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13.08 Acoustics in Indoor Spaces, Part 1

Numerical study in sound absorption ability of curtain in random incidence condition
Time: 6:20 am

Author: Zenong Cai

Abstract ID: 1624

Woven fabric can provide variety application scenarios in acoustic field as flexible and light features. Folded curtain can be made from fabric, which is a good application example of woven fabric in noise control as sound adjuster in multi-function halls. Many geometric parameters can affect the sound absorption ability of folded curtain, such as folding shape, folding depth, the average distance of air cavity and folding period, etc. However, in random incidence condition, the relationship of geometry parameters and sound absorption ability is not clear in previous works. To obtain this relationship, Finite Element Method is used in this work. Because of the different folded shape, the contribution fractions of different angles are changed by the different geometry parameters. A series of three dimensional models is established with different geometric conditions. Different angles of incidence plain sound waves are introduced in three dimensional models. Numerical results show the detailed contribution fractions of different angles. A new formula that can predict sound absorption ability of folded curtain in random incidence condition can be gained.

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An explicit time-domain FEM for acoustic simulation in rooms with frequency-dependent impedance boundary: Comparison of performance in 2D simulation with frequency-domain FEM
Time: 5:40 pm

Author: Takumi Yoshida

Abstract ID: 1757

Accurate boundary modelings that address the frequency-dependent sound absorption characteristics of various sound absorbers are crucial for wave-based room acoustic simulation. In time-domain simulations, however, a computationally demanding convolution appears in frequency-dependent impedance boundary conditions. The present paper proposes a room acoustic solver with a fourth-order accurate explicit TD-FEM, incorporating a frequency-dependent absorbing boundary condition efficiently using a recursive convolution method, namely the auxiliary differential equation (ADE) method. Its performance against the fourth-order accurate frequency-domain FEM is examined via 2D real-scale room acoustic problems, solving a sound propagation in an office room up to 4.5 kHz.  Firstly, we describe briefly the formulation of the proposed room acoustics solver based on the explicit TD-FEM. Then, the discretization error property of the proposed method is evaluated via an impedance tube problem, including a frequency-dependent impedance boundary of porous sound absorber. Finally, the accuracy and efficiency of the proposed method are demonstrated with the comparison of frequency-domain FEM solver, which uses a sparse direct solver for the solution of the linear system at each frequency. Results showed the proposed method can perform an acoustic simulation with significantly low computational costs compared to the frequency-domain solver while keeping an acceptable level of accuracy.

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Digitalizing sound in personal spaces
Time: 8:40 am

Author: Ramana Kappagantu

Abstract ID: 1884

Design specifications for appliances are usually in the context of standard acoustic rooms like anechoic (full or hemi) and sometimes reverberant.  However in the world of infotainment industry the devices are operated in your personal space - a generic environment like that of a living room and they continuously interact with other devices in real time.  One has to take into account the scattering and absorption of sound from different surfaces and how they constructively and destructively interfere in generating a signature sound for the room and the devices. This environmental impact increases the design space significantly and makes it impractical to consider physical prototyping and testing.  Simulating the acoustic behavior of the devices in a room environment has been attempted in the past and were successful only for lower frequency ranges or for smaller rooms. High end Multipole BEM and FEM Adaptive Order technologies have emerged in the recent past and together with parallel cloud computing make the modeling of generic room environment more feasible, up to a few kHz given adept hardware setup. A different, more asymptotic method like Ray Tracing provides a real breakthrough here and enables taking on the full audible frequency range and large rooms, in at least one order of magnitude faster solving times compared to the more conventional FEM and BEM method, which further supports optimization possibilities for different configurations in reasonable time.

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Studying acoustical capacity and quality of verbal communication in occupied restaurants
Time: 1:00 pm

Author: Jared Paine

Abstract ID: 1888

Sound level data and occupancy data has been logged in five restaurants by the research team at the University of Nebraska – Lincoln. Sound levels and Occupancy at 10 second intervals were documented over time periods of two to four hours during active business hours. Noise levels were logged with dosimeters distributed throughout each restaurant, and occupancy was obtained from images recorded by infrared cameras. Previous analyses of this data have focused on average sound levels and statistical metrics, such as L10 and L90 values. This presentation focuses on each restaurant’s Acoustical Capacity and Quality of Verbal Communication, as introduced by Rindel (2012). Acoustical Capacity is a metric describing the maximum number of persons for reasonable communication in a space, calculated from the unoccupied reverberation time and the volume of the space. Quality of Verbal Communication is a metric describing the ease with which persons in the space can communicate at a singular point in time, depending on the reverberation time, the volume of the space, and the number of occupants in the space.

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Acoustic analysis of snoring sound from different microphones
Time: 6:20 am

Author: li ding

Abstract ID: 1962

Snoring is a common symptom of obstructive sleep apnea-hypopnea syndrome. The results show that there are obvious differences for most microphones in terms of the data distribution of features in the time and frequency domain. The results of snoring analysis from different recordings devices would be totally divergent. In view of this, when developing snoring analysis devices based user selected microphones (i.e. smartphone) recorded, we should take into account the discrepancy between different microphones.

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Room acoustics criteria and measurements of lobbies and atria for various building types
Time: 1:20 pm

Author: Ted Pyper

Abstract ID: 2132

The lobby or atrium for a building may serve many purposes -- entryway, welcome area, circulation zone, and architectural point of interest. Increasingly, lobbies and atria serve more and more functions: gathering area, presentation area, music and event space, study area, and dining, among other uses. Since variable acoustics in lobby spaces are not typically feasible or desirable, the acoustical design of lobby spaces must strike a balance for the variety of events planned for the space. Working with design teams and owners to understand the needs of each space, acoustical design criteria evolve based on project-specific needs and previous experience. In this presentation, lobbies are considered for various building types, including education facilities, student commons, museums, and performing arts buildings. In addition to studies of existing spaces and modeling of buildings in design, this presentation expands on the authors' previous efforts by documenting the measured reverberation and background noise in several lobbies and atria after the completion of design and construction.

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The effects of different ceiling structures and plan typologies on acoustical conditions of historical mosques
Time: 7:00 am

Author: FATMA YELKENCİ SERT

Abstract ID: 2166

Mosque is a building type used by Muslim people consists of speech and music rituals. Good acoustical condition in mosques is an important issue to provide desired acoustical environment for prayers and Imams during different worship rituals. Prayers need to feel individuality in praying and the sense of unity in recitation of the Quran, hymns. Worship activities need a high level of speech intelligibility and to satisfy prayers in the spiritual aspects which make people feel closed to the God. In the context of study, six historical mosques in Turkey, with different types of cover structures and plan typologies, are designated as study areas. The present study contains two methods which the first one is collecting acoustical data by measurements and the second consists of mathematical modelling software program. The purpose of study to investigate effects of different plan typology and ceiling structures on acoustical characteristics in mosques with similar volume. Also, distribution of acoustical parameters and the suitability of the values ??obtained through acoustic simulations and measurements to the recommended values are aimed to be investigated. As a result of the investigations, it was concluded that the objective acoustic parameters of mosques changed according to the geometric parameter properties.

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Noise and acoustics in complicated rooms with the sound particle method
Time: 6:40 am

Author: Thomas Judd

Abstract ID: 2197

The analysis of noise and acoustics in indoor spaces is often performed with geometrical methods from the ray-tracing family, such as the sound particle method. In general, these offer an acceptable balance between physical accuracy and computational effort, but models with large numbers of objects and high levels of detail can lead to long waits for results. In this paper, we consider methods to assist with the efficient analysis of such situations in the context of the sound particle diffraction model. A modern open-plan office and a large cathedral are used as example projects. We look at space partitioning strategies, adaptive placement of receivers in the form of mesh noise maps, and graphics-card-style hardware acceleration techniques, along with iterative modelling methods. The role of geometrical detail in the context of uncertainties in the input data, such as absorption and scattering coefficients, is also studied. From this, we offer a range of recommendations regarding the level-of-detail in acoustic modelling, including consideration of issues such as seating, tables, and curved surfaces.

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Occupant noise exposure in a fitness classroom setting
Time: 1:40 pm

Author: Madeline Didier

Abstract ID: 2595

Fitness facilities characteristically place an emphasis on the health and wellness of their occupants. Very loud amplified speech and music in group fitness rooms creates energetic spaces at the expense of the health and wellness of our hearing organs. The authors measured spectral sound pressure levels from fitness programs and occupants in over 40 group fitness classes (cycling, yoga, strength training, and other types) at facilities throughout the USA. Measurements occurred continuously throughout the entire duration of the classes. Variables measured include class type, loudspeaker position and type, time of day, day of the week, fitness class instructor, number of occupants, and the athletic club where the classroom is located. This paper discusses the overall findings from these noise surveys with an emphasis on noise exposure and typical frequency spectra for various fitness classes. This paper also includes a discussion of noise management and recommendations for best management practices to help achieve energetic spaces that are protective of health and wellness of hearing organs.

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Development and application of an integrated virtual thermal-acoustic manikin design used inside an office space
Time: 12:40 pm

Author: Eusebio Conceição

Abstract ID: 2637

In this study an integrated virtual thermal-acoustic manikin design used inside ventilated and occupied office spaces is developed and applicated. The component of the virtual thermal manikin evaluates the internal airflow and occupants’ thermal, thermo-physiology and clothing systems and calculates the thermal comfort and the indoor air quality levels. The component of the virtual binaural manikin evaluates the direct and indirect sound and calculates the reverberation time. The space geometry with complex topology is developed using a Computer Aid Design (CAD), while the occupants’ geometry is made using geometric equations. The grid generation, in the surrounding space surfaces and around the external occupants’ surfaces geometry, is used to calculate the radiative heat exchanges and the sound propagation. In this study, performed in an office room occupied by eight persons and equipped with personalized ventilation system, the thermal comfort level, the air quality level and the space reverberation time is evaluated and discussed. In accordance with the obtained results the values are, in general, in accordance the actual standards.

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Re-evaluation acoustic quality in lecture halls using G and C50: University of Sharjah Case Study
Time: 6:00 am

Author: Hussein Elmehdi

Abstract ID: 2703

In our previous studies, we focused on the common approach of measuring Reverberation Time (RT) for assessing acoustic quality in various types of lecture halls at the University of Sharjah (United Arab Emirates). The absorbing surfaces at the lecture halls at the University of Sharjah are limited to one surface (hanging ceiling), which has been shown in the literature to affect the accuracy in the description of the acoustic response as a result of the introduced uncertainty in the measured reverberation times. Because of these reasons, it has been highlighted in the literature that RT is considered not a good predictor of acoustic quality, namely speech intelligibility, in the lecture halls. Therefore, additional acoustic parameters need to be measured of calculated to accurately predict the acoustic response in lecture halls, especially speech intelligibility during activities that takes place within the lecture hall. The focus of our current research is to extend our precious work on RT to calculate additional acoustic parameters, namely the acoustic strength, G, and the speech clarity, C. Our goal is to investigate the practical use of G and C to describe acoustic response in the examined lecture halls. In addition to special variations with frequency, we will examine the effects source position, room dimensions at different locations within the lecture hall. The measurements were conducted in the same lecture halls under the same conditions including the acoustic absorbers and sound diffusers, which have shown to influence measured acoustic parameters. The results were compared to standards for the purpose of providing recommendations for range of acoustic parameters to support adequate speech communication during various teaching and learning activities in lecture halls.

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An experimental study on acoustical performance of cross rib diffuser
Time: 8:40 am

Author: Takumi Yoshida

Abstract ID: 2731

The preset paper proposes a novel acoustic diffuser which we call cross rib diffuser (CRD) and investigates its acoustical performance in rooms experimentally. CRD consists of overlapping two one-dimensional periodic rib diffuser (OPRD) with different structural configurations. CRD can achieve high scattering coefficient with wider frequency band than OPRD. Moreover, unlike other diffusers with high scattering property such as metadiffuser and two-dimensional quadratic diffuser, CRD keeps simple and familiar design of OPRD suitable for use in various architectural spaces. In the paper, we firstly evaluated random-incidence scattering coefficient of CRD using 1/5 scaled reverberation room. Then, random-incidence absorption coefficient was measured in 1/1 reverberation room. Finally, an implementation experiment was conducted to examine applicability of CRD in improving acoustics in small meeting room with small absorption treatments. The results indicated that CRD reduced EDT and reverberation time, and increased D50 more than JND values. Additionally, CRD improved reverberation and speech intelligibility more significantly than OPRD with same installation area.

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Measurement survey using acoustic measurement network and sound environment evaluation system by experience sampling
Time: 2:00 pm

Author: Kengo Togashi

Abstract ID: 2952

The use of open-plan offices is increasing as they are effective in improving intellectual productivity by fostering a communication among workers. Previous research on the relationship between the indoor sound environment and intellectual productivity has mostly reported the impact of the sound environment on the tasks that individuals work on. However, there has been no research on the impact of sound environment on office spaces where multiple workers are actually working. In this study, we developed a system that can analyze the individual characteristics of workers in relation to the sound environment by simultaneously measuring their evaluation to the sound environment and the sound environment of the office. The system collected workers’ evaluation of their impressions to the sound environment through a regular questionnaire using the experience sampling method. At the same time, it measured the sound environment of the office with multiple small measurement devices. The obtained sound environment evaluation data and the acoustic data of the office were stored in a single database. Finally, this system was run in a working environment to evaluate the sound environment on a trial basis.

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