John Pearse

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.

Sound absorption of elastic framed porous materials in combination with impervious films: effect of bonding

Abstract The absorption characteristics of elastic framed absorbers in combination with impervious films has been investigated. The effect of bonding the film to the absorber and the absorbers to their rear surface was examined. The results have been modelled using established methods for predicting the absorption of elastic framed porous materials. The absorption of a foam with a film bonded to its top surface was most sensitive to the rear surface bonding condition. Plain foams and foams with loose-laid surface films were less sensitive to the rear surface bonding condition. The results demonstrate that test data used to predict absorption performance need to reflect the absorber mounting conditions.

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.

The average specific forced radiation wave impedance of a finite rectangular panel.

The average specific forced radiation wave impedance of a finite rectangular panel is of importance for the prediction of both sound insulation and sound absorption. In 1982, Thomasson published numerical calculations of the average specific forced radiation wave impedance of a square of side length 2e for wave number k in half octave steps of ke from 0.25 to 64. Thomassons calculations were for the case when the forced bending wave number kb was less than or equal to k. Thomasson also published approximate formulas for values of ke above and below the published results. This paper combines Thomassons high and low frequency formulas and compares this combined formula with Thomassons numerical calculations. The real part of the approximate formula is between 0.7 dB higher and -1 dB lower than the numerical calculations. The imaginary part of the approximate formula is between 2.3 dB higher and -2.6 dB lower than the numerical calculations. This paper also gives approximate formulas for the case when kb is greater than or equal to k. The differences are between 0.8 and -1.2 dB for the imaginary part and between 6.2 and -2.4 dB for the real part.

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.

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.

Predicting the Sound Insulation of Lightweight Sandwich Panels

The sound insulation of three sandwich panels was modelled using simple sound insulation prediction methods, but the agreement between theory and experiment was not very good. The effective Youngs modulus was determined over a wide frequency from the resonant frequencies of three beams of different lengths. The effective Youngs modulus was found to reduce with increasing frequency as has been predicted in the literature. This decrease is due to the core starting to shear rather than bend because its Youngs modulus is much less than the Youngs moduli of the skins. Unfortunately the agreement between theory and experiment was still not very good. This is because many of the prediction frequencies occur in the critical frequency dip because of the variation of the Youngs modulus with frequency.

The Significance of the Incident Sound Field on the Sound Transmission Loss of a Finite Panel

Results are presented for the numerically predicted sound transmission loss of a finite panel excited by plane wave sources at various angles of incidence. It is shown that the limitation commonly imposed upon the integration of the ‘mass law’ is not arbitrary. Rather, it is the upper integration limit at which a function dependent on cos2 (the ‘mass law’), when integrated, becomes equal to a function dependent on cos (the method used in this study, the ISO 140 experimental method) which has been integrated from zero to 90 degrees. The current definition of sound transmission loss implicitly assumes that a plane wave sound source at normal incidence to the panel surface will produce the highest level of excitation in the panel, and as the angle of incidence is increased the panel will experience decreasing levels of excitation. However, it is shown here that the excitation experienced by a panel due to a plane wave source is almost independent of the angle of incidence.

The sound insulation of single leaf finite size rectangular plywood panels with orthotropic frequency dependent bending stiffness

Current theories for predicting the sound insulation of orthotropic materials are limited to a small range of infinite panels. This paper presents a method that allows for the prediction of the sound insulation of a finite size orthotropic panel. This method uses an equation for the forced radiation impedance of a finite size rectangular panel. This approach produces an equation that has three nested integrals. The long numerical calculation times were reduced by using approximate formulas for the azimuthally averaged forced radiation impedance. This reduced the number of nested integrals from three to two. The resulting predictions are compared to results measured using two sample sizes of four different thicknesses of plywood and one sample size of another three different thicknesses of plywood. Plywood was used for all the tests because it is somewhat orthotropic. It was found during testing that the Youngs moduli of the plywood were dependent on the frequency of excitation. The influence of the frequency dependent Youngs moduli was then included in the prediction method. The experimental results were also compared with a simple isotropic prediction method.

The Influence of the Wall Cavity on the Transmission Loss of Wall Systems — Experimental Trends

Numerous experimental investigations have been conducted into the sound transmission loss of double leaf wall systems. From these investigations, it has been observed that the properties of the wall panels, material placed within the wall cavity as well as the type of wall connections used, greatly influence the sound transmission through the wall system. In all of these cases the wall cavity greatly affects the extent of this influence and in some cases it can even nullify their effect when changes are made. In this paper the influence of the wall cavity based on experimental trends is investigated. The investigation revealed that a wide variety of conclusions were obtained by different researchers concerning the role of the cavity and the properties of any associated sound absorption material on the sound transmission loss through double leaf wall systems. Consequently recommendations about the ways in which sound transmission through cavity systems can be improved should always be qualified with regard to the specific frequency range of interest, type of sound absorption material, wall panel and stud characteristics.