On the Use of Perforated Sound Absorption Systems for Variable Acoustics Room Design

An important challenge for acoustic engineers in room acoustics design is related to the acoustic performance of multi-purpose auditoriums, which are typically designed to suit several performance requirements. With this intent, the analysis of several scenarios is usually performed individually, and then an acceptable solution, that may be adapted to several situations, is selected. One way of providing a more appropriate acoustic performance for each function of the auditorium is using variable sound absorption techniques to control reverberation and other relevant acoustic phenomena associated to sound perception. In this paper, the acoustic behavior of a perforated system that may be suitable for achieving a variable acoustic solution for room acoustic design is addressed. In the design of a cost-effective solution, the surface appearance is kept unchanged, while variable acoustic behavior is achieved either by closing the holes in the back face of the perforated panel or by placing a porous material in varying positions inside the backing cavity, thus accomplishing different acoustic requirements within a multipurpose auditorium. An analytical approach, based on the transfer matrix method is employed for preliminary acoustic sound absorption assessment provided by the system and to develop optimized solutions. Diffuse sound absorption is then computed and used to simulate, by the ray-tracing method, the acoustic behavior of a multipurpose auditorium to demonstrate efficient acoustic performance for different types of use.

Evidence of stereotyped contact call use in narwhal (Monodon monoceros) mother-calf communication

Narwhals (Monodon monoceros) are gregarious toothed whales that strictly reside in the high Arctic. They produce a broad range of signal types; however, studies of narwhal vocalizations have been mostly descriptive of the sounds available in the species’ overall repertoire. Little is known regarding the functions of highly stereotyped mixed calls (i.e., biphonations with both sound elements produced simultaneously), although preliminary evidence has suggested that such vocalizations are individually distinctive and function as contact calls. Here we provide evidence that supports this notion in narwhal mother-calf communication. A female narwhal was tagged as part of larger studies on the life history and acoustic behavior of narwhals. At the time of tagging, it became apparent that the female had a calf, which remained close by during the tagging event. We found that the narwhal mother produced a distinct, highly stereotyped mixed call when separated from her calf and immediately after release from capture, which we interpret as preliminary evidence for contact call use between the mother and her calf. The mother’s mixed call production occurred continually over the 4.2 day recording period in addition to a second prominent but different stereotyped mixed call which we believe belonged to the narwhal calf. Thus, narwhal mothers produce highly stereotyped contact calls when separated from their calves, and it appears that narwhal calves similarly produce distinct, stereotyped mixed calls which we hypothesize also contribute to maintaining mother-calf contact. We compared this behavior to the acoustic behavior of two other adult females without calves, but also each with a unique, stereotyped call type. While we provide additional support for individual distinctiveness across narwhal contact calls, more research is necessary to determine whether these calls are vocal signatures which broadcast identity.

Acoustic behavior prediction of monodisperse foams using polynomial surrogates

Acoustic properties of foams, such as macroscopic transports and sound absorption, are significantly influenced by their local morphology. The present paper develops a polynomial chaos expansion (PCE)-based surrogate model for characterizing the microstructure-properties relationships of acoustic monodisperse foams. First, the acoustic properties of the considered structures are estimated numerically by homogenization techniques using an idealized periodic unit cell and the Johnson-Champoux-Allard-Pride-Lafarge (JCAPL) model. The reference maps of transport parameters are then used to construct the PCE–based surrogates in the design space involving a set of foamy microstructural parameters such as membrane content, cell size, and porosity. Finally, after a validation phase and assessing convergence characteristics, the generated surrogates are employed to design some foam-based absorbers to illustrate the accuracy and computational efficiency of the proposed method.

Influence of the Blade Design Parameters on Hydraulic Noise Generation by a Low Specific Speed Radial Pump With Narrow Channel Flow

Present work aims to investigate the hydro acoustic behavior of a typical low specific speed radial type centrifugal pump with narrow channel impeller passage. The blade design parameters play an important role in hydraulic noise generation by a low specific speed radial pump with narrow impeller channels. Though, these pumps are hydraulically efficient for a given design point, the hydraulic noise production may be higher at duty point. The blade passage length along with the outlet width of the impeller are the two main design parameters of a radial impeller with narrow channels, which can impact the flow quality along the impeller blade passage. To understand the effect of the narrow channel, initially steady state simulation is conducted to predict and validate the hydraulic performance. Then transient simulations were conducted using Detached Eddy Simulation (DES) using STAR-CCM+ to predict the hydro acoustic behavior of the pump in terms of pressure fluctuations and far field noise spectra of the pump at specific points. The velocity profiles along the impeller channels, shows the formation of wake region, which strongly affects the jet wake flow phenomenon near impeller trailing edge. This results in high pressure fluctuations near impeller outlet.

Sonographic features of various dental materials and foreign bodies

Objective: To reveal the sonographic characteristics of various foreign bodies and dental materials to aid diagnosis. Methods and materials: 24 objects consisting of various dental materials and foreign bodies were included in the study. Objects were embedded in bovine gelatin. Images of the objects were obtained by conventional radiography and ultrasonography (USG). Opacities were evaluated by conventional radiography. Their visibility and posterior acoustic behaviors were examined by USG. In addition, the actual sizes of the objects and their dimensions measured by USG were compared. Results: All objects included in the study, including non-opaque ones, could be visualized by USG. When the posterior acoustic behavior of objects was examined, 15 of the objects (62.5%) caused posterior acoustic shadowing on USG. While 6 of the objects (25%) did not have any USG artifacts, 2 of them (8,3%) had comet tail artifact and 1 of them (4,2%) had reverberation artifact. There was no statistically significant difference between the actual dimensions of the objects and their dimensions measured by USG (p > 0,05). Conclusion: USG is a very useful technique for imaging foreign bodies and dental materials, it can even show objects that cannot be seen in X-rays on in-vitro environment.

Influence of fineness, length and hollow section of fibers on acoustic absorption

A fibrous material is characterized by its fineness, flexibility and high length/fineness ratio and it is used to reduce noise in indoor rooms due to their porous structure. The aim of this work is focused on investigating the structure of two different fibers (acrylic and polyester) from the analysis of the macrostructural parameters, such as fineness, length and cross-section (solid or hollow). Furthermore, the degree of influence of these parameters on the average sound absorption has been investigated. The sound absorption coefficient of fibers is measured at normal incidence in the impedance tube. In acrylic fibers, results showed that the fineness of the fiber has a significant influence on the sound absorption compared to the length of the fiber. In polyester fibers, hollow fibers have a better acoustic behavior compared to solid fibers.