Transmission Loss Measurements Research Articles

Design and characterization of tabletop anechoic and sonication chambers

Access to anechoic chambers for acoustic testing can be an expensive and limited resource for acousticians. The purpose of this work was to develop small scale, portable anechoic and sonication chambers that could be used for rapid and simultaneous testing. Using consumer off the shelf (COTS) products, low cost anechoic and sonication chambers were designed and built. Upon completion the prototypes were characterized for their acoustic performance. Both the anechoic and sonication chambers were characterized by their ability reduce ambient noise. The characterization was completed by measuring transmission loss (TL) through the chamber walls. Second, the sonication chamber was tested for spatial sound pressure level (SPL) variation. The procedure for spatial testing inside the chamber included measuring SPL along a horizontal stage using mini microphones. The performance and characterization of these chambers will be presented and discussed.

Reduction in edge effects for small panels characterized by a parametric array source.

This study sought to explore effects of panel size on underwater acoustic transmission and reflection measurements made with a truncated parametric array source. The transmission loss (TL) and reflection loss spectra of aluminum panels of several different sizes were determined experimentally, and compared to predictions from plane wave theory in the 5-100 kHz frequency range. For the smallest panel size, there were significant discrepancies between experimental data and plane wave theory, which were attributed to contributions from edge-diffracted waves and interferences from the mounting fixture for the panel. For reflection measurements, the latter interference could be corrected for in part by measurement of the reflected signal from the sample holder (with no panel present), and subtracting this signal from reference and test panel waveforms. In order to reduce the contributions from edge diffracted waves in TL measurements, an alternative panel mounting system was investigated, which involved surrounding the panel in a reflective baffle. There was a significant improvement in agreement of experimental TL spectra with plane wave theory for the smallest aluminum panel when the baffle mounting arrangement was used.

Characterizing the thermal and mechanical properties and improvement in sound insulation performance of magnetite containing nonwovens depending on coating conditions

The scope of this work consists in studying the effects of different processing parameters such as magnetite grinding, magnetite loading amount, type of coating polymer and also sound frequency on the sound insulation property of layered nonwoven structures. Thermal stability and mechanical properties were also investigated. To achieve this goal, nonwoven fabrics were coated with styrene butadiene copolymer latex and ethylene vinyl acetate polymers by using raw and ground magnetite in three different amounts, i.e., 100, 200 and 400 g/m2. Sound transmission loss measurements were performed on the samples using an impedance tube equipped with four microphones. Independent of the coating polymer, addition of magnetite improved thermal stability and mechanical properties. But, sound insulation property was substantially changed depending on the coating polymer. Magnetite incorporation provided noticeable improvements in the ethylene vinyl acetate coated samples (increment values of 3–16 dB), while the effect of magnetite usage was limited in the latex coated samples (0.1–2.9 dB).

Transmission loss measurements of plastic scintillating optical fibres

The wavelength dependent attenuation spectra of a range of commercially available and in-house fabricated scintillating polymer optical fibres have been measured using cut-back and side induced fluorescence techniques. The fibre transmission loss was found to be dependent on the scintillator formulation, core size and cladding, the effects of which are discussed in relation to various intrinsic and extrinsic loss sources.

Speed of sound and geo-alpha in clayey silt derived from concurrent inversion of geo and bio-acoustic parameters from transmission loss data and co-located chirp sonar measurements

Application of the concurrent geo and bio-acoustic inversion method (Diachok and Wales, 2005) to broadband (0.3–5 kHz) transmission loss (TL) measurements, and co-located normal incidence chirp sonar measurements provided measures of geo-acoustic properties of clayey-silt in the Santa Barbara Channel. Inversion calculations assumed that the geological environment may be characterized by the interfacial sound speed, unconsolidated layer thickness, sound speed gradient, g, and geo-alpha, αG; and that the biological environment may be characterized by the layer depth, layer thickness, and bio-alpha (attenuation coefficient within the layer). Co-located cores provided ground truth; echo sounder and trawl measurements provided biological truth. Both the concurrent inversion and the chirp-based methods yielded approximately the same value of g, 6.5/s, in the top 9 m thick layer of clayey-silt. The value of αG, based on TL measurements, was quite low, approximately 0.02 dB/λ, in good agreement with Holland and Dosso’s (2013) only previously reported in-situ estimate of geo-alpha in silty-clay in this frequency-depth range. These results have important implications for estimation of geo parameters from TL measurements in biologically intense environments. Refinements to envisioned follow-on experiments will be discussed. [This research was supported by the Office of Naval Research Ocean Acoustics Program.]Application of the concurrent geo and bio-acoustic inversion method (Diachok and Wales, 2005) to broadband (0.3–5 kHz) transmission loss (TL) measurements, and co-located normal incidence chirp sonar measurements provided measures of geo-acoustic properties of clayey-silt in the Santa Barbara Channel. Inversion calculations assumed that the geological environment may be characterized by the interfacial sound speed, unconsolidated layer thickness, sound speed gradient, g, and geo-alpha, αG; and that the biological environment may be characterized by the layer depth, layer thickness, and bio-alpha (attenuation coefficient within the layer). Co-located cores provided ground truth; echo sounder and trawl measurements provided biological truth. Both the concurrent inversion and the chirp-based methods yielded approximately the same value of g, 6.5/s, in the top 9 m thick layer of clayey-silt. The value of αG, based on TL measurements, was quite low, approximately 0.02 dB/λ, in good agreement with Holland and D...

Measuring with noise? We can do better!

It has long been established that correlation-based measurement techniques, using, e.g., maximum length sequences and swept sines, outperform classical methods based on random Gaussian noise. Among the advantages of these modern techniques are better rejection of background noise and reduced measurement duration to achieve similar or better precision. These advantages are especially interesting in room and building acoustics, where many measurement positions typically have to be covered and background noise is often an issue, especially when measuring sound transmission loss or velocity level differences. Unfortunately, there is currently no provision in the ASTM standards on room and building acoustics that would allow the use of these modern measurement methods. To demonstrate the advantages of these methods, this contribution will present an example of measurements of the apparent sound transmission loss, i.e., measurements of sound pressure level differences and reverberation times. In addition to the standardized measurements according to ASTM E336, all measurements were repeated with maximum length sequences and swept sines. The results will be compared and the advantages of the modern techniques will be highlighted.

Inferring low-frequency compressional sound speed and attenuation in muddy sediments from long-range broadband sound propagation

While researchers have successfully applied many geo-acoustic inversion methods, involving normal mode analysis or matched field processing, to invert seabed parameters in sandy bottoms, inferring low-frequency compressional sound speed and attenuation in mud is still a challenging problem, especially for a marine sediment where a mud layer overlies a sandy bottom. Recent studies show that there is an ambiguity between the low-frequency attenuation of mud and sand in three different inversion algorithms based on (1) modal amplitude, (2) transmission loss, and (3) spatial coherence measurements [JASA 143, 1798 (2018)]. An increase (decrease) of mud attenuation can be compensated by decreasing (increasing) the attenuation in the sandy basement. In this paper, an inversion method combining these three inversion algorithms and statistical inference techniques (e.g., Bayesian-Maximum Entropy, [JASA 138, 3563–3575 (2015)]) is utilized to analyze the long-range broadband acoustic signals measured by several vertical and horizontal line arrays during the Seabed Characterization Experiment 2017 conducted in the New England Mud Patch. Reliable estimates of the low-frequency mud properties are obtained by removing the ambiguity. Finally, the inverted results are compared with historical experimental data and theoretical predictions. [Work supported by ONR Ocean Acoustics.]While researchers have successfully applied many geo-acoustic inversion methods, involving normal mode analysis or matched field processing, to invert seabed parameters in sandy bottoms, inferring low-frequency compressional sound speed and attenuation in mud is still a challenging problem, especially for a marine sediment where a mud layer overlies a sandy bottom. Recent studies show that there is an ambiguity between the low-frequency attenuation of mud and sand in three different inversion algorithms based on (1) modal amplitude, (2) transmission loss, and (3) spatial coherence measurements [JASA 143, 1798 (2018)]. An increase (decrease) of mud attenuation can be compensated by decreasing (increasing) the attenuation in the sandy basement. In this paper, an inversion method combining these three inversion algorithms and statistical inference techniques (e.g., Bayesian-Maximum Entropy, [JASA 138, 3563–3575 (2015)]) is utilized to analyze the long-range broadband acoustic signals measured by several vert...

Variability of target echo and clutter in the 2013 Target and Reverberation Experiment

The Target and Reverberation Experiment was conducted in the Gulf of Mexico, off Panama City, Florida. Reverberation, noise, and target echo measurements were carried out for more than a month during April and May 2013, using a fixed source and fixed horizontal array receiver deployed in about 20 m of water. To support modeling efforts, a considerable number of ancillary environmental and transmission loss measurements were made. Various pulses in the 1.8–3.6 kHz frequency band were transmitted day and night, and have produced a rich data set. Initial results by various authors were published in the recent TREX13 Special Issue of the IEEE Journal of Oceanic Engineering. This work extends the analysis, concentrating on the variability of the echoes from various targets: a vertical hose, vertical arrays, a towed echo repeater, the hull of the towing ship, and other persistent bottom scatters, such as shipwrecks. In addition to the ping-to-ping variability of the echoes there are consistent trends, which are not understood, though probably due to oceanographic effects. An attempt will be made to relate the echo variability to measured and modeled reverberation and transmission loss. [Work supported by ONR, Ocean Acoustics, Code 22.]

Temporal variability of propagation and reverberation during TREX13

During the Target and Reverberation Experiment in 2013, a bottom-mounted, mid-frequency source and horizontal line array were deployed on the seafloor to measure reverberation over the course of the experiment. Extending from the source and parallel to shore was the “main reverberation track,” a 7-km long and 1.5 km wide region where a majority of the acoustic and environmental measurements were made. Along this track, two vertical line arrays were deployed to continuously collect propagation data. The combination of the HLA and VLAs made it possible to make contemporaneous measurements of both transmission loss (TL) and reverberation level (RL) over a 3-week timespan. During this time, a storm passed through the site and the variability in the TL is found to be driven by different mechanisms. Prior to the storm, the variability was primarily driven by changes in the sound speed profile; after the storm, the water was well-mixed and the variability was a steady decay of TL while the rough sea surface decayed. This talk examines the variability in TL during these time periods and the associated changes in the measured RL. [Work supported by ONR.]

Assessment of the temporal and spatial dependence of reverberation mechanisms for KOREX-17

Mid-frequency reverberation data were obtained over a 9-day period off Geoje Island, Republic of Korea, complemented by transmission loss and backscatter measurements. The reverberation data were collected using the Autonomous Reverberation Measurement System (ARMS), a benthic lander with a source and receive array mounted on a rotation stage in order to collect reverberation data as a function of bearing angle. The ARMS was repeatedly deployed in roughly the same location over the course of the experiment. The surficial sediments close to the ARMS are known to be composed primarily of mud with occasional rock outcrops. Beyond a range of 2 km, the sediment composition is uncertain and a geoacoustic measurement survey has been planned to collect additional data in this region. Using contemporaneous measurements of the sea surface directional wave spectrum and the currently limited geoacoustic data, modeling is used to estimate the relative importance of sea bottom and surface reverberation. [Work supported by of the Office of Naval Research.]

Searching for the FishOASIS: Using passive acoustics and optical imaging to identify a chorusing species of fish

Marine protected areas have been established off the California coast to ensure the persistence and resiliency of the marine ecosystems found here. Kelp forest habitats, in particular, support a diverse assemblage of fishes, many of which produce sound. From May to September 2017, a low-frequency (325–545 Hz) chorus was recorded near the kelp forests off La Jolla, California. The chorus begins each day approximately a half-hour before sunset and lasts for about 3–4 hours. During these times, spectral levels around 400 Hz increased by approximately 30 dB over, although there is significant day-to-day variability in received level. To identify the chorusing fish species, a Fish Optical and passive Acoustic Sensor Identification System (FishOASIS) was developed, consisting of a four-channel SoundTrap ST4300 acoustic recorder and four Sony α7s II cameras. Frequency-domain beamforming was used on signals recorded by the four-element, 20-m aperture, tetrahedral-shaped array to estimate the location of the fish chorus, which appears to be fairly fixed over time. The chorus also was used as a source of opportunity to measure transmission loss in order to determine whether kelp forests can act as acoustic refuges by sufficiently attenuating chorusing sounds. [Research supported by California Sea Grant and NSERC Postgraduate Scholarship-Doctoral.]

Evaluation of the bias error of transmission tube measurements of normal-incidence sound transmission loss using narrow tube reference elements.

The bias errors of transmission tube measurements are evaluated using an empty test tube condition, implying full sound transmission, normal-incidence sound transmission loss (nSTL) = 0, and two narrow tube elements presenting a theoretically known sound transmission loss (which includes modeling of thermo-viscous losses), varying in frequency around moderate non-zero nSTL levels, and approaching insulation levels more typically found in applications. Results show that the different reference conditions are virtually equivalent in presenting negligible amounts of bias error within the corresponding measurement uncertainties, typically within ±1 dB, in the full 6000 Hz measurement frequency range in this particular case. Slight differences are evident only in the upper third of this range, from 4000 to 6000 Hz, in which bias errors for the narrow tube elements are found very slightly beyond the measurement uncertainties, suggesting the existence of additional sound loss mechanisms. Measurements of a typical insulating test sample are also presented for illustration of the possible non-significance of bias errors in practical cases.

Predicting the sound insulation of finite double-leaf walls with a flexible frame

With double-leaf wall systems such as plasterboard walls, a high sound insulation can potentially be achieved with a relatively low weight. The accurate sound transmission analysis of this type of wall is challenging since the leafs are usually coupled to a common frame, and since the finite dimensions play a role at lower frequencies. Existing analytical models for sound insulation prediction account for the deformation of the wall in an approximate way, while detailed numerical models are computationally very demanding. In this work, a sound insulation prediction model that achieves a high prediction accuracy at a low computational cost is developed. The wall components that display low geometrical complexity, such as the wall leafs and the cavity, are modelled in an analytical way. Sound absorbents in the cavity are modelled as equivalent fluids. The metal studs, which have a highly deformable cross section, are modelled in full detail with finite elements. The sound fields in the sending and receiving rooms are modelled as diffuse; they are rigorously coupled to the deterministic wall model by employing a hybrid deterministic-statistical energy analysis framework. With the resulting room-wall-room model, the airborne sound insulation is predicted for a range of double-leaf plasterboard walls with single, double and triple plating and with different cavity depths. The obtained transmission losses are validated against the results of an extensive set of experimental tests. A very good agreement between predicted and measured transmission loss values is observed. The single number ratings for the airborne sound insulation for nearly all walls differ from the experimental values by 0–2 dB, which is close to the average experimental reproducibility. At the same time, the computational cost is more than three orders of magnitude lower than for recently proposed models of similar accuracy.

Measurement of Sound Transmission Loss in a Sound Barrier Filled with the Rice-Straw Particles by the Transfer Function and Laboratory Measurement Methods

The sound insulation capacity of a barrier is indicated by its transmission loss. In this study, the sound transmission loss of a sound barrier filled with rice-straw particles was measured by the transfer function method and a laboratory measurement method. The results of the two measurements were compared. The transmission losses measured by the two methods were similar above a frequency of 500 Hz. The loss increased greatly upon the introduction of a plywood to the sound barrier. The results of this study are expected to be used to design sound barriers for roads.

Analysis of the measurement of transmission loss in rigid building materials with a standing wave tube

We explore the limits of the use of the Kund’s tube and the transfer matrix method for the measurement of transmission loss with common building materials. The results of several tests performed in a standing wave tube with two different building materials (concrete and gypsum board) and mounting the samples in the tube using four different sealing methods are presented.With the analysis of the obtained data, it is proved that the “two loads” method in the Kundt’s tube cannot be used to measure the transmission loss of rigid construction materials like the tested ones due to the high variability of the data.

Validation of set up for experimental analysis of reactive muffler for the determination of transmission loss: Part 1

The internal combustion engine is the major source responsible for noise pollution. In an engine, the exhaust noise and the noise produced due to friction of various parts of the engine share maximum contribution to noise pollution. A muffler is a device used to reduce noise within the exhaust system. It is arranged along the exhaust pipe for the purpose of noise attenuation. In this article, the set up for experimental analysis is developed to predict the acoustic performance of reactive muffler using the two-load method, and it is validated by measuring transmission loss of known reactive muffler model by using finite element method. For the model, transmission loss obtained from experimental analysis was compared with that obtained from the finite element method. From the result, it can be concluded that the setup developed for experimental analysis is reliable to determine transmission loss of exhaust muffler, for low to mid frequency range.

An impedance tube submerged in a liquid for the low-frequency transmission-loss measurement of a porous material

According to the standard ASTM E2611 an impedance tube can be used to measure the sound transmission and reflection losses in an absorption material. However, application in a liquid medium in the low-frequency range presents difficulties with respect to the size of the structure and the waveguide-related distortion of the plane-wave propagation. In this paper a four-microphone impedance tube for use in liquids in the low-frequency range, complying with the transfer-matrix method for transmission-loss measurements, is presented. The impedance tube is validated on the basis of research on an underwater, two-microphone impedance tube. It is demonstrated that in the low-frequency range the loudspeaker couples well into the plane-wave propagation. Furthermore, existing methods for measuring the group velocity and the complex wavenumber, applicable to the impedance tube, were investigated and compared to the new methods developed in this article. The results showed the best fits for the cross-correlation and the new approach of amplitude matching, respectively, for the cases of the velocity and the wavenumber measurements. Thus, the validated impedance tube was used for acoustic measurements of metal-foam samples. Problem-specific equations for calculating the dissipation coefficients of cavity-backed samples were derived from the transfer matrix and the scattering matrix. Stable results in agreement with the expected low absorption were obtained.

Modeling and Sound Insulation Performance Analysis of Two Honeycomb-hole Coatings

During the sound transmission loss test in the standing-wave tube, the unavoidable reflected wave from the termination of downstream tube would affect the precision measurement of sound transmission loss(TL). However, it can be solved by defining the non-reflected boundary conditions when modeling based on the finite element method. Then, the model has been validated by comparing with the analytical method. Based on the present model, the sound insulation performance of two types of honeycomb-hole coatings have been analyzed and discussed. Moreover, the changes of parameters play an important role on the sound insulation performance of honeycomb-hole coating and the negative Poisson’s ratio honeycomb-hole coating has better sound insulation performance at special frequencies. Finally, it is summarized that sound insulation performance is the result of various factors that include the impedance changes, the waveform transformation and so on.

투과손실 측정용 소형잔향실의 성능향상에 관한 연구

투과손실 측정용 소형잔향실의 성능향상에 관한 연구

Reliability of Strip Line Method for Determination of Conductivity for Lossy Conductive Materials

Designing electro-textile antenna requires complex analysis as the material cannot be simply modeled as a conventional antenna with perfect metallic surface. Electro-textile has relatively lower conductivity compared with an ideal conductor. Due to its inhomogeneous and unique thread structure, exact conductivity, $\sigma _{c}$ , is difficult to be determined, which will result in inaccurate modeling during antenna designing. Significant deterioration in antenna efficiency can be observed when low conductivity element is used, and thus, accurate determination of bulk conductivity for customized electro-textile shall be performed. Previously, a strip-line method was proposed, and however, the reliability of the technique in correlation with material’s loss characteristics was not clarified. Furthermore, the practicality of the technique for higher frequency, such as ISM band, was not demonstrated. In this paper, the validity of the technique for lossless, low-loss, and high-loss materials for 2.45-GHz wearable application is clarified. A more practical and straightforward equation to calculate electro-textile’s bulk conductivity is derived, and the accuracy and reliability range of the equation is demonstrated through comprehensive electromagnetic simulation. Through analysis, the correlation between $\sigma _{c}$ , dielectric loss and attenuation loss is shown. For validation, two samples that consist of two conductors, namely copper and SHIELDIT, are fabricated on a low-loss RO5880 substrate. The $\sigma _{c}$ values of the conductors are calculated from transmission loss (S21) measurement. Good agreement of $\sigma _{c}$ is obtained for both cases, particularly when the actual $\sigma _{c}$ is within the threshold range of around 107 S/m.