Sound Transmission Measurements Research Articles

An objective measure for the sensitivity of the room impulse response

This study is relevant for a number of important acoustic measurements in reverberation rooms such as measurement of sound transmission and measurement of sound power levels of noise sources. From a pair of impulse responses measured in a room differing only in the position of the sound source, it might be possible to quantify the sensitivity of the room due to changes in initial conditions. Such changes are linked to mixing. The proposed measure is the maximum of the absolute value of the cross-correlation between the time windowed sections of the two impulse responses. By integrating this quantity normalized by the energy of the impulse response of the room, a single number rating is obtained. The proposed measure is examined experimentally, and the results are discussed. The results indicate that the number of absorbers and diffusers in the room influences the proposed measures systematically.

Underwater sound transmission through thin soft elastomers containing arrays of pancake voids: Measurements and modeling

Measurement of underwater sound transmission through thin (~750 micron) layers of the soft elastomer polydimethylsiloxane (PDMS) containing microfabricated arrays of pancake-shaped cavities is presented. Cavities are 120 microns in diameter and 5 microns in height with a nominal lattice spacing of 300 microns. A sound transmission minimum is found at 282 kHz which agrees with predictions of a finite-element model of the array and the value for monopole resonance frequency of an air-filled single pancake cavity in unbounded PDMS. This resonance is a factor of 0.62 lower than the null that would occur for spherical cavities of equivalent volume. The width of the null is also significantly broader than that which would be obtained with spherical voids. Modeling results incorporate careful measurements of attenuation for both shear and compression waves in PDMS done in a separate effort. Acoustic transmission variation as a function of lattice spacing and the number of layers is discussed. [Work sponsored by the Office of Naval Research]

Aperiodicity effects on sound transmission through arrays of identical cylinders perpendicular to the ground

Results of laboratory measurements of sound transmission through 5 × 10 arrays of meter long polyvinyl chloride pipes with lattice constants of 5 and 10 cm with filling fractions of 13% and 50% located either on medium density fibreboard or a layer of felt are reported. Ground effects and sonic crystal effects are found to be additive. Measurements and predictions show that, while there is little broadband advantage in a periodic configuration compared with a random one, a quasi-periodic arrangement in which the perturbation has a standard deviation equal to the scatterer diameter gives the best overall attenuation.

Complement to standard method for measuring normal incidence sound transmission loss with three microphones

Complement to standard E2611-09 of the American Society for Testing and Materials [Standard Test Method for Measurement of Normal Incidence Sound Transmission of Acoustical Materials Based on the Transfer Matrix Method (American Society for Testing and Materials, New York, 2009)] is proposed in order to measure normal incidence sound transmission loss of materials in a modified impedance tube using a three-microphone two-load or one-load method. The modified tube is a standard two-microphone impedance tube, where a third microphone is mounted on a movable hard termination. This method is conceptually identical to the four-microphone two-load or one-load method described in the standard; however, it requires fewer transfer functions and one microphone less. The method is validated on (1) symmetrical homogeneous and (2) non-symmetrical non-homogeneous specimens.

On the measurement of angular dependent sound transmission through airborne, supercritical plates.

Angular dependence of sound transmission through airborne plates, at frequencies above their critical frequencies (supercritical), is discussed. Experimental measurements of this angular dependence have been conducted using phased array methods. Theory governing the sound transmission through supercritical plates is already well developed; however, experimental results are known to depart from theory near grazing incidence. The details of the measurement apparatus and issues involved in making this type of measurement will be discussed. The results of the measurements will be compared to theory, focusing on the departure of experiments from theory.

고부가가치선의 Unit Cabin Mock-up을 이용한 캐빈소음 저감 연구

Unit cabin means room, which is installed in the high value-added vessel such as drill ship, offshore platform and FPSO, after pre-assembled. In order to develop the noise control design for a unit cabin, a variety of acoustic tests such as sound absorption, transmission and radiation measurements were carried out by using the deckhouse mock-up. From the tests, it was found out that the sound transmission loss between cabin and corridor was 13 dB below than FPSO standard and the combined noise level of the unit cabin was dominated by the radiated noise from wall panel in low frequency range. Based on the test results, design guidelines for the noise control of the unit cabin were fully established, such as the improvement of sound transmission loss between the cabin and corridor, and radiated cabin noise reduction.

Predictions and measurements of sound transmission through a periodic array of elastic shells in air

Analytical and numerical approaches have been made to the problems of (a) propagation through a doubly periodic array of elastic shells in air, (b) scattering by a single elastic shell in air, and (c) scattering by a finite periodic array of elastic shells in air. Using the Rayleigh identity and the Kirchhoff-Love approximations, a relationship is found between the elastic material parameters and the size of the bandgap below the first Bragg frequency, which results from the axisymmetric resonance of the shells in an array. Predictions and laboratory data confirm that use of a suitably "soft" non-vulcanized rubber results in substantial insertion loss peaks related to the resonances of the shells. Inclusion of viscoelasticity is found to improve the correspondence between predictions and data. In addition the possible influences of inhomogeneity due to the manufacturing of the elastic shells (i.e., the effects of gluing sheet edges together) and of departures from circular cylindrical cross-sections are considered by means of numerical methods.

Array measurement and imaging of sound transmission through the lungs.

Non‐contacting scanning laser Doppler vibrometry (SLDV) was used to measure torso surface motion at an array of points caused by sound introduced into the lungs in human subjects. The SLDV serves as a gold standard as it does not have the complexity of surface contact dynamics. Additionally, a sensor array integrated into a compliant mesh fabric chair was constructed and tested as a less expensive and faster means of acquiring similar acoustic array data. Silicone gel‐coupled, piezoelectric contact sensors for the detection of subsurface acoustic sources at the skin surface were used in the array. Array measurements were processed to determine the response at each measurement point as a function of frequency up to 1.6 kHz. Acoustic images were generated indicating the amplitude level at each point relative to the amplitude measured at the suprasternal notch, which served as the reference input. The acoustic measurements illustrated the complexity of sound transmission in the human lung and chest. Expected attenuation over the scapulae and below the diaphragm was observed. There were other significant variations as a function of location and frequency; measurement results are discussed. [Work supported by NIH Grant # EB008373.]

Laboratory measurements of sound transmission at low frequencies.

The ability of acoustic materials to attenuate sound is usually determined in accordance with ASTM E-90 or ISO 140-3, both based on the diffuse field theory. However, the reality is that the size of typical reverberant chambers does not provide a sufficiently diffuse field at low frequencies. As a result, there is significant variation in sound transmission data of tested materials below 150 Hz. Several attempts were undertaken to improve the accuracy of measuring TL such as increasing field diffuseness by using reflecting surfaces, installing near-field array of loudspeakers, and using sound intensity probes on the receiving sides. None of these proved totally satisfactory. This work presents studies on using various approaches to more accurately determine acoustic mitigation of low-frequency transmitted noise. A metal box consisting of a very rigid frame supporting elastic panels on all sides was acoustically excited by a loudspeaker suspended inside of the box. The panels and box interior were designed to have very low-fundamental frequencies. The box was suspended by its frame in an anechoic room. An intensity probe was used to measure the transmitted sound from the box panels. The acoustic performance of various acoustic materials was compared for frequencies below 500 Hz.

Predicting the Sound Transmission Loss of Honeycomb Panels using the Wave Propagation Approach

The sound transmission properties of sandwich panels can be predicted with sufficient degree of accuracy by calculating the wave propagation properties of the structure. This method works well for sandwich panels with isotropic cores but applications to panels with anisotropic cores are hard to find. Honeycomb is an example of anisotropic material which when used as a core, results in a sandwich panel with anisotropic properties. In this paper, honeycomb panels are treated as being orthotropic and the wavenumbers are calculated for the two principle directions. These calculated wavenumbers are validated with the measured wavenumbers estimated from the resonance frequencies of freely hanging honeycomb beams. A combination of wave propagation and standard orthotropic plate theory is used to predict the sound transmission loss of honeycomb panels. These predictions are validated through sound transmission measurements. Passive damping treatment is a common way to reduce structural vibration and sound radiation, but they often have little effect on sound transmission. Visco-elastic damping with a constraining layer is applied to two honeycomb panels with standard and enhanced fluid coupling properties. This enhanced fluid coupling in one of the test panels is due to an extended coincidence range observed from the dispersion curves. The influence of damping treatments on the sound transmission loss of these panels is investigated. Results show that, after the damping treatment, the sound transmission loss of an acoustically bad panel and a normal panel are very similar.

Transmission characteristics of a tee-junction in a rectangular duct at higher-order modes

Numerical and experimental studies were undertaken to characterize the noise transmission and scattering properties in higher-order modes across the tee-junction of a rectangular duct used in ventilation and air-conditioning systems. To measure these properties, a formulation of a transmission matrix based on the transfer function and a two-microphone method was devised. The measurement of modal sound transmission and scattering coefficients is demonstrated for a duct element in a rectangular duct. The results of numerical simulations were verified by experiments. The results show that sound transmissions of fundamental mode and higher-order modes across the main duct are high at the eigen-frequencies of the main duct and sidebranch. Weak modal coupling of the branch-modes and the traveling wave in the main duct is observed at or very close to the eigen-frequencies of the sidebranch, which shifts excitation of the higher-order branch-modes at higher frequencies. A decrease in sound transmission and increase in sound scattering into higher-order modes occur with excitation of the axial branch-mode. Excitation of the longitudinal branch-mode due to branch-end reflection also results in lower sound transmission of higher-order modes across the junction along the main duct.

A fully automated procedure for the measurement of human middle ear sound transmission.

Article A fully automated procedure for the measurement of human middle ear sound transmission. was published on January 1, 1974 in the journal Biomedical Engineering / Biomedizinische Technik (volume 19, issue s1).

Measurement of sound transmission through mud at Dodge Pond, Connecticut.

Questions important to the sonic detection of buried ordinance are whether the sound dispersion and attenuation of muddy bottoms can be predicted and verified. Wood and Weston [Acustica (1964)] measured compressional speeds in harbor mud 3% less than that of water with attenuation considerably less than those of sandy/silty sediments. A recent theoretical treatment [Pierce and Carey, POMA, 7001 (2009)], making use of the Mallock–Wood equation and of a card‐house theory of the structure of mud, estimates the slow sound speed to depend on porosity as 1−(0.35)(1−φ). Present measurements at frequencies between 1 and 10 kHz with a buried array in the depositional mud at the bottom of Dodge Pond, which contains considerable gas microbubbles, yield speeds of the order of 60% of the sound speed in water. The initial measurements on the disturbed sediment were found to be strongly influenced by scattering from larger bubbles whereas the results after a period of 10 months showed the effect of a smaller size distribution of bubbles. Estimates based on the Dodge Pond measurements and on the card‐house theory of the propagation characteristics and of the effect of micro‐bubbles are discussed. [Sponsored by SERDP‐NSWC‐PCD.]

Tape as a surface protector for field tapping machine tests.

Impact sound transmission measurements of floor‐ceiling constructions are often performed in the field. This leads to a wide range of testing environments; some of which can be high‐end, multi‐family residences with expensive floor finishes. Some residents can be concerned that testing may damage or scuff their floor. The ASTM e1007‐04E1 standard does not discuss or provide allowances for acceptable methods of floor protection. This study investigates various kinds of tape including storage, masking, duct, and aluminum tape to find options that act as good surface protectors while minimally influencing measurement results. Testing was conducted on hard‐wood and tile floors. Results will be shown comparing the impact sound transmission frequency spectra of the floors using each tape with the frequency spectra measured using the bare floor. Suggestions for modifications to future standards are proposed to address this concern.

Impact noise and walking noise in multifamily housing

Field measurements of impact sound transmission using the ISO standard tapping machine are compared with field measurements of human walkers in both wood and concrete buildings. In wood frame construction, low-frequency noise dominates the spectrum with most floor coverings. In concrete buildings, high-frequency noise is the controlling factor in non-carpeted areas. The relative effectiveness of different noise mitigation measures will also be discussed.

Enhancing low frequency sound transmission measurements using a synthesis method

The characterization of low frequency sound transmission between two rooms via a flexible panel is investigated experimentally in this work. Previously, the individual effects of the transmission suite on the measured sound reduction index have been studied analytically, and the results have been compared with the ideal case of having free field radiation conditions on both sides of the panel. A new approach is proposed using a near-field array of loudspeakers driven by a set of optimized signals such that a diffuse pressure field is reproduced on the surface of the partition to be tested. The practical effectiveness of this method is assessed when using a set of 16 acoustic sources located in the source reverberant room in close proximity to an aluminium panel. The experimental results obtained confirm the dependence of the characterized sound reduction index on the particular test chamber considered in the low frequency range. They also validate the proposed synthesis method for providing an estimate that only depends on the properties of the partition itself.

The experimental synthesis of random pressure fields: Methodology

This paper presents a methodology for the off-line reproduction of random pressure fields with given spatial correlation characteristics. The simulation method is first presented, together with an outline of the signal processing techniques required. The design of an experimental setup is then detailed in relation with the nature of the simulated pressure fields. Of particular interest is the laboratory synthesis of three different types of partially correlated random excitations: an acoustic diffuse field, a grazing incident plane wave, and a turbulent boundary layer. The corresponding excitations are generated in a semianechoic chamber over a test panel using a near-field array of 16 loudspeakers driven by a set of optimal signals. The loudspeakers are positioned at a suitable distance above a sufficiently dense grid of microphones close to the simulation surface. The mutually correlated drive signals are determined from both the target correlation properties and the acoustic transfer functions measured between the loudspeakers and the microphones. This approach could provide a cost-effective method of reducing the variation of low frequency sound transmission measurements as well as simulating the propeller-induced noise and the boundary layer noise transmitted through aircraft fuselage structures.

Experimental evaluation of bone quality measuring speed of sound in cadaver mandibles

To demonstrate in vitro the feasibility of speed of sound (SOS) measurements through the mandible and to investigate the relationships between mandibular SOS, local bone mineral density (BMD), and the ratio between trabecular and cortical thicknesses (Tb.Th/Cort.Th). The long-term goal is to find a safe, simple test for bone quality in sites for dental implant placement. Excised human mandibles (N = 23) were used for the measurement of sound transmission with two 1.6 MHz transducers. Three regions of interest (ROIs) were selected in each of the specimens, namely incisor, premolar, and molar regions. To determine short-term precision, 10 measurements (with repositioning between measures) were performed for each ROI. Local BMD and mandibular cross-sectional morphological characteristics were determined by dual x-ray absorptiometry (DXA) and computed tomography (CT). The coefficient of variation for SOS was found to be 1%. SOS measurements at different sites were significantly different. A significant linear relationship was found between SOS and BMD (r2 = 0.62; P < .0001), whereas a nonlinear relationship was found between SOS and Tb.Th/Cort.Th (r2 = 0.53; P < .0001). This in vitro study demonstrated the feasibility of SOS measurement through the mandible. Mandibular SOS reflects local BMD and Tb.Th/Cort.Th. In vivo studies are now required to confirm the predictive power of SOS measurement for bone quality assessment and its potential usefulness as a clinical diagnostic technique.

Bone Mineral Density (BMD) Assessment of Central Skeletal Sites From Peripheral BMD and Ultrasonographic Measurements: An Improved Solution Employing Age and Weight in Type 3 Regression

The objective of this study was to develop a method whereby bone mineral density measurements of the heel and finger, as well as ultrasonographic measurements of calcaneal sound transmission, could identify individuals with a diagnosis of osteoporosis or osteopenia by the World Health Organization criteria for these diagnoses in the central skeleton (i.e., the lumbar spine (LS) and hip [femoral neck] [FN]). Two hundred and forty-four women in a university hospital laboratory setting had dual-energy X-ray absorptiometry measurements of bone mineral density (BMD) in the calcaneus, finger, hip, and spine, and quantitative ultrasound of the calcaneus. Regression equations were developed to predict central bone mineral T-scores from T-scores of peripheral measurements, adjusted by age and weight. Equations were validated by predicting the cut point for osteopenia at the lumbar spine and hip (T-score=-1.0). Ninety-five percent confidence intervals of the mean predicted LS or FN T-score from each peripheral site included -1.0. We conclude that our derived regression equations (taking into account interaction of peripheral BMD with patient age and weight) are useful for predicting T-scores in the central skeleton. This approach reduces the potential for misdiagnosis, which can result if one uses unadjusted peripheral T-scores, which are only moderately correlated with the central measurements of BMD.

Investigation of noise issues at U-Hill Elementary School

University Hill Elementary School (U-Hill) has a reputation amongst its teachers, staff and parents as being a noisy school. The present work is an assessment of the acoustical environment at U-Hill with a focus on evaluating how various noise sources contribute to the total noise levels measured in four classrooms. A questionnaire was completed by several of U-Hill’s teachers to determine their reactions to the school’s acoustical environments and what they perceived to be the prevalent noise sources. Standard physical measurements of classroom background noise and reverberation time were made and compared to existing acceptability criteria. Measurements of sound propagation and transmission were made to determine how noise propagates in the hallway, as well as into and between adjacent learning spaces, and the effect of open doors and door grates. Dosimeters were used to monitor sound levels at various hallway source locations and received in the four classrooms studied. Octave-band measurements of typical noise-source levels, such as children walking in the hallways and entering through school doors were made. The measurement data was used to estimate the contributions to total noise levels in the four classrooms of the various noise sources inside and outside the classrooms.