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Published Articles

The Volume 5, No 1, March 2000

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Catholic Churches, Sound-Reinforcement Systems and RASTI

Antonio P.O. Carvalho and Margarida M.F. Lencastre


This paper concentrates on the Rapid Speech Transmission Index (RASTI) values within churches and on their differences with the sound-reinforcement systems (SRS) off and on. The RASTI was measured in 31 unoccupied Portuguese Catholic churches built in the last 11 centuries. Four receiver locations were used in each church, with and without the use of the SRS from the altar area. The vast majority of churches tested with the SRS off have RASTI values not greater than 0.45 giving a poor rating in the quality of speech intelligibility. It was determined that only for distances greater than about 11 m from the altar area is the SRS useful in increasing the RASTI values. In general, the standard SRS systems used in Portuguese churches provide an average increase of 7 per cent in the RASTI values when all receiver positions are considered. Excluding the closest position to the sound source, the average increase of the RASTI is about 19 per cent from the RASTI values measured with the SRS off.

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The Effect of Structural Coincidences on The Acoustic Fields Radiated from a Ribbed Plate under Light Fluid-Loading

Nicole J. Kessisoglou, Jie Pan


In this paper, the acoustic fields radiated from a ribbed plate under light fluid-loading are examined. In the ribbed plate system, the reinforcing beam affects both the propagation of the flexural waves in the plate, as well as the sound radiation from the structure. A subsonic incident flexural wave in the plate impinging on the beam discontinuity generates transmitted and reflected propagating waves, and transmitted and reflected near-field waves in the plate. The scattering of the structural wave field gives rise to supersonic wavenumber components of the plate vibration, which subsequently leads to sound radiation into the surrounding fluid field. Two structural coincidence conditions have been identified in this paper. Physically, they correspond to the optimal trace wave matching between the flexural waves in the plate and the flexural and torsional waves in the beam. This paper reports for the first time a new observation concerning the characteristics of the radiating sound fields that occur because of structural coincidence conditions.

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Piezoelectric Accelerometer Modification Based on the Finite Element Method

B. Liu and B. Kriegbaum


The paper describes the modification of piezoelectric accelerometers using a Finite Element (FE) method. B el & K r Accelerometer Type 8325 is chosen as an example to illustrate the advanced accelerometer development procedure. The deviation between the measured and FE simulated results of Accelerometer Type 8325 is below 6%. It is proved that the specifications of the accelerometer can be effectively predicted using the FE method, especially when modifications of the accelerometer are required.

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Active Noise Control with a Simplified Multichannel Genetic Algorithm

Antonio Minguez, Manuel Recuero


A multichannel genetic adaptive algorithm has been developed for active noise control applications. This algorithm is based on the classical genetic algorithms. The FIR/IIR filter coefficients are searched for in a random way, following the biological evolution stages: reproduction, mutation and selection. In an active noise control configuration these algorithms do not require the cancellation path estimations between the control speakers and the error microphones, so there is a huge complexity reduction compared with filtered-X LMS algorithms, which make on-line estimates. Besides, they do not present the local minima problem of the conventional gradient descent-type algorithms (such as filtered-U LMS). However, genetic algorithms show some disadvantages: slow convergence and high residual error noise. The algorithm presented overcomes these disadvantages and reduces the computational complexity removing the reproduction stage. The slow convergence and the final residual are improved by controlling the mutation parameter, generation after generation, and with small chromosome populations. Good results have been obtained for periodic signals, with attenuations between 15 and 20 dB. It has also been tested in a real active noise control application for reducing the automobile engine noise.

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Weather Effects on Outdoor Sound Propagation

Conny Larsson


The results of long-term measurement of ambient sound levels at two locations north of Uppsala are presented. These data are interpreted using records of meteorological information that were collected simultaneously at one of the locations. The results are given as sound profiles. These are surface or contour plots of sound level versus the time of the day and the year.

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A Literature Review of Diesel Engine Noise with Emphasis on Piston Slap

Samir N.Y. Gerges, Julio Cesar de Luca, Nicholas Lalor


The major sources of noise pollution, especially in urban areas are caused by traffic noise generated by internal combustion engines (ICE) and related systems. Much work has already been carried out on ICE noise and piston slap, trying to answer the questions: how to measure it?, how to separate it from other excitation sources?, how does it affect the engines operation and total radiated noise?, etc. Piston slap is still an important mechanical excitation source and a noise generator in ICE. This literature review presents a synthesis of the main technical contributions already published about ICE noise and piston slap assessment and also the important influence of the oil film on this impact phenomenon. More than seventy references, including papers, theses, dissertations and books were studied for this purpose. The following presents the summary of this review.

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