On the practical application of the impulse response measurement method with swept-sine signals in building acoustics.

Impulse response (IR) measurement methods with deterministic signals have been used in various fields of acoustics for decades, yet there is still a hesitancy to apply them by some practitioners, especially in the building acoustics community. This hesitancy is also the topic of discussion in ASTM standards committees because IR methods are not allowed in ASTM standards. The criticism that prevents a more widespread adoption is that the description of IR methods in existing standards such as ISO 18233 is not sufficient to enable practitioners and equipment manufacturers to reliably implement them. Previous publications have described the theoretical background well, but they have not given sufficient guidance for the practical application with respect to the parameters of the measurement signal. To provide more guidance and show the practical advantages of IR measurement methods, this paper investigates the effects of the design parameters of swept-sine signals. Measurements in a reverberant chamber are used to highlight potential problems and appropriate solutions derived from a theoretical background. Suggestions for the design of measurement signals and for the post-processing of the measured data are provided to achieve optimal and reliable results. This contribution hopefully gives practitioners more confidence in applying the method in the future.

Relationship between the privacy index and the speech privacy class.

It is regularly debated which metric to use for the assessment of architectural speech privacy. For open-plan offices, the Privacy Index, derived from the Articulation Index according to ASTM E1130 (2016), is usually used. For closed offices, the Speech Privacy Class is determined according to ASTM E2638 (2010). Disregarding the measurement method, and the fact that the metrics show different behavior regarding the Signal-to-Noise Ratio, both metrics are directly related and values of the Speech Privacy Class can thus be converted to Privacy Index values. The relationship is demonstrated and the result is validated with field and laboratory measurement data.

Acoustic source localization with microphone arrays for remote noise monitoring in an Intensive Care Unit.

An approach is described to apply spatial filtering with microphone arrays to localize acoustic sources in an Intensive Care Unit (ICU). This is done to obtain more detailed information about disturbing noise sources in the ICU with the ultimate goal of facilitating the reduction of the overall background noise level, which could potentially improve the patients' experience and reduce the time needed for recovery. This paper gives a practical description of the system, including the audio hardware setup as well as the design choices for the microphone arrays. Additionally, the necessary signal processing steps required to produce meaningful data are explained, focusing on a novel clustering approach that enables an automatic evaluation of the spatial filtering results. This approach allows the data to be presented to the nursing staff in a way that enables them to act on the results produced by the system.

Uncertainty analysis of standardized measurements of random-incidence absorption and scattering coefficients.

This work presents an analysis of the effect of some uncertainties encountered when measuring absorption or scattering coefficients in the reverberation chamber according to International Organization for Standardization/American Society for Testing and Materials standards. This especially relates to the uncertainty due to spatial fluctuations of the sound field. By analyzing the mathematical definition of the respective coefficient, a relationship between the properties of the chamber and the test specimen and the uncertainty in the measured quantity is determined and analyzed. The validation of the established equations is presented through comparisons with measurement data. This study analytically explains the main sources of error and provides a method to obtain the product of the necessary minimum number of measurement positions and the band center frequency to achieve a given maximum uncertainty in the desired quantity. It is shown that this number depends on the ratio of room volume to sample surface area and the reverberation time of the empty chamber.

Effect of boundary diffusers in a reverberation chamber: standardized diffuse field quantifiers.

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.

On the in situ impedance measurement with pu-probes--simulation of the measurement setup.

High-quality numerical simulations in room acoustics require a detailed knowledge of the acoustic reflection characteristics of the materials in the room, in order to realistically model the interferences between multiple sound reflections at the room boundaries. While different standardized measurement methods exist for the determination of the absorption coefficient and reflection factor these methods can generally not be applied in situ. Thus time-consuming laboratory measurements and the supply of material samples are required. Driven by the obvious demand for a reliable in situ measurement technique, a pu-probe based method has emerged during the last years, which derives the reflection factor based on the simultaneous measurement of sound pressure and velocity. However, previous investigations of the setup and publications by other authors have shown that the measurement results are affected by various uncertainty factors. The present study aims at the identification, separation, and quantitative assessment of the uncertainty factors related to reflection and diffraction effects at the loudspeaker, sensor, and the absorber geometry. Therefore, a purely simulative approach will be used that replicates the actual measurement situation in every detail, including the geometries of sensor, loudspeaker, and absorber. The simulation setup is validated by measurements and is used to systematically separate the different uncertainty factors.