Renzo Vitale

Objective and perceptual assessment of the scattered sound field in a simulated concert halla)

Acoustic scattering audibility thresholds are needed for the efficient design of performance spaces and to increase the accuracy of geometric room acoustic models. This paper focuses on the evaluation of the perceptual thresholds of the scattering coefficient through listening tests in simulated concert halls. It also deals with an investigation on the sensitivity of room acoustic parameters to scattering coefficients. A rectangular concert hall has been simulated with three prediction models, in which scattering coefficients of 0.1, 0.3, 0.5, 0.6, 0.7, and 0.9 were applied to the ceiling and walls in six different configurations. The analysis was performed comparing the results of the three-alternative forced choice listening tests and considering the objective parameters T30, early decay time (EDT), C80, and G. An increase in EDT and a decrease in C80 have been observed for increasing scattering coefficient values for all three types of software, while no similar trend was observed for the other parameters. The perceptual evaluation has shown that differences of ∼0.4, relative to an anchor value of 0.9 of the scattering coefficient, were perceived in the listening test conducted with one of the three kinds of software, while no clear differences in auralizations were perceived with the other two kinds.

Perception of scattering coefficient in auralized concert halls.

The scattering coefficient has become a determinant parameter in room acoustic software because it enhances the precision of simulation results. Although there is a wide agreement on the necessity of using scattering coefficients for characterizing surfaces and pattern elements within an enclosed space such as a concert hall, there is still a lack of knowledge on the influence of this on the human perception. The primary purpose of this study is to investigate how changes in scattering coefficients of diffusing surfaces could possibly affect the perception of music among the audience in concert halls. A simplified shoebox‐like geometry was used to generate binaural room impulse responses under various scattering conditions for different seats. Computer simulation results were convolved with sound examples, which were properly selected as representative of typical music textures. Results from listening tests will be shown and discussed.

Investigation of the just noticeable difference of scattering coefficient in auralized concert halls.

The use of scattering coefficient in room acoustics simulations has proved to be an essential factor for improving the validity of results, as it quantifies the amount of the diffuse sound field in enclosed spaces. Measurement methods have been described in the norm ISO 17497. Available data, whose lack is still one of the weak points, are fairly growing. Moreover, the relationship between the physical quantity and perceptual aspects still remains unclear. Aim of this study is a first investigation toward the comprehension of the influence of scattering coefficient on the sound as perceived from the audience. The target is to quantify the just noticeable differences for variable scattering coefficients associated with lateral wall diffusers of a simulated concert hall. Several musical stimuli convolved with binaural room impulse responses are used as source signals for listening tests. Results focusing on perceptual aspects will be presented and discussed.

A revised scale model reverberation chamber for measurements of scattering coefficients.

For measurements of random‐incidence scattering coefficients according to ISO 17497‐1, scale models have proven to yield results with reasonable time and effort. Especially, handling the samples becomes much easier so that several measurements, which may be difficult or even unfeasible in a full‐scale reverberation chamber, turn out to be possible. Despite these advantages, using a scale model environment poses other difficulties that are related to the extended frequency range. In order to achieve a better repeatability and stability of the measurements, a revised scale model room is proposed. As a further development from the ordinary scale model rooms, the turntable can now be lowered so that the rotating base plate is mounted flush with the floor. The previously used hanging panels have been replaced with wall‐panel diffusers. Furthermore, the chamber includes temperature and humidity sensors to enable correction for air absorption. Measurements in the new model room are performed to evaluate the quality of the results compared with reference data from calculation and the repeatability of the measurements. Results will be compared for different room setups.

Describing measurement uncertainties in room acoustics with the concept of GUM

Considering the uncertainties in room acoustical measurements is a crucial step towards quality evaluation, comparability between different measurements methods and instrumentation. In the preceding discussion it was shown that the concepts specified in the Guide to the expression of Uncertainty in Measurements (GUM) can well be applied for room acoustical measurement tasks. In this initiatory step a detailed analytical formulation of a model function was avoided for reasons of simplicity and practicability. The waiving of complex modeling, however, requires comprehensive series of measurements to assess the measurement uncertainties. In this paper it is discussed how modeling can reduce such requirements. A special focus is placed on the influence of the directional radiation properties of sound sources.

Measurement uncertainty of scattering coefficients in scale models.

The measurement of the scattering coefficient is defined in ISO 17497‐1. The method evaluates random‐incidence absorption coefficients obtained from measured reverberation times for four different configurations. Measurements in a scale model reverberation chamber are preferred to real scale chambers for several reasons. Requirements in terms of time invariance are easier to fulfil and the handling of samples is simpler. Although the use of a scale model renders the measurements easier, results are still affected by an uncertainty that is currently not considered when using these results for ongoing simulations or predictions. Moreover, air absorption at very high frequencies causes the measured reverberation times to be very similar, thus influencing the validity of the results in this frequency range. This paper aims to determine the measurement uncertainty of the scattering coefficients in a scale model reverberation chamber. A simplified uncertainty model will be presented taking into account the unce...

The influence of the source directivity on the measurement uncertainty

Modelling can play a key role in assessing the measurement uncertainties, as specified in the Guide to the expression of Uncertainty in Measurements (GUM). A model is presented that is used to quantify the influence of the source directivity on the measurement uncertainty. On the grounds of image sources and radiosity methods the propagation of sound in rooms is simulated. In this model the characteristics of dodecahedron sound sources are implemented with their statistical properties and characteristics. In Monte Carlo Simulations these two core concepts are combined and the results are compared with measurement results. This comparison allows a quality assessment of the model. In a conclusion the input quantities that affect the measurement uncertainty that is introduced by the source directivity are identified.