Sound Transmission Measurements Research Articles

Experimental reproduction of random pressure fields in laboratory conditions

The design and the physical implementation of an experimental set-up are discussed for the off-line reproduction of random wall-pressure fluctuations with given spatial correlation characteristics. This approach could provide a cost-effective laboratory method of both reducing the variability of low frequency sound transmission measurements as well as measuring the boundary layer noise transmitted through aircraft fuselage structures. Three different types of random excitations are considered, namely an acoustic diffuse field, a turbulent boundary layer excitation and an acoustic progressive wave at grazing incidence angle. The corresponding excitations are generated in a semi-anechoic chamber using a near-field array of 4×4 loudspeakers optimally driven and located above a set of 13×16 microphones. The microphones are positioned a short distance apart from an aluminum test panel. The optimal driving signals are determined from acoustic transfer functions measurements between the grid of microphones and the array of loudspeakers. Given this number of loudspeakers, a reasonable reproduction of the boundary-layer excitation is achieved up to about 200 Hz and a good approximation of both the acoustic diffuse field and the progressive wave is obtained over the frequency range of interest, i.e. up to about 700 Hz. [Work supported by ANVAR.]

Measurements of sound transmission through panels of locally resonant materials between impedance tubes

We present a method for the measurements of complex transmission coefficient through high transmission loss samples using three-sensors, two impedance tubes, monotonic wave excitation, and phase sensitive detection. Having demonstrated the effectiveness of the method on perforated plates measurements have been made on locally resonant sonic materials (LRSMs). The transmission losses of perforated plates are found to decrease with decreasing frequency down to 120 Hz, following the mass law. For the LRSM’s panels with the same area mass density but different compositions, the local resonance frequency (at which the transmission loss is maximum) is found to vary according to the predesigned value. Transmission losses as high as 96.5 dB at 630 Hz and 87 dB at 250 Hz can be measured with good accuracy, with corresponding phase spectra that match the theoretical prediction of LRSMs, confirming the reliability of the transmission data.

ACOUSTIC PROPERTIES OF TWO URBAN SONG DIALECTS IN THE ORANGE-TUFTED SUNBIRD (NECTARINIA OSEA)

Abstract Biologically important acoustic signals must be transmitted from a signaler to a receiver. Over distance, however, sounds may undergo modification through attenuation, degradation, and masking. Recent anthropogenic habitat modification occurring in many places—in urban habitats, in particular—has rapidly changed local topography and atmospheric conditions and generated new patterns of noise that are likely to interfere with communicative signals. As part of a study of microgeographic song dialects in an urban population of Orange-tufted Sunbirds (Nectarinia osea) in Israel, we examined the environmental influences on song transmission and reception in a rapidly developing human-altered environment. We examined the physical properties of the two dialect song types, which exhibit a large difference of 2–3 kHz in the maximum frequency of the trill, using sound transmission measurements to test how both song types propagate through a highly obstructed habitat of buildings and vegetation. Additionally...

Acoustic Properties of Two Urban Song Dialects in the Orange-Tufted Sunbird (Nectarinia Osea)

AbstractBiologically important acoustic signals must be transmitted from a signaler to a receiver. Over distance, however, sounds may undergo modification through attenuation, degradation, and masking. Recent anthropogenic habitat modification occurring in many places—in urban habitats, in particular—has rapidly changed local topography and atmospheric conditions and generated new patterns of noise that are likely to interfere with communicative signals. As part of a study of microgeographic song dialects in an urban population of Orange-tufted Sunbirds (Nectarinia osea) in Israel, we examined the environmental influences on song transmission and reception in a rapidly developing human-altered environment. We examined the physical properties of the two dialect song types, which exhibit a large difference of 2–3 kHz in the maximum frequency of the trill, using sound transmission measurements to test how both song types propagate through a highly obstructed habitat of buildings and vegetation. Additionally, we examined how ambient noise—in particular, low-frequency noise arising mainly from automobile traffic—affects the transmission of both dialect songs. Finally, using song playback, we investigated the consequences of sound degradation on dialect recognition and discrimination by sunbirds. The dialect containing higher frequencies in the trill was found to undergo severe frequency-dependent attenuation, in which the maximum frequency of the trill notes drops by >2 kHz over a distance of 70–100 m (less than two territories away). Also, the possibility that the use of higher frequencies in that dialect group's song is intended to overcome masking by urban ambient noise, which is concentrated mainly in lower frequencies, was not supported by our findings. Males singing the high dialect responded differently to playbacks of an intact and an attenuated form of their dialect song. Taken together, our results suggest that the dialect containing higher frequencies in the trill may be unsuitable for effective long-range transmission through this particular sunbird habitat.Propiedades Acústicas de Dos Dialectos del Canto Urbano de Nectarinia osea

Variability of low frequency sound transmission measurements

In this paper we discuss the characterization of low frequency sound transmission between two rooms via a flexible panel. A fully-coupled modal model is used to investigate the individual effect of the source room and the receiving room on the measured sound reduction index, and the results are compared with the ideal case of having a free field on both sides of the panel. The effect of the source room on the measured sound reduction index at low frequencies can be reduced by using a number of suitable-driven loudspeakers close to the panel to simulate a diffuse incident field. However, the effect of the receiving room was found not to be reduced by calculating the transmitted acoustic power from a dense array of acoustic intensity measurements, instead of an array of microphones in the receiving room.

Measurement of sound transmission and signal gain in the complex Strait of Korea

The experiment, The Acoustic Characterization Test III, was conducted in the oceanographically complex Strait of Korea to accurately measure the sound transmission under known environmental conditions. Geoacoustic profiles derived from geophysical measurements, measured bathymetry, and sound-speed profiles were the basis for range dependent parabolic equation (PE) calculations. Agreement between measured and calculated transmission loss was obtained with an attenuation profile in the near water-sediment interface layer with a dependence on frequency to the 1.8 power consistent with measurements in other sand-silt areas. Since the environment was oceanographically complex and the shipping noise levels were high, the coherency of the sound transmission was estimated using relative signal gain (RSG). RSG was taken as the difference between the gain calculated with PE and measured with the array and at longer ranges and higher frequencies was found to be approximately -2 dB with a signal gain coefficient of variation of 5%. This RSG degradation, attributed to the random signal phase fluctuations resulting from scattering from the surfaces and volume of the waveguide, yielded using a Gaussian coherence function a spatial coherence length of 30/spl lambda/ @ 400 Hz-40 km. In addition, high resolution imaging of five targets with two bottom mounted arrays illustrate the achievable performance of low-to-mid frequency active sonar in this environment.

Prediction of Sound Insulation at Low Frequencies Using Artificial Neural Networks

Low frequency noise, generated by outdoor and indoor sources, is an increasing problem and there is a need for methods of measurement and prediction of low frequency sound transmission, particularly between dwellings. This work presents a new approach to the low frequency sound transmission problem. Artificial Neural Networks, ANNs, are information processing systems that can store knowledge from their environment through a learning process and thus can be used in developing models for prediction. ANNs were applied to existing field data, in the standard frequency range, to confirm the classical mechanisms of sound transmission between dwellings. They then were applied to Finite Element Method modelled data for the frequency range 40–100 Hz. Results show the influence of parameters in sound transmission at low frequency that are not important at higher frequencies. Of particular significance is the main room dimension, normal to the plane of the party wall, and the edge conditions of the party wall. The results of applying ANN to sound transmission at low frequencies are promising but there remains a need for larger data sets, particularly to improve the prediction of equal room configurations where maximum acoustic coupling takes place.

Modeling and analysis of sound transmission in the Strait of Korea

The experiment called the Acoustic Characterization Test III was performed in the oceanographically complex Strait of Korea. It was designed to provide accurate measurements of sound transmission and array signal gain under known environmental conditions. Bottom sampling and sub-bottom surveys coupled with archival geophysical information provided the basis for the geoacoustic depth profiles of sound speed, density and attenuation. The bottom was a sand-silt sediment for which shear wave propagation at experimental frequencies was determined to be unimportant. Using the compressional wave profiles, the measured bathymetry and the water sound speed as input parameters, good agreement was obtained between measured and calculated narrowband transmission loss when an attenuation profile with a frequency dependence to the 1.8 power in the near sediment-water interface layer was used. This power law was determined by using an effective attenuation coefficient and a least squares comparison of calculated and measured sound transmission of five narrowband tones between 47 and 604 Hz. The resulting geoacoustic model was used to compare measured and calculated broadband sound transmission and signal spread and excellent agreement was found. These results are consistent with measurements in other sand-silt areas where site specific frequency dependent characteristics have been observed.

Measurement-based geoacoustic modeling for the Acoustic Characterization Test III

The Acoustic Characterization Test III was performed in the oceanographically complex Strait of Korea to provide accurate measurements of sound transmission and coherence (array signal gain) under known environmental conditions. Bottom sampling and sub-bottom surveys, coupled with archival geophysical information, provided the basis for geoacoustic profiles of sound speed, density, and attenuation versus depth. These profiles and the measured bathymetry and water sound speed were used as input parameters for parabolic equations computations. Very good agreement was obtained between measured and calculated narrow-band transmission loss by employing slightly modified geoacoustic profiles and an attenuation profile with a near-water-sediment interface power-law frequency dependence of 1.8. This power law was determined through the use of an effective attenuation coefficient and a least-square analysis of transmissions from five narrow-band tones between 47 and 604 Hz. These results are consistent with measurements in other sandy–silty areas. Using these parameters, comparisons were made between independent measurements and calculations of broadband transmissions and of signal spread, and excellent agreement was found. [Work supported by ONR.]

Inter-Laboratory Test of Sound Insulation Measurements on Heavy Walls: Part I — Preliminary Test

The intention of sound reduction index (SRI) measurements in transmission suites is to obtain more reliable values of the specific test element's sound insulation properties. Unfortunately, these values are influenced by the mounting of the test element itself and the construction design of the test facility. Both the mounting of the test element and, in part, the design of the test facility can effect the damping of the test element. From previous studies a suggested solution has been to take into account the damping in terms of the test element's loss factor. By incorporation of the loss factor in SRI measurements, of heavy walls, it has been suggested that this could reduce the deviations in SRI values due to laboratory influences. To determine the variance of sound transmission measurements in test facilities for a heavy wall, an inter-laboratory test (ILT) was performed in twelve different institutes. This ILT study included the measurement of sound reduction index, velocity levels and damping. In this first part, of a two part paper, a review concerning the principle previous studies is given. Furthermore, decisions regarding the choice of the test element, principal measurements and participating laboratories are reported.

Development of standardized impact sources for laboratory measurement of sound transmission through lightweight walls

Constructing housing by using lightweight walls is still a trend, and people are skeptical about the sound of such walls. Following the result of a questionnaire survey it was found that impact sound through lightweight walls is the fourth annoying noise source in Taiwan. Since there is no standard method of measuring impact sound through walls, this study looks at the possibility of developing a standardized impact source for measuring impact sound in a laboratory. Therefore various impactors were designed to relate certain impact sources to real life situations. The standardized impactor design is designed by comparing the characteristics of the real-life impactor with that of the designed impactors. The results of this study shows that there are two classifications of impactors to be considered. A steel ball of 50 mm in diameter is regarded as a hard impactor, and, a silicon ball of 100 mm in diameter is a soft one. A system for measuring impact sound through lightweight walls in the laboratory is also proposed.

Comparison between sound transmission measurements made in working offices and in the laboratory

Field and laboratory sound transmission measurements on office partitions are compared. The measurements were carried out both in working offices and in a laboratory setting on virtually identical full partition constructions. The effects of various performance-enhancing construction details are examined in both settings. The effects of these details are also compared to expectations based on the architectural acoustics ‘‘folklore.’’ Implications are noted for using laboratory sound transmission data in predicting field performance and in guiding the design and specification of partitions intended for use in offices.

Complaints about poor sound insulation between dwellings in england and wales

This paper presents the findings of a small study, undertaken in England and Wales between April 1992 and March 1994, where we investigated complaints about poor sound insulation between dwellings. The purpose of the project was to determine the types of noise that cause complaint and to see if it was common for complainants to live in dwellings having sound insulation below the level generally regarded as reasonable. A total of 40 case studies of complaints were investigated. Each case study involved interviews with the complainant and adjacent residents, together with physical measurements of airborne sound insulation and impact sound transmission. The main noises heard by complainants are music/television/radio, voices, footfalls, closing and banging doors, sockets, switches, impacts on kitchen work surfaces and plumbing noises. Noises from modern household appliances such as washing machines, vacuum cleaners and telephones are also commonly mentioned as part of a complaint about domestic sound insulation. The study has shown that, in the main, complainants do live in dwellings having sound insulation below the standard generally regarded as reasonable for Building Regulations purposes. However, the survey also indicates that some people are dissatisfied even when their home meets the intended standard—although these complaints are often concerned with banging doors and other noises not controlled by Regulations.

Underwater sound radiation from a spherical bubble cloud encapsulated by a thin spherical shell

Measurements of sound transmission versus frequency are performed (in the Rickover Hall Hydrodynamics Tow Tank Facility) for a submerged spherical bubble cloud that is encapsulated by a thin spherical shell. The bubble cloud is driven by a miniature spherical PZT transducer unit that is suspended in the center. A theoretical model has been developed which predicts the resonant frequencies for the case where the shell thickness has negligible effect. Therefore, the resonances will depend on the radius of the cloud and the sound speed in the bubbly media (which is a function of the air volume void fraction). A shell of urethane elastomer is molded as a single piece by using the ‘‘lost wax technique.’’ Hemispherical molds are used. The first set is for making the ‘‘inner’’ spherical wax ball. The second set forms the ‘‘outer’’ boundary of the casting for the spherical shell with filling ports on the north and south poles. The shell’s inner wax material is then melted out to complete the process. The shell is nearly acoustically transparent since ρ=1.03 g/cm3, clong∼1450 m/s and ctran∼70 m/s. The bubbly fluid consists of castor oil that has been whipped in a microblender.

Recent shallow‐water acoustic measurements of sound transmission, reverberation, and coherence.

Recent experiments performed in the shallow waters (100 m deep) of the Gulf of Mexico, East Continental Shelf of America, and the Korean Straits under the condition of downward refraction with sandy–silty clays are discussed. These experiments were performed with both explosive, air gun, and continuous sources covering the 100‐Hz to 1‐kHz frequency range. The receivers were both horizontal arrays on the bottom and vertical arrays which spanned the water column. Precise navigation was employed to eliminate range uncertainties and all measurement systems were calibrated to a traceable standard. The results are presented in the categories of sound transmission, reverberation, and coherence. Sound transmission results were found to generally agree with wave‐theoretic numerical codes and shear was not found to be important. The reverberation was found to have a frequency‐dependent characteristic consistent with sediment layering. Coherence lengths are estimated from array signal gain measurements in the midfre...

Shallow-water sound transmission measurements on the New Jersey continental shelf

Calibrated acoustic measurements were made under calm sea state conditions on the New Jersey shelf near the AM COR 6010 borehole, a surveyed area with known geophysical properties. The experiment was conducted in 73 m water with supporting measurements of salinity, temperature, and sound speed. Acoustic measurements were obtained with a vertical array of 24 hydrophones spaced equally at 2.5m intervals; one of which was near the bottom. A source towed at 1/2 the water depth transmitted one of two sets of four tones spaced between 50 and 600 Hz for each run to ranges of 4 and 26 km. The data were processed with both a Hankel transform and a high resolution Doppler technique to yield horizontal wave-number spectrum at several depths. Results were obtained along both constant and gradually varying depth profiles. Similar modal interference patterns were observed at the lower frequencies. The constant depth-profile radial results were compared to calculations performed with several shallow water acoustic models using geoacoustic profiles derived from geophysical parameters and shear wave inversion methods. Calculated and measured sound transmission results were found to agree.

Inter-laboratory comparisons of low-frequency sound transmission: II. Narrow-band measurements and computer simulations

Sound transmission through nominally identical 1.5×1.25-m steel plates was measured in two laboratories; NRC, Canada and PTB, Braunschweig in Germany. This sound paper presents results from a more detailed examination of the behavior of the sound fields at low frequencies in the laboratories. The long-term aim of the work is to understand reasons for poor reproducibility of low-frequency sound reduction measurements in laboratories. Narrow-band sound transmission measurements were made between the two pairs of rooms at PTB and NRC. In each case, the same procedure was used; loudspeakers were fed with a pseudorandom sequence and the impulse response was calculated using a Hadamard transform. The two sound transmission suites were also simulated using FEM and BEM programs. Comparisons between the measured and calculated results will be presented and discussed.

The measurement of structure-borne sound transmission at plate junctions by an energy intensity method

Energy intensity methods have been used in an investigation of bending vibration transmission at a T-junction of thin plates subjected to point excitation. The attenuation at the junction was estimated in a simulation of anechoic conditions where the plate edges are damped in order to produce nonreflective terminations. This was only partially successful and increased discrimination was obtained by use of impulse response methods and by spatial averaging. Peaks in transmission loss between coplanar plates are indicated theoretically and experimentally, but there are discrepancies with respect to the angles at which these peaks occur. The increase in level difference with increased angle of incidence is seen for the case of transmission between plates at right angles.

Sound transmission through wood joist floor/ceiling systems: A study of the effects of sound absorbing materials and changes to the ceiling structure

A wood joist floor system was constructed in the Acoustics Laboratory at NRC. Measurements of airborne and impact sound transmission were made for different types and amounts of sound absorbing material in the cavity. Differences between materials were small. Different makes of resilient metal channels were installed; all gave about the same results. Methods of improving an unsatisfactory floor were examined. Over 20 floor systems were measured. The study was funded by Canada Mortgage and Housing Corporation. Measurements were made down to 63 Hz and revealed that in many cases there are resonances occurring below 125 Hz that have a strong influence on transmission loss values at and above 125 Hz. While the causes of the resonances are not always clear, measurements to these low frequencies give a clearer picture of the effect of changes to the structure. This paper will give a summary of the results obtained.

Reflection and transmission of elastic waves from a fluid-saturated porous solid boundary

Based on the classical work of Biot [J. Acoust. Soc. Am. 28, 168 (1956)] which predicts that three different kinds of bulk waves may propagate in the fluid-saturated porous solid, the wave equation is solved to determine the energy reflection and transmission coefficients of plane elastic waves at oblique incidence on an interface between a fluid and a fluid-saturated porous solid. For this purpose, the necessary formalism of the energy equation, the Poynting energy flux vector, and the sound intensity of elastic waves in fluid-saturated porous media are presented. Two general cases of mode conversion have been investigated: (1) The initial wave is incident from the fluid to the interface and generates three transmitted bulk waves in the fluid-saturated porous solid, and (2) the initial wave is incident from the fluid-saturated porous solid to the interface and generates three reflected bulk waves in the same medium. Furthermore, the transmission of sound through a fluid-saturated porous solid plate immersed in fluid is calculated. Measurement of sound transmission through a porous plate was carried out using experimental techniques suggested by Plona [Appl. Phys. Lett. 36, 259 (1980)]. Good correlation between measured and calculated values of the angular behavior of the transmission coefficients for fast, shear, and slow waves was obtained after adjusting the theory for experimentally obtained attenuation.