Jeffrey Mahn

The Uncertainty of the Proposed Single Number Ratings for Airborne Sound Insulation

A replacement of the ISO 717-1 standard for the calculation of the single number ratings for airborne sound insulation has been proposed. The proposed replacement, ISO 16717-1 introduces new single number ratings for airborne sound insulation. The weighted sound reduction index which has traditionally been calculated from the sound reduction index measured in the 1/3 octave bands from 100 Hz to 3150 Hz will be replaced by a new single number rating Rliving which is calculated from the 1/3 octave bands between 50 Hz and 5000 Hz. The uncertainty of the proposed single number ratings has been estimated using the ISO Guide to the Expression of Uncertainty in Measurement (GUM) and validated using Monte Carlo simulations. The uncertainty of the single number ratings of 200 building elements was evaluated. It was found that the uncertainty of the single number ratings is highly dependent on the shape of the sound reduction index curve. The uncertainty of the new single number rating Rliving was found to be greater than the uncertainty of the traditional weighted sound reduction index for 98% of the 200 lightweight building elements included in the evaluation. It is recommended that the current weighted sound reduction index be maintained in the replacement standard until the uncertainty of the calculation of the sound reduction index at the low frequencies can be reduced through a redefinition of the measurand.

A systematic approach toward studying noise and vibration in switched reluctance machines: preliminary results

A systematic approach is taken to investigate the noise and vibration of switched reluctance motor (SRM). Although it has been shown that SRM are well within the noise specifications for most applications, there is significant interest in applying this technology in applications with stringent noise requirements. This paper describes the calculation of magnetically-induced forces, and the dynamic response of the motor structure to those forces. Unlike previous studies, a step-by-step approach is taken in the construction of a finite element (FE) model of the mechanical system. Each component is modeled and analyzed, and the results compared with experimental measurements. In this way the model is calibrated against the real motor at the component level, the sub-assembly level, and as a complete motor. This approach yields a reliable model of the mechanical system without accumulated errors from its component parts. The model, together with experimental measurements, allows the accuracy of different methods of electromagnetic-force prediction (which is otherwise unmeasurable) to be compared. The study yields a complete and accurate magnetic and mechanical model of the system which can be used to predict motor vibration under any operating condition. In addition, a much simplified and computationally faster mechanical analysis is presented. This is intended to give the machine designer an indication of noise and vibration levels without resorting to more complicated FE analysis.

The prediction of flanking sound transmission below the critical frequency

Although reliable methods exist to predict the apparent sound reduction index of heavy, homogeneous isotopic building constructions, these methods are not appropriate for use with lightweight building constructions which typically have critical frequencies in or above the frequency range of interest. Three main methods have been proposed for extending the prediction of flanking sound transmission to frequencies below the critical frequency. The first method is the direct prediction which draws on a database of measurements of the flanking transmission of individual flanking paths. The second method would be a modification of the method in existing standards. This method requires the calculation of the resonant sound transmission factors. However, most of the approaches proposed to calculate the resonant sound transmission factor work only for the case of single leaf homogeneous isotropic building elements and therefore are not readily applicable to complex building elements. The third method is the measurement or prediction of the resonant radiation efficiency and the airborne diffuse field excited radiation efficiency which includes both the resonant and the non-resonant radiation efficiencies. The third method can currently deal with complex building elements if the radiation efficiencies can be measured or predicted. This paper examines these prediction methods.

On the Uncertainty of the EN12354-1: Estimate of the Flanking Sound Reduction Index Due to the Uncertainty of the Input Data:

Equations to calculate the uncertainty of the EN12354-1 estimate of the flanking sound reduction index due to the uncertainty of the input data are derived using the method of the ISO Guide to the Expression of Uncertainty in Measurement (GUM). The uncertainty equations have been validated using Monte Carlo simulations. It is shown that the magnitude of the uncertainty depends on the uncertainty of the resonant sound reduction indices of the elements, the uncertainty of the vibration reduction index and the uncertainty of the equivalent absorption lengths and areas of the elements. However, equations could not be derived to calculate the uncertainty of the EN12354 estimate of the apparent sound reduction index which has a lognormal probability density function and is therefore outside of the scope of the method of GUM. Monte Carlo simulations must be used to calculate the uncertainty of the apparent sound reduction index. It is recommended that guidance for calculating and declaring the uncertainty is included in future versions of EN12354, ISO10848 and ISO15712.

Separation of Resonant and Non-Resonant Components—Part I: Sound Reduction Index:

There is much interest in applying EN12354-1 to lightweight buildings elements which may have critical frequencies above the frequency range of interest. The standard requires that only the resonant component of the sound reduction index be used in the predictions and therefore a reliable method of calculating the resonant component is needed for these elements. Several methods of calculating the resonant component are examined in this study. It was found that the various predictions of the resonant component can differ by as much as 18 dB. Calculation of the resonant component by subtracting the theoretical non-resonant component from the measured value was unreliable due to measurement uncertainty. Calculation of the resonant component using correction factors based on the components of the mean square velocity may be possible but may also be susceptible to measurement uncertainty. Definitive guidance for calculating the resonant component is needed in future revisions of EN12354-1 if it is to be applied to lightweight constructions.

Separation of Resonant and Non-Resonant Components—Part II: Surface Velocity

In this second paper, the separation of the resonant and non-resonant components of the mean square velocity of lightweight building elements is investigated for use with EN12354. Two methods for separating the components are presented. The first involves measuring the mean square velocity of a series of panels, each with a different amount of damping. A modified least squares approach is then used. The second method uses the velocity level difference between building elements measured according to EN10848 and the measurement of the mean square velocity of the elements due to excitation by an airborne noise source. This offers advantages since it adds a few additional steps to the measurements for EN10848. However this method was not successful over the entire frequency range when applied to the elements used in this study.

On the Probability Density Functions of the Terms Described by the EN12354 Prediction Method

The probability density functions of each of the terms described in the standards, EN12354-1 and ISO10848-1 are identified in this study using experimental data and data from Monte Carlo simulations. Identification of the probability density functions is essential if the uncertainty of the prediction methods described in the standards is to be determined. It is concluded that the uncertainty of most of the logarithmic terms of the standards may be calculated using the guidelines of the ISO Guide to the Expression of Uncertainty in Measurement. However, Monte Carlo simulations will need to be used to calculate the uncertainty of the apparent transmission loss, the apparent sound reduction index and all of the linear terms of the standards. As a result of this study, alternative calculations for the direction averaged velocity level difference and the flanking transmission loss are proposed for lightweight building elements.

Assessment of the noise emission of sheep shearing systems

There is concern in New Zealand over the growing number of new cases of noise-induced hearing loss amongst sheep shearers each year. The sound pressure level in the woolsheds where the sheep shearing takes place can be in excess of 97 dBA, due in part to the noise emission of the shearing systems used to shear the sheep. The purpose of this study was to benchmark the noise emission of sheep shearing systems inclusive of the shearing plant, the down tube and the hand piece. In addition, the sources of the noise emission were identified using narrow band data and sound intensity mapping to focus future efforts at reducing the noise emission of the shearing systems.

Reciprocity and the Prediction of the Apparent Sound Reduction Index for Lightweight Structures According to EN12354

EN12354 makes use of reciprocity to cancel the radiation efficiency terms from the equations used to predict the apparent sound reduction index. The use of reciprocity works well for the application of EN12354 to massive, concrete structures with diffuse wave fields and with critical frequencies below the frequency range of interest. However, lightweight constructions may have critical frequencies above the frequency range of interest and may not support diffuse wave fields. The use of reciprocity for application to lightweight structures may introduce errors into the predictions. This study investigates the uncertainty introduced into the predictions of the apparent sound reduction index of lightweight constructions due to the use of reciprocity.

Apparent sound insulation in cross-laminated timber buildings

The proposed National Building Code Canada 2015 (NBCC15) is set to replace the traditional design objective - the Sound Transmission Class (STC) - with a requirement including the effect of flanking transmission, namely the Apparent Sound Transmission Class (ASTC). Such a transition requires a supporting set of technical standards for measuring direct and flanking sound transmission for typical assemblies and junctions, plus a credible procedure for calculating system performance from these inputs. As part of this change, the National Research Council Canada has written a guide and construction specific research reports to calculate the ASTC of concrete, concrete block, steel frame, wood frame and cross-laminated timber (CLT) buildings. This paper discusses the calculation method and examples that are contained in the National Research Council Canada’s report RR-335 “Apparent Sound Insulation in Cross Laminated Timber Buildings”.