electric voltage are derived. Recommendations applicable for the system's design based on both theoretical and empirical results are provided. (C) 2017 Elsevier Ltd. All rights reserved.
Source distance determination based on the spherical harmonics
This paper deals with the processing of signals measured by a spherical microphone array, focusing on the utilization of near-field information of such an array. The processing, based on the spherical harmonics decomposition, is performed in order to investigate the radial-dependent spherical functions and extract their argument – distance to the source. Using the low-frequency approximation of these functions, the source distance is explicitly expressed. The source distance is also determined from the original equation (using no approximation) by comparing both sides of this equation. The applicability of both methods is first presented in the noise-less data simulation, then validated with data contaminated by the additive white noise of different signal-to-noise ratios. Finally, both methods are tested for real data measured by a rigid spherical microphone array of radius 0.15 m, consisting of 36 microphones for a point source represented by a small speaker. The possibility of determination of the source distance using low-order spherical harmonics is shown.
Aeroacoustics research in Europe: The CEAS-ASC report on 2015 highlights
The Council of European Aerospace Societies (CEAS) Aeroacoustics Specialists Committee (ASC) supports and promotes the interests of the scientific and industrial aeroacoustics community on the European scale, and European aeronautics activities internationally. Each year, the committee highlights several of the research and development projects in Europe. This paper is the 2015 issue of this collection of Aeroacoustic Highlights, compiled from contributions submitted to the CEAS-ASC.
Monoaurální objektivní akustické parametry k hodnocení kvality přednesu uzavřeného prostoru
This article deals with a summary of monaural objective acoustical
parameters of closed spaces. Every parameter is introduced with its mathematical
definition and its subjective meaning for the audience. Also, recommended values of
the parameters for concert and multipurpose halls referring to various sources are
This paper describes the preliminary trial of computer keyboards sounds
as the first acquaintance with the psychoacoustic listening test. The description of
preparation, process and evaluation is presented as well.
Comparison of force and moment behavior of bimorph actuator
This paper deals with an actuator based on piezoelectric bimorphs developed at CTU for applica-
tions of ASAC on thin structures. The actuator takes the form of two pairs of bimorphs connected
separately, so that the actuator can act in both moment and force configurations simultaneously. The
ASAC system using this actuator was tested on a simple structure in the form of a steel strip fixed
at both ends. The behavior of the actuator was compared with theoretical assumptions including
efficiency of the actuator as a function of the position and power input. A good agreement has been
demonstrated between the model results and the measurement.
Complex alarm strategy in the most basal termite species
Studying basal taxa often allows shedding a light
on the evolution of advanced representatives. The most basal
termite species, Mastotermes darwiniensis, possesses unique
morphological and behavioural traits, of which many remain
scarcely studied. For these reasons, we conducted a comprehensive
study of the alarm communication in this species and
compared its components to behavioural modes described in
other termites. In M. darwiniensis, the alarm is communicated
by substrate-borne vibrations resulting from vertical vibratory
movements. Another similar behaviour consists in longitudinal
movements, by which the alarm is delivered to other termites
in contact with alerted individual. Both these two behavioural
modes could be used in synergy to create complex
movements. M. darwiniensis also uses chemical alarm signals
produced by labial gland secretion, in contrast to Neoisoptera
in which this function is fulfilled exclusively by the frontal
gland secretion. Moreover, we demonstrated in
M. darwiniensis the presence of a positive feedback mechanism
thought to occur exclusively in the crown group
Termitidae. This positive feedback consists in both oscillatory
movements of alerted individuals in response to alarm signals
and release of alarm pheromone by excited soldiers. Our results
confirm that M. darwiniensis is a remarkable example of
mosaic evolution, as it combines many primitive and advanced
features, and its alarm communication clearly belongs
to the latter category.
Measurement of behavior of a force-moment actuator in general working mode
The present paper deals with the testing of a force-moment bimorph actuator designed for
ASAC applications. The actuator was tested on the third natural mode of a steel strip fixed
on both ends baffled in the rigid board. The strip was excited by a point force in its center
at a frequency corresponding to the third mode. The presented results show the efficiency
of the actuator as a function of the actuator’s working mode. Measurements were realized
in an anechoic room to simplify measurement of the radiated sound field. The resulting
efficiency was evaluated by means of sound pressure in the position of microphone 0.5 m
above the strip. The behavior of the force moment actuator in general working mode is
The paper describes properties of the pneu-acoustic transducer
with variable waveguide. Basic principles of its function and influence of the
waveguide length are described and evaluated. Analysis of the transient after
opening of the valve is studied using wavelet transform.
The nature of alarm communication in Constrictotermes cyphergaster (Blattodea: Termitoidea: Termitidae): the integration of chemical and vibroacoustic signals
Alarm signalling is of paramount importance to communication in all
social insects. In termites, vibroacoustic and chemical alarm signalling
are bound to operate synergistically but have never been studied
simultaneously in a single species. Here, we inspected the functional
significance of both communication channels in Constrictotermes
cyphergaster (Termitidae: Nasutitermitinae), confirming the hypothesis
that these are not exclusive, but rather complementary processes. In
natural situations, the alarm predominantly attracts soldiers, which
actively search for the source of a disturbance. Laboratory testing
revealed that the frontal gland of soldiers produces a rich mixture of
terpenoid compounds including an alarm pheromone. Extensive testing
led to identification of the alarm pheromone being composed of
abundant monoterpene hydrocarbons (1S)-α-pinene and myrcene,
along with a minor component, (E)-β-ocimene. The vibratory alarm
signalling consists of vibratory movements evidenced as bursts; a series
of beats produced predominantly by soldiers. Exposing termite groups to
various mixtures containing the alarm pheromone (crushed soldier
heads, frontal gland extracts, mixture of all monoterpenes, and the alarm
pheromone mixture made of standards) resulted in significantly higher
activity in the tested groups and also increased intensity of the vibratory
alarm communication, with the responses clearly dose-dependent.
Lower doses of the pheromone provoked higher numbers of vibratory
signals compared to higher doses. Higher doses induced long-term
running of all termites without stops necessary to perform vibratory
behaviour. Surprisingly, even crushed worker heads led to low (but
significant) increases in the alarm responses, suggesting that other
unknown compound in the worker’s headis perceived and answered by
termites. Our results demonstrate the existence of different alarm levels
In this paper, the concept of psychoacoustic loudness is discussed and in particular, objective methods for its evaluation.Two prominent methods are considered; the method proposed by Zwicker and the method proposed by Moore and Glasberg. Algorithms for each method are implemented in MATLAB in order to evaluate loudness
for a variety of stimuli including pure tones, bandpass noise and industrial noise. Quantifiable differences are observed in the outputs of the two methods and the possible causes of these differences are discussed.
This paper deals with a recently developed actuator based on piezoelectric bimorphs which are useful for ASAC applications. The actuator takes the form of two channels with pairs of bimorphs. Each of the bimorph transducers in the couple is connected separately so that the actuator can act in both moment and force configurations simultaneously. The control algorithm allows the ratio between the moment and force excitation to be adapted according to the desired mechanical output. The ASAC system using this actuator was tested on a simple structure in the form of a fixed beam. Configurations with maximum attenuation were selected and discussed.
Experience with measurement of diffusion coefficient in a free field
The acoustic behavior of diffusers is usually described by three parameters: sound absorption co-efficient, scattering coefficient and diffusion coefficient. The first two coefficients are measured in a reverberation room and have been standardized for many years. This contribution deals with the measurement of the diffusion coefficient of surfaces in an anechoic room characterizing the directional uniformity of the sound scattering. The diffusion coefficient is defined in ISO 17497-2 issued in 2012. The measurement technique was tested on an MLS diffuser of the 4th order. Measured results were in good conformity with theoretical assumptions.
The paper describes acoustic properties of the pneu-acoustic transducers.
Basic acoustic parameters as a sensitivity, frequency response and directivity were evaluated.
The simple model of the finite conical horn based on Webster's equation
is presented as well.
Active Structural Acoustic Control on Double-Layer Acoustic Panel
The paper deals with active structural acoustics control (ASAC) applied to the lightweight structure in order to increase transmission loss at low frequencies. Presented results show efficiency of moment actuators developed especially for ASAC mounted on a double-layer acoustic panel consisting of two metal sheets separated by air gap.
Broadband active structural acoustic control with moment actuator
Sufficient transmission loss of lightweight structures is always a challenge, especially at low frequencies. The paper deals with application of the moment actuator developed at CTU specifically for active structural acoustic control (ASAC) to the double-layer structure consisting of two metal sheets separated by an air gap. The efficiency of the actuators and the entire system were experimentally tested using various noise signals, particularly low-frequency broadband noise. A comparison of results obtained from application of actuators to the incident plate and to the radiating plate of the double layer structure is presented. The filtered-x LMS algorithm was used in the experimental part of ASAC with promising results in the frequency range from 60 Hz to 200 Hz.
Holographic reconstruction of an incident field assuming the spherical waves scattered by a rigid sphere
This paper deals with the reconstruction of an acoustic field in the near-field around a rigid sphere using Near-field Acoustical Holography (NAH) based on an expansion in terms of the spherical harmonics. By employing the rigid sphere providing stable inversion of the propagation function one has to take into account the scattering effect that could significantly affect the total field around the sphere. This effect is commonly accounted for the separation of the incident and scattered field from the total measured field. In applications performing sound field reconstruction by NAH, the presence of source in the near-field of the sphere is to be expected. In this study, such a source in the near-field is considered and a method for determination of the source distance is examined. We consider the spherical waves scattered by a rigid spherical surface for the separation and subsequent reconstruction of the only incident field in this paper. The results are presented in a model simulation.
This paper deals with the measurement of the diffusion coefficient
of surfaces in anechoic room characterizing the directional uniformity of the
sound scattering. The diffusion coefficient is defined in ISO 17497-2. Measurement
technique was tested on MLS diffuser of 4th order. Measured results
were in good conformity with theoretical assumptions.
Aplikace momentového aktuátoru v systémech aktivního řízení neprůzvučnosti dvojitého panelu
One of the dominant research areas in the field of active structural acoustics control (ASAC) is improvement of transmission loss in lightweight structures. The present paper deals with the application of the moment actuator
developed for ASAC on a double-panel structure consisting of two metal sheets separated by an air gap. The first experiments show promising results in the frequency range from 60 Hz to 150 Hz.
Dual channel feed-forward active structural acoustic control of test mock-up
The paper describes the design, system arrangement, and results evaluation of a dual- channel feed-forward ASAC experiment. As a testing structure, a three dimensional mock-up (machinery casing) excited by polyharmonic signal was used. Sound pressure level measured by two error microphones was employed as an error criterion. The overall system performance was evaluated by means of the total radiated power measured by intensity scanning. Finally, the results are discussed in detail.
Monaural and binaural parameters of Rudolfinum concert halls in Prague
Objective parameters for the evaluation of the Rudolfinum concert hall in Prague, Czech Republic are the
focus of the present article. The measured results for Reverberation parameters, Energy parameters, Intelligibility
parameters, and Spatial parameters of the building's two halls are presented and discussed
including a comparison with recommended values or theory, as well as several unique architectural
and acoustical qualities of the halls. The early lateral energy fraction parameter is measured by the intensity
probe method discussed in the supplement. The performance is verified by tests in anechoic and
Reconstruction of normal surface velocity from measurement of acoustically induced vibration of a thin membrane
This paper deals with the theoretical study of extension of the laser scanning vibrometer measurement
for reconstruction of acoustic quantities by Nearfield Acoustical Holography (NAH). This approach
could be applied in a situation where the direct measurement of source vibration is complicated or
impossible. A thin rectangular membrane with reflective coating is inserted in the near field of the
source and its normal velocity is measured by a laser scanning vibrometer. Using a model equation
considering acoustically induced vibration of the membrane, the original sound field radiated by the
source is calculated and used for reconstruction of the normal source velocity. The presented paper
presents preliminary theoretical results obtained in a mathematical model of the real situation.
Active structural acoustic control of thin plate with mixed boundary conditions
The paper deals with active structural acoustic control of the experimental mock-up (baffled thin plate with mixed boundary conditions). The aim of the experiment is to globally reduce radiated sound pressure level by actions of distributed forces and line moments used as secondary actuators.
Akustická holografie v blízkém poli založená na kombinovaném modelu vlnových funkcí
The paper deals with reconstruction of sound field sources distribution using Near-field Acoustic
Holography (NAH) based on elementary wave models. In our approach we decide to use combination of
planar (SONAH) cylindrical or spherical (HELS) waves models according to frequency and measured aperture size.
Non-equidistant k-space sampling in statistically optimized near-field acoustic holography
The paper compares different regularization techniques for ill-posed inverse problems like near-field acoustical holography (NAH). Experiments with simple planar source excited by mechanical force(s) were performed and velocity distribution of the vibrating plate was reconstructed by means of NAH from measured complex pressures. Special attention is aimed to patch holography algorithms (especially SONAH) allowing to measure only small portion of a real source and providing reconstruction on part of a source beneath the measured surface.
Methods for the Assessment of Pleasantness in Sound Quality
Recently, listener tests of certain products have shown that the sense of pleasantness is significant in sound quality
evaluation. For instance, pleasantness was an attribute frequently selected by subjects in the free word description
of vacuum cleaner sounds. However, the relationship between the sense of pleasantness and psychoacoustic metrics
is specific for each product. Present predicting models of pleasantness are not always suitable and have certain
limitations, hence a new model of pleasantness was developed in our research. The development was based on
the evaluation of specific products (vacuum cleaners and computer fans). The new model was then applied in
two cases: first, for the evaluation of vacuum cleaners, which strongly correlated with the psychoacoustic metrics.
Equally, the new model can be applied to a product for which the correlation coefficients between the standard
psychoacoustic metrics and pleasantness were not significant.
For suppression of radiated power various kinds of secondary actuators as shakers, piezoelectric stacks or smart materials can be used. In addition to the force actuators moment actuators can be applied. Piezoceramics based line moment actuators are used in presented experiments. Sound radiation of simple two-dimensional vibrating structure excited by mechanical force(s) is controlled by the moment actuators minimizing radiated power. Description of moment actuator as well as tested structure and achieved experimental results are presented.
Active control of sound transmission using moment actuators
The paper deals with strategies of active structural acoustic control, method intensively developed within the last decade. Special interest is dedicated to the sound transmission through thin plate (wall). As the secondary control source moment actuators are selected. Active control is focused on control of radiating modes of the plate.
Comparison of sound absorption measurement methods
The paper deals with comparison of two sound absorption measurement methods: handheld p-u probe method and standard Kundt's tube measurement. The p-u probe method represents relatively new and unverified approach for which practical employment repeatability and reliability tests are needed.
Experiments with active control of sound radiation from vibrating plates
The paper deals with particular problems of active structural acoustic control of thin plates. As primary excitation, force and incident sound wave was used. The active control system was tested with secondary actuators producing force and line moment.
In situ sound absorption measurement in car interior
The paper deals with in situ measurement of sound absorption in small enclosures, e.g. car interior. The handheld device based on p-u intensity sensor was tested. Basic characteristics of the method with respect to its practical usage were examined. Various types of surfaces were measured and results were compared with other measurement approaches. Applicability of the new method was discussed.
Intenzitní p-u sonda pro měření akustické impedance
Článek se zabývá měřením akustické impedance a absorpčního koeficientu pomocí p-u intenzitní sondy od firmy Microflown Technologies. Jsou prezentovány základní charakteristiky a také princip sondy i celého měření.
Active Control of Sound Radiation from Vibrating Bodies Using Piezoelectric Actuators
The choice of auditory attributes is the first task to be considered at the beginning of sound quality evaluation. In addition, the following procedure of sound quality evaluation is based on these chosen attributes. Therefore, the choice of attributes has to be carefully and correctly performed. Two basic methods can be used for the choice of attributes, which are described in this paper. Next, the choice of attributes of sounds of vacuum cleaners and switched reluctance machines is included.
Návrh buňky pro aktivní řízení vyzařování a vibrací
Specific Loudness, as a distribution of loudness with the respect to critical bands, is important in the investigation of the influence of loudness on pleasantness. In this paper, the loudness spectra of each evaluated product are compared.
Výzkum na katedře fyziky elektrotechnické fakulty ČVUT
Active control of noise and vibration is a technique suitable mainly for low frequencies for which passive methods are usually inefficient. The approach presented in this paper is based on elementary sources (cells) that change the sound radiation of a structure to the far field by active modification of structure vibrations. The elementary cell uses piezoelectric bending actuators to actuate vibrations of the secondary (active) surface of the cell. Both theoretical and experimental results are presented.
Differences in Influence of Loudness on Sense of Pleasantness
The sound of the each product has the specific features. Therefore, the product sound quality calls for the specific methods of the evaluation. The several subjective tests were performed in previous research. In these tests, the sounds of several devices (vacuum cleaners, computer fans and hair dryers) are evaluated. However, these subjective tests show the differences of the evaluation among the tested devices. The structure of sounds significantly affects the evaluation of human subjects.
Differences of Sound Quality Evaluations of Vacuum Cleaners, Computer Fans and Hair Dryers
The aim of this paper is the investigation of the dependence between the specific features of structure of each evaluated devices and the values of the auditory characteristics. Two auditory characteristics, pleasantness and general impression, were shared by each evaluated device. The relationship between two auditory characteristics and the physical features is presented in this paper and differences in physical features are also described. Eventually, the values of the pleasantness and general impression will be compared with Zwicker's formula of psychoacoustic annoyance. Psychoacoustics metrics are significant for sound quality evaluation, they help compare the test results with the physical features. Similarly, loudness spectra help compare the specific features of sound structure with the values of the auditory characteristics.
Influence of Pleasantness on the General Impression of Tested Sounds
Many factors (e.g. sound, colour, appearance of product etc.) influence the overall quality of a certain product. Sound quality, as a highly important component of the overall quality, is related to human perceptual reaction to the sound of a product. In this research, the products' sound quality is investigated. The aim of this contribution is to investigate the dependence between the sense of pleasantness and the sense of general impression for the evaluated sounds.
Porovnání dvou konfigurací sekundárních zdrojů systému ANC umístěného v opěrce hlavy
Secondary sound field is created around an obstacle when incidental wave is scattered and diffracted on the obstacle. Having the description of such a secondary sound field is important from technical point of view. For example measuring microphone, which has a cylindrical shape, affects an acoustical field that is measured. Because of this affection we can, for example, consider correction coefficients which can correct a value measured. We would like to propose different possibilities to obtain a description of secondary sound field around a cylindrical obstacle and prepare them for future usage.
Description of Secondary Sound Field Around a Spherical Obstacle
The development of a measuring method to serve as the basis for a numerical description of secondary sound fields affected by inserted bodies has been considered. Experiments were performed in an anechoic chamber, which is the model of a free field. For testing of the measuring methods, models of rigid sphere-shaped bodies were used. The mathematical model of a received secondary sound field is presently under development. The comparrison with analytical model is also planed.
Model Order Selection Using Penalty Criteria and Bayesian Evidence
This paper will present the results of several subjective tests. In these tests, the sounds of several devices (vacuum cleaners, computer fans and hair dryers) are investigated, with some tests verifying the previous tests. The aim of this paper is to determine the dependence between physical features and the judged characteristics of evaluated sounds. The semantic differential test was used in this research. The results were processed by use of statistical methods (multiple linear regression, correlation coefficient, etc.).
Scattering and Diffraction of Acoustical Waves on Sphere
Byla připravena metoda pro mapování sekundárního aksutického pole v okolí těles různých tvarů. Tato metoda byla testována nejprve na tělese typu koule, protože pro toto těleso jako jediné existuje analytické řešení tohoto problému. Měření byla prováděna v bezodrazové místnosti, která je ideálním modelem volného pole. Při porovnání experimentálních výsledků se známým analytickým řešením bylo dosažené velmi dobré shody.
Příkladem reálného akustického pole může být akustické pole generované větrnou turbínou. Metoda měření jejího hluku je popsána v evropském standardu měření Standard IEC 61 400-11: Wind Turbine Generator Systems - Part 11: Acoustic Noise Measurement Techniques publikovaném v roce 1998. K tomuto měření se používá kruhová deska, ke které je připevněn měřicí mikrofon. Výsledek měření je ovšem ovlivněn ohybem a rozptylem zvuku na této desce, což může na některých frekvencích hrát velmi významnou roli. Byla sestavena metoda měření odrazu a rozptylu na kruhové desce. Naměřená data byla zpracována. Práce směřuje k navržení korekčních koeficientů, které budou záviset na rozměrech desky a úhlu dopadu. Tyto koeficienty by pak v praxi mohly být využity při měřeních hluku, kde norma vyžaduje např. měření s použitím kruhové desky.
Experiments with local active noise control in passenger seat
Publikovaná práce pojednává o metodě měření, která je obvykle užívána pro měření hluku větrné turbíny. Byly testovány některé modifikace metody měření navrhované v mezinárodním standardu IEC 61 400-11 (Wind turbine generator systems - Part 11: Acoustic noise measurement techniques). Například byla provedena měření pro různé polohy umístění mikrofonu na desce. Měření byla prováděna v bezodrazové komoře, která je modelem volného pole. Byl diskutován vliv ohybu a rozptylu na výsledky měření a dále výhody a nevýhody daného způsobu měření.
Signal Processing of Time - Depending Signals of Periodically Working Machines
Signals of periodically working machines, which were measured, were processed by classical methods of signal processing - Short Time Fourier Transform and Wavelet transform, and by a new method - Order Tracking Analysis. Some characteristics of processed signals and their physical interpretation has been surged. Psychoacoustical tests are in preparation; psychoacoustical indexes will be obtained by usual statistical method. On their basic the suppressions of the most disturbing frequencies will be suggested to improve acoustical properties of tested machines.
Presented in this paper are the results of sound testing of computer fans. The entire procedure of sound computer testing is explained. First, the procedure of processing the test results and the statistical method are described. The second part deals with the method of evaluating sound quality and the subjective test. The aim of this paper was to search for a dependence between the results of the subjective test and psychoacoustical metrics (loudness, sharpness roughness). Finally, the results of the subjective test are presented.
Na výsledky akustických měření má vliv ohyb a rozptyl akustických vln na předmětech, která se v daném poli nachází. Řešení ohybu a rozptylu pro těleso typu koule a válce publikoval již roku 1877 Lord Rayleigh v knize Theory of Sound. Pouze pro těleso typu koule existuje přesné analytické řešení. Na jeho práci navazovala řada dalších autorů, kteří se zaměřili především na získání experimentálních výsledků pro tělesa, která byla zajímavá z hlediska technické praxe. Prostudovaná teorie bude využita při přípravě matematického modelu sekundárního akustického pole. Model bude vytvořen nejprve pro těleso typu koule. Číselné výsledky získané na základě tohoto modelu budou porovnávány s výsledky experimentálními i analytickými. Dále budou vytvořeny matematické modely i pro další tělesa, která jsou zajímavá z hlediska technické praxe.