Structure-borne Sound Sources Research Articles

Applicability of the structure-borne sound source characterisation Two-Stage method as well as the parameters derived in sound pressure level predictions in lightweight constructions

When predicting structure-borne sound-induced sound pressure levels, in addition to describing the sound propagation path through the building structure as exactly as possible, it is necessary to characterise the vibration behaviour of the structure-borne sound sources. The investigations described here were carried out to extend the applicability of the structure-borne sound source characterisation two-stage method described in EN 15657 and to describe its uncertainties. Furthermore, the suitability of the structure-borne sound parameters determined with TSM in the sound pressure level prediction according to EN 12354–5 was tested and statements on the achievable accuracy were derived. For both methods - characterisation of structure-borne noise sources and prediction of structure-borne noise-induced sound pressure levels - data on prediction accuracy are only available to a very limited extent but are essential for a reliable prediction model.Firstly, different sources of structure-borne sound were characterised using the two-stage method on different reception plates. In the process, structure-borne sound sources with defined acting moments were also investigated to analyse their influence on characterisability. Using the characterised vibration parameters of the structure-borne sound sources, the power introduced into different reception plates was then calculated and compared with measurements to establish the achievable accuracy of the characterisation method.Subsequently, the investigated structure-borne sound sources were installed in a lightweight test stand and the resulting sound pressure levels were measured in an adjacent receiving room. These were compared with the sound pressure levels predicted according to EN 12354–5 to obtain reliable statements on the achievable accuracy when using source quantities determined using TSM in the normatively described prediction procedure for structure-borne sound-induced sound pressure levels. A mean deviation between predicted and measured sound pressure levels of approx. 7 dB could be determined across all investigated sources.

Uncertainty of structure-borne sound source quantities and the installed power from interlaboratory test results according to EN 15657

Structure-borne sound sources affect the acoustic quality inside buildings. Based on many years of research, methods have been standardised to characterise structure-borne sound sources in the laboratory (EN 15657) and to predict the sound transmission from these sources when installed in buildings (EN 12354-5). This contribution is about the uncertainty of the source descriptors used in EN 15657 and the predicted installed sound power which is the input quantity for EN 12354-5. Recently an interlaboratory test with 7 participating laboratories has been performed. The task was to measure the blocked force, free velocity and mobility of an artificial source and the blocked force of the ISO tapping machine. From the evaluation of the measurement results estimates for the uncertainties of the source quantities and the installed power could be deduced.

Characterisation of time-varying structure-borne sound sources using a reception plate to predict maximum Fast time-weighted levels in heavyweight buildings

Structure-borne excitation from many mechanical appliances leads to structural vibration which can be transmitted to nearby rooms and cause annoyance for building occupants. The reception plate method provides a simplified characterisation procedure to obtain the power input for SEA prediction models. Empirical corrections based on the relationship between Leq and LFmax are introduced to predict sound transmission from time-varying source vibrations in buildings. For this purpose, the reception plate method is used to capture the maximum power input. Using different ramped noise signals as idealised versions of time-varying signals from machinery has allowed empirical corrections to be identified such that short Leq measurements can be used with the reception plate. When using SEA or EN12354 it is shown that LFmax in a room can be predicted for a time-varying structure-borne sound source with one-third octave band errors within ±3 dB. Similar results occurred for predicted LAFmax levels calculated from frequency-dependent A-weighted LFmax. A case study with a toilet flush was performed on the reception plate to replicate the empirical corrections derived from ramped noise signals which resulted in close agreement.

Structure-borne sound sources in buildings – Estimating the uncertainty of source properties and installed power from interlaboratory test results

A low immission due to structure-borne sound sources is a major component of the acoustic quality inside buildings. After many years of research, methods have been standardised to characterise such sources (EN 15657) and to predict their impact in buildings (EN 12354-5). This contribution is dedicated to the question what the uncertainty of the source descriptors and the predicted installed sound power is. To answer this question, an interlaboratory test with an artificial source was performed. Altogether seven laboratories participated, and estimates for the uncertainties of the source quantities could be deduced from the measurement results. Additionally, measurements were performed with a standardised structure-borne sound source, the ISO tapping machine, by all participating laboratories. The measured source quantity for this source turned out to be in good agreement with the theoretically predicted values thereby validating this theoretical prediction.

A simple method for predicting sound levels generated by structure-borne sound sources in buildings

A simple method is proposed for predicting in situ sound levels generated by structure-borne sound sources in buildings from input quantities defined in the newly revised measurement standards EN 15657 (Laboratory measurement of service equipment) and EN ISO 10848-1 (Laboratory and field measurement of flanking transmissions), which lead to using the prediction method defined in EN ISO 12354-1 for airborne sound insulation. The method proposed is valid for any source-receiver conditions and for any type of construction, lightweight or heavyweight.

Source substitution method for obtaining the power transmission from vibrating sources in buildings

This paper describes a method analogous to the airborne sound source substitution method, to estimate the vibrational power injected by a structure-borne sound source into the supporting building element. The injected vibrational power is required for prediction of the structure-borne sound pressure from vibrating equipment in buildings. The paper focuses on high-mobility sources connected to low-mobility receivers, a situation which is commonly encountered in heavyweight construction. The mobility mismatch simplifies the transformation of laboratory measurement data to prediction of transmitted power in-situ. Three case studies were performed. In the first study, the power injected by a simple test source into a resiliently supported aluminium plate was determined using direct and indirect methods. Source substitution was investigated with different calibration options: steady-state excitation, transient excitation, and spatial averaging. The source power could be determined within 4 dB, compared with direct measurements of the injected power. In the second study, the power injected by a second source into a concrete transmission suite floor was determined. The third study was of a combined heating and power unit on a masonry wall. In this study, a reference sound pressure level in a receiver room was calculated and compared with a criterion curve for the assessment of low-frequency noise complaints. The case studies demonstrate that structure-borne sound source substitution is a promising development of the reception plate method. While the latter can be used if a free reception plate is available, the former circumvents problems of determining the transmitted power into coupled plates and therefore has application to real building conditions. The use of the instrumented hammer for the calibration and the use of spatial averaging significantly simplify the method.

Predicting In Situ Sound Levels Generated by Structure-Borne Sound Sources in Buildings

Predicting In Situ Sound Levels Generated by Structure-Borne Sound Sources in Buildings

Predicting sound radiation and sound transmission in orthotropic cross-laminated timber panels

In the last decades, new materials and new technologies which satisfy sustainability and energy efficiency demands have been developed for the building construction market. Lightweight structures are becoming increasingly popular, but it has been proved that they cannot provide satisfactory sound insulation. Therefore a proper acoustic treatment needs to be specifically designed, considering both airborne and structure-borne sound sources. Cross-laminated timber (CLT) elements, for example, have had great success in the last twenty years, both in Europe and North America. CLT plates, due to their peculiar sub-structure, exhibit an orthotropic behavior; they have different stiffness properties along their two principle directions. This paper investigates prediction models for orthotropic plates designed to evaluate sound radiation due to mechanical excitation, and sound transmission due to acoustic excitation. Particular attention is paid to the influence on sound radiation of non-resonant vibration, or near-field vibration, in the case of mechanical excitation. The purpose of these simplified models is to be an efficient tool for acousticians, architects and engineers, helpful in the design process for new buildings and retrofitting of existing ones. The validation of numerical results with experimental data are reported. The applicability of the models and their limitation are finally discussed.

Indirect determination of the mobility of structure-borne sound sources

Methods are considered for the indirect determination of the mobility of structure-borne sound sources. Instead of performing measurements on the source in the free state, the source mobility is obtained from measurements made in-situ. This approach is beneficial if the source is difficult to suspend, or if it contains nonlinear structural elements. Two formulations for an indirect source mobility are derived theoretically. The first requires measurement of velocities at or near to the contact points. The second involves measurement of remote velocities only. Neither of the methods requires excitation at the contacts in the coupled state. Numerical simulations of coupled beams are used to validate the two methods and investigate their accuracy and reliability with respect to typical measurement errors, such as background noise and inaccuracies in sensor positioning. It is found that these can have a significant effect on the methods considered. Several experimental case studies with single-contact and multi-contact sources are performed. The results confirm the validity of the two methods in principle, but highlight their sensitivity to experimental errors. In a representative case study with a fan unit, average errors range between ±5dB and ±10dB, with occasional errors of up to 30dB.

Impacted lightweight stairs as structure-borne sound sources

The requirements and methods of characterising impacted lightweight stairs as sources of structure-borne sound and of predicting the resultant sound pressure in buildings are described. The approach is to treat the stair system and the excitation as a single active source. In this study, the stair is excited by a tapping machine or an instrumented shaker, although the approach lends itself to the use of walkers ascending and descending the stair. The approach provides laboratory data suitable for prediction of the structure-borne power transmission from the stair to the supporting wall in a building and thence the resultant sound pressure in adjacent spaces. For the case studied, the primary transmission path is through a bolt to a supporting wall, which also is the separating wall between dwellings. This is a common situation in Germany. The source data can be the velocity of the free source at the contact point and the associated point mobility. Alternatively, a reception plate method is considered, which yields the source power. The approaches provide laboratory data appropriate for prediction of the resultant sound pressure in adjacent rooms using existing building propagation models. By comparison of predicted and measured sound pressure levels, the achievable accuracy is assessed and sources of uncertainty are highlighted.

Predicting the Interaction Between Structure-Borne Sound Sources and Receiver Structures from Independently Measured Quantities: Case Study of a Washing Machine on a Wooden Joist Floor

Predicting the Interaction Between Structure-Borne Sound Sources and Receiver Structures from Independently Measured Quantities: Case Study of a Washing Machine on a Wooden Joist Floor

Algorithm Development for Minor Damage Identification in Vehicle Bodies Using Adaptive Sensor Data Processing

Abstract The paper presents an approach for fully-automatic detection and recognition of minor vehicle body damages in a scenario of frequently changing drivers, such as in the car rental or car sharing businesses. It utilizes a sensor network integrated into the vehicle body. The algorithmically contribution is the multi sensor-data fusion of the signals from these sensors and the subsequent reasoning framework stage. The present research assignment is the inclusion of additional information from the network of the vehicle's electronic control units. This additional information about the vehicle state (e.g. closed or opened door status, speed, changing fuel level) is used to verify the calculated damage events. The efficiency of a structural damage detection directly depends on the acoustical vehicle noise level. Additional structure-borne sound sources also introduce oscillations into the vehicle body (e.g. road and engine noise, opening and closing doors). Some of this information uses a central electronic unit for adaptive sensor data processing of the damage detection system. The higher confidence of correctly identified damages increases the credibility of the system.

Interface mobilities for characterization of structure-borne sound sources resiliently mounted via multiple contact points

This paper introduces an expansion of the interface mobility method for structure-borne sound sources that are resiliently mounted to a receiving structure at multiple discrete contact points. Subsystems of source, receiver and isolators are represented by Fourier transforms of their mobility matrices. Along with the source activity, a formulation for the transmitted power fed into the receiver is obtained. Furthermore, the source descriptor and a coupling function for resiliently mounted multi-point sources are obtained which both form recognized concepts for structure-borne sound source characterization. The method is based on a neglection of cross-order terms which describe a coupling between Fourier coefficients of different order. With regard to a subsystem of discretely placed isolators, cross-order terms were found to account for variations of isolator parameters along the contact points. In a set of numerical studies it was shown that errors introduced by neglecting cross-order terms are most pronounced in the higher frequency region where isolators show resonant behavior due to internal wave effects. A subsystem of identical isolators is completely described by equal-order terms, therefore no error is introduced considering such cases. Moreover, errors inherent in the rigidly mounted case due to cross-order source or receiver mobilities are reduced significantly when isolator mobilities are large compared to those from source and receiver. Findings from theoretical studies were validated in practical settings considering structure-borne sound transmission from a ship diesel engine and a magnetic resonance imaging (MRI) device.

Multi-component power transmission from structure-borne sound sources into lightweight structures

The power transmission between structure-borne sound sources and adjacent structures is generally of complex nature. For an accurate description, the interaction between multiple contact points and several directional components must be taken into account. While calculation methods to predict the transmitted power are generally available, the main problem is the acquisition of extensive source and receiver data. This is especially true with regard to lightweight structures where source and receiver mobilities exhibit matched conditions and when rotational components of motion are involved. Therefore, the description needs to be simplified while at the same time a sufficient accuracy has to be retained. This work investigates the power transmission of a fan unit source that is mounted to a rib-stiffened aluminium plate at several contact points. Full data sets of source and receiver have been measured using a finite difference technique, including translational motion perpendicular to the structure as well as moment excitation around the in-plane axes of the plate. Both a rigid connection as well as a connection using resilient mounts is considered. Contributions of different components of motion are discussed and possible simplifications are deduced.

Intrinsic characterization of structure-borne sound sources and isolators from in-situ measurements

The paper addresses the problem of how to characterize vibration sources and isolators with measurements made in-situ, either on a working installation or on a test bench. For example, automotive components are often characterized by test bench measurements, but there is a need to know how they will behave when coupled to components with potentially different properties in a vehicle. Ideally all components should be characterized by intrinsic properties, which can then be transferred to other installations. In the paper, some novel in-situ measurement methods for obtaining these properties are presented. First, the active properties of a source are characterized by the blocked force measured in situ. Structural dynamic properties are represented by frequency response functions (mobilities) and it is shown how, if necessary, these may be obtained by indirect measurements, for example when access to measurement points is difficult. New results for dynamic stiffness of isolators are then presented obtained using a novel in-situ measurement approach. The method allows rotational (moment) as well as translational (force) dynamic stiffness to be obtained over a wider frequency range than many test rigs. Results are validated by measurement on an ideal laboratory structure.

Characterisation of Structure-Borne Sound Source Using Reception Plate Method

A laboratory-based experiment procedure of reception plate method for structure-borne sound source characterisation is reported in this paper. The method uses the assumption that the input power from the source installed on the plate is equal to the power dissipated by the plate. In this experiment, rectangular plates having high and low mobility relative to that of the source were used as the reception plates and a small electric fan motor was acting as the structure-borne source. The data representing the source characteristics, namely, the free velocity and the source mobility, were obtained and compared with those from direct measurement. Assumptions and constraints employing this method are discussed.

Interface Mobilities for Characterization of Structure-Borne Sound Sources with Multi-Point Coupling

The concept of source descriptor and coupling function is commonly recognized to form a rigorous basis for structure-borne sound source characterization. While this concept initially is valid for the single-point case only, it can be extended to sources with multi-point coupling by including the interface mobility approach. By considering a continuous interface that passes all contact points, the velocities, forces and mobilities are series expanded into interface orders by means of a spatial Fourier decomposition. The use of a continuous formulation for the multi-point case, however, can be problematic from a practical point of view. This paper discusses a reformulation of the interface mobility approach for a simplified calculation and clarified interpretation of the interface orders. With a discrete Fourier series as a basis for the interface mobility approach, the interface is reduced to a set of points and the interface orders are shown to describe the interplay of the data at the contact points. A discrete formulation furthermore yields simplified equations and a strict upper bound for the number of orders that have to be included, thus enhancing the practicability of interface mobilities for source characterization.

Single Equivalent Approximation for Multiple Contact Structure-Borne Sound Sources in Buildings

The work reported in the paper addresses structure-borne sound transmission between multiple contact sources and non homogeneous plate receiver structures. This study concentrates on a practical method of predicting the installed structure-borne sound power from mechanical installations in lightweight buildings. The structure-borne sound power is a function of source activity, source mobility and receiver mobility, and all three quantities must be known to some degree. It is rarely practical to consider all transmission paths individually and in detail, and therefore, reduced data sets and less computationally demanding procedures are proposed. The paper examines how source data can be used to assemble single equivalent values, using spatial averages and magnitudes. Single equivalent values of receiver mobility also are proposed for lightweight, point-connected ribbed plate constructions. In case studies, the single equivalent values are used for predicting the structure-borne power in the installed condition.

Investigation Into the Importance of the Degrees of Freedom for the Characterisation of Structure-Borne Sound Sources: Case Study of a Washing Machine on a Wooden Floor

Investigation Into the Importance of the Degrees of Freedom for the Characterisation of Structure-Borne Sound Sources: Case Study of a Washing Machine on a Wooden Floor

Investigation Into the Importance of the Degrees of Freedom for the Characterisation of Structure-Borne Sound Sources

Structure-borne sound sources are ideally characterised by taking into account six degrees of freedom: three translational components and three rotational components. The complexity of such a characterisation is immense and the effort to measure all components is not realistic or even impossible. If a practical characterisation of structure-borne sound sources in building acoustics is aimed for, reliable information about the importance of the different components is essential. In search for possible simplifications of the degrees of freedom, a series of measurements was carried out on a scale model of an excentric motor connected to a plate on a small receiving room of one cubic metre. The sound pressure in the receiving room was used to verify whether a prediction based on the measured normal source components leads to a correct result. The deviations between the direct pressure measurement and the calculation give some guidance to whether the simplification can be justified or not for the particular structure-borne sound source under test. Once the relevant degrees of freedom have been determined, a simplified prediction based on separately measured source and receiver characteristics can be carried out. The measurement procedure is meant as a method to verify potential simplifications for the characterisation of structure-borne sound sources. It also quantifies in advance the accuracy of a prediction based on those simplifications.