Robin R. Wareing

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.

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.

Assessment of the effectiveness of adaptive active vibration control for the minimisation of radiated sound from panels

In many practical situations noise is radiated from a noise or vibration source into adjacent areas through vibration of plates. This paper is concerned with the reduction of this radiated noise via active vibration control of such panels. An LMS based adaptive controller is implemented and the experimental results are compared to an ideal model of the noise reduction, this allows the effectiveness of the adaptive controller to be assessed. The plate used in tests is a 1546mm by 946mm simply supported panel. This has been modelled in Matlab allowing the sound field above the plate to be evaluated. Using the theories developed by Nelson et al [1] the theoretical optimal noise reduction can then be calculated. The panel is excited via a point force; the sound pressure at a number of points is then measured. The active control is actuated via a coil based inertial actuator. The sound pressure is measured following the implementation of active control, thus allowing the practical noise reduction to be calcula...