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Abstract-For the evaluation of the acoustic performance of electrical machines in variable operating conditions, a real-time auralization procedure applicable in virtual reality environments is developed. Electromagnetic forces, structural dynamics and acoustic radiation as well as room acoustic aspects are considered. The combination of electromagnetic simulation with a unitwave response-based approach and a room acoustic virtual environment software allows for an efficient implementation. Simulation results are shown for two different types of electrical machines-one induction machine and one permanent magnet synchronous machine. Practical experiments are used to finetune and validate the numerical models.

In a number of independent empiric studies it was shown that room acoustic single number parameters vary severely with small changes of the source and microphone position. Presently there is no evidence that these spatial fluctuations can be modelled using simulated impulse responses. As a result there is limited knowledge about the origin and the contributing influence factors of this variance over space. In this contribution the results of simulations using wave based as well as ray tracing simulations are compared to each other. It will be discussed if these simulations are able to predict the fluctuations that were found in measurement series taken in a number of different auditoria. Comparison of Strategies to Model Spatial Fluctuations of Room Acoustic Single Number Quantities Second it is discussed whether the sharp time windowing of the RIR, which is part of the algorithm to calculate many predictors such as C 80 or LF, will enhance the fluctuations. Although de Vries et al. shows an example in which a smoothly fading time window reduces the fluctuations, there is reason to believe that other influences potentially contribute to this phenomenon. This aspect can be illustrated when the 522 RIRs of the Concertgebouw measurement data are reanalysed and both C 80 and "center time" are calculated. The results are shown in figure 1. Both sound field parameters shown in figure 1 are accepted predictors for the perceived clarity of sound. In contrast to clarity, "center time" doesn't rely on sharp time windows. Still the spatial characteristics of both parameters show measurable fluctuations. In both cases the fluctuations exceed the values for the just noticeable differences (for C 80 = 1 dB and t c = 0.01 s) published in ISO 3382 1. Therefore the significance of other influence factors for the spatial fluctuations needs to be considered.

This paper investigates a way of determining and modeling uncertainty contributions in measurements of room acoustic parameters, which are commonly used to describe the acoustic situation of a room in an objective manner. If the range of uncertainty and the confidence interval are not given, the results remain incomparable to other measurement teams, since modern PC-based measurements still show appreciable sources of measurement errors. The Guide to the Expression of Uncertainty in Measurement (GUM) defines a unified guideline for determining uncertainties in all fields of measurement. Its application is increasingly required by modern measurement standards. However, the GUM procedures have not been applied to room acoustics yet. Hence, a scalable linear approach for calculating the combined uncertainty of room acoustic parameters with regard to the input quantities is proposed. In-situ measurement results of specially designed experiments show the significance of the main influence factors and are used to build the uncertainty budget.

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