Rhc Remy Wenmaekers

Measuring room impulse responses : impact of the decay range on derived room acoustic parameters

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On measurements of stage acoustic parameters : time interval limits and various source-receiver distances

The most widely recognized objective stage acoustic parameters are the Early Support (STearly) and Late Support (STlate ). In these parameters the early and late reflected sound energy is measured within a certain time interval. Different time interval limits have been proposed for the stage acoustic parameters but there is no agreement on the preferable limits. There is a growing interest to measure stage acoustic parameters at various source to receiver distances. In this paper the influence of perceptual and architectural parameters, synchronicity, source to receiver relationship and the measurement system on stage acoustic parameters is discussed. Based on existing and new insights an optimization and extension of the ST parameters is proposed such that they can be measured at any distance between source and receiver using the most appropriate time interval limits. Theoretical assumptions were checked and confirmed based on systematic analyses of measured results for different concert hall stages with various conditions and various source to receiver distances.

Acoustic modelling of sports halls, two case studies

To achieve a preferable sound field in traditionally shoebox-shaped sports halls, the sound absorbing material is often applied in the upper part of the hall. The applicability of predicting the acoustics of sports halls by three different acoustic calculation methods is investigated: a diffuse field method, a geometrical acoustics method and a full wave-based method. The predicted reverberation time and sound pressure level are compared to measured data for two sports halls in the low frequency range up to the 630 Hz ⅓ octave band. From the three methods, results from the wave-based method agree best with the measured results. Results indicate the importance of the chosen material properties in the prediction methods used. Sound pressure levels resulting from the diffuse field method are comparable with results from the other prediction methods, but the reverberation time prediction is not reliable using this method.

The effective air absorption coefficient for predicting reverberation time in full octave bands

A substantial amount of research has been devoted to producing a calculation model for air absorption for pure tones. However, most statistical and geometrical room acoustic prediction models calculate the reverberation time in full octave bands in accordance with ISO 3382-1 (International Organization for Standardization, 2009). So far, the available methods that allow calculation of air absorption in octave bands have not been investigated for room acoustic applications. In this paper, the effect of air absorption on octave band reverberation time calculations is investigated based on calculations. It is found that the approximation method, as described in the standard ANSI S1.26 (American National Standards Institute, 1995), fails to estimate accurate decay curves for full octave bands. In this paper, a method is used to calculate the energy decay curve in rooms based on a summation of pure tones within the band. From this decay curve, which is found to be slightly concave upwards, T20 and T30 can be determined. For different conditions, an effective intensity attenuation coefficient mB ;eff for the full octave bands has been calculated. This mB ;eff can be used for reverberation time calculations, if results are to be compared with T20 or T30 measurements. Also, guidelines are given for the air absorption correction of decay curves, measured in a scale model.

Early and Late Support Measured over Various Distances: The Covered versus Open Part of the Orchestra Pit

The Early and Late Support parameters (STearly and STlate) are used to describe acoustic conditions on stage. Recently, extended Support parameters have been introduced which can be measured at various distances: STearly,d and STlate,d. This way, the amount of reflected sound energy can be studied for sound paths with distances between source and receiver larger than 1 meter. Occasionally, Early and Late Support are also used to investigate orchestra pits. Using the extended Support parameters, the mutual support from reflections between the positions in the open and covered part of the orchestra pit has been investigated. It is found that, when plotting STearly,d as a function of distance, three different trends are found each having a distinctive shape for different types of source and receiver positions: both positions in the open part; both positions in the covered part; and just one of both positions in the open or covered part. When comparing the different trends, a large increase is found in early reflected sound energy when either source or receiver or both are in the covered part of the pit. In the covered part, at 1 meter distance the level of reflected sound can even be in the same order of magnitude as the direct sound. When considering the late reflected sound energy it was found that STlate,d was not dependent on the source to receiver distance and less difference was found between the open and covered part of the orchestra pit.