Sound Transmission Mechanism Research Articles

Effect of the static compressive load on vibration propagation in multistory buildings and resulting heavyweight floor impact sounds.

Experiments were performed to identify the mechanism of heavyweight floor impact sound transmission through floors in a high-rise apartment building. Vibration and sound levels on each floor of the multistory building were measured. The vibration generated at a given floor was transferred to multiple adjacent floors with decreasing amplitudes proportional to the distance from the excited floor. This vibration transfer introduced significant sound transmissions. The structural static load varied depending on the floor location due to differences in the weight of the structure above the floor, especially for wall construction buildings. The static load at the wall of the bottom floor was the largest among the different floors. The influence of this static load on the impact sound generation was investigated through tests in the actual building and the scale model, respectively. The results were numerically analyzed using the spectral element method. With the increasing static load, the resonance frequencies of the floor increased due to the change in the vibration modes of the structure. The modulated sound generation from the floor vibrations transmitted to multiple layers with larger magnitudes due to this static load.

Protocetid (Cetacea, Artiodactyla) bullae and petrosals from the middle Eocene locality of Kpogamé, Togo: new insights into the early history of cetacean hearing

Extant cetaceans are fully aquatic mammals with deep modifications of their sensory organs, notably of the sound perception pathway. Early diverging cetaceans, known as archaeocetes, show a diversity of morphologies of the petrotympanic complex and middle ear ossicles, documenting a variety of sound transmission mechanisms from a mostly terrestrial configuration to a fully aquatic layout. Protocetids are a paraphyletic assemblage of semi-aquatic archaeocetes known from the Eocene. The auditory region of these ‘transitional’ forms is only partly known. The middle Eocene locality of Kpogamé, Togo (46–43 Ma) has yielded abundant material of protocetid whales documenting the auditory region, including isolated bullae, one petrosal and a skull fragment preserving the petrotympanic complex. Detailed study of this material leads us to reassess the original taxonomic attribution of this material, first attributed to Togocetus traversei, and to recognize three different protocetid taxa on the basis of bullar and petrosal remains: ?Carolinacetus sp., Togocetus traversei and Protocetidae indeterminate (morphotype γ). Associating isolated petrosals or bullae with dental remains solely based on size criteria can be misleading and we show here that there is no correlation between the size of tympanic bulla and size of dental remains in protocetids. CT-scan investigation of the in situ petrotympanic complex reveals that Protocetidae retained a complete tympanic ring similar to that of terrestrial artiodactyls and that the involucrum could probably articulate with the medial side of the ventral surface of the petrosal. This bulla/petrosal articulation is absent in fully aquatic cetaceans. Finally, the close phylogenetic relationships between protocetids from Kpogamé and North American protocetids suggest successive dispersals of these non-fully aquatic archaeocetes from African coasts to North America.

Research on effecting mechanism of environmental parameters on human ear

Sound and air pressure both have an important effect on the ear of human beings. In this paper, we established the finite element model of human middle ear to study the sound transmission mechanism and the stress of human ear under the three conditions of acoustic environment, low pressure acoustic environment and pressure fluctuation environment. Experiment and theoretical calculation were also done in the analysis process. The results show that the surface state of the tympanic membrane can reflect the human auditory sensation to a certain extent. Low pressure can reduce the acoustic energy into human ear, and pressure fluctuation leads the ear to bear great stress and temporary hearing loss. In this paper, the quantification of some objective factors is of great significance to the optimization of some standards and the decoupling of multi environmental effects.

A study of the sound transmission mechanisms of a finite thickness opening without or with an acoustic seal

This work is concerned with the transmission of sound through an opening in a wall of finite thickness where the opening may be filled with an acoustic seal represented by a pair of mass layers. Unlike past work where efforts were made on either developing a prediction model or investigating the influence of opening parameters on the sound transmission performance, the work presented here aims at studying the coupling mechanism of the system by considering the fluid-loaded opening as a resonant system. This treatment allows a better understanding of the system property at both resonance and off-resonance frequencies. It is found that, unlike that for the opening of vanishing thickness, the transmission loss for an opening of finite thickness exhibits obvious oscillation with maxima and minima in the frequency spectrum. The latter are associated with the resonance of the fluid-loaded opening. At resonance, the opening extracts the acoustic energy from a region much larger than its physical dimension, causing more energy to transmit through the opening. As a result, negative value of transmission loss occurs. At frequencies off the resonance, the way in which energy flows into the opening is found to be dependent upon the reactance of the wave impedance of the fluid-loaded system. For a sealed opening, the reactance of the wave impedance is greatly increased due to the large surface density of the mass layers of the acoustic seal, resulting in less energy injected into and thereby transmitted through the opening. The underlying physics leading to the improvement in sound insulation is sought by using a wave impedance expression from which equivalent system representation is derived in different frequency ranges.

Sound Transmission Through a Double-Wall Structure Coupled with Two Trapezoidal Acoustic Cavities

This paper aims at investigating the sound transmission mechanism of a flexibly-linked finite length double-wall structure. The problem stems from the modeling of sound transmission through corrugated core sandwich panels for predicting its transmission loss. The spatial segmentation of the acoustic gap and fully structure-acoustic coupling effect between the flexural vibration of the inclined mechanical link and the two adjacent trapezoidal acoustic cavities are considered. The theoretical model of the considered vibro-acoustic system is developed by using the modal superposition method in conjunction with envelope rectangular technique. Based on the developed theoretical model, the general vibro-acoustics characteristics of the system is presented. Particularly by using the [Formula: see text] mode of the acoustic cavity and the first structural modal frequency, the ratio between the aerostatic stiffness and the structural stiffness is formulated, and a criterion is proposed to determine whether the sound insulation performance of the vibro-acoustic system is controlled mainly by the structure or the acoustic cavity. Numerical investigations reveal that with different stiffness ratio, the acoustic cavity affects the sound transmission through both the added stiffness and added mass following different mechanisms. Besides, the influence of the inclined angle of the connecting beam on sound insulation performance of the double-wall structure is also studied. The obtained results are believed to be helpful in the optimal design of corrugated core sandwich panels for sound insulation.

An halisaurine (Squamata: Mosasauridae) from the Late Cretaceous of Patagonia, with a preserved tympanic disc: Insights into the mosasaur middle ear

Halisaurinae is a subfamily of enigmatic, small- to medium-sized mosasauroids, which retain a mosaic of primitive and derived features. The first record of a South American Halisaurus with precise stratigraphic information includes a quadrate carrying a tympanic disc together with twelve vertebrae, collected in the Late Maastrichtian of Jagüel Formation in northern Patagonia (Argentina). The preservation of a tympanic disc allows exploring and discussing the mechanisms of sound transmission in these mosasauroids. The location of the tympanic disc resembles that one formed by the extracolumella of aquatic turtles and at least one extant lizard. Based on morphological comparison of the middle ear we discuss previous hypotheses on the modification of the tympanic middle ear system of mosasauroids for underwater hearing, in a manner similar to that observed in aquatic turtles.

Research on the Prediction of Impact Sound Insulation to a Homogeneous Wall

In this paper, a theoretical model to evaluate impact sound transmission through a homogeneous wall is proposed. The model which is based on the Statistical Energy Analysis framework exhibits a system with room-wall-room. For the purpose to explore the mechanism of impact sound transmission through a wall, the impact sound reduction index between two rooms are predicted. Meanwhile, the variation of impact sound reduction index with the walls properties are also taken into account. The results reveal that the density, elastic modulus and thickness of a homogeneous wall have diverse effects on its impact sound insulation and can be chosen adequately to achieve ideal insulation values.It provides an approach to optimize impact sound insulating properties of the walls.

The Study on Application of Artificial Board Materials in Musical Instrument-Manufacturing Engineering

This study introduced the sound transmission mechanisms, current situation of application and selective criteria about musical instruments materials, and summarized the major problems of musical instrument-manufacturing engineering, as well as the feasibility of artificial board materials as a alternative material of the musical instruments, and the application prospect of artificial board materials widely as a musical instrument manufacturing materials was elaborated. This study aimed at providing a scientific theory for the musical instrument-manufacturing engineering.

An analytical study on active control and mechanisms of sound transmission through double panel-cavity system.

Combing the subsystem modal coupling theory and the impedance-mobility approach, a general analytical model is developed for the analysis and active control of structural acoustic transmission through the double panel-cavity structure into the free field, in which control methods including incident panel piezoelectric (PZT) actuator, acoustic actuator in cavity, and radiating panel PZT actuator are considered. The matrix formulae for the modal response of the coupled structural acoustic system and optimal secondary source strengths are obtained. On the basis, active control of sound transmission is studied analytically and numerically in detail. Simulations and analyzes are conducted to compare the control effects between different control strategies and examine the dominant control mechanisms involved in each control case, and the effect of system parameters on control effect is also examined. The results demonstrate that the incident panel actuator can obtain sound attenuation by modal suppression or rearrangement of three subsystems so many complex control mechanisms are involved and it is effective for incident panel modes, cavity modes, and radiating panel modes. Using the secondary acoustic source in the cavity is a better control strategy compared to the other control strategies due to the dominance of the acoustic mode (0,0,0) in the modal couplings and energy transmission in low frequency range.

Active Control of Sound Transmission with Modal Excitation (Investigation of Control Mechanism with Acoustic Power Mode and Experimental Study)

This paper deals with active control of transmitted sound power of a panel subjected to an incident sound wave. Based upon modal actuation reported in previous works, this paper presents modal actuation-based control for the purpose of reducing transmitted sound power of a panel. From a viewpoint of acoustic power modes, a dominant factor in structure-borne sound, a fundamental mechanism of sound transmission power of a panel is clarified, followed by a numerical analysis. It is shown that the (1, 3) structural mode (one of the elements of the first acoustic power mode) plays an important role in the sound transmission mechanism, and hence the (1, 3) mode needs to be extracted and suppressed. For this end, three cases of actuation method are presented, control effect in terms of each control strategy being discussed. Finally, an experiment is conducted, demonstrating the significant control effect achieved by suppressing the transmitted sound power at low frequencies using the proposed method in this work.

Sound transmission in archaic and modern whales: Anatomical adaptations for underwater hearing

The whale ear, initially designed for hearing in air, became adapted for hearing underwater in less than ten million years of evolution. This study describes the evolution of underwater hearing in cetaceans, focusing on changes in sound transmission mechanisms. Measurements were made on 60 fossils of whole or partial skulls, isolated tympanics, middle ear ossicles, and mandibles from all six archaeocete families. Fossil data were compared with data on two families of modern mysticete whales and nine families of modern odontocete cetaceans, as well as five families of noncetacean mammals. Results show that the outer ear pinna and external auditory meatus were functionally replaced by the mandible and the mandibular fat pad, which posteriorly contacts the tympanic plate, the lateral wall of the bulla. Changes in the ear include thickening of the tympanic bulla medially, isolation of the tympanoperiotic complex by means of air sinuses, functional replacement of the tympanic membrane by a bony plate, and changes in ossicle shapes and orientation. Pakicetids, the earliest archaeocetes, had a land mammal ear for hearing in air, and used bone conduction underwater, aided by the heavy tympanic bulla. Remingtonocetids and protocetids were the first to display a genuine underwater ear where sound reached the inner ear through the mandibular fat pad, the tympanic plate, and the middle ear ossicles. Basilosaurids and dorudontids showed further aquatic adaptations of the ossicular chain and the acoustic isolation of the ear complex from the skull. The land mammal ear and the generalized modern whale ear are evolutionarily stable configurations, two ends of a process where the cetacean mandible might have been a keystone character.

Eocene evolution of whale hearing.

The origin of whales (order Cetacea) is one of the best-documented examples of macroevolutionary change in vertebrates. As the earliest whales became obligately marine, all of their organ systems adapted to the new environment. The fossil record indicates that this evolutionary transition took less than 15 million years, and that different organ systems followed different evolutionary trajectories. Here we document the evolutionary changes that took place in the sound transmission mechanism of the outer and middle ear in early whales. Sound transmission mechanisms change early on in whale evolution and pass through a stage (in pakicetids) in which hearing in both air and water is unsophisticated. This intermediate stage is soon abandoned and is replaced (in remingtonocetids and protocetids) by a sound transmission mechanism similar to that in modern toothed whales. The mechanism of these fossil whales lacks sophistication, and still retains some of the key elements that land mammals use to hear airborne sound.

Control of sound transmission into a large composite cylinder using passive, adaptive–passive and active control strategies

This work is directed at the goal of controlling the high noise levels experienced in launch vehicle payload fairings. The problem frequency range is typically below 300 Hz where passive structural damping and sound absorption treatments perform inadequately. In this paper the work conducted at Virginia Tech over the last 3 years on techniques for reducing the interior noise levels at launch using an eight ft. diameter composite cylinder as a test platform is summarized. First the theoretical development will be presented with an overview of the mechanisms of sound transmission. Then, passive control methods using optimally damped structural distributed vibration absorbers (DVAs) and acoustic Helmholtz resonators will be presented. Both theoretical results and experimental results using high level acoustic excitation (132 dB) will be described. A set of adaptive Helmholtz resonators were also built and tested and are capable of tracking changes in acoustic resonances automatically. Finally, the results from a fully active structural acoustic control experiment using distributed active vibration absorbers will be presented.

Vibro-acoustic interaction of components in hard disk drive under seek process

With the increasing use of electro-mechanical systems such as hard disk drives, CD-Rom drives, and DVD drives in the consumer electronics industry, there is a growing demand for quieter products. The noise emitted from these devices may originate from the vibration of mechanical components in operation, such as bearings, gears and actuators. The vibration is then transmitted to other parts of the devices, such as the cover, and the noise emitted may then be amplified. This paper aims to develop a method for identify the acoustic noise emitted from hard disk drive seek process. In order to determine effective noise and vibration control of seek noise during the seek process, we first investigate the dynamic characteristic of the head actuator assembly under the different electrical drive signal using finite element method. In this paper, a bearing stiffness matrix (6 × 6) is adopted and performed using ANSYS element (Matrix 27). Using this method, we can understand the vibro-acoustic characteristics of hard disk drives and their components, and the mechanisms of vibration and sound transmission. Experiments are being conducted to demonstrate its validity through experiments. The method will also enable design optimisation for noise to be carried out at the design stage, before a new product is built, or help guide design changes on an existing device.

Analytical evaluation of the acoustic insulation provided by double infinite walls

The acoustic insulation provided by infinite double panel walls, when subjected to spatially sinusoidal line pressure loads, is computed analytically. The methodology used extends earlier work by the authors on the definition of the acoustic insulation conferred by a single panel wall. It does not entail any simplification other than the assumption that the panels are of infinite extent. The full interaction between the fluid (air) and the solid layers is thus taken into account and the calculation does not involve limiting the thickness of any layer, as the Kirchhoff or Mindlin theories require. The problem is first formulated in the frequency domain. Time domain solutions are then obtained by means of inverse Fourier transforms using complex frequencies. The model is first used to compute the sound reduction provided by a double homogeneous brick wall, with identical panels, when illuminated by plane sound waves. The results are then compared with those provided by the simplified method proposed by London, which was later extended by Beranek (London–Beranek method). The limitations of the simplified London–Beranek model, namely, its applicability only to double walls with identical mass, subjected to plane waves, and its failure to account for the coincidence effect, are overcome by the method proposed. Time signatures are produced to illustrate the different sound transmission mechanisms. Several types of body and guided waves are originated, giving rise to a complex dynamic system with multiple reflections within the solid and fluid layers and the global resonance of the system. The effect of the cavity absorption is considered by attributing a complex density to the air filling the space between the two wall panels. Absorption attenuates the dips of insulation controlled by the cavity resonances. Several simulations are then performed for different combinations of wall and air layer thickness to assess the influence of this variable on the final acoustic insulation. The influence of the air cavity on sound reduction was found to be dependent on the frequency. At low frequencies a better performance was achieved for thicker air layers, while at higher frequencies a thinner air layer is preferable. The use of wall panels with different mass resulted in the wall performing better, particularly for high frequencies.

Head sinuses, melon, and jaws of bottlenose dolphins, Tursiops truncatus, observed with computed tomography structural and single photon emission computed tomography functional imaging

The head sinuses, melon, and lower jaws of dolphins have been studied extensively with various methods including radiography, chemical analysis, and imaging of dead specimens. Here we report the first structural and functional imaging of live dolphins. Two animals were imaged, one male and one female. Computed tomography (CT) revealed extensive air cavities posterior and medial to the ear as well as between the ear and sound-producing nasal structures. Single photon emission computed tomography (SPECT) employing 50 mCi of the intravenously injected ligand technetium [Tc-99m] biscisate (Neurolite) revealed extensive and uptake in the core of the melon as well as near the pan bone area of the lower jaw. Count density on SPECT images was four times greater in melon as in the surrounding tissue and blubber layer suggesting that the melon is an active rather than a passive tissue. Since the dolphin temporal bone is not attached to the skull except by fibrous suspensions, the air cavities medial and posterior to the ear as well as the abutment of the temporal bone, to the acoustic fat bodies of each lower jaw, should be considered in modeling the mechanism of sound transmission from the environment to the dolphin ear.

Review of Active Techniques for Aerospace Vibro-Acoustic Control

This paper presents a review of active techniques for aerospace vibro-acoustic control. First, the mechanisms of airborne or structure-borne sound generation and transmission in aerospace vehicles are briefly reviewed. The main approaches of passive and active noise/vibration control are then summarised, and three examples of active systems that have already been developed into practical aerospace applications are briefly described. Finally the actuator, sensor, and control system requirements for aerospace applications are discussed.

Prediction of Sound Insulation at Low Frequencies Using Artificial Neural Networks

Low frequency noise, generated by outdoor and indoor sources, is an increasing problem and there is a need for methods of measurement and prediction of low frequency sound transmission, particularly between dwellings. This work presents a new approach to the low frequency sound transmission problem. Artificial Neural Networks, ANNs, are information processing systems that can store knowledge from their environment through a learning process and thus can be used in developing models for prediction. ANNs were applied to existing field data, in the standard frequency range, to confirm the classical mechanisms of sound transmission between dwellings. They then were applied to Finite Element Method modelled data for the frequency range 40–100 Hz. Results show the influence of parameters in sound transmission at low frequency that are not important at higher frequencies. Of particular significance is the main room dimension, normal to the plane of the party wall, and the edge conditions of the party wall. The results of applying ANN to sound transmission at low frequencies are promising but there remains a need for larger data sets, particularly to improve the prediction of equal room configurations where maximum acoustic coupling takes place.

Modelo computadorizado 3-D para el estudio de la biomecánica del oído medio con el método de los elementos finitos (Mef)

Based on known data about the behavior of the sound transmission mechanism, we generate a model that reproduces the real mechanics of the middle ear by the finite elements method in the most exact manner possible. We designed a computerized model to simulate the biomechanic behavior of the ear drum / ossicular chain. The investigation focused on a possible clinical application, given that the variables neccesary for simulation of several conditions can be introduced in our model: tympanic perforation, fixation of the ossicular chain, chain interruption, etc. Introducing the characteristics of the lesion virtually in a simulator program maket is possible to reach conclusions about the conductive hypoacusis created and about therapeutic possibilities. The 3-D modelling of the tympanic membrane, malleus, incus and stapes is presented, considering form, weight, density, Young’s module (N/m2) and Poisson coefficient for the different parts of each ossicle. The modeling of the union of the different tympanic-ossicular elements, including muscles and ligaments, is also shown.

Sound transmission through double-leaf corrugated panel constructions

A simple mass law based procedure developed by Sharp for the sound transmission loss (STL) prediction of an isotropic double wall is extended to the case of a double-leaf corrugated panel construction. Relative expressions are adopted for the STL estimation for a construction consisting of a layer of fiber reinforced corrugated roof panel and a layer of profiled steel sheet with sound absorption infilled inside the cavity between the two face panels. The STLs of some single and double-leaf corrugated panel constructions are measured in the laboratory to investigate into the sound transmission mechanism and to identify the important effects on the sound insulation performance of the constructions. Based on these experimental results, possible design modifications are presented for improving the sound reduction of double-leaf corrugated panel constructions.