R.J.M. Craik

Sound transmission through double leaf lightweight partitions part I: airborne sound

Statistical energy analysis (SEA) is used to model sound transmission through double leaf lightweight partitions. It is found that the best SEA model depends on the frequency range considered and the method of construction. At low frequencies the wall can be modelled as a single subsystem while at higher frequencies it should be modelled as a number of interconnected subsystems. The structural connection between the two panels can be modelled either as a series of independent points or as a line connection, depending on the nail spacing. The results show that the basic SEA model is appropriate for this type of structure and that structural coupling can be accurately predicted. However, it was found that the theory for transmission into (and out of) large rooms cannot always be used with confidence to predict transmission into (and out of) a cavity. The error in this transmission path can lead to large errors when predicting transmission through the complete double wall if transmission is dominated by transmission paths involving the cavity.

Sound transmission through lightweight parallel plates. Part II: structure-borne sound

Abstract In Part I of this paper sound transmission through double leaf lightweight partitions was examined. It was shown that an important part of the overall transmission is determined by structure-borne sound transmission between the two leaves of the wall. In this report, Part II of the paper, structural coupling is examined in more detail. Two theories are presented. One is appropriate where the connection behaves as a series of points and the other where the connection behaves as a continuous line. It was found that an appropriate transition frequency between these two theories was where a half bending wavelength on the plate fitted between the nails or screws that form the coupling. In the most common forms of construction the connection will behave as a series of independent points for most of the frequency range. The continuous line model included the frame either as a beam or as a short plate. It was found that the agreement with the experimental data was better when the frame was modelled as a plate.There was good agreement between the measured and predicted data for transmission between the two leaves of the wall for a wide variety of structures. These theories can be incorporated into a statistical energy analysis model to enable the sound transmission throughout the entire structure to be predicted as was shown in Part I of this paper.

Non-resonant sound transmission through double walls using statistical energy analysis

Abstract Although SEA is a suitable framework for predicting sound transmission through double walls it has been found that the standard method of computing the non- resonant coupling loss factor from a room to cavity underestimates the coupling. A revised model for computing this coupling loss factor is presented which gives much better agreement with measured data. This allows better predictions to be made of sound transmission through lightweight double walls.

The prediction of sound transmission through buildings using statistical energy analysis

Abstract Measurements were carried out on a building to evaluate the uses of statistical energy analysis for determining sound transmission performance. Coupling loss factors were measured and compared with predicted values. It was found that, in general, good agreement was obtained. The coupling loss factors were also used to calculate the sound pressure level, or surface velocity, of each subsystem in the building for a number of different sources. Comparison with the measured results gave an average error of 4 dB. Some large errors were obtained but these were due mainly to the omission of airborne flanking paths from the SEA model or due to the breakdown of the theory for specific coupling loss factors.

STATISTICAL ENERGY ANALYSIS OF STRUCTURE-BORNE SOUND TRANSMISSION AT LOW FREQUENCIES

Abstract If statistical energy analysis is to be used for the study of structure-borne sound transmission then it is necessary for the response of the structure to be controlled by resonant modes. At low frequencies there are few modes and this places a limit on the frequency range over which statistical energy analysis can be used. It is shown that for transmission between plates it is the modes in the receiving subsystem that affect the power flow.

Damping of building structures

Abstract Design charts are presented which enable the total loss factor of walls and floors to be quickly calculated. A comparison with measured results shows very good agreement. For normal walls and floors it is shown that the damping due to coupling can be approximated by 1/ f 1 2 and that the spread of results from many different walls is small. The approximation can therefore be used for a large variety of walls and floors.

The effect of workmanship on sound transmission through buildings: Part 1—Airborne sound

Abstract A study of airborne sound transmission through a building has shown that parts of the building which appear to be identical do not have the same acoustic performance. This difference cannot be explained by differences in the dimensions or material properties, nor by variations in flanking transmission. It is therefore concluded that the variation, which is approximately 2 dB, is due to workmanship.

The effect of workmanship on sound transmission through buildings: Part 2—Structure-borne sound

Abstract A study of structure-borne sound transmission through a building has shown that parts of the structure which appear to be identical do not have the same acoustic performance. This difference cannot be explained by differences in the material properties, nor by variations in flanking transmission. It is therefore concluded that the variation, which is approximately 2 dB, is due to variations in workmanship.

Impact sound transmission through a floating floor on a concrete slab

Abstract In this paper a theoretical model to predict bending wave transmission through parallel plates connected by a resilient line is presented. The model is based on the interaction of semi-infinite plates intersecting along an infinite boundary. A full model is developed together with some approximations for the more common cases. The results of the model are then used in a statistical energy analysis (SEA) framework to predict transmission through a chipboard floating floor attached to battens which in turn are supported on a concrete floor. Acoustic transmission through the cavities is also considered. The results show that transmission through the battens is the most important path when there is no resilient layer but that this path is insignificant if any resilient layer is present. A comparison between measured and predicted results gave generally good agreement except at high frequencies when a resilient layer was present.

Sound transmission through a double leaf partition with edge flanking

Lightweight double leaf partitions are widely used and with proper design give good sound isolation. However, when these walls are used as party walls between dwellings, then precautions are necessary to prevent the transmission of fire and smoke. This is usually carried out by placing a firestop in the cavity. This firestop introduces flanking transmission paths reducing the airborne transmission loss of the wall. A simple model is developed which can predict vibration transmission across this type of structural connection. The structural vibration transmission loss can then be used with a more general statistical energy analysis model to give the sound transmission through the entire system. Predicted airborne transmission loss results for a variety of different materials are compared with measured results and good agreement is obtained.