Prediction Models in Building Acoustics

Abstract

There is strong interest in being able to predict the apparent sound insulation in completed constructions so that the suitability of the construction details and materials may be assessed at the design stage. Methods do exist that provide estimates of the apparent sound insulation. An example of which is SEA. However, this method is likely too complex to be suitable for most practitioners and consultants as it relies heavily on the user to model the transmission mechanisms from first principles. Thus, from a practitioner's point of view, a model that makes use of commonly available data for the acoustic performance of building products and elements-as measured by standardised laboratory measurement methods ISO 140-and relates this to the acoustic performance in the completed buildings would be more useful. In response to this, CEN has started to create prediction models for several acoustic aspects in buildings beginning with separate models for the apparent airborne sound insulation and the apparent impact sound insulation. Practical models that allow the prediction of the sound reduction of the individual flanking paths in heavy monolithic constructions are now available (EN 12354-1 for the apparent airborne sound insulation and EN 12354-2 for the apparent impact sound insulation). A new quantity has been introduced in these models to characterise the structure-borne sound transmission at junctions of building elements. Work is now focusing on reliable input data to these models, describing measurement methods to determine the junction quantity, extending application to constructions that are not heavy and monolithic, and verifying the accuracy of the models. Further work is concentrating on models for other aspects such as facade sound transmission from outside to inside and vice-versa and the sound levels caused by mechanical equipment in buildings. This paper provides an overview of prediction models in building acoustics as an introduction to the special session at the Forum Acusticum 1999 in Berlin.

The relationship between the in situ flanking sound reduction index and the laboratory measured flanking normalized level difference

“…Equation ( 33) is consistent with Equation 13 of Gerretsen's 1994 paper. 8 Earlier definitions such as in Gerretsen's 1979 paper 16 had not yet included the l ij term. Substituting equations ( 15) and (33) into 10 where the sound absorption area of a room is defined as:…”

“…is the bending wave phase speed. 14 The equivalent absorption length is introduced 8 which describes all of the absorption at the plate boundaries by using a single length. The absorption length is the ratio of the power absorbed by the plate boundaries to the intensity incident on them.…”

“…Equation (33) is consistent with Equation 13 of Gerretsen’s 1994 paper. 8 Earlier definitions such as in Gerretsen’s 1979 paper 16 had not yet included the l i j term.…”

“…To perform the calculations, the measured normalized flanking level difference D n f ij lab , , , measured in the flanking transmission loss facilities according to the ISO 10848 [4][5][6][7] series of standards needs to be converted into the in situ flanking sound reduction index R ij situ , as described in ISO 12354-1. In a 1984 paper about the prediction method, Gerretsen 8 discusses the conversion of the sound reduction index R and the vibration reduction index K ij made according to standardized laboratory measurement methods to in situ values to predict the flanking transmission loss in actual buildings. The relationship between the laboratory and in situ values for the sound reduction index and the vibration reduction index were presented in Equation 22 of the paper as:…”

“…In a 1984 paper about the prediction method, Gerretsen 8 discusses the conversion of the sound reduction index R and the vibration reduction index K i j made according to standardized laboratory measurement methods to in situ values to predict the flanking transmission loss in actual buildings. The relationship between the laboratory and in situ values for the sound reduction index and the vibration reduction index were presented in Equation 22 of the paper as:…”