Comparison of Strategies to Model Spatial Fluctuations of Room Acoustic Single Number Quantities

Abstract

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.

Measurements in room acoustics

“…That's why it is important that the collected data be suitable for this analysis. Previously, pilot studies (Witew, Dietrich, de Vries, & Vorländer, 2010;Witew, Dietrich, Pelzer, & Vorländer, 2013) showed how the collected data from regularly sampled sound fields could be processed to determine the model function f . The rationale to establish f is discussed in detail in Section 7.…”

“…In this regard it is particularly important to study whether geometrical methods can correctly predict fluctuations when their rationale does not consider modal effects. First steps were already made by Witew, Dietrich, et al (2013).…”

Sound Goes Round the Quest for Omnidirectional Radiation

“…Maximizing the driver opening angle, which effectively defines the diameter of the vibrating piston, lowers the summation of acoustic output contributions from adjacent drivers and reduces lobing interferences [9]; 8. Driver equalization can reduce group delay variations within a given bandwidth to minimize low-frequency group delay from affecting the room impulse response that is time-windowed before filtering [2].…”

The Effect of Changes in Position of Sound Source and Microphone on Acoustic Measurements in Small Rooms. A Case Study

“…In the paper [3] it was shown what accuracy is required when reporting the position of a receiver was used for room acoustic measurements (C 80 was discussed).…”