David T. Bradley

Speed of Sound in Four Primary Alcohols as a Function of Temperature and Pressure

Sound velocities have been measured in methyl, ethyl, n‐propyl, and n‐butyl alcohol for temperatures and pressures in the ranges 0°C < T < 60°C and 14.7 lb/in2 < P < 14000 lb/in2. The data obtained for ethyl alcohol have been used to compute the ratio of specific heats for this alcohol.

The effects of simple coupled volume geometry on the objective and subjective results from nonexponential decay

This project focuses on the individual and interactive acoustic effects of three architectural parameters on the double slope profile from a simple coupled volume system created in the computer modeling program ODEON. The three variables studied are the volume ratio between the main and secondary spaces, the absorption ratio between the two spaces, and aperture size. The resulting energy decay profiles are analyzed using T30∕T15 coupling coefficient ratios and Bayesian analysis. Coupling coefficient results show general trends in the effects of the three architectural parameters that match previous research results and the predominant interactive effect between the three variables involving a large coupled volume. Similar results are suggested by the Bayesian analysis based on the newly developed quantifiers, decay ratio and ΔdB, although a more complex relationship among the variables may exist at larger volume ratios. A subset of the simulated sound fields have been auralized and used to conduct psychoa...

Sound images of the ocean: In research and monitoring

This article reviews Sound images of the ocean: In research and monitoring by Peter Wille 472 pp , Berlin, 2005.

Sound Propagation in Near‐Stoichiometric Ti‐Ni Alloys

129.00. ISBN3540241221 (hardcover).

Optimum absorption and aperture parameters for realistic coupled volume spaces determined from computational analysis and subjective testing results

Experimental data on sound velocity illustrate the unusual velocity‐temperature relationship of near‐stoichiometric nickel‐titanium alloys. The effect of temperature cycling, annealing, pressure, minimum exposure temperature, and time is also shown.

Comparison of Measured and Computer-Modeled Objective Parameters for an Existing Coupled Volume Concert Hall

This project utilizes computational modeling to study the effects of varying two architectural parameters, absorption ratio and aperture size, in a realistic coupled volume concert hall. Coupled volumes have been shown to exhibit non-exponential sound energy decay profiles, referred to as double slope effect. A number of objective metrics (T30/T15, LDT/T10, decay ratio, and DeltaL) have been used to quantify the double slope effect of the profiles generated in the virtual hall. T30/T15 and LDT/T10 showed similar trends across all hall configurations, indicating decreasing double slope effect with increasing coupled volume absorption ratio for each aperture size, and producing highest values at a specific aperture size for each absorption ratio. Generally, LDT/T10 provides finer resolution than T30/T15 when analyzing the decay profiles in this study. Results from the two metrics derived from Bayesian analysis, decay ratio and DeltaL, seem less consistent. Subjective testing has also been conducted to determine the effect of varying the two architectural parameters in the hall, and multidimensional scaling analysis shows that, in general, listener preference is inversely proportional to the level of double slope effect, with the highest levels of preference occurring at low and medium levels of double slope effect. Recommended design guidelines for coupled volume halls are provided based on these computational and subjective results.

Effect of boundary diffusers in a reverberation chamber: Standardized diffuse field quantifiersa)

This paper details the comparison of a built coupled volume concert hall and a computer-generated model of the hall. Coupled volume spaces typically have an auxiliary volume connected to the main volume through an acoustically transparent aperture. In this type of space, architectural parameters such as volume size and surface absorption can be designed to produce a non-linear reverberant decay, known as double-slope decay. Objective reverberation and clarity parameters were calculated for the sound fields measured in the built hall and predicted in the computer modeled hall. These objective parameters were compared between the two modalities for several configurations of the hall to determine the accuracy of the computer modeling prediction scheme for coupled volume spaces. The results showed a high level of computer model accuracy in the high frequency range, with differences in reverberation parameters being less than 1 just noticeable difference (jnd). Lower frequencies proved computer modeling to be less accurate, particularly for the clarity parameter, which had differences up to 8 jnd.

Quantifying the double slope effect in coupled volume room systems

The sound field inside a reverberation chamber must have a high degree of diffusivity to allow for the accurate measurement of various acoustic quantities. Typically, hanging or rotating diffuser panels are installed in the chamber in an effort to achieve this diffusivity. However, both of these diffuser types have certain limitations, and adequate sound field diffusivity is often difficult to realize. A 1:5 scale reverberation chamber has been used to systematically analyze the relative effectiveness of hanging diffusers versus an alternative diffuser type referred to as a boundary diffuser. To characterize sound field diffusivity, three quantifiers from the ASTM E90, ASTM C423, and ISO 354 standards have been used: maximum absorption coefficient, standard deviation of decay rate, and total confidence interval. Analysis of the quantifier data reveals that boundary diffusers and hanging diffusers produce roughly equivalent diffusion in the sound field. The data also show that the standards have certain inconsistencies that can obfuscate the characterization of sound field diffusivity, which may explain reproducibility and repeatability issues previously documented in the literature.

Comparison of Hanging Panels and Boundary Diffusers in a Reverberation Chamber

Coupled volume spaces are typically defined as a main volume connected to an auxiliary volume through an acoustically transparent aperture. Given certain architectural parameters, coupled volumes can exhibit a non-exponential sound energy decay, referred to in this paper as double slope effect (DSE). This paper provides an overview and comparison of several quantifiers of DSE. Four numeric DSE quantifiers, T30/T15, LDT/EDT, Decay Ratio, and ΔdB were used to analyze the energy decays produced in a computational model of an existing coupled volume concert hall. Each quantifiers ability to indicate changes in DSE was determined through comparative analysis. LDT/EDT was found to differentiate most between the levels of DSE in the sample decay curves. T30/T15 was also able to demonstrate changes in DSE, although not with the same level of sensitivity as LDT/EDT. Decay Ratio and ΔdB as determined from Bayesian analysis results did not indicate any DSE across the four cases studied; further research is recommended on applying Bayesian analysis to decay curves from realistic coupled volume scenarios.

Experimental quantification of a novel reverberation chamber diffusing panel.

Achieving a diffuse sound field in a reverberation chamber is crucial for measurements of acoustic quantities such as sound absorption coefficient, scattering coefficient, and sound power level. Toward this aim, diffusing elements such as hanging panels or rotating diffusers are typically installed in the chamber. However, previous research has suggested that hanging panels violate certain theoretical assumptions regarding diffusivity. Also, rotating diffusers cause the chamber to be a time-variant system, precluding the use of some measurement approaches such as sine-sweep integrated impulse response techniques. Boundary diffusers are offered as an alternative in the current study. The effects of both hanging panels and boundary diffusers on sound field diffusivity in a scale reverberation chamber are systematically and comparatively analyzed. The field diffusivity is characterized based on the guidelines set forth in American and international standards, including ISO 354, ASTM C423, and ASTM E90. Resulting data suggests that these standardized methods do not adequately or rigorously quantify diffusivity. The relative effectiveness of hanging diffusers vs. boundary diffusers will be discussed.