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In tropical climate countries, the house structure with a vent hole is widely used. The vent hole has a structure that penetrates the house's outer wall, allowing fresh air from outside to enter the room. However, external traffic noise also enters the living spaces through the vents. A novel type of soundproof vent hole unit with both soundproofing and ventilation functions was proposed in previous work. An elliptical cavity was used for this unit, but it is difficult to manufacture an elliptical cavity with a high eccentricity; also, the installation and adjustment work are expected to be difficult. A rectangular cavity with an inlet and outlet in orthogonal planes fitted to the house walls is used in this study to provide soundproofing functionality to the vent hole. First, the generation mechanism of sound pressure components propagating inside the unit was theoretically elucidated using the three-dimensional wave equation. Second, to maximize soundproofing ability, methods for reducing the number of resonances and reducing the effect of higher-order sound pressure components are described. [ABSTRACT FROM AUTHOR]

An important part of evaluating impact sound insulation is to measure the reverberation time in the receiving room. The increasing trend of using wooden structures for residential buildings has made it increasingly important to have control of the measurement procedure at low frequencies. The present ISO standards do not give any specific guidelines for how to deal with frequencies below 50 Hz. It cannot be taken for granted that the present guidelines developed for higher frequencies are also appropriate for lower frequencies. This paper includes an empirical study of the spatial variation of reverberation time, measured from 20 Hz in two different rooms, with about 100 microphone positions in each room. The results from two alternative methods are compared, based upon the impulse response and the interrupted noise respectively. The accuracy of an intended normal measurement procedure is estimated with respect to the number of microphone positions. [ABSTRACT FROM AUTHOR]

An imperfect sealing system would be the main path of the noise propagating into the interior compartment of a high-speed vehicle. The study on the sound insulation modeling of automotive door sealing systems, which involve complicated threedimensional sealing structures and gap cavities, has attracted more and more attention. This study employs hybrid finite element-statistical energy analysis (FE-SEA) models to predict the sound transmission loss of three simplified sealing specimens and an actual automotive door sealing system. For the actual sealing system under compression, a three-dimensional FEmodel is built to simulate the nonlinear compression, which can acquire the compressed geometries and pre-stress modal results of the seals for further prediction of the sound transmission loss. The hybrid FE-SEA method is firstly verified by the experimental result of a doubleplate vibro-acoustic system and another numerical method. Several factors concerning the modeling, including the boundary conditions, the equivalent elastic modulus for the hyper-elastic rubber, the specimen length, and the structural grid size, are considered to study their impacts on the sound transmission loss. The effects of using shell elements and using solid elements to model the sealing rubber layers are also compared. The results of this study can provide guides regarding the tradeoff between themodeling efficiency and accuracy, so that it has significance for engineering modeling, as well as the design and optimization of automotive door sealing systems. [ABSTRACT FROM AUTHOR]

The unit cabin has been used to construct internal ship space for improved efficiency and to reduce budgetary costs in shipbuilding. Because the cavity is placed between unit cabins, the noise of one room is transmitted through the sound insulating panel, the cavity, and the opposite sound-insulating panel. In this study, by developing a transfer matrix of the cavity between structures, airborne noise between unit cabins was predicted. A sandwich panel, which is usually used in ships, was employed to construct a double panel, and the sound insulation performance was confirmed by changing the thickness of the cavity. To improve the reliability of numerical results, they were compared with those from experiments conducted. The results showed that as the cavity size increases, the overall sound insulation performance improves. A parameter study was also conducted on the density, Young's modulus, thickness, and thickness ratio of the core of the sandwich panel. To improve the sound insulation performance, increasing the density of the core is preferable to increasing the core thickness. The panel thickness ratio should be increased to avoid performance degradation as a result of the resonance frequency. [ABSTRACT FROM AUTHOR]

Micro-perforated panels (MPPs), as an alternative to porous materials for sound absorption, have been commonly used in electronic industries and aircraft engines but are barely used in aircraft cabins. The effect of MPPs on the sound insulation and absorption properties of aircraft cabin panels has been investigated in this article. Theoretical modeling has been conducted on an aircraft cabin panel structure with a trim panel replaced by an MPP trim panel, using the transfer matrix method and the classic MPP theory. It is indicated by the theoretical results that, although the sound transmission loss (STL) of the cabin panel with an MPP trim panel is lower than that with an un-perforated panel, the MPP trim panel can significantly enhance the sound absorption coefficient of the entire cabin panel structure. Based on the well-developed MPP theory, the sound absorption coefficient of an aircraft cabin panel with an MPP trim panel can be improved by optimizing the MPP's parameters at a specific frequency. Taking an engine frequency 273 Hz as an example, the optimization can increase the sound absorption coefficient to 1 by using the doublelayered MPPs. When the thermal acoustic insulation blanket is considered, although the STL of the proposed structure with double-layered MPP trim panels in a diffuse field is lower than those without MPP trim panels, the sound absorption in the cabin is significantly enhanced due to the double-layer MPP trim panel at the specific engine frequency and across all frequencies. The STL of the structure with double-layered MPP trim panels and TAIB can be higher than 40 dB from 880 Hz in a diffuse field, which implies its effectiveness as sound insulation structure in aviation industry. MPP trim panels provide a new idea for the design of aircraft cabin panels and are worthy of further research. [ABSTRACT FROM AUTHOR]

This article coincides with recent publications of international standards, which provide methods of predicting the performance of both heavyweight and lightweight buildings in terms of airborne sound insulation and impact sound isolation, from the performance of individual elements such as walls and floors. The performances of the elements are characterized by the sound reduction index and the impact sound pressure level. To predict the sound pressure level due to vibrating sources (i.e., mechanical installations, water services and other appliances), source data are required in a form appropriate as input for prediction models similar to the above, i.e., as equivalent single quantities and frequency band-averaged values. Three quantities are required for estimating the structure-borne power for a wide range of installation conditions: activity (the free velocity or the blocked force of the operating source), source mobility (or the inverse, impedance) and receiver mobility (or impedance) of the connected building element. Methods are described for obtaining these source quantities, including by using laboratory reception plates. The article concludes with a proposed database, based on laboratory measurements and simple mobility calculations, which provides a practical approach to predicting structure-borne sound in buildings. [ABSTRACT FROM AUTHOR]

The development of soundproofing materials with exceptional acoustic properties has been of great interest in recent years. The acoustic characterization of such materials using full-scale reverberation chambers requires the preparation of relatively large-sized specimens, fulfilling the requirements of the ISO 10140 standards; this is a costly and time-demanding process. Recently, various methods based on the utilization of small-sized specimens have been developed by numerous researchers, so that the acoustic performance of a large selection of materials can be more rapidly assessed in the laboratory. However, such attempts to experimentally characterize soundproofing materials have specific limitations with regard to the validity of the measured sound reduction index. The article addresses the use of a small-scale measuring setup which can be used to study the sound insulation characteristics of a variety of materials, taking into account the limitations and applicability of the setup. The experimental analysis was performed on three materials that are widely used in building and civil engineering applications but have completely different internal structures and mechanical properties. It is shown that the use of the proposed small-scale measuring setup is more appropriate for materials with lower structural stiffnesses and with higher critical frequencies, as well as for porous materials with open pores. [ABSTRACT FROM AUTHOR]

Low-frequency impact sound insulation, down to 20 Hz, has a significant effect on humans' dissatisfaction due to noise in timber buildings. Today, the low-frequency procedure of the ISO 16283-2:2015 impact sound measurement standard covers the frequency range down to 50 Hz for the use of an ISO tapping machine, but does not yet cover the use of an ISO rubber ball. Here, microphone grid measurements were made in two small rooms that were excited by an ISO rubber ball from the rooms above. In each grid, 936 microphone positions were used to capture data representing the full spatial fields of impact sound pressures from 10 to 500 Hz for one excitation location for each room. The data show that the positions at the radiating ceiling surfaces have lowmaximumsound pressure levels compared to the pressure levels at the floors, especially in the floor corners. First, a measurement procedure to predict the maximumexposure of low-frequency sound in a room is proposed It is suggested that themaximum values for each frequency band in the corners opposite to the partition being excited (i.e., the floor corners) be used. Second, a procedure to predict the room average sound pressure level and the prediction's normal distribution is suggested. Iterative measurements with random microphone locations and random excitation locations are used. The advantage of this method is that the required precision and information about the sensitivity due to different excitation points are obtained. [ABSTRACT FROM AUTHOR]

The low noise design must be embedded in every design phase of the train vehicles. The vehicle noise calculation models are established by taking full account of vehicle geometrical dimensions, measuring point location, noise sources, sound insulation and sound absorption. These models can (1) complete quantitative assessment of acoustic structures and noise sources of the vehicles to achieve the top-down quantitative control of acoustic index; (2) calculate interior noise and exterior noise under static conditions, running conditions, as well as tunnel environment conditions; (3) calculate and analyze noise limit values of main noise sources when the sound insulation of walls have been given, such as floor, side wall and gangway; and (4) calculate and analyze sound insulation limit values when the sound power of main noise sources have been given. The average differences between the A-weighted measured and predicted levels are less than 2 dB. The models show a very important guiding role for quantitative acoustics design of metro trains. [ABSTRACT FROM AUTHOR]

The impact sound transmission provided by floors is a complex phenomenon that usually includes direct transmission and flanking transmissions. There are, however, situations where impact sound propagates between spaces only by flanking paths, such as those when noise is generated in lower rooms and annoyance is perceived in overlying rooms. This type of transmission can be relevant, for example, in buildings where the commercial space (emitting space) is located on the lower floor and the dwelling (receiving space) is positioned on the upper floor, a typology that is common in countries such as Portugal. In these cases, the quantification of impact sound insulation between rooms is not an easy task. For its accurate prediction, numerical modeling can be employed, using the finite element method, boundary element method or statistical energy analysis (SEA). In the design phase, simple approaches to tackle the problem are usually preferred, such as those described in standard EN 12354-2. Nevertheless, the described situation is not under the scope of this standard and no other simple alternatives are yet available. In the present study, the authors propose a simplified methodology to approach the problem, where empirical formulas are developed, for prediction of flanking sound transmission on heavy weighted building structures. From a large number of experiments and taking into account similar parameters to those defined in the methodologies prescribed in the standard EN 12354-2, a genetic algorithm is used to find out the optimal values that are used to build the simplified expressions. [ABSTRACT FROM AUTHOR]

Measuring reverberation time is normally one of the steps within the procedure of determining sound insulation in dwellings where 100 or 50 Hz usually serves as the lower frequency limit. However, even lower frequencies have become a matter of interest as research in the field recently indicated that the range 20-50 Hz seems to be of great importance when it comes to the perception of impact sound in lightweight buildings. A major issue in this context is then whether it is appropriate to measure and evaluate reverberation time at such low frequencies. This paper presents an empirical study of reverberation time measurements made in two rooms using more than 100 microphone positions in each. The measurement uncertainty with respect to microphone position and combinations of positions are compared for the frequency bands from 16 to 1600 Hz. Furthermore, it is analyzed how many microphone positions are needed in order to, with a reasonable probability, end up with an uncertainty in the related standardized impact sound level insulation L'n,T within ±1 dB. [ABSTRACT FROM AUTHOR]

Multilayer panels made of sheet steel, a poro-elastic layer and an impervious mass are widely used in noise control for increasing sound insulation. A complete description of the vibro-acoustical behavior of the poro-elastic material used in these panels requires knowledge of mechanical parameters (i.e. complex modulus and Poisson's ratio) in order to model the wave propagation through the elastic structure constituting its skeleton. Although many of the materials used for noise and vibration control have viscoelastic behavior, prediction models currently make use of the linear elasticity theory. As a consequence, acoustical quantities, such as sound transmission loss, are predicted by using static or quasi-static values of mechanical properties. In this research, an experimental time domain approach in combination with an analytical model for linear viscoelasticity is utilized for determining the frequency-dependent complex modulus and increasing the accuracy of sound transmission loss simulations in practical applications. [ABSTRACT FROM AUTHOR]

Green walls covered with vegetation are used in urban areas to purify the air, improve the appearance of the landscape and reduce heat-island effects. They also improve the noise environment. It has been reported in previous studies that the surfaces of green walls have good sound-absorbing performance. However, the contribution of the greenery to the sound-insulation performance of green walls, which are also used as noise barriers, has not been verified quantitatively. In this study, the enhancement of the sound-absorption performance of a wall due to greening was verified via measurements using actual green walls and the results were compared with those of a steel noise barrier, which has limited sound-absorption performance. Numerical analyses using the boundary element method (BEM) were also conducted. As a result, it was confirmed that the sound-absorbing effect generated by wall greening reduces the diffracted noise, thus contributing to sound-insulation performance enhancement in areas above the noise barrier. [ABSTRACT FROM AUTHOR]

The importance of flanking paths to sound transmission in buildings has been studied recently. Damping treatments make it possible to increase the internal losses in structures and provide an opportunity to enhance the attenuation of long transmission paths. A number of numerical comparisons have been made to demonstrate the effectiveness of a global increase in structural damping of nine different physical systems using both bending only and three-wave models. Statistical energy analysis (SEA) has been adopted as the analytical framework. The results show that, by applying a damping treatment, the contribution of flanking paths to sound transmission can be reduced and sound insulation improved. [ABSTRACT FROM AUTHOR]

The purpose of this article is to describe generally usable methods to measure the sound insulation of a facade in cases where a setup according to standards such as ISO 140/5 or ISO 16283/3 cannot be achieved. The methods discussed use a loudspeaker as the source of a test signal since background noise on the interior receiving side in many cases prevents the use of traffic as a noise source. The measurements presented in this article have been made using two loudspeaker positions at different angles. Three different ways of placing the microphone are considered. The microphone can be placed in fixed points directly on the facade, in fixed points at the same distance in front of the facade, or swept in front of the facade. The data presented are all taken from actual field measurements. The results are shown as a comparison between the levels acquired and the uncertainty associated with the different methods. [ABSTRACT FROM AUTHOR]

Laboratory measurements provide more accurate sound insulation results than calculation methods for multi-layered elements, especially for those with local materials. In this study, the sound insulation values of traditional Turkish hollow brick masonry cavity walls are measured in test rooms, and the results are discussed. Horizontally perforated hollow brick walls with two different thicknesses are used to build double brick walls with varying cavity depths and mineral wool thicknesses. The aim of this study is to discover the sound insulation characteristics of traditional Turkish cavity brick wall elements and to discuss the factors, especially cavity depth and filling thickness, that affect the sound insulation values of these walls. [ABSTRACT FROM AUTHOR]

We investigated on an efficient masker for speech privacy protection. We first proposed a speaker-dependent (SD) masker created from speech spoken by the speaker to be masked (maskee). This masker decreased the speech intelligibility to a much lower level than conventional babble maskers, by up to 40%. However, this masker needs to be prepared for each potential speaker, and may be expensive to create and maintain. We also investigated a same gender single-speaker (SSGD) masker, where the masker is created from a different speaker of the same gender. We found that this masker works just as well as the SD maskers for some speakers, while it was not as efficient for some other speakers. Accordingly, we also created gender-dependent maskers from multiple same-gender speakers (MSGD). This masker was proven to mask as well as the SD maskers for all the same gender speakers tested. We now only need to maintain two maskers, one masker per gender, which makes the maintenance and administration of these maskers much more efficient. In order to mask a speaker, we merely need to determine the gender of the speaker, and play out the gender-dependent masker of the estimated gender. [ABSTRACT FROM AUTHOR]

Frame structures in urban rail trains have been manufactured with extruded aluminum panels. This study proposes prediction methods of the sound transmission loss (STL) of the aluminum extrusion panels and their combined structures with different acoustical treatment materials. The main contributions of this paper are (1) the establishment of STL calculation models of aluminum extrusions and their combined structures with damping or with fillings of sound-absorption materials; (2) proposed selection principles of damping material at aluminum extrusions surface and (3) specification of maximum size of the gap between sidewall doors or gangway less than 3 mm. Analysis method can be utilized to predict the sound insulation performance of the aluminum extrusion panels in the early design stage or suggest improvements. [ABSTRACT FROM AUTHOR]

This paper presents the results of the experimental vibroacoustical and modal testing of a triple pane insulating glazing structure. The testing was performed in the sound transmission facility using acoustic excitation, force excitation and a laser scanning vibrometer for measurement of frequency response functions and volume velocity. The results of the identification include the modal mass, damping and stiffness, vibratory modes and volume velocity distribution. A new measurement method is presented in order to identify the global vibratory modes of all three combined transparent glass panes simultaneously. These results are essential for updating the analytical model of triple glazing for calculation and prediction of sound transmission loss over a wide frequency range. The calculated and measured sound transmission loss is presented and discussed. [ABSTRACT FROM AUTHOR]

Urban development has led to increased traffic noise within cities in recent years. In addition, modern architectural tendencies include large glazed areas in the facades of buildings, and this requires the use of window solutions with higher acoustic performance to provide proper acoustic comfort. For windows composed of heavy frames and with very low air permeability, either without roller shutter boxes or fitted with duly treated ones, the sound insulation depends mainly on the acoustic behavior and area of the glazing. We have revisited this topic by testing single, double and triple glazing with the aim of finding window designs with higher acoustic performance. Parameters that influence the acoustic performance of glass are addressed, including the area, the type of glazing, thickness of the air-gap and the introduction of absorbing material around the edge. Particular attention is paid to acoustic phenomena such as coincidence, and the vibration modes and resonances of glazing. [ABSTRACT FROM AUTHOR]

The uncertainty of field measurements of a lightweight wall and a heavy floor was analysed by Round Robin Test (RRT), conducted in a full-scale experimental building at ITC-CNR. Each of the 9 teams involved in the I-RRT replicates the tests 5 times, for a total of 45 measurements, while the repetitions of reverberation time were 110. Both for sound insulation and reverberation time the main variations are in the low frequency range. The differences between D, R', Dn and DnT and their reproducibility and repeatability standard deviations values were also analysed. The study is also focused on the single numbers evaluation: true value and uncertainty. Single numbers were evaluated in both narrow and extended range. The extension to low frequencies implies a variation in single number values that reaches its maximum in the case of X +Ctr in the extended range. This is because this index is the most influenced by low frequencies. Thus the measurement uncertainty at low frequencies has to be more deeply investigated, before including the low frequency range in the on-field measurements [ABSTRACT FROM AUTHOR]

The international standard ISO 140-5 for the measurement of the sound insulation of building façades will be replaced by the new standard ISO 16283-3 soon. Together with solving a few limits of the existing standard, the review is going to introduce the procedures for measurements at low frequencies. This paper investigates the uncertainties related to the position of the instruments in sound insulation measurements of building façades. The positions proposed by the international standard ISO 140-5 are compared with those proposed in other standards and with the draft standard prISO 16283-3. The limits of measurement of the sound pressure level in front of the façade are investigated by comparing different placements both of the external source and the receiver. This shows that the average among different measurements is necessary in order to reduce the effect of interferences. The average of the sound pressure levels in different microphone positions is easier than the average obtained by movements of the loudspeaker. Later, different placements of the receiver inside the rooms are compared. In particular, corner and center room positions are assessed and their energy-average values according to the ISO 16283-1 are considered. Finally, the uncertainties related to equipment positions are discussed and suggestions to improve the future ISO 16283-3 are reported [ABSTRACT FROM AUTHOR]

Double-panel structures have issues with sound insulation at low and mid-frequencies due to mass-air-mass resonance. Various approaches have been proposed to solve this problem and to achieve higher transmission loss. The traditional approach is ?lling cavities with porous material. Another method is the application of microperforated panel (MPP) which is widely accepted as next-generation sound absorption materials. However, the sound insulation performance of double-panel structures connected by connectors made of viscoelastic materials has not been circumstantially investigated. Therefore, an analytical model is proposed for the theoretical study of the improvement in the sound insulation performance achieved by equipping such a structure with damping materials. The effect of connectors on the sound insulation performance of double structures is investigated by considering the relation of the location, numbers, and properties of connectors with the vibrational mode of the panel. Our results indicate that the effect of mass-air-mass resonance on the sound insulation performance can be suppressed by appropriately selecting these connector parameters. [ABSTRACT FROM AUTHOR]

A draft standard was presented by a working group within ISO in April 2011. It describes six methods to simplify the measurement of a spatially averaged sound pressure level in a room, in order to determine an airborne sound insulation between two rooms. The draft standard is intended to replace ISO 140 part 4. The proposed methods are based on various spatial sampling techniques, where a microphone is moved continuously or kept steady at ?xed positions in differ¬ent parts of the room. The uncertainty of the average is to a large extent related to the ability of the sampling method to sample sound pressure levels uniformly from all parts of the room. The uncertainties of the simpli?ed methods of the draft standard have been estimated empirically by means of measurements made in ?ve rooms with different acoustic conditions. The result of each type of simpli?ed method is compared to an average of sound pressures recorded in a dense mesh of microphone positions throughout the permitted space in the same room. Some results that may be useful when an averaging method is to be decided: • the standard deviations may actually be higher above 100 Hz than below, the 160 and 200 Hz third octave bands may even contain the most uncer¬tain results • the ?xed positions method is practical and may be used in all types of room • the special corner method gave higher average sound pressure levels and lower uncertainties compared to the other methods • moving microphone methods are dif?cult to apply in small furnished rooms where there is not enough space to complete several indepen¬dent microphone paths • moving microphone methods may be sensitive to operator generated background noise • microphone positions should be spread over the entire room volume. This study has not estimated the uncertainty of the sound pressure level differ¬ence between two adjacent rooms, used for sound reduction index estimates. [ABSTRACT FROM AUTHOR]

In this paper, sound insulation performance of a prefabricated cabin mock-up is studied. The cabin mock-up consists of two identical rooms whose partition, ceiling, and side walls are sandwich panels composed of thin metal sheets and mineral wools. The floor is a steel plate with stiffeners, and plate thickness is 6 mm. It is shown that sealing gap between the floor and the partition improves STL (Sound Transmission Loss) significantly above 2000 Hz. Even after all gaps are sealed, the weighted sound reduction index Rw of the partition measured in the mock-up is lower than that from laboratory measurement by 9 dB. To find out how flanking transmission of noise degrades Rw of the partition, we measure structure-borne noise (SBN) of room surfaces. It is found that SBN of the steel floor is the most important factor in flanking transmission of SBN. Although SBNs of sandwich panels in the source room are larger than that of the floor, they decrease rapidly as they propagate to the receiving room, because sandwich panels provide considerably more damping than the steel floor. Consequently, SBN of the floor becomes dominant in the receiving room. Statistical energy analysis is performed, where SBN transmission along the floor is investigated. It is concluded that that the most effective way to reduce flanking transmission of SBN is to increase damping of the floor. [ABSTRACT FROM AUTHOR]

The low-frequency broadband noise generated by vehicles may be disturbing for the neighboring residents when vehicles enter or leave underground (or semi-underground) parking garages. A special structural ramp was designed to reduce noise emissions at the entrance or exit of garages. Two-layer steel grilles with rectangular slots evenly distributed, on which the tires of vehicles run, were installed on the original cement ramp. Damping perforated plates sandwiched between the upper and under grille layers fixed on the original cement ramp, formed a resonance sound absorption structure together with the cavity in the layer under the grille. In addition, aluminum foams were embedded in the upper grille layer, and waterproof porous sound absorption materials filled the cavity of the under layer. Field tests using light cars with less than 8 seats were performed to evaluate the effect of the special structural ramp on noise reduction compared to the original concrete ramp. Results show that, when all seats were taken, noise reduction in the A-weighted level of 8 dB on the uphill ramp and 6 dB at the downhill ramp were achieved at the distance of 0.5 m away from the tires outside the vehicle, and a 13 dB and a 8 dB reduction at ears of the passenger respectively. Meanwhile, only a reduction of 2 dB or less could be achieved with further treatment of sound absorption on the middle of the pavement. [ABSTRACT FROM AUTHOR]

JIS A 1418-2 standardized two heavy soft impact sources, "car-tire source" and "rubber ball source", for measurement of the heavy-weight floor impact sound. The rubber ball source is defined in ISO 140-11. The impact force and frequency characteristic differ between the car-tire source and the rubber ball source. Therefore, the effect of change in impact force due to heavy-weight impact sound was investigated in two types of construction. Moreover, the changes in impact characteristic of two heavy soft impact sources by changing the drop height were measured. It is indicated that there is linearity in the drop height of two heavy soft impact sources and the impact force exposure level. However, the correspondence between the impact exposure level and the heavy-weight floor impact sound pressure level using the car-tire source is low for the wood-frame construction. VC 2011 Institute of Noise Control Engineering [ABSTRACT FROM AUTHOR]

This paper examines the potential of using composite porous materials to design robust noise control packages. Composite porous are meso-perforated porous materials in which perforations are filled with another porous material. The work presented here shows that the association of two carefully selected materials could lead to interesting combined properties of sound absorption and sound insulation. A canonical plate/cavity system excited with an internal acoustic source is chosen to illustrate the potential of these materials for noise enclosures. The coupled problem is solved using Finite Element Method. The sound propagation in composite porous materials is described by Biot-Allard's poroelasticity equations. Noise reductions obtained using composite porous are compared to those obtained using homogeneous materials. The sound powers dissipated into the system are also examined to give further insights into the physics of the involved phenomena. The results show that the achieved performances take full benefit of the efficiencies of either materials which form the composite porous for different frequency rangesVC 2011 Institute of Noise Control Engineering. [ABSTRACT FROM AUTHOR]

Sound absorbers using a microperforated panel (MPP) is usually not strong enough for room interior surfaces because MPPs are in general very thin. In order to solve this weakness, the authors proposed to use a honeycomb attached behind an MPP in the air-back cavity. In the authors previous studies a honeycomb is effective to improve the sound absorption performance of an ordinary wall-backed single-leaf MPP sound absorber. The honeycomb can also be applied to a space sound absorbing structures such as a double-leaf MPP space absorber (DLMPP). In this study, the effect of a honeycomb in the aircavity on the sound absorption characteristics of a DLMPP is theoretically analysed. In the theory a Helmholtz-Kirchhoff integral formulation is utilised. The theory is validated with experimental results. The effect of the honeycomb on the sound absorption characteristics is discussed through the numerical examples calculated by the present theory. The results show that the honeycomb enhances the resonance peak and shifts it to lower freqeuencies. Although the honeycomb is effective to improve the sound absorption performance of a DLMPP at around resonance peak, it does not affect the additional low frequency absorption which is particular to a DLMPP. [ABSTRACT FROM AUTHOR]

The limits of the procedure for the measurement of the sound insulation of building façades represent the main subject of this paper. To calculate the façade insulation, standard ISO 140-5 requires that the difference between outdoor and indoor sound pressure levels is determined. However, the measurement of outdoor pressure levels presents several critical challenges, not fully considered in the standard. In fact, the placement of an external source and receiver according to ISO 140-5 is flexible to permit adapting the measurement configuration to specific building characteristics. Unfortunately, according to the relative external source and receiver positions, destructive interferences among waves may occur in different frequency bands. Comparisons between different source-receiver combinations are hence investigated theoretically, before being compared with field measurements. The paper investigates circumstances which might lead to destructive interferences in the external final sound field. The increasing attention of reproducibility in building acoustics suggests an investigation of possible measurement errors that may occur. The influence of interference effects on the single number rating of the sound insulation is finally given. [ABSTRACT FROM AUTHOR]

This study was designed to investigate the reduction of road noise by vegetation along the ring road of Thessaloniki. Road noise was measured at two sites, one through a belt of trees and the other on a grass-covered ground. A total of 245 measurements were taken from each site over a two-month period and expressed as differences in LAeq. Also measurements of the number of vehicles per minute, the type of vehicles and analytic description of vegetation were taken at both sites. The results showed higher noise reductions through the belt of trees than over the grass-covered ground. According to the results of this research the largest reduction, 6 dB, was seen in the Pinus brutia belt of trees, 60 m away from the road. This noise reduction is considered satisfactory due to the tree belts extending on both sides of the ring road. [ABSTRACT FROM AUTHOR]

Auditory masking of unwanted sounds by wanted sounds has been suggested as a tool for outdoor acoustic design. Anecdotal evidence exists for successful applications, for instance the use of fountain sounds for masking road traffic noise in urban parks. However, basic research on auditory masking of environmental sounds is lacking. Therefore, we conducted two listening experiments, using binaural recordings from a city park in Stockholm exposed to traffic noise from a main road and sound from a large fountain located in the center of the park. In the first experiment, 17 listeners assessed the loudness of the road traffic noise and fountain sounds from recordings at various distances from the road, with or without the fountain turned on. In the second experiment, 16 listeners assessed the loudness of systematic combinations of a singular fountain sound and a singular road traffic noise. The results of the first experiment showed that the fountain sound reduced the loudness of road traffic noise close to the fountain, and that the fountain sound was equally loud or louder than the road traffic noise in a region 20-30 m around the fountain. This suggests that the fountain added to the quality of the city park soundscape by reducing the loudness of the (presumably unwanted) traffic noise. On the other hand, results from the second experiment showed that road traffic noise was harder to mask than fountain sound, and that the partial loudness of both sources was considerably less than expected from a model of energetic masking. This indicates that auditory processes, possibly related to target-masker confusion, may reduce the overall masking effect of environmental sounds. [ABSTRACT FROM AUTHOR]

The acoustic characteristics of various kinds of water sounds were investigated to evaluate their suitability for improving the soundscape with road traffic in urban spaces. Audio recordings were made in urban spaces with water features such as fountains, streams, water sculptures, or waterfalls. The temporal and spectral aspects of the sounds were clarified, and subjective evaluations were performed to find the proper level difference between water sounds and road traffic noise for making urban soundscape more subjectively pleasant. The results indicated that the perceptual difference of the water sound level was around 3 dB with noises from road traffic in the background. The water sound, which had 3 dB less sound pressure level, was evaluated as preferable when the levels of road traffic noise were 55 or 75 dBA. It was also found that water sounds with relatively greater energy in low-frequency ranges were effective for masking noise caused by road traffic. The results of the present study will be valuable to urban designers and planners by providing guidelines for improving design solutions for water features in urban soundscape. [ABSTRACT FROM AUTHOR]

Peak sound pressure level measurements conducted at indoor firing ranges ranged from 157-168 decibels (dB). Exposure to high-intensity impulsive noise during target shooting at indoor firing ranges has been identified as a significant contributor to noise-induced hearing loss among shooters. In addition, firing ranges that are constructed with adjacent areas or housed within a larger building structure require minimal sound transmission to occur outside the firing range. Several principles of noise control engineering can be applied to improve the absorption of impulse noise inside the firing ranges and limit the transmission of such impulses to adjacent areas and spaces. Although little can be done to control the direct exposure of shooters to the firing of their own firearms, several noise control solutions are presented to reduce the secondary exposure off reflected surfaces and from other shooters. This paper will provide a general overview of noise control solutions aimed to improve sound absorption inside the firing range and reduce the transmission of airborne and structural-borne sounds to adjacent areas and facilities. [ABSTRACT FROM AUTHOR]

A microperforated panel (MPP) absorber is known as one of the most promising alternatives of the next-generation sound absorbers. However, MPPs are usually made of thin limp materials and need to be reinforced by a supporting element. The authors proposed to use a honeycomb attached behind an MPP for this purpose, and have shown that the honeycomb in the back cavity of an MPP absorber is not only useful to stiffen the MPP but improves its sound absorption performance, particularly at low frequencies. In the authors' previous studies an electro-acoustical circuit model was used to analyse its sound absorption characteristics, however, the model inevitably includes an approximation, and more exact theory needs to be established for better prediction of its characteristics. In this paper, the absorber is analysed with the wave theory based on Helmholtz-Kirchhoff integral equations. First, the formalism based on the Helmholtz-Kirchhoff integral is presented. Next, an experiment is made to validate the theory. Finally, a parametric study is made to discuss the effect of the parameters of the sound absorbing system on its sound absorption characteristics. [ABSTRACT FROM AUTHOR]

Various researchers have investigated microcellular polymeric foams extensively over the last twenty years or so; however, little work has been conducted on the acoustic performance of these foams when their microstructural components are modified by controlling the manufacturing process parameters. The studies discussed in this paper represent an initial stage in the development of open cell foams that exhibit optimized acoustic performance as a result of controlling processing parameters. This study was focused to understand and control certain parameters that dictate the material's microstructure, such as cell size, and link them to the main macroscopic parameters, such as the airflow resistivity and porosity, which govern the overall sound absorption of an open cell material. In this paper, we investigate a new processing technology to manufacture open-cell sound absorbing PMMA(Poly Methyl Methacrylate) materials using a gas foaming/particulate leaching method. An acoustic parametric study is conducted by altering the main processing parameters such as foaming temperature, particle size, and percentage of foaming agent, which affect the cell morphologies and thus control the macroscopic properties. As such, we explore the effects of the adjusted processing parameters on the acoustic performance of the manufactured PMMA samples. The correlations between the resulting cell morphologies and the sound absorption properties indicate that understanding and controlling the porous material's inner structure is crucial for developing any type of open-cell porous material with optimal acoustical efficiency. [ABSTRACT FROM AUTHOR]

The evaluation of hearing protectors for use against high-amplitude impulse noise remains the subject of research with objective testing techniques using acoustic test fixtures offering the only realistic method of providing performance data for protector design and qualification. The work presented in this paper demonstrates the use of an enclosed shock tube arrangement and acoustic test fixtures as a means of evaluating hearing protectors for use against high-amplitude impulse noise. [ABSTRACT FROM AUTHOR]

In power plants and petrochemical plants, the piping systems form a network that extends throughout the facility. Various components in a piping system can be major sources of in-plant and community noise, both the pipe and the contained fluid can be noise propagation paths, and noise radiation can occur from the external surface of the piping. Though the basics of these phenomena are often understood, the translation into workable predictive tools has been slow. Several possible piping system noise sources are described and the experimental test program being undertaken to generate the required non-dimensionalized spectral data is outlined. The accuracy of pressure fluctuation scaling for pressure and flow rate is also reviewed based on the equal tee test program. [ABSTRACT FROM AUTHOR]

Wood working machines are usually characterized by their machine capabilities represented by cutting performance, their power rating and their accuracy. These parameters represent the value of the machine given by its customer. If the machine capability is high but the noise level of the machine is high, the value of the machine depreciates. Therefore, there is a need to focus on the noise, especially at the work station. [ABSTRACT FROM AUTHOR]

The design, construction and qualification of a small-scale sound transmission loss (STL) facility are described. STL measurements were made using the sound intensity technique based on ASTM E 2249-02. The volume of the irregular-shaped reverberant source chamber was 15 m³, and the volume of the regular-shaped anechoic receiver chamber was 20 m³. The facility was tested between 315 Hz and 10 kHz. Good spatial diffusion, and good repeatability for same and repeat installations were demonstrated in the above frequency range. The results from the small-scale facility were compared to tests conducted at a full-scale facility. The STL values of flat, lightweight sandwich panels measured at the small-scale chamber were greater than those measured in the full-scale facility. However, the results from the small-scale facility showed trends that were consistent with the sandwich panel theory above 1 kHz. The results demonstrated that the small-scale STL facility could be successfully used for qualitative comparisons of lightweight, sandwich panels above 1 kHz. [ABSTRACT FROM AUTHOR]

In order to develop the noise control design for a ship's cabin, a series of acoustic tests were carried out in a large scale noise test facilities with two reverberation rooms and deckhouse mock-up. From the tests, it was found that the combined noise level of a cabin was dominated by the radiated noise from the floor structure, which is a combination of a stiffened steel deck and deck covering. In this paper, the dynamic characteristics of floor structure are firstly identified through the structure-borne noise transmission test in the deckhouse mock-up. Based on the result, multi-layer floating floor systems were applied on the steel deck to reduce the radiated noise from the floor structure. Before the application, numerical simulations using assumed modes and structure-borne noise transmission tests are carried out for the floating floor itself to extract the optimum structure. Finally, the considered floating floor systems were applied in the cabin of deckhouse mock-up and the cabin noise reductions are compared. Through a series of numerical simulations and structure-borne noise transmission tests, it is found that the cabin noise reduction of a multi-layer floating floor can be greatly improved over the entire frequency range if the visco-elastic deck covering is installed between the steel deck and the mineral wool of floating floor. [ABSTRACT FROM AUTHOR]

In this work, the sound transmission through various dimensions of slit-shaped apertures is investigated. Both laboratory measurements and theoretical predictions are considered. The lower part of a door without a doorsill is represented by 18 examples with different size slits. The sound transmission through the slit-shaped apertures was more dependent on the width than the depth of the slit. The weighted sound reduction index (SRI) was found to rapidly degrade as the slit width increased, and unfavorable deviations between the measured curve and the reference curve based on ISO 717-1 appeared mainly around the first resonance frequency of the slit. In terms of the weighted SRI, the values predicted by Gomperts' theory have a good one-to-one correspondence with the measured values and are accurate to within 2 dB (average 0.7 dB). [ABSTRACT FROM AUTHOR]

This paper discusses the various challenges faced in the acoustical remodel of a Burn Acute Care Unit. A specific focus is placed on the debridement treatment facility, where patients undergo daily removal of dead tissue. Debridement is extremely painful for patients and loud distress sounds are common. The existing facility consisted of institutional tiled walls, plaster ceiling, and ceramic tile floors. Privacy curtains provided the only separation between patient debridement stations and sound isolation between the debridement facility and the rest of the ward was inadequate. Patient distress sounds could clearly be heard throughout the ward, likely creating anxiety for the patients. The design philosophy for the remodeled facility was to create true treatment rooms, with "Spa-like" finishes. Details of the remodel are presented, including creation of sound locks for enhanced sound isolation and selection of absorptive treatment that met high sanitary standards. The L1 values for typical patient distress sounds as measured in adjacent spaces were reduced from 88 dBA before remodel to 55-58 dBA after the remodel. The result was enhanced privacy and acoustical comfort within the remodeled debridement treatment facility as well as to patient rooms throughout the ward. [ABSTRACT FROM AUTHOR]