Sound Transmission Properties Research Articles

Effect of Acoustic Enclosure on the Sound Transmission Loss of Multi-Layered Micro-Perforated Plates

This study presents an examination of the transmission properties of multilayered partitions made up of multiple micro-perforated plates (MPPs) coupled to acoustic enclosures with general impedance boundaries. Multi-layered MPPs can lower the transmission while minimizing reflection in the source and receiving enclosure. Previous research has mainly focused on the double MPPs or triple MPPs partition itself. However, it is vital to analyze the in-situ sound transmission loss of the multi-layered MPP and their efficiency in a complex vibro-acoustic environment. The case when the multilayered MPPs are coupled to a receiving enclosure or coupled to both a source and receiving enclosure is investigated. The objective is to provide an analytical method to evaluate the transmission properties of multilayered MPPs coupled to acoustic enclosures while being computationally more efficient than the finite element method (FEM). Using the modified Fourier series for the acoustic pressure, a variational form for the acoustic and structure medium yields a completely coupled vibroacoustic system. A comparison between the sound transmission loss of the double MPPs, when mounted on an impedance tube and coupled to acoustics enclosures, shows the modal effect of the enclosures. The effect of enclosure shape, impedance boundary, perforation ratio, air gap thickness on the sound transmission properties of the double MPPs structure is examined for both cases. Finally, in both situations, the performance of triple MPP structure insulation is evaluated.

A hybrid test method for measurement of airborne sound transmission loss of building partitions and elements

Single-number ratings, such as sound transmission class (STC), outdoor to indoor transmission class (OITC), and weighted sound reduction index (Rw), have been widely used to indicate the sound transmission properties of the building elements. The required transmission loss values over the frequency spectrum can be obtained from the two reverberation rooms test method (ASTM E90, ISO 10140), field measurement method (ASTM E966), or intensity method (ISO 15186). The limitations of the number of testing facilities that can provide the diffused field, minimum cut-off frequency, and other standard laboratory requirements, made the sound transmission loss measurement a costly and time-consuming procedure. In this study, alternative methods to measure the sound pressure and intensity have been investigated. The main objective of this research was to eliminate the complicated requirements of the diffused field and the room absorption measurement by averaging the direct sound amplitude at several angle of incidents and using the intensity probe to measure the sound intensity. In conclusion, the sound transmission loss, STC, and OITC values of double-glazed windows obtained from the hybrid method have been compared with predictions from the existing theory and the ASTM E90 standard test results.

Investigation of acoustic, mechanical, thermal, and moisture properties of milled alkali‐treated coconut tree secondary flower leaf stalk fiber‐reinforced polymer composite

AbstractThe current research study centers on exploring natural fibers due to the increasing need for sustainable and eco‐friendly alternatives in various industries. In India, where coconut trees are widely grown for their tender coconuts and by‐products, the leftover fruit leaf stalks become agricultural waste once the coconut is harvested from the trees. So this research work involves the development of composite materials with natural fiber components by using unsaturated polyester resin (UPR) as the matrix material along with alkali‐treated coconut tree secondary flower stalk fiber (ACSF) for reinforcing. The composite materials were formed using the compression molding technique with different weight compositions of 20%, 30%, and 40% of ACSF and 80%, 70%, and 60% of UPR, respectively. From the results, the 30ACSFC reveals a maximum value of 42 N/mm2, 58 N/mm2, 10 kJ/m2, and 48 HD in flexural, tensile impact, and hardness tests, respectively. In the water absorption analysis, 20ACSFC had observed a lower moisture content, which explains the low weight percentage of ACSF in the composite. From the TGA analysis, 30ACSFC had a residual mass of 18% due to the significant change in the cellulose because of alkali, leading to strong adhesion in the composition matrix. The SAC analysis reveals that at the peak and trough levels of frequency, varying the composition of composite materials leads to improved sound absorption coefficients that surpass the performance of the 30ACSFC composite. The SEM study was carried out to identify the mechanism of failure in the elongated specimens of the tensile test, which was based on the phenomena of matrix crack, fiber pull‐out, fiber shearing, void and interfacial bonding, and de‐bonding. These results indicate the possibility of creating lightweight composites with improved strength and stiffness, making them suitable for use in roof panels, door panels, insulation, and other related applications. The incorporation of ACSF as a reinforcing material introduces new prospects for sustainable and environmentally friendly composite materials, showcasing promising mechanical and thermal properties.Highlights Enhanced mechanical strength: Evaluation of tensile strength, flexural strength, and impact resistance showcases how ACSF reinforcement improves the composite's load‐bearing capacity and durability. Effective acoustic dampening: A study of sound absorption and transmission properties reveals the composite's potential in noise reduction applications, such as architectural acoustics and automotive soundproofing. Thermal insulation potential: An assessment of thermal conductivity and expansion helps identify whether the composite is suitable for applications requiring enhanced insulation or efficient heat transfer. Moisture resistance and stability: An analysis of moisture absorption and dimensional changes informs the composite's suitability for humid environments, ensuring its resistance to degradation and maintaining the dimensional stability.

Development of tunable acoustic materials with inline cavity structure for enhanced sound absorption and transmission loss

This article presents an innovative approach to design and characterize an acoustic material with tunable sound absorption and transmission properties. The material incorporates an inline cavity structure, created by extracting a sphere and a cylinder from a cubic unit cell, resulting in unique inlet and outlet ports. Four samples of varying thicknesses (in multiples of 5 mm) were prepared using 3D printing technology from UV-cured standard resin. Sound Absorption Coefficient (SAC) and Sound Transmission Loss (STL) were determined in the frequency range of 0.5–6.3 kHz using an Impedance Tube Apparatus. Peak SAC values gradually declined from 0.99 to 0.85 with sample thickness increasing from 5 to 20 mm. Likewise, the corresponding peak absorption frequencies of the test samples decreased from 4.95 to 1.95 kHz. The STL values varied between 4 dB to as high as 50 dB within the frequency range of 0.5–2 kHz. In addition, the STL values clearly showed a periodic pattern over the entire range of measurement, irrespective of the changes in thickness. Beyond 2 kHz, the periodic variation remained within a range of 18–38 dB for all the samples. Hence multiplying the unit cells along the transmission path had no remarkable effect on STL. Also, the impact of air gap thickness (10 mm, 20 mm, and 30 mm) on the acoustic properties of the samples was investigated. With the insertion of an air gap thickness of only 10 mm, the peak absorption frequency drastically shifted from 4.95 kHz to 1.275 kHz in the case of a 5 mm thick sample. Similar changes in the material's resonant behaviour with changing air gaps were visible for all other samples. The experimental results, summarily illustrate the role of thickness, internal structure, and air gap thickness in tailoring sound absorption and transmission capabilities. Hence the acoustic properties of the developed material are tunable which offers promising applications in soundproofing and noise reduction across both indoor and outdoor installations. In conclusion, this research demonstrates a novel approach to acoustic material design and its characterization, paving the way for optimized acoustic performance in engineering applications.

The acoustic streaming effects and transmission mechanisms of a micro-cavity acoustic black hole structure with an abrupt cross-section

This paper investigates the acoustic streaming effects (ASEs) and mechanisms behind the transmittance of sound in a metallic micro-cavity acoustic black hole (ABH) structure with an abrupt cross-section and examines the sound field flow characteristics inside the micro-cavity ABH under the sound excitation, such as the velocity, acceleration and pressure fields. And the sound transmission mechanisms are characterized by the ASEs which can be obtained by solving Navier–Stokes equations. The numerical results show that the sharp increase in the velocity and acceleration at the ABH tip position is the main reason for the focusing of the sound energy. And the dramatic increase in the tip cross-section reduces the acoustic streaming velocity, which is the main reason for the attenuation of the sound energy. Additionally, the thermoviscous effect of the acoustic boundary layer can also dissipate the low-frequency sound energy. The sound insulation experiment shows that the proposed micro-cavity ABH structure has a sound transmission loss (STL) of over 15[Formula: see text]dB in the low-frequency regime. This research reveals the mechanisms of the ASE’s work on the sound transmission properties of the micro-cavity ABH and provides new insight into low-frequency sound wave suppression. The ABH structure proposed in this paper has excellent strength, bearing capacity and long lifecycle, so it can be applied in the construction industry through its integrated design of structure and performance.

Influence of Geometric Structure, Convection, and Eddy on Sound Propagation in Acoustic Metamaterials with Turbulent Flow

The problem of reducing noise in the transportation is an important research field to prevent accidents and to provide a civilized environment for people. A material that has recently attracted attention in research to reduce noise is acoustic metamaterial, and most of the research projects so far have been limited to the case of static media without flow. We have studied the sound transmission properties of acoustic metamaterial with turbulent flow to develop acoustic metamaterial that be used in transportation. In this paper, the effect of geometrical structure, the convective effect, and the eddy effect on sound propagation in acoustic metamaterial with turbulent flow are investigated, and the relationships between them are analyzed. The convective effect and the eddy effect both reduce the resonant strength of sound transmission loss resulting from the unique geometry of the acoustic crystal, but shift the resonant frequencies in opposite directions. In addition, when the convective effect and the eddy effect of the airflow, as well as the intrinsic interaction effect generated from the unique geometrical structure of the acoustic metamaterial cannot be ignored, they exhibit competition phenomena with each other, resulting in a widening of the resonance peak. As a result, these three effects cause the shift of the resonance frequency of the sound transmission loss and the widening of the resonance peak. The results of this study show that even in the case of turbulent flow, acoustic metamaterial can be used for transportation by properly controlling the geometric size and shape of the acoustic metamaterial.

Sound transmission properties of a porous meta-material with periodically embedded Helmholtz resonators

The main scope of this work is to study the effect of embedding a periodic pattern inside a porous material, in order to passively improving its acoustic performance in terms of sound transmission loss. A contemplated application is the improvement of classical aeronautical soundproofing packages. In order to reach this goal, numerical models of an acoustic package including periodic patterns are implemented using the finite element method and the Transfer Matrix Method. Firstly, some of the proposed configurations are experimentally tested, providing a comparison and validation of the obtained numerical results. Afterwards, several configurations of inclusions are numerically studied, and incorporate hollow cylindrical inclusions, half-cut hollow cylindrical inclusions and cylindrical Helmholtz resonators. The improvements in terms of transmission loss, essentially brought by a periodicity peak, are evaluated under plane wave excitation with various incidence angles. The main novelties of the present work are represented by an experimental validation of the proposed acoustic meta-materials that were only numerically studied in previous works. The effect of the inclusion of a periodic pattern of Helmholtz resonators inside the foam core is also considered. The presented numerical results are also evaluated for different incidence angles of an exciting acoustic plane wave.

The evaluation of electrical circuits for adjusting sound transmission properties of piezoelectric metamaterials

In rods and beams, piezoelectric patches with external circuits have been extensively studied to dampen structural vibrations at the sound source. This work uses a large flat-layer type of piezoelectric acoustic metamaterial (AM) model for noise attenuation in the sound transmission stage rather than at the sound source. This could be directly implemented as a large space sound transmission barrier at the interface of diverse media including gas, liquid, and solid materials. The general analytical model to derive acoustic properties of the piezoelectric acoustic metamaterial is established by the equivalent transfer matrix approach for normal incidence waves. This has been validated numerically using the finite element method and experimentally in the solid medium propagation for the first time. Moreover, a parametric study of sound transmission properties in air, water, and steel is conducted by adjusting external circuit parameters, flat-layer structures, and piezoelectric materials. The findings demonstrate the ability to control sound resonance frequency and bandwidth through the propagation process over a wide range using external circuit parameters alone. This endows the piezoelectric acoustic metamaterial with great versatility relative to conventional, fixed structure, metamaterials used as sound barriers at the interface of diverse media. In addition, the size of the piezoelectric AM can reach a deeply sub-wavelength level, less than 10−3 of the resonance wavelength in both water and solid media, which goes far beyond the wavelength-to-thickness ratio of classical acoustic metamaterials. The layer-type piezoelectric AM thus shows excellent performance in tunability and compactness for space-sensitive applications as well as great potential in combining metamaterials with electronic control.

Sound Transmission Properties of a Porous Meta-Material with Periodically Embedded Helmholtz Resonators

Sound Transmission Properties of a Porous Meta-Material with Periodically Embedded Helmholtz Resonators

Sound transmission of active elastic wave metamaterial with double locally resonant substructures surrounded by external mean flow

The elastic wave metamaterial with active feedback control is presented to discuss its dynamic effective parameter and sound transmission properties. Both studies are initiated from the local resonance with the active feedback control and dynamic structural response. The acoustic-structure coupling of the metamaterial with resonators and orthogonal stiffeners are analyzed with effects of the external mean flow. Different analytical methods are used to derive the effective mass density and sound transmission loss (STL) of the elastic wave metamaterial. The effective density is obtained by the dynamic effective medium method firstly. And the second one applies the spatial harmonic expansion method with the principle of virtual work for the STL based on the Bloch–Floquet theorem and Poisson summations. The effective mass density shows frequency-dependent properties and appears positive and negative values in a certain frequency region simultaneously. This research also illustrates both characteristics can be tuned by the active feedback control with the acceleration and displacement feedback control actions. Numerical results of coupled structures show that the changes of transmission characteristics in the certain frequency region are consistent with the effective mass density properties of uncoupled unit cell structure. In addition, influences of the lattice constants, incident angles and Mach number on the STL are illustrated and discussed.

Free vibration and sound transmission properties of beetle elytron plate: structural parametric analysis

Honeycomb plate (HP), which is a high-strength and lightweight structure, has good vibration characteristics, while beetle elytron plate (BEP) has better mechanical properties. To promote the engineering application of BEPs, the vibration and sound transmission characteristics of aluminium BEPs were investigated in this paper with HP as the comparison object. This paper investigated the effects of the number of trabeculae, the ratio of length and width, skin thickness, core height and core thickness on the first 4 frequencies using finite element method. The results show that (1) the vibration characteristic of BEP is optimal when the number of trabeculae is 6, and its 3rd and 4th modes show mixed mode, i.e., torsion-bending or bending-torsion mode. (2) The frequencies of BEPs are generally lower than those of HPs. Compared with HPs, the ratio of length and width and core thickness have a smaller influence on the mode shapes of BEPs, and the core height has a smaller influence on BEPs’ frequencies. When the skin thickness is small, increasing the thickness can effectively change the natural frequencies of BEPs and HPs. (3) Considering the common frequencies of four applications (aircrafts, unmanned aerial vehicles, high-speed trains and automobiles) of sandwich plates, the effects of the abovementioned parameters including the ratio of length and width, skin thickness, core height and core thickness are analysed. (4) Combined with the theoretical calculation formula, the effect of the above structural parameters on the sound transmission characteristic is explored using the index of sound transmission loss, and targeted recommendations are given. This paper progresses the application in engineering.

A Partial Ossicular Replacement Prosthesis With a Concentric Ball Joint in the Headplate.

In passive middle ear prosthetics, rigid implants have proven successful in reconstructing the ossicular chain. However, these cannot fully replicate the physiology of the ossicular chain. Pressure fluctuations cause high stresses in rigid passive prostheses, which can result in dislocation, protrusion, and pre-tension in the annular ligament resulting in unsatisfactory hearing results. In collaboration with MED-EL, we developed a new passive middle ear prosthesis that features a balanced, centered ball joint between the headplate and shaft of the prosthesis. We compared the sound transmission properties of this new prosthesis with those of a standard rigid prosthesis. Using Laser-Doppler-Vibrometry, we measured the sound-induced velocity of the stapes footplate relative to a given acoustic stimulus. The new prosthesis showed equivalent sound transmission characteristics compared to the rigid prosthesis, whereas retaining the ability to compensate for pressure fluctuations due to its ball joint. This ensures good transmission properties even during displacements of the tympanic membrane. This development is a further step toward a physiological reconstruction of the ossicular chain. NA Laryngoscope, 133:1717-1721, 2023.

Experimental evaluation of pseudo-sound in a parametric array.

Parametric arrays have been widely investigated due to their high directivity in the low-frequency region when measuring the acoustic characteristics of materials, such as sound transmission and reflection properties, in the limited space of acoustic water tanks. Because a parametric array utilizes nonlinear interaction across the frequency components, nonlinear phenomena arise in both the acoustic medium and the hydrophone system. The unwanted nonlinear sound generated in the hydrophone and instrumentation is termed pseudo-sound. This study devised an experiment to measure the pseudo-sound without a truncator to assess the effect of the pseudo-sound in the near field. In order to separately measure the pseudo-sound, the hydrophone was placed close to the projector so that the pseudo-sound was dominantly generated. The method is based on the fact that, if we can suppress a parametric signal by minimizing the propagation path length in the medium, the resulting measured signal can be attributed to the pseudo-sound. The resultant signal levels were matched to the levels at corresponding distances based on the primary levels of a (separately conducted) distance-varying experiment. Finally, the suitability of the proposed technique was evaluated by comparing its results with the pseudo-sound levels measured using a truncator.

Experimental measurement for assessing pseudo-sound effect in parametric array

The parametric array that generates narrow beams at low frequencies with apertures shorter than the wavelength and has been widely investigated when measuring the acoustic characteristics of materials, such as sound transmission and reflection properties. Because the parametric array utilizes nonlinear interaction across the frequency components, nonlinear phenomena arise in both the acoustic medium and the hydrophone. The unwanted nonlinear sound generated in the hydrophone and instrumentation is termed pseudo-sound. This work devised an experiment to measure the pseudo-sound for the purpose of isolating the “real” nonlinear difference frequency sound from the total nonlinear sound. Experimental results were validated by comparing its results with the pseudo-sound measured with a truncator (i.e., acoustic filter) to identify hydrophone nonlinearity.

The impact of tympanic membrane perforations on middle ear transfer function

PurposeInjury or inflammation of the middle ear often results in the persistent tympanic membrane (TM) perforations, leading to conductive hearing loss (HL). However, in some cases the magnitude of HL exceeds that attributable by the TM perforation alone. The aim of the study is to better understand the effects of location and size of TM perforations on the sound transmission properties of the middle ear.MethodsThe middle ear transfer functions (METF) of six human temporal bones (TB) were compared before and after perforating the TM at different locations (anterior or posterior lower quadrant) and to different degrees (1 mm, ¼ of the TM, ½ of the TM, and full ablation). The sound-induced velocity of the stapes footplate was measured using single-point laser-Doppler-vibrometry (LDV). The METF were correlated with a Finite Element (FE) model of the middle ear, in which similar alterations were simulated.ResultsThe measured and calculated METF showed frequency and perforation size dependent losses at all perforation locations. Starting at low frequencies, the loss expanded to higher frequencies with increased perforation size. In direct comparison, posterior TM perforations affected the transmission properties to a larger degree than anterior perforations. The asymmetry of the TM causes the malleus-incus complex to rotate and results in larger deflections in the posterior TM quadrants than in the anterior TM quadrants. Simulations in the FE model with a sealed cavity show that small perforations lead to a decrease in TM rigidity and thus to an increase in oscillation amplitude of the TM mainly above 1 kHz.ConclusionSize and location of TM perforations have a characteristic influence on the METF. The correlation of the experimental LDV measurements with an FE model contributes to a better understanding of the pathologic mechanisms of middle-ear diseases. If small perforations with significant HL are observed in daily clinical practice, additional middle ear pathologies should be considered. Further investigations on the loss of TM pretension due to perforations may be informative.

Sound Transmission Comparisons of Active Elastic Wave Metamaterial Immersed in External Mean Flow

Using the active feedback control system on the elastic wave metamaterial, this research concentrates on the sound transmission with the dynamic effective model. The metamaterial is subjected to an incident pressure and immersed in the external mean flow. The elastic wave metamaterial consists of double plates and the upper and lower four-link mechanisms are attached inside. The vertical resonator is attached by the active feedback control system and connected with two four-link mechanisms. Based on the dynamic equivalent method, the metamaterial is equivalent as a single-layer plate by the dynamic effective parameter. With the coupling between the fluid and structure, the expression of the sound transmission loss (STL) is derived. This research shows the influence of effective mass density on sound transmission properties, and the STL in both modes can be tuned by the acceleration and displacement feedback constants. In addition, the dynamic response and the STL are also changed obviously by different values of structural damping, incident angle (i.e., the elevation and azimuth angles) and Mach number of the external fluid with the mean flow property. The results for sound transmission by two methods are compared, i.e., the virtual work principle for double plates and the dynamic equivalent method corresponding to a single one. This paper is expected to be helpful for understanding the sound transmission properties of both pure single- and double-plate models.

Vibration and sound properties of metamaterial sandwich panels with periodically attached resonators: Simulation and experiment study

The vibration and sound properties of a type of metamaterial sandwich panels are investigated in this paper. The metamaterial sandwich panels consisting of a host sandwich panel and periodically attached resonant units are designed. Both the panels with and without damping are considered. Via the comparison of metamaterial and bare panels, the effects of the periodic design on wave propagation, vibration, sound radiation and sound transmission properties are analysed and compared numerically. The reduction on the vibration and sound is studied. The numerical results indicate that the vibration, sound radiation and sound transmission are significantly reduced over a wide frequency range. The reduction is obviously larger than that obtained only by increasing the mass. In addition, the experiment specimens of bare and metamaterial sandwich panels are designed. The vibration and sound properties of them are tested and compared. According to the experimental results, the reduction is also observed in a wide frequency range. The simulation results and corresponding analysis are verified. Further, the effects of structural parameters of sandwich panels on the reduction of vibration and sound properties from periodic design are investigated. Several typical cases are analysed concretely. The reasons for the reduction and other effects on the vibration and sound properties from periodic design are analysed. For the panels with various parameter settings, a nice reduction of vibration and sound is generated also form periodic design; on the other hand, the reduction characteristics are changed.

Nitinol in Passive Ossicular Reconstruction-First Results From Temporal Bone Experiments.

Nitinol is a suitable material for passive middle ear prosthesis. In modern ear microsurgery, the restitution of hearing is tremendously important. In passive ossicular reconstruction, rigid alloplastic materials are widespread in use. However, rigid prostheses fail to adapt to atmospheric pressure changes. We describe the use of the super-elastic material nitinol in passive ossicular reconstruction to overcome this limitation. Together with an industrial partner, we developed a nitinol clip prosthesis equipped with a flexible prosthesis headplate. The new prosthesis was evaluated for flexibility and its sound transmission properties were compared with standard clip prostheses. For this purpose, the sound-induced acceleration of the stapes footplate was measured by laser-doppler vibrometry in temporal bones. Furthermore, the flexibility of the prosthesis plate was tested in a load-cell experiment. On average, the pure tone transmission characteristics of the nitinol prosthesis is statistically not distinguishable from standard titanium clip prostheses. The tests in the load cell confirmed the flexibility of the prosthesis. Any measured prosthesis returns to its original state after deformation. The newly developed nitinol clip prosthesis shows similar sound transmission properties in comparison to established prostheses with high flexibility indicating a step forward to a physiological ossicular chain reconstruction.

Tasorakenteiden ilmaääneneristävyyden arvioinnista

Artikkelissa tarkastellaan rakenteiden ilmaääneneristävyyden laskennalliseen mää­rit­tämiseen liittyviä kysymyksiä rakennusinsinöörin näkökulmasta. Erityisesti tarkastellaan laat­to­ja ja niistä koostuvia kerroksellisia tasorakenteita. Johdetaan esiteltyjen yhtälöiden analyyttisia rat­kaisuja ja demonstroidaan niitä käyttäen ääneneristävyyden laskennallista määrittämistä.

An investigation of the sound transmission loss for elastomeric vehicle door seals

The reduction of noise in vehicle body components is one of the main themes of the acoustics profession for vehicles. At high vehicle cruising speeds, the predominant contributor to wind noise occurs via the sealing system. Accordingly, understanding the sound transmission loss (STL) through a vehicle’s sealing system is an essential engineering context for reducing interior wind noise levels. The STL through a sealing system is affected by the material, cross-section design of the profiles, overall design of the sealing system and the dynamics of the system. In this study, a brief method is described to explore the acoustic properties of vehicle door seals. Material characterization is performed both for hyperelastic and viscoelastic regions and realized using mechanical tests. The method described for studying the STL covers an analytical approach, numerical analysis, and, finally, experimental validations for several door seals, which form a major part of the sealing system located around a passenger door (closing all direct noise paths and attenuating noise from the body). Finally, the effects of fundamental parameters on the sound transmission properties are presented.