Estimation of Reverberation Time in Rectangular Rooms with Non-Uniformly Distributed Absorption Using a Modified Fitzroy Equation

Abstract

One of the major objectives of architectural acoustics is to predict the reverberation time in a room. At this time there are several calculation methods to compute the reverberation time, but still Sabine's and Eyring's classical equations are used. In many practical cases the assumption of diffuse sound field conditions for applying Sabine's theory are not in agreement with the existing sound absorption distribution. Therefore, Sabine's formula, as well as other classical reverberation equations like Eyring's or Millington-Sette's, cannot be applied accurately. In 1959 Fitzroy published a paper devoted to the problem of a more accurate calculation of the reverberation time with non-uniformly distributed absorption. In real rooms Fitzroy's equation may therefore become a useful design tool for estimating reverberation time, however, only if it is modified. A modification of Fitzroy's equation is discussed in this paper and some practical examples are presented which compare predicted and measured values of reverberation time in real rooms. A suggested modification of Fitzroy's equation is presented. Differences between results derived from Fitzroy's, Sabine's, Eyring's and the modified Fitzroy equation as well as results obtained using a room acoustic computer simulation program are compared. Additionally, results are presented and compared using the calculation method of Annex D of prEN 12354-6.

Binaural auralization of proposed room modifications based on measured omnidirectional room impulse responses

“…More specific estimations (e.g. Fitzroy correction 29,30 ) which consider a non-uniform distribution of the added absorbers are not used in this approach, but could be easily added. In a previous publication 19 we perceptually evaluated the ModRIR algorithm in a psychoacoustic experiment according to ITU-R Recommendation BS.1116-1 31 and found surprisingly small perceptual differences between the modified BRIR and a measured reference BRIR.…”

“…Such an overestimation is often obtained when absorbers are only placed on one of the walls in a rectangular room. Applying a Fitzroy correction 29 or a similar method 30 in the ModRIR algorithm could enhance the results. However, this would increase the effort for the user because additional information on the shape of the room and the positions of the absorbers would be required to run the algorithm.…”

Investigation Studies on the Application of Reverberation Time

“…The reverberation time of a room can be calculated using the empirical formulas described in the works of (Arau-Puchades, 1988; Eyring, 1930;Fitzroy, 1959;Millington, 1932;Neubauer, Kostek, 2001;Pujolle, 1975;Sabine, 1922;Sette, 1933). Equation (1) for the prediction of reverberation time shows that the reverberation time of a room can be determined basing on the interior volume V and on its sound absorption A.…”

“…The research results provided by McMinn also confirm the observations of many researchers quoted in this paper. It is also worthwhile mentioning another work (Neubauer, Kostek, 2001) in which other cases have been analyzed, e.g. the work presenting reverberation time as a function of the volume of the poorly damped room, with reverberation times being calculated with the application of different equations.…”

“…Many empirical equations have been formulated for rectangular rooms. The first one was offered in the work of (Fitzroy, 1959), then (Pujolle, 1975; Hirata, 1979), but also (Neubauer, Kostek, 2001), or (Arau-Puchades, 2005) and others. The said scientists presented different approach to their empirical equations.…”