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.

A B S T R A C TOne of the main goals of building acoustics is the prediction of airborne sound insulation between rooms to determine the quality of sound protection. In many practical cases, however, the objective measures of the airborne sound insulation using procedures in standards are not in agreement with the subjective assessment. This paper, therefore, after reviewing the conventional model to calculate airborne sound insulation, introduces a calculation scheme based on loudness level linked with specific fluctuation strength, yielding a weighted normalised loudness level difference, L nor,w . By analysing the difference between standard airborne sound insulation values and the introduced weighted normalised loudness level difference, it is revealed that the sound pressure level that is transmitted through a partition decreases with increasing frequency, and this is independent of the type of signal and of the airborne sound insulation values (R' w -values), whereas if the transmitted signal is converted into a loudness level, it tends to rise with increasing frequency. Moreover, it is found that, whereas a simple level difference does not exhibit the effect of a given signal to the frequency-dependent airborne sound insulation curve, using L nor,w , a significant change can be observed, in terms of both computed and measured results. Furthermore, the frequency-dependent results allow more details to be investigated for a certain sound insulation. A comparison between the measured and predicted airborne sound insulation with no obvious malfunction suggests that at some frequency ranges, a hypothetical subjective related failure might occur. Overall, the proposed L nor,w could reveal detailed insights into the in situ measured airborne sound insulation compared with standard airborne sound insulation values. The frequency-dependent values discussed in this paper form a basis for developing a single-number index.

There is a long history of adapting airborne sound insulation in buildings to the actual needs. A first pan-European work was published with COST Action TU0901: Integrating and Harmonizing Sound Insulation Aspects in Sustainable Urban Housing Constructions in which the differences between the sound insulation measure and the standard sound level difference were documented. Furthermore, ISO 16283-1: Field measurement of sound insulation in buildings and of building elements—Part 1: Airborne sound insulation states: Compared to DnT, R’ has a weaker connection to the subjective impression of airborne sound insulation. To investigate this relationship a simplified listening test and a computer-simulated variation studies of a synthesized airborne sound insulation were carried out. A test sound was generated from a speech, a music, and a noise signal, each of which was filtered by six frequency responses of solid structures. In a paired comparison task, 16 participants judged the loudness of the resulting 18 sounds. The results of the listening test show that perceived loudness is significantly correlated to the single number quantity DnT,w but less to the single number quantity R’w. This finding was confirmed across all signal types. Thus, the results confirm the statement in ISO 16283-1, that the single number quantity DnT,w has a stronger connection to the subjective impression of airborne sound insulation as the quantity R’w.

In DIN 4109 wird die Schalldämmung, ausgedrückt mit der kennzeichnenden Größe R′w, zur Beschreibung des Schallschutzes verwendet. Schalldämmung und Schallschutz beschreiben jedoch unterschiedliche Sachverhalte. Die Schalldämmung kennzeichnet eine Qualität eines Trennbauteils als „Widerstand” mit der kennzeichnenden Größe „Schalldämm‐Maß, R” und der Schallschutz beschreibt eine Qualität des Schutzes zwischen zwei Räumen vor Schallübertragungen und wird mit der kennzeichnenden Größe „Schallpegeldifferenz, D” ausgedrückt. Durch Vergleich beider Kenngrößen wird klar, dass ein Unterschied bestehen muss, der sich nicht nur algebraisch in den Gleichungen darstellen lässt. Werden gleiche Räume objektiv und subjektiv untersucht, zeigen sich Unterschiede sowohl in der Einzahlangabe als auch in der Wahrnehmung. Insbesondere im Hörvergleich hat sich gezeigt, dass das bewertete Schalldämm‐Maß (R′w) uneinheitlich in subjektiver Hinsicht bewertet wird, wohingegen die bewertete Standard‐Schallpegeldifferenz (DnT,w) eine deutliche „Korrelation” zeigt.

In many practical cases, the objective measures of airborne sound insulation using standard procedures do not agree with subjective assessments. This paper describes a calculation scheme based on the loudness level linked to the specific fluctuation strength and yields a weighted normalized loudness level difference. Evidence has been presented through a subjective evaluation that the model can be considered to be a link between an objective and subjective evaluation. The stimuli offered in the experiment were electronically filtered sound samples representing the sound insulation of interest. Steady-state and non-steady state signals are used as stimuli. To differentiate the signal in terms of psychoacoustic measures, investigations of music type signals were focused on specific fluctuation strength. An assessment of identical airborne sound insulation experimental results has shown that steady-state signals were assessed to be significantly quieter than non-steady-state signals, which also yield greater specific fluctuation strength. As expected, sound insulation was judged differently for different sound samples. A simple level difference is shown not to exhibit the effects of a given signal to the frequency-dependent airborne sound insulation curve. This study supports findings in the literature that airborne sound insulation performance is significantly dependent on what type of sound signal is used.