Amplitude modulation depth discrimination in hearing‐impaired and normal‐hearing listeners
Journal of the Acoustical Society of America
Geometrical-acoustics ͑GA͒ modeling techniques assume that surfaces are large relative to the wavelengths of interest. For a given scenario, practitioners typically create a single 3D model with large, flat surfaces that satisfy the assumption over a broad range of frequencies. Such geometric approximations lead to errors in the spatial distribution of the simulated sound field because geometric details that influence reflection and scattering behavior are omitted. To compensate for the
... ations, modelers typically estimate scattering coefficients for the surfaces to account stochastically for the actual, wavelength-dependent variations in reflection directionality. A more deterministic approach could consider a series of models with increasing geometric detail, each to be analyzed at a corresponding frequency band for which the requirement of large surface dimensions is satisfied. Thus, to improve broadband spatial accuracy for GA simulations, we propose a multiresolution modeling approach. Using scale model measurements of a corrugated wall, comparisons of our method with non-GA techniques, and some simple listening tests, we will demonstrate that multiresolution geometry provides more spatially accurate results than single-resolution approximations when using GA techniques, and that this improved accuracy is aurally significant. 8:20 5aAAa2. On the analysis of the time spreading of sound diffusers. Since the invention of sound diffusers three decades ago a substantial effort has been made to predict the acoustic behaviour of these structures. BEM methods are well established for this purpose after a systematic comparison between simulations and experimental data. Volumetric methods such as finite element methods ͑FEM͒ or the finite difference time domain method ͑FDTD͒ are not often used, due to their large computational cost. However, near to far field transformations ͑NFFT͒ can overcome that problem. Recently some of the authors have shown that the FDTD method is a useful technique to analyse the time domain signature of sound diffusers. In this paper a careful analysis of the performance of diffusers in the time domain ͑"time spreading"͒ are reported, opening a new field of research. Invited Papers 8:40 5aAAa3. Diffraction modeling in acoustic radiance transfer method. Samuel Siltanen The room acoustic radiance transfer method is a solution to recently presented room acoustic rendering equation which formulates the mathematical basis for all the ray-based ͑geometrical͒ room acoustic modeling algorithms. The basic acoustic transfer method gives as accurate results as the state-of-the-art commercial room acoustic modeling software. However, the basic method still lacks, e.g., diffraction modeling and modeling of complex reflections from surfaces. In this paper we discuss different diffraction modeling methods in the light of the acoustic radiance transfer method. The problems as well as benefits of each diffraction modeling method are summarized to understand which one of them can be implemented together with acoustic radiance transfer. Finally, some implementation examples are given. 9:00 5aAAa4. Can also diffracted sound be handled as flow of particles? Some new results of a beam tracing approach based on the uncertainty principle. Uwe M. Stephenson ͑Hafen City University Hamburg, Nelkenweg 10, 23843 Bad Oldesloe, Germany, post @umstephenson.de͒ In computational room acoustics as well as noise immission prognosis efficient ray or beam tracing methods are well approved -but the problem of the neglected diffraction is still unsolved in general. The author's successful approach of 1986 based on Heisenbergs uncertainty principle was extended to the more efficient beam tracing technique and presented at the ICA 2007. The algorithm has now been generalized to recursive higher order diffraction. Now, not only single edge, but also multiple edge diffraction could be simulated 5a FRI. AM 3759 3759 ͑slit and "wide obstacle" with two edges͒. The results have again been compared with Svensson's exact wave-theoretical secondary edge source model. With some restrictions, they seem to indicate, that indeed even diffraction of sound -like light -may be handled as flow of particles. To avoid the feared explosion of computation time with higher order diffraction, a beam reunification may now be achieved by Quantized Pyramidal Beam Tracing. Finite-differences in the time domain ͑FDTD͒ are among the most accurate numerical techniques to simulate wave phenomena. The main drawback of FDTD numerical schemes is their computational cost in large scale simulations. The recently developed Fourier pseudospectral time-domain ͑PSTD͒ techniques, by approximating the spatial derivatives more efficiently, have improved significantly the accuracy and time costs of the simulations of electromagnetic fields. As a step towards applying PSTD techniques to room acoustic problems, we present here a framework to properly deal with material modeling in terms of generic impedance boundary conditions, beyond the common perfectly matched layer absorbing boundaries. We apply our results to a few representative cases ͑simple but reverberant rooms͒ and analyse its performance in terms of accuracy and computational resources. In particular we analyse whether the mild constraints that PSTD imposes on space-time discretization lead to good enough results in room acoustic simulations. 9:40-11:00 Posters Lecture sessions will recess for presentation of poster papers on various topics in acoustics. See poster sessions for topics and abstracts. Invited Papers 11:00 5aAAa6. Ray-tracing prediction of sound-pressure and sound-intensity fields in empty and fitted rooms. A Monte-Carlo ray-tracing model has been adapted to the prediction of sound-pressure and sound-intensity fields in rooms with surfaces of arbitrary surface impedance, and containing parallelepiped obstacles. Phase changes due to propagation distance and wall reflection were accounted for. Diffraction around obstacle edges was modeled by the Unified Theory of Diffraction. The model was also extended to include the out-of-phase secondary sound source of a single-channel, global active-noise-control ͑ANC͒ system. The new model was validated in comparison with predictions by reference models ͑e.g. FEM͒ and with the results of experiments in an anechoic chamber and in real rooms. It was used to predict the effectiveness of ANC. This paper discusses the development of the new models, the results of the validation tests and ANC predictions. 11:20 5aAAa7. The intensity in a reverberant field as an acoustic energy-density gradient. Vincent Valeau ͑Laboratoire d'Etudes The classical assumption for diffuse reverberant sound fields is that the acoustic energy flow at any location in a room --i.e., the acoustic intensity --is null. For rooms with disproportionate dimensions and"or uneven absorption distributions, this assumption no longer holds. Over the past few years, a room-acoustic diffusion model has been developed that can be seen as an extension of the statistical theory to nondiffuse sound fields. This work investigates the basic gradient-equation underlying this diffusion theory: it states that the energy-flow vector is proportional to both the gradient of the acoustic energy density, and to the room diffusion constant. The gradient equation for the acoustic intensity is confirmed numerically by comparison with calculations of the intensity vector using a particle-tracing model and a ray-tracing model. Examples are presented for a room with a diffuse sound field, and for elongated rooms where the sound field is strongly non-diffuse, in the case of both diffuse and specular reflections. 3760 Enclosures with diffuse reflection boundaries are modeled with an energy-intensity boundary element method using uncorrelated broadband directional sources. An absorption-based perturbation analysis shows the spatial variation of the acoustic field obeys certain scaling laws. A series expansion in terms of average absorption gives separate boundary integral problems at each order. The lowestorder solution has a uniform level proportional to the reciprocal of the average absorption. The next-order solution is independent of average absorption and primarily responsible for spatial variation of the acoustic field. This solution depends on the spatial distribution of absorption and input power sources, but not their overall level. For the primary spatial variation, the effects of the relative distributions of absorption and input power are linear and uncoupled. These distributions can be expressed in terms of constituent spatial modes corresponding to the ways absorption and input power can be distributed. Solved numerically once for each mode, the acoustic field can be expressed in terms of the modal amplitudes in closed form. These amplitudes can be adjusted to tailor the spatial variation. Examples include how to distribute absorption to minimize sound levels in one location, or how to achieve a uniform interior field. ͑Sponsor: NSF͒ Contributed Papers 12:00 5aAAa9. Analysis of room transfer function and reverberant signal statistics. A new theory is developed which makes quantitative predictions for energy transport that are consistent with localization. The theory promises ultimately to apply to a wide variety of systems. It is based on an assumption of S-matrices that are incoherent -as conventional diffuse field theories would have it -but then corrected to assure exact energy conservation. It is shown that the resulting system responses ͑they are concatenations of S matrices͒ have coherence, are consistent with localization, and predict Greens function retrieval. Localization emerges naturally from competition between rates of transport and rate of eigen-mode resolution. Examples are presented corresponding to coupled rooms and to diffusion in a multiply scattering medium. Future generalizations are discussed and the mathematical challenges are outlined. This is the second talk in a pair begun in a different session. Laboratory test reports are an important source of information regarding anticipated performance of a sound barrier construction. However, differences in construction conditions between the laboratory and a real building can greatly affect, usually negatively, the performance of a sound barrier assembly in the field. This reality, combined with the typical client's focus on reducing construction costs, requires that for a sound barrier construction to be successful, the effect of abutting constructions must be well understood. This paper reports on our firm's experience in translating lab-tested lightweight sound barrier assemblies to the field, relating design conditions to field results in terms of physical construction and noise reduction results. This paper provides an overview of a unique monitoring system used in England and Wales for tracking the sound insulation performance for 110 000 new build homes per annum. The regulatory approach, known as Robust Details was established within the building regulations and passed by parliament in 2004 after an 18 month initial research project. Annually over 5000 construction sites now use this system approach for separating walls and floors for attached houses and apartments. Acoustic site inspections and sound insulation field testing reports provide systematic feedback to the design and performance review. Since the RD systems inception on-site sound insulation compliance rates have risen from 40% to 97%. This paper will discuss the role of laboratory benchmark testing for products and also the role of acoustic ЉfieldЉ inspectors in tracking the airborne and impact performance. In addition the role of intervention and statistical analysis in upgrading or withdrawing specific wall and floor constructions will be presented. 3762 8:40 5aAAb3. Changed sound properties due to minor construction changes in a lightweight building. Fredrik Ljunggren ͑Luleå Univ. of Technology, Div. of Sound and Vibration, S-97187 Luleå, Sweden, fredrik.ljunggren@ltu .se͒ This paper relates to building acoustic measurement inside a two-story office house. The construction, which is known as lightweight, is prefabricated in volumes at a factory and is then transported to the building yard for assembling. It is build up of a wooden frame with particle boards and plaster boards attached. The building consists of a number of nominally, or almost nominally, identical rooms with assumed identical sound properties. In the projection stage, the construction was slightly modified in some of the rooms in order to see in what way the sound properties would be affected. In total eight impact sound pressure level measurements and eight sound reduction index measurements were performed and analysed for the different setups. Invited Papers 9:00 5aAAb4. The drying process influence on the brick walls sound reduction index: laboratory evaluations and theoretical analysis. Chiara Scrosati ͑Construction This paper presents experimental results showing the sound reduction index of different types of brick walls; the analysis was in particular carried out on double walls, single walls, and single walls with external lining. Its main purpose is to find the minimum drying time of the structure necessary to obtain the sound reduction indexes of brick walls as close as possible to laboratory real values. Moreover, it aims at making results of different laboratories as comparable as possible in terms of repeatability and reproducibility. All the fundamental quantities, such as the sound reduction index ͑R͒, the weighted sound reduction index ͑R_͕w͖͒, the spectrum adaptation terms C and C_͕tr͖, and temperature ͑T͒ and relative moisture, have been analyzed. A qualitative analysis of the curves slope of the sound reduction index versus frequency has been conducted for each drying time for each type of evaluated wall. The measurements were carried out in the acoustic laboratory of ITC-CNR ͑the Construction Light brick walls 8-10 cm thick are typical structures frequently used in Italian building constructions as a internal partitions between dwellings and as internal layer of double façade walls. Due to low surface mass and rigid connection to other horizontal and vertical structures, light brick walls are often responsible of high flanking transmission. The simplest acoustic modeling of this structure for the evaluation of sound transmission in buildings, is the approach proposed by the EN 12354 standards, where the brick wall can be considered as a homogeneous structure and main acoustic parameters required are the sound reduction index and the vibration reduction index Kij. The aim of this paper is to analyse results of physical and acoustical properties ͑sound reduction index, structural reverberation time, radiation efficiency͒ of a typical 8 cm thick brick wall measured in laboratory testing facility, used as a partition in different test configuration: single layer wall, double brick layer wall with internal thermal layer and as a component of lateral wall, where the Kij index flanking transmission were also evaluated. Experimental results are then compared with theoretical values in order to analyse difference with homogeneous structures. 9:40-11:00 Posters Lecture sessions will recess for presentation of poster papers on various topics in acoustics. See poster sessions for topics and abstracts. The role and possibilities of lightweight mineral wool is known for quite some years, acting as the optimum spring in a mass spring mass system one can reach high acoustic values. Compared to the massive constructions ͑e.g., concrete͒ the use of a mass spring mass construction has also other advantages ͑e.g., logistic, dimension of foundation and labour costs͒. Saint-Gobain Isover developed a wall system called Technostar, originally defined for cinema walls. In this construction an optimal mass spring mass construction is created. The theory of mass spring mass systems will shortly come up. All elements of the system are described. The acoustical performance of the Technostar construction is calculated with acoustic software ͑Stiff͒ and compared with laboratory measurements; the influence of different parameters on the measured acoustical performance will be shown. The practical use of the Technostar wall will be shown on the basis of the project CCTV tower in Beijing. For this project the acoustic requirements, the translation in terms of the wall construction with the specific details will be shown. The system will be build in March 2008. The mechanisms governing the acoustic transmission through building elements such as floor"ceiling assemblies are complex. The vibroacoustic interactions between the finite size structure and the enclosed volume are, in particular, rendered more complex at low frequencies when the finite dimensions of the building are taken into consideration. A model developed to predict the low frequencies vibroacoustics response of mutliplates systems offers the opportunity to explore, among other geometrical and material parameters, the effects of a fibrous material in the ceiling plenum on the acoustics behaviour of the whole structure. This paper presents the theoretical approach employed to predict the interactions between the floor, the ceiling panel and the enclosed volume. It also explores the effects of varying the material characteristics and overall thickness on these interactions. 12:40-1:40 Lunch Break 3764 The control of low frequency impact noise is of great importance in Japan and Korea. For impact noise rating, both countries use standardised heavy and soft impactors that inject high levels of low frequency power into a wood-frame floor due to the high force applied and "good" impedance match between the source and the floor. This paper reports on a parametric study designed to confirm the important parameters for controlling low frequency impact noise and how these parameters are affected by changes to construction details. The paper shows that increasing the drive point impedance floor surface while minimising the structural coupling between the gypsum board ceiling and the structural framing ͑joists͒ are important elements. Additionally, a well-designed floor topping can be very effective when applied to a suitable floor. The paper presents data to show the relative importance of direct and flanking transmission paths. Furthermore, it is shown that repeated impacts by the Bang Machine physically change the floor assembly and as a consequence resulting impact sound pressure levels in the receive room also change. The paper concludes with a general discussion and recommendations. Contributed Papers 2:00 5aAAb12. Field airborne and impact sound insulation of wood truss floor systems. Chad N. Himmel ͑JEAcoustics, 1705 West Koenig Lane, Austin, TX 78756, USA, Himmel@JEAcoustics.com͒, Daniel J. Kupersztoch ͑JEAcoustics, 1705 West Koenig Lane, Austin, TX 78756, USA, Kupersztoch@JEAcoustics.com͒ A series of field measurements on wood truss floors of various types was recently completed at four residential apartment complexes. About 40 floors with different floor finishes, gypsum concrete underlayment, noise control underlayment systems, truss span lengths, ceiling types, and resilient metal channel types were constructed and measured. Trusses were all similar engineered prefabricated parallel chord wood trusses. Room volumes and room absorptive characteristics are varied and nonstandard. Measurements are normalized according to ASTM E 1007 and proposed normalized impact sound rating ͑NISR͒ procedures to provide a reasonably consistent set for analysis. Low frequency measurements were conducted to 12.5 Hz one-third octave band. For both transmission loss and impact sound, many of the results compare well with predictions using simple regression analysis developed by others using variables such as the mass of the layers, truss depth and spacing, insulation thickness and density, and resilient metal channel spacing. The measurements and results will be presented in the paper. Access floor are raised floor systems consisting of modular panels supported by posts at a certain height to create a gap below the floor surface. Electrical wires and pipes can be placed inside the gap in order to avoid exposed installations and to simplify operations involving the inspection, repair, changing, or adding of system elements. This paper presents the results of the measurement campaign carried out on seven different access floor configurations, obtained by changing different floor elements: panels, surface finishes, damping materials under the posts base. Impact sound insulating properties of access floors combined with false ceilings were also tested and are reported in the paper. The tests were executed in two overlapping reverberating rooms available at the Acoustics Laboratory of the University of Perugia using the procedures given by ISO 140-6 Standard. The results are expressed in terms of normalized sound impact pressure level Ln and of the corresponding single number index Ln,W. Invited Papers 2:40 5aAAb14. Measurement of room-to-room airborne sound insulation with an access floor in a dwelling unit of condominium. It is preferred covering a wooden access floor on the concrete floor for condominium apartments in Japan. The access floor usually installed after every partition in each dwelling unit. If access floor and ceiling were done before partition, one can obtain accuracy of construction and reduce waste material. Therefore, one can provide building more green. But, there is concern that may deteriorate sound insulation because of flanking path through under the access floor. On the other hand, there is also another dominant flanking path irrespectively to these construction methods: via doors leading into hallway. A number of field measurements of sound insulation were done with opening"closing doors to evaluate the flanking transmission via the doors. These results show that the doors affect especially in high frequency, but not significant in low-mid frequency. Next, the sound transmission performances of access floors and ceilings measured at laboratory are compared with direct sound transmission through wall itself. As a conclusion, field measurement results show that this construction method difference less affect to airborne sound insulation performance. 3:00 5aAAb15. The acoustical effect of reveal blocks, from measuring method to prediction. Frigyes Reis ͑Budapest University of Technology and Economics, Lab. of Building Acoustics, Mûegyetem rakpart 3., 1111 Budapest, Hungary, email@example.com͒, Balázs Tóth ͑Wienerberger Co., Bártfay str. 34, 1119 Budapest, Hungary, firstname.lastname@example.org͒ The analysis of the efforts to create high quality building from the point of view of energy-efficiency, and the resulting variety of new products, building constructions and systems leads to the conclusion: there are characteristic deficiencies in the field of measuring and prediction methods related to sound insulation, and there is a need to stop the gap. The example on which the problem is shown is 5a FRI. AM 3765 3765 the acoustical effects of reveal blocks, used around window openings, to reduce heat propagation and increase energy efficiency. The reveal blocks include more sound propagation paths, the sound insulation of which can not be determined using the existing measuring standards. The paper describes new measuring concept and method to characterise the sound insulation characteristics of reveal blocks in their built-in form. The methods are fitted to the standardised measuring methods of sound insulation. Proposal is presented for the modification in the prediction procedure of sound insulation of façade constructions, utilising the results of the new measuring method. FRIDAY MORNING, 4 JULY 2008 P2-B, LEVEL 2, 9:40 TO 11:20 A.M. All posters will be on display from 9:40 a.m. to 11:20 a.m. To allow contributors an opportunity to see other posters, contributors of odd-numbered papers will be at their posters from 9:40 a.m. to 10:30 a.m. and contributors of even-numbered papers will be at their posters from 10:30 a.m. to 11:20 a.m. Contributed Papers 5aAAc1. Enhancement of impact sound insulation for "Gründerzeit-Häuser" build around 1900 during refurbishment using concrete-wood composite floors or suspended ceilings. Thomas Bednar ͑University of Technology, Karlsplatz 13"206, A-1040 Vienna, Austria, email@example.com͒ During refurbishment of Viennese buidlings that have been erected around 1900 an important aspect is to enhance the impact sound insulation of the old wooden floors. Usually the floors are wood beam floors and the uppermost floor is a massive wooden floor called Dippelbaumdecke. Two important measures are taken to increase the impact sound insulation to achieve the minimum requirement of LnTwϽϭ48ഛdB. The paper describes the design of an optimal suspended ceiling to avoid additional measures and as an alternative the impact of an additional thin concrete floor on top of the Dippelbaum-floor to achive minimum floor heights. As the thin concrete floor has a much larger area than the rooms below the measured results showed a big influence of concrete floor area on the impact sound level. 5aAAc2. Sound insulation properties of building elements, considering the frequency range below 100 Hz. Herbert Muellner ͑TGM Federal Institute of Technology, The constantly increasing standard of comfort in general and the rising number of apartment buildings in lightweight mode of construction directed the focus of research to the sound insulation properties of timber frame and massive wood element buildings. The complaints of the residents of terraced houses and multiple dwellings in lightweight buildings mainly concern noise events characterised by dominant low frequency. This problem regards airborne sound insulation as well as impact sound insulation. Based on empirical data the comparison of the sound insulation properties of the building elements investigated shows the specific problem of each category of construction mode in the frequency range below 100 Hz. The typical sound insulation characteristics regarding the low frequency range are discussed in the light of the current applied sound insulation requirements as well as in relation to the problem to comply with the resident's apperception of sound insulation quality. 5aAAc3. Effect of the frequency spectrum trend on the determination of the weighted normalized impact sound pressure level for floor structures. The most common floor constructions in Italian buildings are composed of two parts: the structural one, made of concrete beams and perforated bricks, and the floating floor. The results of the in situ measurements of the impact sound pressure level, realized on the structural part of the floors, show a frequency spectrum trend that increases with the frequency. The spectrum is also characterized by many peaks and dips at the high frequency range that strongly influence the determination of the weighted normalized impact sound pressure level, also for structures with similar mass and geometry. The frequency trend of the beam and brick structures is completely different from the characteristic spectrum of homogeneous concrete slabs or lightweight structures. Considerations on how those differences can influence the obtainable results in terms of the reduction of impact sound pressure level referred to the same floating floor typology, the spectrum adaptation terms and the other acoustic quantities described in the standards are reported. 5aAAc4. Influence of flanking transmission in typical Italian constructions. Simone Secchi ͑Univ. of Florence, Via San Niccolò 89"a, Actually acoustic performance of building components are analysed with reference to standardised conditions, in laboratories with suppressed flanking transmission. Laboratory results often show values of the performances quite different from those measured in real buildings, as a consequence of flanking transmission and of different conditions of realisation in 3766 3766 Although small-size windows are used in a ship, shipboard windows are a multilayered structure with glasses and air-gaps for high sound insulation. This paper discusses how to improve the sound insulation performance of shipboard windows. First, the sound transmission loss ͑STL͒ obtained from various experiments with shipboard windows are introduced and studied. The results show the layer arrangement as well as the material property of each layer makes an effect on the window's STL. It is also found that the higher the sound insulation performance of the window is, the more important the effect of the window frame is. Next, theoretical investigations are carried out and discussed in comparison with the experimental results. The comparison provides possible clues to increase the STL of the window. 5aAAc7. Acoustic analysis of the framework and walls stage in the construction of a housing block. Maria Jesus Ballesteros ͑Universidad de Castilla-La Mancha, The noise in the construction process is one of the main environmental and industrial noise sources. There are no specific regulations in several European countries for assessing such kind of noise, neither reference indexes for its evaluation. Therefore, the limits adopted are those for environmental and industrial noise, although they do not take into account the intrinsic characteristics of this noise. A measurement procedure has been stated for assessing the noise in building sites in which, the most appropriate indexes for this noise have been analyzed and used to derive the acoustic characteristics of the framework and walls stage. This stage is considered as one of the most annoying in the construction process of a housing block. 5a FRI. AM 3767 All posters will be on display from 9:40 a.m. to 11:20 a.m. To allow contributors an opportunity to see other posters, contributors of odd-numbered papers will be at their posters from 9:40 a.m. to 10:30 a.m. and contributors of even-numbered papers will be at their posters from 10:30 a.m. to 11:20 a.m.