Journal articles on the topic 'Acoustics and noise control (except architectural acoustics)'

This is a case study about noise and vibration control problems, and the design constraints and solutions for a proposed installation of a magnetic resonance imaging system (MRI) in an existing medical research facility. Manufacturer's data indicated that airborne sound level emissions over a broad frequency span could exceed permissible noise criteria for nearby occupied rooms. The building structure also required reinforcement to accommodate the MRI magnet's concentrated load, but invasive disturbance to a transgenic research mouse vivarium on the floor below was prohibited. The structure borne vibration paths needed attenuation or isolation. Design parameters included structural strength, stiffness and the specific platform resonant frequency (non-coincident with known vibration sources or building structure). In addition, acoustical containment was required for anticipated noises from the magnet room, to prevent excessive or annoying and distracting noise in the MRI control room or other adjacent (but unrelated) research, animal holding and office spaces. Structural “de-tuning” and architectural “decoupling” concepts were employed. A resonant frequency criterion was recommended for the new structural floor design. A combination of vibration spectrum analysis, dynamic analyses of alternate structural concepts and existing physical conflict constraints led to the design of an independent platform floor above the existing building floor. Post construction floor vibration measurements were compared to earlier measurement data to show quantitative change in performance. The modifications satisfied acoustical criteria and occupants' subjective evaluations.

The Graduate Program in Acoustics at Penn State offers graduate degrees (M.Eng., M.S., Ph.D.) in Acoustics, with courses and research opportunities in a wide variety of subfields. Our 820 alumni are employed around the world in a wide variety of military and government labs, academic institutions, consulting firms, and consumer audio and related industries. Our 40+ faculty from several disciplines conduct research and teach courses in structural acoustics, nonlinear acoustics, architectural acoustics, signal processing, aeroacoustics, biomedical ultrasound, transducers, computational acoustics, noise and vibration control, acoustic metamaterials, psychoacoustics, and underwater acoustics. Course offerings include fundamentals of acoustics and vibration, electroacoustic transducers, signal processing, acoustics in fluid media, sound and structure interaction, digital signal processing, experimental techniques, acoustic measurements and data analysis, ocean acoustics, architectural acoustics, noise control engineering, nonlinear acoustics, outdoor sound propagation, computational acoustics, biomedical ultrasound, flow induced noise, spatial sound and three-dimensional audio, and the acoustics of musical instruments. This poster highlights faculty research areas, laboratory facilities, student demographics, successful graduates, and recent enrollment and employment trends for the Graduate Program in Acoustics at Penn State.

Owing to a steep rise in urban population, there has been a continuous growth in construction of buildings, public or private transport like cars, motorbikes, trains, and planes at a global level. Hence, urban noise has become a major issue affecting the health and quality of human life. In the current environmental scenario, architectural acoustics has been directed towards controlling and manipulating sound waves at a desired level. Structural engineers and designers are moving towards green technologies, which may help improve the overall comfort level of residents. A variety of conventional sound absorbing materials are being used to reduce noise, but attenuation of low-frequency noise still remains a challenge. Recently, acoustic metamaterials that enable low-frequency sound manipulation, mitigation, and control have been widely used for architectural acoustics and traffic noise mitigation. This review article provides an overview of the role of acoustic metamaterials for architectural acoustics and road noise mitigation applications. The current challenges and prominent future directions in the field are also highlighted.

The Graduate Program in Architectural Acoustics has been constantly advanced from its inception in 1998 with an ambitious mission of educating future experts and leaders in architectural acoustics, due to the rapid pace of change in the fields of architectural-, physical-, and psycho-acoustics, and noise-control engineering. Since years the program’s pedagogy using “STEM” (science, technology, engineering, and mathematics) methods has been proven to be effective and productive, including intensive, integrative hands-on experimental components that integrate architectural acoustics theory and practice. The graduate program has recruited graduate students from a variety of disciplines including individuals with B.S., B.Arch., or B.A. degrees in Mathematics, Physics, Engineering, Architecture, Electronic Media, Sound Recording, Music and related fields. Graduate students under this pedagogy and research environment have been succeed in the rapidly changing field. RPI’s Graduate Program in Architectural Acoustics has since graduated more than 120 graduates with both M.S. and Ph.D. degrees. Under the guidance of the faculty members they have also actively contributed to the program’s research in architectural acoustics, communication acoustics, psycho-acoustics, signal processing in acoustics as well as our scientific exploration at the intersection of cutting edge research and traditional architecture/music culture. This paper illuminates the evolution and growth of the Graduate Program.

The Great Mosque of Yogyakarta was built in 1773. This mosque has a traditional architectural style. This study investigates the relationship between the mosque's architectural form, the activities inside it, and its acoustic characteristics. It employed quantitative and qualitative methods, including sound pressure level (SPL) measurement, reverberation time, and architectural and activity observations. Acoustic measurements, architectural observations, and activities are conducted inside and outside the mosque from morning to night for one week. The research finding is a spatial continuity pattern identified as the gradation of SPL value. Consistent continuity of SPL values in accordance with the nature of activities hierarchy. The result of this study is to improve mosque noise control by arranging outdoor and indoor spaces in a sustainable manner.

The acoustics research at Tongji University began in the mid-1950s. The Institute of Acoustics (IOA) of Tongji University, which is one of the earliest institutions engaged in acoustics research in China, was formally established in 1984. The IOA has decades of experience in acoustics education, including offering a master's degree program for approximately 40 years, a Ph.D. program for 35 years, and a postgraduate program for 25 years. The IOA is one of the oldest acoustic research facilities in China with outstanding acoustics laboratories. Research at the IOA is performed in many areas of acoustics, which focus on detection acoustics and marine acoustics, laser ultrasonics and photoacoustics, medical ultrasonics and bioacoustics, architectural acoustics, environmental acoustics, noise control, functional and microstructural acoustic materials, aeroacoustics and aeronautical acoustics, and vehicle acoustics. This paper presents acoustics education at the undergraduate and graduate levels of Tongji University and its outstanding acoustics research facilities in detail.

The Graduate Program in Acoustics at Penn State has been providing access to graduate level education in Acoustics for remote students across the country and around the world for more than 35 years. This poster summarizes the distance education Acoustics program from Penn State by showcasing student demographics, capstone paper topics, enrollment statistics and trends, and the success of our graduates. Our distance education program is offered in conjunction with our resident graduate program—course lectures are broadcast as a live stream over Zoom from a hybrid multimedia classroom allowing remote students to engage with faculty and students during live lectures; archived recordings are available for offline viewing afterward. Courses offered for distance education students include: fundamentals of acoustics and vibration, electroacoustic transducers, signal processing, acoustics in fluid media, sound and structure interaction, digital signal processing, aerodynamic noise, acoustic measurements and data analysis, ocean acoustics, architectural acoustics, noise control engineering, nonlinear acoustics, outdoor sound propagation, computational acoustics, flow induced noise, spatial sound and 3D audio, marine bioacoustics, and acoustics of musical instruments. Distance Education students can earn the M.Eng. in Acoustics degree remotely by completing 30 credits of coursework and writing a capstone paper.

A few case studies regarding small room architectural acoustics concerns are presented. These address problematic and unanticipated low-frequency room modes, constraints regarding vertical sound isolation in a tenant-space theater, and challenges pertaining to control of a chiller plant in commercial office space. Our approach to criteria, analyses, noise control recommendations, and lessons learned will be presented.

In this study, we have used wind data obtained from an earlier work covering several locations in Nigeria to estimate the possible impact of wind on sound pressure levels. Estimated Weibull parameters were used to compute the most probable wind speed, the average wind speed and the duration for which wind speed exceeds or equal the most probable speed. Adopting the proposed criteria that wind is able to strengthen or weaken sound pressure levels by 3dB depending on wind direction, the effect of wind on sound pressure level was determined. Results showed that wind effect seemed more predominant for the sub-sahelian stations such as Sokoto, Kano, and Maiduguri where the impact was found to be +/- 3dB obviously due to the characteristic high wind speeds recorded at those stations. The situation is almost the same for the midland region except that moderate impacts were found in some of the stations like Yola, Yelwa and Bauchi. However, moderate wind impacts generally characterize the Guinea Savannah and the coastal regions with the exception of Enugu with an impact of +/- 3dB. The result for Warri was found to be insignificant. It was concluded that most locations within the Nigerian environment may attain the wind conditions that would necessitate an adjustment in noise level measurements for application in architectural acoustics. In order to further validate the results of this preliminary study, it was recommended that detailed field survey where all relevant parameters such as wind speeds, wind directions and noise levels are simultaneously measured be conducted.

Those interested in pursuing graduate studies and conducting research in acoustics are invited to learn more about opportunities at the University of Nebraska – Lincoln (UNL) within the College of Engineering. Dr. Lily Wang and Dr. Erica Ryherd work on architectural acoustics and noise control topics (http://nebraskaacousticsgroup.org ) within the Durham School of Architectural Engineering and Construction, based at UNL's Scott Campus in Omaha. Dr. Jinying Zhu in Civil and Environmental Engineering (also based on UNL’s Scott Campus in Omaha) is active in structural acoustics, using ultrasonic waves for concrete evaluation (https://engineering.unl.edu/cee/faculty/jinying-zhu/). Dr. Joseph Turner in Mechanical and Materials Engineering (based at UNL’s City Campus in Lincoln) focuses on ultrasound propagation through complex media for quantitative characterization of materials/microstructure (http://quisp.unl.edu ). This poster presents the graduate-level acoustics courses and lab facilities at UNL within the College of Engineering, and highlights the research interests and achievements of our faculty, graduates, and students. Extracurricular experiences are available through an Acoustical Society of America student chapter based on the Scott Campus and collaborations with Boys Town National Research Hospital.

In June 2020 with the advent of COVID emergency plans were put in place to deliver the Masters course in Environmental and Architectural Acoustics totally on-line. This was necessary as although the acoustics laboratory is large, it was deemed to be unsafe for face-to-face teaching due to a complete lack of ventilation in the anechoic and reverberation chambers. Hence, it was necessary to create an alternative. It was decided that a "lab in a box" supported by on-line demonstrations and pre-recorded films would create the best alternative experience for the students. The "lab in a box" allowing the demonstrations to be replicated at home or in the garden. The results showed that the students gained from more independence, increased flexibility in deliver achieving very similar marks. This has opened up the possibility of increasing student numbers by reusing these alternative teaching strategies.

Amplified music outdoors poses many challenges in regard to sound abatement and requires a multi-disciplinary approach that includes sound system design and monitoring, programming considerations, architectural and landscaping sound control elements, and conditions for outdoor sound propagation including atmospheric, ground impedance, barrier and topographic effects. An interdisciplinary study was performed on the Brushy Creek Amphitheater in Hutto, Texas involving a local sound reinforcement company, audio equipment manufacturer, a local acoustical consulting firm, and a national atmospheric research group. This paper will provide the elements and findings of a multi-disciplinary investigation to minimize impact of a newly located amphitheater on the local community.

An important part of the design and acoustical performance of music education spaces are the sound isolation systems employed to reduce sound bleed between and among different spaces and the designed control of noise and vibration from building mechanical systems. Three case studies present challenges addressed in actual projects. One is a multi-story fine arts building at a university where all of the major acoustical spaces are built as rooms within rooms and the HVAC is distributed from a large rooftop mechanical room. The second is a single storey building at a public high school where primary, secondary, and tertiary sound separations, and HVAC system zones are clearly defined and describe the basic architecture of the facility. The third describes the steps in design required to transform significant acoustical difficulties in sound transmission and HVAC system noise into an expressive architectural and acoustical space built on a very modest budget.

Acoustic wave propagation in hard-walled ducts is of interest in many fields including vehicle design, musical instruments acoustics, and architectural and environmental noise-control. For the case of small sinusoidal perturbation of the cross-section, it is possible to derive simple though approximate analytical formulas of its plane wave acoustic reflection and transmission spectral response that resembles the optical situation of uniform Bragg gratings. The proof is given here, starting from the “horn equation” and then exploiting the coupled-modes theory. Examples of the results obtained with these analytical formulas are shown for some sinusoidally perturbed ducts and compared to results obtained through a numerical method, revealing a very good agreement.

Abstract This study presents the indoor soundscape framework in detail by describing the variables and factors that form an indoor soundscape study. The main objective is to introduce a new indoor soundscaping framework and systematically explain the variables that contribute to the overall evaluation of an indoor soundscape. Hence, the dependencies of physical and psychoacoustical factors of the sound environment and the spatial factors of the built entity are statistically tested. The new indoor soundscaping framework leads to an overarching evaluation perspective of enclosed sound environments, combining objective room acoustics research and noise control engineering with architectural analysis. Therefore, it is hypothesised that case spaces with certain plan organisations, volumetric relations, and spatial referencing lead to differentiated sound pressure level (SPL) and loudness (N) values. SPL and N parametric variances of the sound environments are discussed through the statistical findings with respect to the architectural characteristics of each library case space. The results show that the relation between crowd level variances and sound environment parametric values is statistically significant. It is also found that increasing the atrium height and atrium void volume, the atrium’s presence as a common architectural element, and its interpenetrating reference and domain containment results in unwanted variances and acoustic formations, leading to high SPL and N values.

Sound insulation under ventilation conditions is an important issue in acoustic fields that has significant applications in various practical scenarios. The emergence of acoustic metasurfaces breaks the limitation of manipulating large-scale waves at subwavelength scales and enables a better ventilating capability, while there is still a problem that the bandwidth of previous studies is usually smaller than half an octave. Here, we design and experimentally implement a ventilated meta-barrier with subwavelength thickness capable of realizing broadband sound insulation while maintaining efficient ventilation. The underlying mechanism is the synergy of the consecutive Fano resonances and superposition of equal-strength monopolar mode of the gradient helical structure and dipolar mode of the central orifice, leading to an efficient blocking of approximately 90% of sound waves coming from various directions in the range from 1145 to 1815 Hz while preserving high-efficiency ventilation. The experiments are conducted to verify the effectiveness of the resulting device, which is in good agreement with the simulated results and theoretical predictions. Our design with functionality and flexibility opens up possibilities for the design of broadband ventilated acoustic devices and may find important application prospects in diverse fields such as noise control and architectural acoustics.

In industrial and architectural applications, noise can be controlled using sound-absorbing materials. Natural materials are now gaining importance in the noise control engineering as they have advantages like low cost, eco-friendly, easy to produce, etc. Jute is one of such natural materials, which can be used as a sound-absorbing material. Micro-perforated panels along with three different types of jute felts are used in a multilayer sound absorber configuration to improve its sound absorption. The sound absorption performance of these multilayer sound absorbers is evaluated by using the transfer matrix method and experimental method. Dependence of sound absorption performance on the placement of micro-perforated panels in a multilayer sound absorber is also studied. It is observed that the sound absorption performance depends on the position of micro-perforated panels in a multilayer sound absorber.

The design of a muffler with wide-band transmission loss (TL) is a basic requirement for automotive exhaust systems where the exhaust noise is spread over several harmonics of the engine firing frequency. This has led to the concept of a double-tuned expansion chamber. In the present paper, the concept of double-tuning is extended to the two-chamber mufflers. The author's classical Velocity Ratio Algorithm is used here to analyze and design such a muffler. The relevant two-row array is manipulated and simplified to arrive directly at the single most significant term out of the 81 non-dimensional terms constituting the relevant Velocity Ratio. Examination of this single term reveals acoustics of the raised wide-band domes of the TL spectrum of the double-tuned two-chamber (DT2C) muffler vis-a-vis that of an equivalent longer double-tuned single-chamber muffler. Except for a low-frequency trough, its TL curve covers the entire frequency range of interest for control of automotive exhaust noise. It is also shown that the corresponding side-inlet side-outlet (SISO) DT2C muffler configuration has an identically similar wide-band TL spectrum to that of the co-axial muffler configuration. Finally, some guidelines are laid out for designing a DT2C muffler.

Abstract: Although in Indonesia has a standard rules about the level of noise in the region and the environment according to the decree of the Minister of Environment No. KEP-48/MENLH/11/1996, but the evaluation and control done to an area is still lacking. Soundscape is an environmentally acoustics part that is closely related to the quality perception of region noise. The purpose of this research is to critically study how architectural elements of the Bandung Film Park, are able to effectively and optimally contribute to the quality of environmental auditory, while also discovering the soundscape benefits as one of the analytical tools in designing. By implementing a qualitative approach with direct observation data retrieval techniques and merge into the phenomenon, the research can be an example of strategic implementation in the creation of good environmental sound quality. In other respects, a soundscape research can be a necessity to raise human awareness or designer in particular to environmental sounds as an aspirational and evaluative means to a sustainable city and community order.Kata Kunci: Soundscape, City Park, Architectural ElementAbstrak: Walaupun di Indonesia memiliki aturan standar tentang tingkat kebisingan dalam kawasan dan lingkungan, menurut Keputusan Menteri Negara Lingkungan Hidup No. Kep-48/Menlh/11/1996, namun evaluasi dan kontrol yang dilakukan terhadap suatu kawasan masih kurang dilakukan. Soundscape merupakan bagian akustika lingkungan yang terkait erat dengan kualitas persepsi kenyamanan bunyi kawasan. Tujuan penelitian ini adalah secara kritis menelaah bagaimana elemen arsitektural pembentuk Taman Film Bandung mampu secara efektif dan optimal dalam memberi kontribusi yang baik terhadap kualitas audial lingkungan, sekaligus menemukan manfaat soundscape sebagai salah satu alat analisis dalam perancangan. Dengan menerapkan pendekatan yang bersifat kualitatif dengan teknik pengambilan data observasi langsung serta melebur dengan fenomena yang terjadi, maka penelitian dapat menjadi contoh penerapan strategis dalam penciptaan kualitas suara lingkungan yang baik. Di lain hal, penelusuran soundscape dapat menjadi kebutuhan untuk meningkatkan kesadaran manusia atau perancang secara khusus terhadap suara-suara lingkungan sebagai sarana aspiratif dan evaluatif menuju tatanan kota dan masyarakat yang berkelanjutanKata Kunci: Soundscape, Taman Kota, elemen Arsitektur

We report both numerical and experimental constructions of a tunnel structure with low-frequency low-reflection bidirectional sound insulation (BSI). The designed tunnel was constructed from a pair of lossy acoustic metasurfaces (AMs), which consists of six ultrathin coiled unit cells, attached on both sides. Based on the generalized Snell′s law and phase modulations for both AMs, the tunnel with the low-frequency BSI was constructed based on sound reflections and acoustic blind areas created by the AMs. The obtained transmittances were almost the same for sound incidences from both sides and were lower than −10 dB in the range 337–356 Hz. The simulated and measured results agreed well with each other. Additionally, we show that the low-reflection characteristic of the tunnel can be obtained simultaneously by thermoviscous energy loss in coiled channels of the unit cells. Finally, an interesting application of the designed tunnel in an open-window structure with low-frequency low-reflection BSI is further simulated in detail. The proposed tunnel based on the ultrathin lossy AMs has the advantages of ultrathin thickness (about λ/35), low-frequency low-reflection BSI, and high-performance ventilation, which may have potential applications in architectural acoustics and noise control.

In this work, a low-frequency, open, sound-insulation barrier, composed of a single layer of periodic subwavelength units (with a thickness of λ/28), is demonstrated both numerically and experimentally. Each unit was constructed using two identical, oppositely oriented Helmholtz resonators, which were composed of a central square cavity surrounded by a coiled channel. In the design of the open barrier, the distance between two adjacent units was twice the width of the unit, showing high-performance ventilation, and low-frequency sound insulation. A minimum transmittance of 0.06 could be observed around 121.5 Hz, which arose from both sound reflections and absorptions, created by the coupling of symmetric and asymmetric eigenmodes of the unit, and the absorbed sound energy propagating into the central cavity was greatly reduced by the viscous loss in the channel. Additionally, by introducing a multilayer open barrier, a broadband sound insulation was obtained, and the fractional bandwidth could reach approximately 0.19 with four layers. Finally, the application of the multilayer open barrier in designing a ventilated room was further discussed, and the results presented an omnidirectional, broadband, sound-insulation effect. The proposed open, sound-insulation barrier with the advantages of ultrathin thickness; omnidirectional, low-frequency sound insulation; broad bandwidth; and high-performance ventilation has great potential in architectural acoustics and noise control.

Noise can become uncomfortable for us in many situations both indoors and outdoors. External noise consists of activities (airplanes flying overhead, traffic on the road, etc.) that are either loud enough to be considered uncomfortable when outdoors, or are of an elevated volume to the extent that they infiltrate buildings at levels considered uncomfortable. In the case of internal uncomfortable noise, this can either stem from noisy activities that occur inside the building (people speaking loudly, printers, etc.), or when an unexpected sound suddenly permeates an area that has a very low level of background noise. The most common manner by which to mitigate excess noise is through the use of certain materials, which either insulate against noise passing through the material, or absorb the noise wavelengths. In the case of the latter, vertical gardens present themselves as not only an aesthetic element in architecture, but also as a potential acoustic control tool in building design. For this work 10 m2 of vertical garden substrate modules was tested in a full size reverberation chamber. The objective was to open the doors for vertical gardens to be used in architectural acoustic design.

Given the importance of classroom acoustics in the academic performance of school grade students, this research aims to assess the acoustical performance of a number of primary and secondary grade classrooms in public schools in Medellin, Colombia. Standardized measurements of classroom noise and reverberation time were taken in 26 classrooms located in seven public schools. The results revealed excessive noise and reverberation problems in all the classrooms assessed. The cause of this poor acoustical performance seems to be an inappropriate architectural design that prioritizes natural ventilation over classroom sound insulation and the lack of sound absorption materials to control classroom reverberation.

Acoustic insulation in ventilated structures is an important problem in acoustic engineering with many potential practical applications, such as the noise control for ventilating ducts of buildings, vehicles, or air conditioners. Acoustic metamaterial is a good candidate for the design of acoustic insulation for ventilated channel (AIVC) because the structural design with hard boundary has longer lifetime than conventional sound-absorbing cotton. In this paper, an AIVC with an open region and narrow channels of different lengths is proposed. We numerically and experimentally demonstrate its acoustic insulation larger than 20 dB (T < 0.01) within approximately 500–1,200 Hz with a subwavelength channel length of λ/6. The parameter dependence and air flow effect are numerically studied. Our findings show an alternative design of AIVC that may have applications in noise control and architectural acoustics.

Thin, lightweight, and durable broadband acoustic absorbers capable of absorbing sounds over a wide frequency range, especially below 1000 Hz, while also surviving harsh operational conditions such as exposure to sprays of liquid and solid debris and high temperatures are desired for many noise control applications. While today’s commercially available broadband acoustic liners are impressive, such as melamine foam and perforate-over-honeycomb structures, each style has its limitations. Motivated by the need to reduce aircraft engine noise pollution NASA has recently patented a broadband acoustic absorber that claims some benefit over existing acoustic liners. Inspired by nature, these structures resemble the geometry and acoustic absorption of bundles of natural reeds, slender grasses that grow in wetlands across the world. Proof-of-concept experiments have begun at NASA. This report summarizes the design, fabrication, and normal incidence impedance tube tests performed for assemblies of natural reeds and additively-manufactured plastic prototypes that resemble the irregular geometry of bundles of natural reeds. Some synthetic prototypes were tested with and without perforated face sheets. Results indicate that there are a number of synthetic designs that exhibit substantial acoustic absorption in the frequency range of 500 Hz to 3000 Hz, and especially below 1000 Hz, as compared to baseline acoustic absorbers of similar thicknesses and weights. Many of these prototypes have an average acoustic absorption coefficient greater than 0.6. Additionally, an annular prototype was designed and printed but not yet subjected to tests. This annular prototype of a multifunctional structure designed to transfer heat and absorb sound was developed to fit inside the NASA Glenn Research Center’s DGEN Aeropropulsion Research Turbofan engine testbed. This invention can be considered and developed for a variety of aerospace, automotive, industrial, and architectural noise control applications.

We report, both theoretically and experimentally, a type of ultra-thin metasurface-based low-frequency sound absorber with bandwidth optimization. Such a metasurface unit consists of an ultrathin resonator (thickness∼1/90 wavelength) with a circular hole on the upper panel and four narrow slits inside a multiple-cavity structure. Eigenmode simulations of the unit show rich artificial Mie resonances, in which a type of monopolar Mie resonance mode can be obtained at 238.4 Hz. Based on the excitation of the monopolar mode, we can realize the near-perfect low-frequency sound absorption with the maximum absorption coefficient and fractional bandwidth of 0.97 and 12.9%, respectively, which mainly arises from the high thermal-viscous loss around the circular hole and four narrow slits of the unit. More interestingly, by combining 4 units with different diameters of the circular hole, we further enhance the fractional bandwidth of the compound unit to 18.7%. Our work provides a route to design ultra-thin broadband sound absorbers by artificial Mie resonances, showing great potential in practical applications of low-frequency noise control and architectural acoustics.

We report the numerical and experimental realization of a type of ultrathin planar wall with low-frequency dual-band sound absorption. The proposed planar wall is constructed by a periodic subwavelength unit cell (with a thickness of λ/19) which consists of two different multiple-cavity resonators embedded into a plate structure with a groove. The sound absorption of the wall exists in two working bands (IandII) below 600 Hz which are created by two different mechanisms. In addition to the band I created by a conventional resonance coupling of the two multiple-cavity resonators, it is worth noting that the band II is realized by a mutual resonance coupling between the resonators and groove structure. The fractional bandwidths of the bands I and II can reach about 34.1 and 10.4%, respectively. Furthermore, the application of the proposed ultrathin planar wall in the design of a barrier-free anechoic room with omnidirectional low-frequency dual-band sound absorption is further discussed in detail. The proposed planar wall has the advantages of ultrathin planar structure and omnidirectional low-frequency dual-band sound absorption, which provides diverse routes to design advanced sound-absorption structures in noise control and architectural acoustics.

The technique of sound insulation has a wide range of potential applications in environment noise control and architectural acoustics. The rapid development of acoustic artificial materials has provided alternative solutions to design sound insulation structures. However, the realization of single-layer planar structures with bidirectional acoustic insulation (BAI) and unidirectional acoustic insulation (UAI) still poses a challenge. Here, we report the theoretical and experimental realization of two types of single-layer phased array lenses which presents the characteristics of broadband BAI and multi-channel UAI. Both types of lenses consist of 12 mode-conversion phased units which are composed of two types of unit cells (I and II) with an opposite phase and a step waveguide. Based on the phase regulation, the designed phased unit can realize the mode conversion between the zero-order and first-order waves and asymmetric sound manipulation, which enables multi-functional sound insulations. Based on the desired theoretical phase profiles, two types of lenses with BAI and UAI are realized for the incidence of the zero-order wave, and their fractional bandwidths can reach about 0.28 and 0.37, respectively. More interestingly, the UAI effect can be reversed for the incidence of the first-order wave. The proposed lenses based on the mode-conversion phased units have the advantages of single-layer planar structure, multi-functional sound insulation, and broad bandwidth, which have wide application prospect.

Our thesis is that the city’s ambience is now an unstable dialectic in which we are watchers and watched, mirrored and refracted in a landscape of iPhone auteurs, eTags, CCTV and sousveillance. Embrace ambience! Invoking Benjamin’s spirit, this article does not seek to limit understanding through restriction to a particular theme or theoretical construct (Buck-Morss 253). Instead, it offers snapshots of interactions at the dawn of the postmodern city. That bricolage also engages how people appropriate, manipulate, disrupt and divert urban spaces and strategies of power in their everyday life. Ambient information can both liberate and disenfranchise the individual. This article asks whether our era’s dialectics result in a new personhood or merely restate the traditional spectacle of ‘bright lights, big city’. Does the virtualized city result in ambient anomie and satiation or in surprise, autonomy and serendipity? (Gumpert 36) Since the steam age, ambience has been characterised in terms of urban sound, particularly the alienation attributable to the individual’s experience as a passive receptor of a cacophony of sounds – now soft, now loud, random and recurrent–from the hubbub of crowds, the crash and grind of traffic, the noise of industrial processes and domestic activity, factory whistles, fire alarms, radio, television and gramophones (Merchant 111; Thompson 6). In the age of the internet, personal devices such as digital cameras and iPhones, and urban informatics such as CCTV networks and e-Tags, ambience is interactivity, monitoring and signalling across multiple media, rather than just sound. It is an interactivity in which watchers observe the watched observing them and the watched reshape the fabric of virtualized cities merely by traversing urban precincts (Hillier 295; De Certeau 163). It is also about pervasive although unevenly distributed monitoring of individuals, using sensors that are remote to the individual (for example cameras or tag-readers mounted above highways) or are borne by the individual (for example mobile phones or badges that systematically report the location to a parent, employer or sex offender register) (Holmes 176; Savitch 130). That monitoring reflects what Doel and Clark characterized as a pervasive sense of ambient fear in the postmodern city, albeit fear that like much contemporary anxiety is misplaced–you are more at risk from intimates than from strangers, from car accidents than terrorists or stalkers–and that is ahistorical (Doel 13; Scheingold 33). Finally, it is about cooption, with individuals signalling their identity through ambient advertising: wearing tshirts, sweatshirts, caps and other apparel that display iconic faces such as Obama and Monroe or that embody corporate imagery such as the Nike ‘Swoosh’, Coca-Cola ‘Ribbon’, Linux Penguin and Hello Kitty feline (Sayre 82; Maynard 97). In the postmodern global village much advertising is ambient, rather than merely delivered to a device or fixed on a billboard. Australian cities are now seas of information, phantasmagoric environments in which the ambient noise encountered by residents and visitors comprises corporate signage, intelligent traffic signs, displays at public transport nodes, shop-window video screens displaying us watching them, and a plethora of personal devices showing everything from the weather to snaps of people in the street or neighborhood satellite maps. They are environments through which people traverse both as persons and abstractions, virtual presences on volatile digital maps and in online social networks. Spectacle, Anomie or Personhood The spectacular city of modernity is a meme of communication, cultural and urban development theory. It is spectacular in the sense that of large, artificial, even sublime. It is also spectacular because it is built around the gaze, whether the vistas of Hausmann’s boulevards, the towers of Manhattan and Chicago, the shopfront ‘sea of light’ and advertising pillars noted by visitors to Weimar Berlin or the neon ‘neo-baroque’ of Las Vegas (Schivelbusch 114; Fritzsche 164; Ndalianis 535). In the year 2010 it aspires to 2020 vision, a panoptic and panspectric gaze on the part of governors and governed alike (Kullenberg 38). In contrast to the timelessness of Heidegger’s hut and the ‘fixity’ of rural backwaters, spectacular cities are volatile domains where all that is solid continues to melt into air with the aid of jackhammers and the latest ‘new media’ potentially result in a hypereality that make it difficult to determine what is real and what is not (Wark 22; Berman 19). The spectacular city embodies a dialectic. It is anomic because it induces an alienation in the spectator, a fatigue attributable to media satiation and to a sense of being a mere cog in a wheel, a disempowered and readily-replaceable entity that is denied personhood–recognition as an autonomous individual–through subjection to a Fordist and post-Fordist industrial discipline or the more insidious imprisonment of being ‘a housewife’, one ant in a very large ant hill (Dyer-Witheford 58). People, however, are not automatons: they experience media, modernity and urbanism in different ways. The same attributes that erode the selfhood of some people enhance the autonomy and personhood of others. The spectacular city, now a matrix of digits, information flows and opportunities, is a realm in which people can subvert expectations and find scope for self-fulfillment, whether by wearing a hoodie that defeats CCTV or by using digital technologies to find and associate with other members of stigmatized affinity groups. One person’s anomie is another’s opportunity. Ambience and Virtualisation Eighty years after Fritz Lang’s Metropolis forecast a cyber-sociality, digital technologies are resulting in a ‘virtualisation’ of social interactions and cities. In post-modern cityscapes, the space of flows comprises an increasing number of electronic exchanges through physically disjointed places (Castells 2002). Virtualisation involves supplementation or replacement of face-to-face contact with hypersocial communication via new media, including SMS, email, blogging and Facebook. In 2010 your friends (or your boss or a bully) may always be just a few keystrokes away, irrespective of whether it is raining outside, there is a public transport strike or the car is in for repairs (Hassan 69; Baron 215). Virtualisation also involves an abstraction of bodies and physical movements, with the information that represents individual identities or vehicles traversing the virtual spaces comprised of CCTV networks (where viewers never encounter the person or crowd face to face), rail ticketing systems and road management systems (x e-Tag passed by this tag reader, y camera logged a specific vehicle onto a database using automated number-plate recognition software) (Wood 93; Lyon 253). Surveillant Cities Pervasive anxiety is a permanent and recurrent feature of urban experience. Often navigated by an urgency to control perceived disorder, both physically and through cultivated dominant theory (early twentieth century gendered discourses to push women back into the private sphere; ethno-racial closure and control in the Black Metropolis of 1940s Chicago), history is punctuated by attempts to dissolve public debate and infringe minority freedoms (Wilson 1991). In the Post-modern city unprecedented technological capacity generates a totalizing media vector whose plausible by-product is the perception of an ambient menace (Wark 3). Concurrent faith in technology as a cost-effective mechanism for public management (policing, traffic, planning, revenue generation) has resulted in emergence of the surveillant city. It is both a social and architectural fabric whose infrastructure is dotted with sensors and whose people assume that they will be monitored by private/public sector entities and directed by interactive traffic management systems – from electronic speed signs and congestion indicators through to rail schedule displays –leveraging data collected through those sensors. The fabric embodies tensions between governance (at its crudest, enforcement of law by police and their surrogates in private security services) and the soft cage of digital governmentality, with people being disciplined through knowledge that they are being watched and that the observation may be shared with others in an official or non-official shaming (Parenti 51; Staples 41). Encounters with a railway station CCTV might thus result in exhibition of the individual in court or on broadcast television, whether in nightly news or in a ‘reality tv’ crime expose built around ‘most wanted’ footage (Jermyn 109). Misbehaviour by a partner might merely result in scrutiny of mobile phone bills or web browser histories (which illicit content has the partner consumed, which parts of cyberspace has been visited), followed by a visit to the family court. It might instead result in digital viligilantism, with private offences being named and shamed on electronic walls across the global village, such as Facebook. iPhone Auteurism Activists have responded to pervasive surveillance by turning the cameras on ‘the watchers’ in an exercise of ‘sousveillance’ (Bennett 13; Huey 158). That mirroring might involve the meticulous documentation, often using the same geospatial tools deployed by public/private security agents, of the location of closed circuit television cameras and other surveillance devices. One outcome is the production of maps identifying who is watching and where that watching is taking place. As a corollary, people with anxieties about being surveilled, with a taste for street theatre or a receptiveness to a new form of urban adventure have used those maps to traverse cities via routes along which they cannot be identified by cameras, tags and other tools of the panoptic sort, or to simply adopt masks at particular locations. In 2020 can anyone aspire to be a protagonist in V for Vendetta? (iSee) Mirroring might take more visceral forms, with protestors for example increasingly making a practice of capturing images of police and private security services dealing with marches, riots and pickets. The advent of 3G mobile phones with a still/video image capability and ongoing ‘dematerialisation’ of traditional video cameras (ie progressively cheaper, lighter, more robust, less visible) means that those engaged in political action can document interaction with authority. So can passers-by. That ambient imaging, turning the public gaze on power and thereby potentially redefining the ‘public’ (given that in Australia the community has been embodied by the state and discourse has been mediated by state-sanctioned media), poses challenges for media scholars and exponents of an invigorated civil society in which we are looking together – and looking at each other – rather than bowling alone. One challenge for consumers in construing ambient media is trust. Can we believe what we see, particularly when few audiences have forensic skills and intermediaries such as commercial broadcasters may privilege immediacy (the ‘breaking news’ snippet from participants) over context and verification. Social critics such as Baudelaire and Benjamin exalt the flaneur, the free spirit who gazed on the street, a street that was as much a spectacle as the theatre and as vibrant as the circus. In 2010 the same technologies that empower citizen journalism and foster a succession of velvet revolutions feed flaneurs whose streetwalking doesn’t extend beyond a keyboard and a modem. The US and UK have thus seen emergence of gawker services, with new media entrepreneurs attempting to build sustainable businesses by encouraging fans to report the location of celebrities (and ideally provide images of those encounters) for the delectation of people who are web surfing or receiving a tweet (Burns 24). In the age of ambient cameras, where the media are everywhere and nowhere (and micro-stock photoservices challenge agencies such as Magnum), everyone can join the paparazzi. Anyone can deploy that ambient surveillance to become a stalker. The enthusiasm with which fans publish sightings of celebrities will presumably facilitate attacks on bodies rather than images. Information may want to be free but so, inconveniently, do iconoclasts and practitioners of participatory panopticism (Dodge 431; Dennis 348). Rhetoric about ‘citizen journalism’ has been co-opted by ‘old media’, with national broadcasters and commercial enterprises soliciting still images and video from non-professionals, whether for free or on a commercial basis. It is a world where ‘journalists’ are everywhere and where responsibility resides uncertainly at the editorial desk, able to reject or accept offerings from people with cameras but without the industrial discipline formerly exercised through professional training and adherence to formal codes of practice. It is thus unsurprising that South Australia’s Government, echoed by some peers, has mooted anti-gawker legislation aimed at would-be auteurs who impede emergency services by stopping their cars to take photos of bushfires, road accidents or other disasters. The flipside of that iPhone auteurism is anxiety about the public gaze, expressed through moral panics regarding street photography and sexting. Apart from a handful of exceptions (notably photography in the Sydney Opera House precinct, in the immediate vicinity of defence facilities and in some national parks), Australian law does not prohibit ‘street photography’ which includes photographs or videos of streetscapes or public places. Despite periodic assertions that it is a criminal offence to take photographs of people–particularly minors–without permission from an official, parent/guardian or individual there is no general restriction on ambient photography in public spaces. Moral panics about photographs of children (or adults) on beaches or in the street reflect an ambient anxiety in which danger is associated with strangers and strangers are everywhere (Marr 7; Bauman 93). That conceptualisation is one that would delight people who are wholly innocent of Judith Butler or Andrea Dworkin, in which the gaze (ever pervasive, ever powerful) is tantamount to a violation. The reality is more prosaic: most child sex offences involve intimates, rather than the ‘monstrous other’ with the telephoto lens or collection of nastiness on his iPod (Cossins 435; Ingebretsen 190). Recognition of that reality is important in considering moves that would egregiously restrict legitimate photography in public spaces or happy snaps made by doting relatives. An ambient image–unposed, unpremeditated, uncoerced–of an intimate may empower both authors and subjects when little is solid and memory is fleeting. The same caution might usefully be applied in considering alarms about sexting, ie creation using mobile phones (and access by phone or computer monitor) of intimate images of teenagers by teenagers. Australian governments have moved to emulate their US peers, treating such photography as a criminal offence that can be conceptualized as child pornography and addressed through permanent inclusion in sex offender registers. Lifelong stigmatisation is inappropriate in dealing with naïve or brash 12 and 16 year olds who have been exchanging intimate images without an awareness of legal frameworks or an understanding of consequences (Shafron-Perez 432). Cameras may be everywhere among the e-generation but legal knowledge, like the future, is unevenly distributed. Digital Handcuffs Generations prior to 2008 lost themselves in the streets, gaining individuality or personhood by escaping the surveillance inherent in living at home, being observed by neighbours or simply surrounded by colleagues. Streets offered anonymity and autonomy (Simmel 1903), one reason why heterodox sexuality has traditionally been negotiated in parks and other beats and on kerbs where sex workers ply their trade (Dalton 375). Recent decades have seen a privatisation of those public spaces, with urban planning and digital technologies imposing a new governmentality on hitherto ambient ‘deviance’ and on voyeuristic-exhibitionist practice such as heterosexual ‘dogging’ (Bell 387). That governmentality has been enforced through mechanisms such as replacement of traditional public toilets with ‘pods’ that are conveniently maintained by global service providers such as Veolia (the unromantic but profitable rump of former media & sewers conglomerate Vivendi) and function as billboards for advertising groups such as JC Decaux. Faces encountered in the vicinity of the twenty-first century pissoir are thus likely to be those of supermodels selling yoghurt, low interest loans or sportsgear – the same faces sighted at other venues across the nation and across the globe. Visiting ‘the mens’ gives new meaning to the word ambience when you are more likely to encounter Louis Vuitton and a CCTV camera than George Michael. George’s face, or that of Madonna, Barack Obama, Kevin 07 or Homer Simpson, might instead be sighted on the tshirts or hoodies mentioned above. George’s music might also be borne on the bodies of people you see in the park, on the street, or in the bus. This is the age of ambient performance, taken out of concert halls and virtualised on iPods, Walkmen and other personal devices, music at the demand of the consumer rather than as rationed by concert managers (Bull 85). The cost of that ambience, liberation of performance from time and space constraints, may be a Weberian disenchantment (Steiner 434). Technology has also removed anonymity by offering digital handcuffs to employees, partners, friends and children. The same mobile phones used in the past to offer excuses or otherwise disguise the bearer’s movement may now be tied to an observer through location services that plot the person’s movement across Google Maps or the geospatial information of similar services. That tracking is an extension into the private realm of the identification we now take for granted when using taxis or logistics services, with corporate Australia for example investing in systems that allow accurate determination of where a shipment is located (on Sydney Harbour Bridge? the loading dock? accompanying the truck driver on unauthorized visits to the pub?) and a forecast of when it will arrive (Monmonier 76). Such technologies are being used on a smaller scale to enforce digital Fordism among the binary proletariat in corporate buildings and campuses, with ‘smart badges’ and biometric gateways logging an individual’s movement across institutional terrain (so many minutes in the conference room, so many minutes in the bathroom or lingering among the faux rainforest near the Vice Chancellery) (Bolt). Bright Lights, Blog City It is a truth universally acknowledged, at least by right-thinking Foucauldians, that modernity is a matter of coercion and anomie as all that is solid melts into air. If we are living in an age of hypersocialisation and hypercapitalism – movies and friends on tap, along with the panoptic sorting by marketers and pervasive scrutiny by both the ‘information state’ and public audiences (the million people or one person reading your blog) that is an inevitable accompaniment of the digital cornucopia–we might ask whether everyone is or should be unhappy. This article began by highlighting traditional responses to the bright lights, brashness and excitement of the big city. One conclusion might be that in 2010 not much has changed. Some people experience ambient information as liberating; others as threatening, productive of physical danger or of a more insidious anomie in which personal identity is blurred by an ineluctable electro-smog. There is disagreement about the professionalism (for which read ethics and inhibitions) of ‘citizen media’ and about a culture in which, as in the 1920s, audiences believe that they ‘own the image’ embodying the celebrity or public malefactor. Digital technologies allow you to navigate through the urban maze and allow officials, marketers or the hostile to track you. Those same technologies allow you to subvert both the governmentality and governance. You are free: Be ambient! References Baron, Naomi. Always On: Language in an Online and Mobile World. New York: Oxford UP, 2008. Bauman, Zygmunt. 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