Non-acoustical Parameters Research Articles

Comparisons between characteristic lengths and fibre equivalent diameters in glass fibre and melamine foam materials of similar flow resistivity

Abstract Flow resistivity, tortuosity, viscous characteristic length and thermal characteristic length of three melamine foam and two glass wool samples have been measured. It has been found that a melamine foam sample with a bulk density 10.3 kg m−3 and a glass wool sample with a bulk density 28.0 kg m−3 have almost the same flow resistivity, however, the bulk density is as much as three times different. The cross-sectional pore shape factors, which are deduced with the non-acoustical parameters in the Johnson–Allard model, of the melamine foam are smaller than those of the glass wool. This paper also discusses a new relationship between the flow resistivity, the fibre equivalent diameter and the bulk density in melamine foam.

Designing acoustic and non-acoustic parameters of synthesized speech warnings to control perceived urgency

To refine synthesized speech warning systems with urgency mapping, various kinds of acoustic and non-acoustic parameters were explored, and the relationship between the parameters and the subjectively perceived urgency was investigated through a series of experiments. The results showed that the speech rate, average fundamental frequency ( F0), warning message, message format, gender of voice, and interval between warning messages strongly influence the subjectively perceived urgency of synthesized voice warnings. For the three quantitative parameters: speech rate, average F0, and interval between warning messages, the results showed that it is possible to use psychophysical techniques (Stevens's power law) to quantify the effects of acoustic changes on perceived urgency.

Experimental determination of the micro- and macrostructural parameters influencing the acoustical performance of fibrous media

Measurements of the two characteristic lengths of 6 glass wool samples (with flow resistivities between 11,900 and 69,900 Pa s m −2) and 6 polyester fibre samples (with flow resistivities between 4100 and 51,000 Pa s m −2) have been made. These data have been used to determine the cross-sectional shape factors which are related to the characteristic lengths introduced by Allard. By using the formulas due to Bies and Allard, it has been found that the two characteristic lengths of the glass wool samples can be independently predicted from the glass fibre diameter. In respect to polyester fibre samples, a new relation between the flow resistivity, the fibre diameter and the bulk density has been proposed and examined. The accuracy of the predictions of the non-acoustical parameters has been confirmed by the measurements and predictions of the absorption coefficient using the Delany and Bazley and Allard models.

Traditional measurement methods for characterizing soundscapes

A soundscape may be defined as the acoustical environment at an outdoor location. The physical sound occurring at the location may be from natural or man‐made sources, or both. Perception of the soundscape can provide comfort and needed information to the listener, or may be annoying. The existing soundscape may be subject to design modifications for a variety of purposes. The goal could be to protect or enhance some sounds, such as the laughter of children and chirps of wildlife in a park, or the speech in an amphitheater. Conversely, the goal may be to reduce or eliminate unwanted sounds, such as transportation or industrial noise. Engineering and aesthetic soundscape design may proceed based on the characterization of the acoustical environment. The soundscape can be characterized by a number of measured acoustical parameters. Traditionally, these parameters have included A‐weighted sound level, spectral content, sound‐level statistics and averages, alone or in combination, and sound‐level time history. Listener perceptions and nonacoustical parameters, such as time of day or year, community relevance, and listener attitudes may also be applied to soundscape characterization and design. Examples of several different soundscapes, their characterizations, and proposed design modifications will be discussed.

Assessment of impact of acoustic and nonacoustic parameters on performance and well-being

It is of interest to estimate the influence of the environment in a specific work place area on the performance and well-being of people. Investigations have been carried out for the cabin environment of an airplane and for class rooms. Acoustics is only one issue of a variety of environmental factors, therefore the combined impact of temperature, humidity, air quality, lighting, vibration, etc. on human perception is the subject of psychophysical research. Methods for the objective assessment of subjective impressions have been developed for applications in acoustics for a long time, e.g., for concert hall acoustics, noise evaluation, and sound design. The methodology relies on questionnaires, measurement of acoustic parameters, ear-related signal processing and analysis, and on correlation of the physical input with subjective output. Methodology and results are presented from measurements of noise and vibration, temperature and humidity in aircraft simulators, and of reverberation, coloring, and lighting in a primary school, and of the environmental perception. [The work includes research with M. Klatte, A. Schick from the Psychology Department of Oldenburg University, and M. Meis from Hoerzentrum Oldenburg GmbH and with the European Project HEACE (for partners see www.heace.org).]

Bioeffects caused by changes in acoustic cavitation bubble density and cell concentration: a unified explanation based on cell-to-bubble ratio and blast radius.

Acoustic cavitation has been shown to load drugs, proteins and DNA into viable cells as a complex function of acoustic and nonacoustic parameters. To better understand and quantify this functionality, DU145 prostate cancer cell suspensions at different cell concentrations (2.5 x 10(5) to 4.0 x 10(7) cells/mL) were exposed to 500 kHz ultrasound (US) over a range of acoustic energy exposures (2 to 817 J/cm(2); peak negative pressures of 0.64 to 2.96 MPa; exposure times of 120 to 2000 ms) in the presence of different initial concentrations of Optison contrast agent bubbles (3.6 x 10(4) to 9.3 x 10(7) bubbles/mL). As determined by flow cytometry, molecular uptake of calcein and cell viability both increased with increasing cell density; viability decreased and uptake was unaffected by increasing initial contrast agent concentration. When normalized relative to the initial contrast agent concentration (e.g., cells killed per bubble), bioeffects increased with increasing cell density and decreased with increasing bubble concentration. These varying effects of contrast agent concentration and cell density were unified through an overall correlation with cell-to-bubble ratio. Additional analysis led to estimation of "blast radii" over which bubbles killed or permeabilized cells; these radii were as much as 3 to 90 times the bubble radius. Combined, these results suggest that extensive molecular uptake into cells at high viability occurs for low-energy exposure US applied at a high cell-to-bubble ratio.

Acoustic granular materials with pore size distribution close to log-normal

The water suction method is used to determine the parameters of the pore size distribution of a representative selection of loose and consolidated granular materials. It is shown that the experimentally determined pore size distribution in granular materials is often close to log-normal. The low- and high-frequency asymptotic behavior of the Biot viscosity correction function for media with log-normal pore size distribution is investigated and used to develop a simple rational approximation. This approximation is used to predict accurately the acoustic characteristic impedance and propagation constant for this class of materials. Unlike many available theoretical models for the acoustic properties of porous media which involve empirical shape factors, the proposed approximation is based entirely on four routinely measurable nonacoustic parameters: the porosity, flow resistivity, tortuosity, and the standard deviation of the pore size. The theoretical predictions for the acoustic surface impedance and absorption coefficient of loose and consolidated granulates are compared against the experimental results. A good agreement is obtained throughout the considered frequency range. [The authors are grateful to the Engineering and Physical Sciences Research Council (EPSRC) in the UK (Grant GR/L54905) for the support of this work. The authors would like to thank Dr. P. Leclaire for his help with the water suction experiments.]

The acoustic properties of granular materials with pore size distribution close to log-normal.

The majority of realistic porous materials are composed of pores of which the shape is variable and the size of the pores normally obeys a distinctive statistical distribution. Although the variation of pore shape is less important, the statistical parameters of pore size distribution can have a considerable effect on the acoustic properties of porous media. This paper discusses the application of a simple model for the prediction of the acoustic properties of porous granular media with some assumed pore geometry and pore size distribution close to log-normal. The model is based on the rational (Padé) approximation approach [K. V. Horoshenkov, K. Attenborough, and S. N. Chandler-Wilde, J. Acoust. Soc. Am. 104, 1198-1209 (1998)] which has been developed for some simple pore geometries. It is shown that the experimentally determined pore size distribution for a representative range of granular materials is often close to log-normal. This assumption enables accurate predictions of the acoustic performance of these materials using the presented model. The water suction method is proposed to determine the parameters of the log-normal distribution, which are the mean pore size, (phi) and its standard deviation, sigma. This method is nonacoustic, modelless and well-adapted to acoustic materials and, unlike the BET method [S. Brunauer, P. H. Emmett, and E. Teller, J. Am. Chem. Soc. 60, 309-319 (1938)], is easy to reproduce in any basic acoustic laboratory requiring no expensive parts or chemicals. The proposed Padé approximation is based entirely on four measurable nonacoustic parameters, the porosity, omega, flow resistivity, Rb, tortuosity, q2 and the standard deviation of the pore size, sigma. The method is successfully tested on a representative selection of consolidated and nonconsolidated porous granular materials.

The effect of consolidation on the acoustic properties of loose rubber granulates

Acoustic measurements performed on non-spherical granular mixtures with different states of consolidation suggest that their acoustic performance can be related to that measured in loose granular mixes. It was found that the non-acoustic parameters of the pore size distribution, porosity, tortuosity and flow resistivity are highly sensitive to the median grain size in the mix, the compaction ratio and the binder content. The effects of these parameters on the acoustic properties have been investigated for a number of loose and consolidated samples with different grain sizes. Several established models for the acoustic properties of rigid-frame porous media have been tested. It is shown that some models can fail to predict accurately the acoustic properties of these materials and can require considerable adjustment of the input parameters. In this respect, the experimental results are of importance in the development of a scientific methodology for the design of granular absorbers with good acoustic efficiency and sound mechanical properties.

A simple tester provides resonant frequency measurements of ferrite devices

Measurements of the two characteristic lengths of 6 glass wool samples (with flow resistivities between 11,900 and 69,900 Pa s m−2) and 6 polyester fibre samples (with flow resistivities between 4100 and 51,000 Pa s m−2) have been made. These data have been used to determine the cross-sectional shape factors which are related to the characteristic lengths introduced by Allard. By using the formulas due to Bies and Allard, it has been found that the two characteristic lengths of the glass wool samples can be independently predicted from the glass fibre diameter. In respect to polyester fibre samples, a new relation between the flow resistivity, the fibre diameter and the bulk density has been proposed and examined. The accuracy of the predictions of the non-acoustical parameters has been confirmed by the measurements and predictions of the absorption coefficient using the Delany and Bazley and Allard models.

Ultrasonic beam transducer

Measurements of the two characteristic lengths of 6 glass wool samples (with flow resistivities between 11,900 and 69,900 Pa s m−2) and 6 polyester fibre samples (with flow resistivities between 4100 and 51,000 Pa s m−2) have been made. These data have been used to determine the cross-sectional shape factors which are related to the characteristic lengths introduced by Allard. By using the formulas due to Bies and Allard, it has been found that the two characteristic lengths of the glass wool samples can be independently predicted from the glass fibre diameter. In respect to polyester fibre samples, a new relation between the flow resistivity, the fibre diameter and the bulk density has been proposed and examined. The accuracy of the predictions of the non-acoustical parameters has been confirmed by the measurements and predictions of the absorption coefficient using the Delany and Bazley and Allard models.

Ultrasonic inspection and fail-safe indication method and apparatus

Measurements of the two characteristic lengths of 6 glass wool samples (with flow resistivities between 11,900 and 69,900 Pa s m−2) and 6 polyester fibre samples (with flow resistivities between 4100 and 51,000 Pa s m−2) have been made. These data have been used to determine the cross-sectional shape factors which are related to the characteristic lengths introduced by Allard. By using the formulas due to Bies and Allard, it has been found that the two characteristic lengths of the glass wool samples can be independently predicted from the glass fibre diameter. In respect to polyester fibre samples, a new relation between the flow resistivity, the fibre diameter and the bulk density has been proposed and examined. The accuracy of the predictions of the non-acoustical parameters has been confirmed by the measurements and predictions of the absorption coefficient using the Delany and Bazley and Allard models.