Correlations between transmission loss measurements and sediment type

The U.S. Navy's Low Frequency Bottom Loss (LFBL) database is released and maintained by the Naval Oceanographic Office (NAVOCEANO) and used as an environmental input to many of the Navy-standard tactical decision aids. It is designed to support the Navy's operational requirements in determining the nature of the interaction of 20-1000 Hz acoustic energy with the sea bottom. The general methodology of generating shallow-water LFBL databases was described in a previous paper. [Harvey, D.W., Lowrie, A., and Filipczyk, R. D., Oceans '02 MTS/IEE Volume 1, pages 358-362.] LFBL is based on acoustic and seismic measurements performed at-sea by NAVOCEANO survey teams and subsequent geo-acoustic inversions of the measured data using the Navy Standard Parabolic Equation (NSPE) model and the resources of the Navy Department of Defense Supercomputing Resource Center (Navy DSRC). LFBL is composed of a global database that is available worldwide and four regional databases for which additional acoustic and geological measurements were made. The global and regional databases use different parameter sets to describe bottom interactions. In the global database, a set of 10 parameters is used to describe an effective one-layer bottom. In the regional databases the bottom is parameterized using a set of effective acoustic layers described by sound speed, density, and attenuation at the top and bottom of each layer. The acoustic properties of the effective layers may not correspond to the actual density, sound speed, or attenuation of the physical bottom at a given location, but collectively, they are found to accurately predict acoustic propagation of bottom-interacting sound paths, and the values are constrained in the geo-acoustic inversion to geologically reasonable values. Hence, the regional databases are also known as "N-Layer" databases. Starting with LFBL Version 11.1, LFBL has also included error metrics in the regional databases to indicate the degree of confidence for the values therein in order to provide improved guidance for operational decision-making. For both the global and regional databases, the geographic region is divided into provinces over which it is assumed that the sub-bottom acoustic parameters are constant, even if the sub-bottom layer depths in the N-Layer regions vary. The sub-bottom layer depths are determined from geological interpretation of acoustic two-way travel times using data gathered concurrent with, but with independent equipment from, the acoustic transmission loss (TL) measurements. A new technique has been devised for determining province boundaries in the regional databases using geographic information systems (GIS). In brief, rough provinces are sketched out by geologists at NAVOCEANO. The locations of the TL measurements are added onto this map, and colored lines (dubbed "geo-acoustic connections") are drawn between the TL measurements to indicate how accurately the inverted parameters from one measurement predict the results of the other. The province boundaries are then adjusted to include (as much as possible) only measurements whose inverted parameters accurately predict TL at the other measurement sites within the province. Parameters are chosen for a given province by selecting the parameter set within the province that produces the best confidence metrics.

An impedance tube is an equipment used for normal incidence sound absorption and transmission loss measurement. Unfortunately, this equipment is considered equally expensive. Therefore, this study presents an effort to develop a cost-effective impedance tube for sound transmission loss (STL) measurement. The development of impedance tube consists of speaker, speaker box, acrylic tube, mechanical coupling, BSWA microphone and, Data Acquisition Unit (DAQ). The design and development of impedance tube along with set up and procedure according to ASTM E2611. In this study, the developed impedance tube is used to measure and analyse the STL for different types of sample material, such as foam, Perspex, and other building element materials. Next, data obtained from the developed impedance tube was compared with a standard commercial tube made by Brüel& Kjær for the validation. According to the data comparison, it turns out that both results are encouraging and in similar trend. In conclusion, a goal to develop an impedance tube for STL measurement was achieved but few methods need to be adjusted in future for a better outcome.KeywordsImpedance tubeSound Transmission Loss (STL)Cost-effective

펄스 튜브를 이용하여 시편의 전달 손실 성능을 측정할 경우, 시편 설치를 위해 필연적으로 시편과 펄스 튜브 내벽 사이에 간극이 존재한다. 본 논문에서는 이와 같은 간극이 전달 손실 측정 결과에 미치는 영향에 대해 평가했다. 평면파에 대해 일정 폭 및 길이를 갖는 간극 전과 후 음압의 비를 구하여 전달 계수를 유도하고 측정 대상 시편의 전달 계수와 조합하여 간극이 포함된 시편의 전달 손실을 구했다. 이와 같은 해석 모델을 이론해가 존재하는 10 mm 두께의 스테인리스 스틸 시편에 적용하여 시험 결과와 비교함으로서 해석 모델의 적절성을 보였다. 마지막으로 해석 모델을 통하여 간극크기 및 시편 전달 손실 성능에 따라 전달 손실 측정에 미치는 영향을 분석했다. There is a gap between the inner wall of a pulse tube and an underwater acoustic material when the measurement for transmission loss by the pulse tube is carried out. In this paper, the effect, which is caused by the gap, for the measurement of transmission loss is analyzed. Transmission coefficient is derived from the ratio of the pressures between front and rear of the gap. Then, transmission loss for specimen with a gap is obtained by combining the transmission coefficients of the gap and specimen. The results of experiment and simulation for a specimen of stainless steel with 10 mm thickness are compared in order to evaluate the simulation model. Finally, simulations with respect to the gap size and transmission loss of a specimen are performed to analyze and evaluate the effect of the gap in measurement of transmission loss.

The sound insulation of common Australian domestic roofing systems was investigated using a 103 m3 room below a 203 m3 transmission room. Both rooms of non‐rectangular shape satisfied recommendations of ISO/R 140. Measurements were conducted in the frequency range 100 Hz to 10 kHz. Initially, measurements of transmission loss (TL) were made using a basic ceiling with 9 mm plasterboard cladding, followed by tests when various commercially available in this were added. The enhancement of TL by infill was negligible at low frequencies. Various types of roof component, such as concrete tiles, asbestos‐cement, and galvanized steel were then studied. Due to the great number of air gaps, the TLs varied little with frequency and were low in magnitude despite large differences in cladding surface density. Finally, various combinations of roof and ceiling samples were investigated. Although inclusion of ceiling infills yielded significant increases in TL values, the enhancements at low frequencies leads to the conclusion that, for acoustic protection against traffic noise, the addition of infills is a rather fruitless exercise unless close attention is paid to proper sealing.

Single leaf transmission loss at low frequencies

Experimental investigation of the sound transmission of vegetated roofs

The Acoustic Characterization Test III (ACTIII) was conducted in the Strait of Korea in 1995. One of the goals of the experiment was to determine limitations on spatial signal processing due to environmental variabilities. Measurements of transmission loss and array signal gain (ASG) provide quantitative estimates of fluctuations in the acoustic field. Analysis of observations is supported by using grab samples, historical cores, and seismic measurements to develop a geoacoustic model. The geoacoustic model along with sampled bathymetry and sound-speed profiles is used to generate simulations of an effective attenuation coefficient, which measures the rate of change of mean transmission loss with range. The introduction of nonlinear frequency dependence into sediment attenuation profiles produces good agreement between the simulations and measured data. The ASG is directly related to the spatial coherence function. By employing procedures we have developed previously for approximating the coherence function, we use the environmental model to compute ASG. This allows further comparisons with experimental data as well as a determination of validity limits for the procedures. [Work supported by ONR.]

Many studies for improving the railway vehicle's performance and comfort such as speed, weight and noise are currently in progress. Improving the structural characteristics of the vehicle for greater noise insulation is considered important for reducing disturbance due to noise, but measuring transmission loss entails large costs. This study explores an alternative method for estimating and measuring the railway vehicle's transmission loss that involves on applying the numerical analysis coupled with scaled reverberation chamber measurement. The transmission loss measurement using scaled reverberation chamber was performed after the compensation value was found through 1mm thickness(1t) specimen. For numerical analysis, a commercially available acoustics solver VA ONE was used. The proposed method is found to lead to transmission loss measurement comparable to the measurements based on large-scale reverberation chamber. Thus, it can be argued that a reliable method has been developed for measuring railway vehicle's transmission loss.

A numerical method for the transmission loss prediction of the water muffler has been provided according to the measuring process of the two-load method. The commonly used acoustic loads can be applied in the proposed method. The accuracy of the proposed method has been proved by comparing the calculated transmission loss with that from the traditional direct predicting method. And then the proposed method is used to discuss effects of test bench on transmission loss measurement. The predicted transmission loss curves are consistent reasonably based on different test models. The location of monitors relative to the muffler inlet and outlet has little influence on the result. But the distance between the two monitors upstream or downstream should be controlled within a certain range based on the concerning frequency band and the main pipe diameter. It is found that modes of the coupled system consisting of the test pipes and the water cause extra peaks on the transmission loss curve. The influence can be reduced by arranging appropriate fixed points. The proposed method can be used to to explain the reasonability and validity of the test bench design.

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

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.]

Acoustic panels are used to overcome noise problems; the purpose of this study was to determine the acoustical properties of particleboard made from Betung bamboo (Dendrocalamus asper). The acoustic parameters measured were the transmission loss (TL) value and sound absorption coefficient. Particleboards of two different densities (0.5 g/cm3 and 0.8 g/cm3) that were made with three particle sizes (fine, medium, and wool or excelsior) were used in this study. The sound TL value was measured in a reverberation room, while the sound absorption coefficient was determined using the impedance tube method. A single-number rating of sound transmission class (STC) was determined based on TL measurements. The results showed that sound TL and STC values of medium-density particleboard (0.8 g/cm3) were better than low-density (0.5 g/cm3) board. However, low-density particleboard performed well as sound absorber panels. Generally, the boards absorbed sound at low ( 1000 Hz) and reflected sound at middle frequencies. The sound absorption coefficient was better with the fine- and medium-sized particles than with the wool size; meanwhile, boards made from wool- or excelsior-sized particles possessed higher TL and STC values.

Satellite launch vehicle during lift-off generates intense dynamic environment mainly the acoustic noise, which in turn acts on the nearby launch pad systems. Reliable operation of these launch pad ground systems needs to be ensured by safeguarding against these dynamic loads with adequate protection measures. For future launch vehicle programs where the launch turnaround time is a crucial aspect, sensitive systems like ground check-out electronic packages are planned to be placed adjacent to the launch vehicle mounting pedestal on the launch pad to ensure minimal time for preparation. The enclosures housing these electronic packages needs to be configured to minimize the transmission of acoustic levels being imposed from the lift-off induced noise. In the present work, an experimental investigation is carried out on acoustic transmission characteristics of metallic enclosures of different material and thickness during the static firing tests of solid rocket motors. Acoustics generated from the supersonic jet noise has a wide frequency band from 100 to 10,000 Hz with sound power peaking near 1,000 Hz. The electronic components and packages, which are generally vulnerable to the high frequency noise, need to be protected from this lift-off induced acoustics. The enclosures are placed in the far field of this jet noise and the transmission loss measurements are obtained. Variation of transmission loss with material and thickness of the enclosures are studied with specific attention to the internal acoustic modes and the coincidence phenomena. Subsequently, the enclosures treated with acoustic blankets of different thickness are investigated to verify its influence on internal acoustic modes and also the additional reduction in transmission of sound in the dominant frequency band of supersonic jet noise.

In the search for more effective noise attenuation methods, a number of candidate materials for road noise barriers and partition walls were tested at the Cooper Union Acoustics Research Center in a specially constructed enclosure divided into two sections by a wall constructed of these materials. The transmission losses of cinder blocks filled with various recycled materials constitute the acoustical property of principal interest. Three tests were executed for each type of material: (1) transmission loss measurements; (2) absorption coefficient measurements; and (3) diffraction effects. The intended applications of the designed materials are as noise barriers for urban highways and subway stations, and as partition walls for factories, classrooms, libraries, etc. Recycled materials experimented with would normally end up in land fills or incinerators. [See NOISE-CON Proceedings for full paper.]

Measurements of sound transmission loss through slotted concrete blocks with attached gypsum board showed that the cavity resonance of the blocks has an important beneficial effect. It counteracts the mass-air-mass resonance that occurs when gypsum board is added to the surface of a concrete block wall leaving an air space behind it. This significantly increases the sound transmission class rating relative to the same systems with normal-weight nonslotted blocks. The effects of the two resonances could be seen at different frequencies when there was no sound-absorbing material in the air space behind the gypsum board. When the air space was filled with sound-absorbing material, however, both resonances moved together and could not be separated, but the transmission losses and sound transmission class for the composite wall were still significantly greater than those for wall systems using nonresonant blocks. Sound absorption measurements for the slotted blocks showed the need for one-third octave band data in place of the octave band data often found in trade literature.