Transmission Loss Measurements Research Articles

A basic study on laboratory measurement of oblique-incidence sound transmission loss of building elements

Understanding the sound insulation performance of building elements under oblique incidence conditions is occasionally required for assessing the indoor sound environment of high-rise buildings that face roads or railways. In order to gain knowledge toward establishing a laboratory measurement method for oblique incident sound transmission loss, a measurement system was set up in a coupled reverberation room and anechoic chamber with a movable sound source. For verification of the system, a pilot measurement was carried out with a large glass pane, while the experimental set-up was also numerically simulated by FEM. In the experimental results, transmission loss was observed to depend on incidence angle in correlation with the coincidence effect, roughly obeying theory. However, it was found that the incident power estimated from the surface sound pressure on the specimen differs somewhat from that estimated using loudspeaker directivity in a free field. This discrepancy is thought due to edge diffraction from the beading around the glass pane, and this was confirmed by the numerical results. Further, this edge diffraction may also have caused the observed coincidence effect under normal incidence.

Effectiveness of Noise Barriers Based on Waste Materials in Case Study of Residential Noise Due to Double-Track Railways

The noise pollution in residential areas adjacent to double-track railways can significantly disturb the comfort and well-being of residents. The noise originates from passing trains on these double-track railways. The research problem aims to compare the noise levels in the residential area with the standard noise threshold and evaluate the effectiveness of a noise barriers based on waste material called sustainable noise barrier. The effectiveness of reducing noise levels for communities residing near the dual railway lines. The sustainable noise barrier is constructed using waste cardboard and sawdust as sound absorbers for reducing noise from passing trains. The objective of the research is to analyze the noise levels in the residential areas near the dual railway lines, referring to the noise threshold value specified in Kep.MenLH No.48 of 1996, which is 55 dBA. Additionally, the research aims to assess the effectiveness of the sustainable noise barrier in mitigating noise pollution in these residential areas. The research employs a quantitative experimental method, following the SNI 8427 of 2017 standard for measuring residential noise pollution and determining the sustainable noise barrier's effectiveness using Insertion Loss (IL) and Sound Transmission Loss (STL) measurements in both laboratory-scale and existing conditions (alongside the double-track railways). The research findings indicate that the noise levels in residential areas adjacent to dual railway lines exceed the threshold value, reaching 78.08 dBA. However, the sustainable noise barrier proves to be effective in reducing noise pollution by 27 dB at a frequency of 1,000 Hz in the residential areas neighboring the double-track railways. This research suggests that limiting noise disturbances in residental areas bordering railway lines is one solution with noise barriers.

A Modeling Approach for Designing New Acoustic Materials

In this study, mathematical modeling design based on Sound Transmission Loss measurement results of new acoustic material samples with natural content was carried out. Using the test samples in question, transfer function of acoustic materials based on electronic filter circuit design and a transition design method for the production of new acoustic materials by utilizing the transfer function is presented. Based on the experimental results of the test samples, it is the most suitable low-pass filter structure for the proposed design. In this study, active Sallen-Key low-pass filter structure is preferred and used. Sound Transmission Losses in dB (decibels) of acoustic samples were obtained experimentally for 500, 1000, 2000 and 4000 Hz. fundamental frequencies in the literature. Based on these data, transfer function simulation suppression gain results were obtained in TINA-TI program, active filter circuit designed, and MATLAB program. When the other results were compared in the experimental results, it was seen that very close values were obtained. It has been demonstrated that the proposed method can be used effectively in the design and examination of new acoustic materials.

Lightweight soundproofing meta-panel for two separate broadband noises

We propose a lightweight soundproofing meta-panel, with a multi-scale lattice structure sandwiched between thin membranes, effectively suppressing two separate broadband noises. By adjusting the geometrical parameters, the meta-panel is designed to induce negative effective mass density and negative effective bulk modulus for two distinct target frequency bands: 100–500 Hz and 1000–1500 Hz, thereby achieving high transmission loss that outperforms the mass density law. A meta-panel sample is fabricated via 3D printing technology and we evaluate its sound insulation performance by measuring transmission loss and insertion loss in an impedance tube and an anechoic chamber. Experimental measurements show that the meta-panel can exhibit excellent insulation performance while being significantly lighter in weight (about 5%) compared to a steel plate, and furthermore, it effectively suppresses low-frequency road noise and high-frequency motor noise from an actual electric car.

An acoustic design project for final year engineering students using resonant arrays

This paper reviews the creation of a design course for mechanical engineering students at the University of Auckland. The primary objective of the course is to introduce students to the field of acoustics, teaching basic theoretical and experimental acoustics principles, together with product design and fabrication methods, in an engaging and educational manner. During the course, students were assigned the task of developing a noise reduction duct jacket that reduced sound propagation whilst allowing free airflow, all within specified dimensions. Students were required to create designs that attenuated a predefined sound spectrum, with both narrow-band and wide-band components. Over six weeks students developed their designs using mathematical modelling and fabricated their prototypes. The performance of their suppressors was assessed through sound pressure level and impedance tube transmission loss measurements. Students then modified their designs to maximise performance before final submission. Four-person teams produced a diverse range of implementations. The most successful designs achieved impressive performance with peak transmission loss up to 70dB, 2kHz bandwidths of 10 + dB transmission loss and a delta dBA reduction of 21.5 dB. Student feedback indicates a high level of satisfaction with the course, highlighting its effectiveness in imparting key knowledge and skills in acoustics engineering.

Influence of mesoscale meteorological observations on near shore excess attenuation prediction

This work focuses on numerical modeling of atmospheric sound propagation in a near-shore environment that is informed by concurrent meteorological observations. The atmospheric acoustic measurement layout places the source approximately 500 m from shore with one acoustic receiver array at the shoreline and a second acoustic receiver array approximately 350 m inland. The space between the shoreline and the inland receiver array consists of highly uniform marsh grass vegetation. The concurrent meteorological observations include high resolution temperature profiling at two locations (one over land and one over water) along with scanning Doppler LIDAR wind profiling measurements in the source-to-receiver direction. These meteorological measurements inform the input parameters used in a parabolic equation solver. The numerical predictions are compared to the measured transmission loss values to evaluate model sensitivity to input parameters.

Effect of Nylon Membrane Thickness on the Value of Sound Transmission Loss as an Alternative Insulation Material

Measurements of sound transmission loss have been successfully carried out on various thicknesses of nylon membrane as an absorbing material. Nylon membrane were prepared using hydrogen chloride (HCl) and acetyl aceton in the casting solution by phase inversion methods. Nylon membrane with different thickness used in this reseach were 1 mm, 2 mm, 3 mm, 4 mm, and 5 mm. Measurement of sound transmission loss was carried out using a reverberation chamber with sound frequencies of 125 Hz, 250 Hz, 500 Hz, 1000 Hz, 2000 Hz, 4000 Hz. The results show that, with the increase of thickness of nylon membrane, sound transmission loss of nylon membran was improved. The sound transmission loss of nylon membrane with thickness of 4 mm is the best, whose sound trasnmission loss was up to 46.39 dB at 4000 Hz. This nylon membrane is suitable for lightweight sound barriers and is promising and worthy of further study.

Acoustic Attenuation Performance Analysis and Optimisation of Expansion Chamber Coupled Micro-perforated Cylindrical Panel Using Response Surface Method

This paper describes boundary element method (BEM), experimental and optimization studies conducted to understand the potential of expansion tube coupled micro-perforated cylindrical panel (MPCP) to enhance the acoustic attenuation for in-duct noise control issues. Due to complex structure of the MPCP and for the correct prediction of acoustic attenuation, BEM is adopted on the basis of PLM Simcenter 3D software to compute the sound transmission loss (TL). As the MPCP is cylindrical in-shape with numbers of sub-milimeter holes, additive manufacturing based 3D printing was utilized for the model prototyping to reduce current design limitation and enabled fast fabrication. The TL measurement based two-load method is adopted for modal validation. Subsequently, a parametric studies of the MPCP concerning the perforation hole diameter, perforation ratio and depth of air space are carried out to investigate the acoustical performance. Optimization via response surface method (RSM) is used as it allows evaluating the effects of multiple parameters as required in this study. The model validation result shows that the error between the BEM and and measured values is relatively small and show a good agreement. The R-square value is 0.89. The finding from parametric study shows that a widen peak attenuation can be achieve by reducing the perforation hole diameter and one way to increase the transmission loss amplitude is by increasing the air cavity depth. Finally, the optimized MPCP model was adopted to the commercial vacuum cleaner for the verification. The sound pressure level (SPL) of the vacuum cleaner is significantly attenuated within the objective frequency of 1.7 kHz and its A-weighted SPL is reduced by 1.8 dB.

Transmission loss measurement of recycled granular material using wave decomposition by impulse response extraction based on deconvolution

A simplified method for measuring transmission loss with a single fixed microphone inside an impedance tube is proposed. The separation of the incident wave from the reflected wave is achieved by deconvolving the loudspeaker driver voltage signal with the microphone signal to extract the impulse response. Random noise and a sinusoidal sweep signal were used as excitation signals for extraction of the impulse response, and two deconvolution methods were employed: linear deconvolution based on the adaptive LMS algorithm and simple spectral division. To avoid the overlap of incident and reflected pulses, a long impedance tube was used. Using a long impedance tube eliminates the need for an anechoic tube termination and the need to calibrate microphones. It is found that a reflective tube termination provides more accurate results compared to an approximately anechoic termination. The approximately anechoic termination shortens the available time window of the reflected pulse because it reflects some of the low-frequency sound. The standard deviation of the results and the dynamic range of the proposed method were determined experimentally. The applicability of the new method was tested on samples of unconsolidated granular material recycled from construction sites. The measured transmission losses of the different granular fractions were compared with a theoretical model for transmission losses at low frequencies. Samples consisting of smaller granule fractions were found to have surprisingly high transmission loss values. The design of the extended vertical impedance tube in combination with the proposed method is cost effective, speeds up the measurement procedure and provides reliable results.

A Lightweight Multilayer Dissipative Material with High Acoustic Performance

A multilayer acoustic treatment constructed of fibrous acoustic absorption material combined with dissipative acoustic material achieves a low profile and is lightweight and multi-functional, with properties that are desirable for NVH (noise, vibration, and harshness) treatments. The dissipative material consists of microfibers and acoustically active particles; this material was introduced in the last SAE NVH conference: A Novel Dissipative Acoustic Material [1]. In this paper, the acoustic performance of the multilayer treatment was evaluated by using random incidence absorption and transmission loss measurements, as well as in-vehicle experiments. Absorption and transmission loss were additionally modeled using the transmission matrix method (TMM). In the in-vehicle test, an OEM wheelhouse liner with Trim, for an SUV, was evaluated utilizing this new multilayer 3M treatment.

Characterizing elastic parameters of isotropic thin plates using impedance tube and transmission loss measurements: a numerical inverse method

Thin plates are widely used in various engineering applications, including aerospace, automotive, and construction industries. The mechanical properties of these plates, such as Young's modulus, Poisson's ratio, and structural damping, are essential in determining their acoustic performance. While there are various methods for measuring these properties individually or simultaneously, accurately obtaining them can be difficult due to the thin plate's delicate structure and the need for high precision and sensitive equipment. In this paper, we present a numerical inverse method for characterizing the elastic parameters of isotropic thin plates using transmission loss measurements obtained from an impedance tube and clamped circular specimen. The proposed method is compared to the Oberst beam technique (ASTM E756-05), and demonstrated through several examples ultimately allowing for the prediction of diffused field transmission loss obtained through intensity measurements in a small reverberant room.

Enhanced sound insulation performance by a staggered phononic crystal with fins

Noise is associated with physical and mental health and well-being. Sound insulation materials allowing ventilation are in demand. A staggered phononic crystal with fins (SPCF), which is a combination of staggered structures and fins, is proposed to improve the sound insulation performance and meanwhile allow ventilation. The maximum peak value (5.2 dB) of the experimentally measured transmission loss of the SPCF is higher than the peak values of the reference samples. The improved sound insulation performance of the SPCF compared with reference samples is attributed to the frequency shift effect and structural coupling effect. The dissipated energy caused by the thermal effect in the SPCF accounts for about 20 %-26 % of the total dissipated energy, suggesting that the thermal effect must be considered to obtain an accurate total dissipated energy. The SPCF sets up a new strategy for the next-generation sound insulation materials allowing ventilation.

Tunable bandgaps and acoustic characteristics of perforated Miura-ori phononic structures

In this study, we introduce a novel perforated Miura-ori phononic structure (PMPS) and investigate the tunability of complete bandgaps or partial bandgaps in specific directions. The validity of the bandgaps was verified against the simulation and experimental measurement of the sound transmission loss of a three-dimensional printed Miura-ori panel. The results reveal that PMPS with different design parameters demonstrates extensive bandgap tunability during deployments and folds. The potential applications of PMPS, such as programmable acoustic waveguides, were also demonstrated. Lightweight PMPSs offer an attractive alternative for designing tunable, programmable and reconfigurable acoustic structures, such as sound waveguides, sound barriers, and broadband wave tailors.

Acoustic properties of glued laminated bamboo and spruce-pine-fir

Noise pollution has become a worldwide issue, which has a negative effect on human health. The sound reduction index and absorption coefficient of glued laminated bamboo (glubam) and spruce-pine-fir (SPF) were firstly measured in this study by using the impedance tube method. The effect of moisture content on the acoustic performance of these materials was also investigated. Experimental results revealed that for thick-strip glubam and SPF, the higher moisture content, the higher sound reduction index but lower sound absorption coefficient. However, moisture content does not have an obvious effect on acoustic properties of thin-strip glubam. By comparing with other materials, it can be found that glubam and SPF have relatively high normal-incidence transmission loss but low absorption coefficient and noise reduction coefficient. Glubam shows the similar but even better acoustic insulation performance than SPF, which confirms the possibility of using glubam as an alternative of wood materials. Moreover, a finite element model was built up to simulate the measurement of sound transmission loss in an impedance tube. Some parametric studies were then conducted using the finite element model to prove the effectiveness of increasing thickness, using composites and double-layer panels on improving the soundproof performance of materials.

Atmospheric acoustic propagation modeling using heterogeneous wind profiles along the acoustic path

This work presents atmospheric sound propagation predictions using a parabolic equation solver that accounts for heterogeneous wind profile distribution along the acoustic path. Transmission loss predictions using both homogeneous and heterogeneous wind speeds information are compared with data. A three-dimensional scanning Doppler LIDAR wind profiler captures real-time wind speed gradients at many locations along the acoustic propagation path providing the heterogeneous wind speed profiles. The wind measurements are concurrent with a pitch catch transmission loss measurements. A long-range acoustic device on an anchored pontoon sends known chirp sequences to a seven-channel receiver array at the water’s edge at ranges up to approximately one kilometer. Additional synchronized meteorological observations include temperature, humidity, and wind measured with anemometers. Key differences in model results are highlighted and an assessment of the value of the computational cost is presented.

Finite Element Approach for Three-Dimensional Linearized Potential Equation with Application to Muffler Acoustic Attenuation Prediction

In this paper, a three-dimensional finite element method for solving the linearized potential equation (LPE) is implemented to predict the acoustic attenuation performance of mufflers in the presence of nonuniform flow. For accurate physical representations, the porous material is modeled as equivalent fluid with complex speed of sound and density while the background mean flow in fluid domain is captured by solving Reynolds-averaged Navier–Stokes equations. The treatment details for boundary integrals at different boundary conditions and expressions for transmission loss are presented. Good agreements of predicted and measured transmission loss of two reactive and a hybrid mufflers validated the present approach. Finally, the convective effect of nonuniform flow on the acoustic attenuation behavior of the hybrid muffler is examined numerically in detail.

Complete acoustic bandgaps in a three-dimensional phononic metamaterial with simple cubic arrangement

In this work, a phononic metamaterial that could be a reliable solution for several sound attenuation applications is examined numerically and experimentally. The proposed structure consists of a spherical shell connected with cylindrical conduits in a simple cubic arrangement. Numerical calculations, using the finite element method, and experimental measurements of the sound transmission loss were performed, providing significant evidence of the applicability of the proposed metamaterial in sound attenuation applications. For the validation of the complete acoustic bandgaps by the structure, the research was expanded to the examination of all high symmetry spatial directions. The results for all the examined spatial directions provided wide acoustic bandgaps, thus validating the evidence of complete acoustic bandgaps by the structure over a wide frequency range of the audio spectrum. Furthermore, the contribution of each part of the structure was separately analyzed, providing the physical insight for a deeper understanding of the response of the structure and the principal mechanism of the bandgap formation. The findings of this research prove that the proposed metamaterial could be a functionable unit for efficient sound attenuation applications.

Extension of frequency range of the sixteen-microphone method in normal-incidence sound transmission loss measurement.

This study deals with development of a high-frequency measurement method of normal incidence sound transmission loss using acoustic impedance tube. On ordinary transfer-function method, measurable frequency of the method is limited by the diameter of the tube. Authors have developed 8 microphone method to measure normal incidence absorption coefficient. This technique lays 4 microphones on the same cross section and cancels rotational acoustic modes. This makes it possible to measure normal incidence absorption coefficient up to 3 times the upper frequency of the ordinary 2 microphone method. In this study, authors apply the same technique to normal incidence transmission loss measurement.

Micro Displacement Sensor With Cascaded Micro Fiber Sagnac Ring Based on Vernier Effect

A cascaded micro fiber Sagnac ring (MFSR) micro displacement sensor based on the Vernier effect is proposed and studied in this article. A single-mode optical fiber is wound into a ring with a diameter of about 10 cm, an MFSR is obtained by fused tapering in the winding area, and another MFSR with a slightly different coupling length is fabricated by the same process. The transmission spectrum of each Sagnac ring is similar to the Vernier scale. The sensitivity of the sensor can be improved through the Vernier effect after the two rings are cascaded with single-mode fiber. The mode of MFSR is analyzed by using finite element analysis software. Its transmission spectrum is calculated through numerical simulation, and its micro displacement sensing characteristics are verified by experiments. Experimental results show that the micro displacement sensitivity of the sensor is as high as <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">${-{1.76} \,\,\text {nm}/\mu \text {m}}$ </tex-math></inline-formula> in the range of 0– <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$35~\mu \text{m}$ </tex-math></inline-formula> , and its resolution is <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">${{0.057} ~\mu \text {m}}$ </tex-math></inline-formula> . Compared with a single MFSR, the sensitivity is improved by 7.65 times, which is consistent with the simulation. The cascaded MFSR micro displacement sensor has the advantages of low transmission loss and high measurement sensitivity and has important application prospects in industrial production and micro displacement detection.

Prediction of sound transmission loss of hemispherical shell using statistical energy analysis and its experimental validation

The hemispherical shells are broadly used in many industries and applications such as aerospace, submarines, tanks, and architectural structures. Sound transmission loss prediction of such structures is essentially required during the design and assessment phases from the acoustic point of view. In the present paper, sound transmission loss of the hemispherical shell is predicted analytically and validated experimentally. The Statistical energy analysis (SEA) technique is employed to formulate an analytical model for computing the sound transmission loss of a hemispherical shell across a wide frequency range. The sound intensity experimental method was used to verify the proposed SEA formulation. The analytical predictions and the measured transmission loss were found to be in good agreement. Based on the proposed SEA model, the influence of design parameters such as the absorption coefficient, thickness, radius, and different materials on the transmission loss was investigated.