The second in a series of articles taken from a paper entitled “Factors Affecting Outdoor Sound Propagation“

The prediction of crowd noise is a problem faced by acoustic consultants. Although consultants are frequently re-quired to predict noise emissions from activities involving crowds of people, there are no prediction methodologies available. This paper discusses the factors influencing crowd noise with the aim of encouraging discussion about how the problem of predicting crowd noise can be overcome. Some simple analysis is presented to show how different situational factors and crowd characteristics influence the noise emitted by a crowd. Four major factors were found to influence the noise level generated by a crowd of people; an individual's voice effort, the total number of people, whether the source is synchronous or random in time and whether the crowd is directional or has a diffused orientation.

An unusual Active Noise Control (ANC) approach using structural sensors and actuators is investigated for its effectiveness in actively attenuating the sound radiation from an irregular enclosure excited by an internal sound field. The intention of the control strategy is to control the enclosure vibrations in such a way that the radiated sound field is minimized. For the case considered here the interior noise spectrum has most of its energy below the first enclosure structural resonance frequency, thus complicating the control design. Here the design of a suitable control system for this problem is described. This is followed by a discussion concerning the type and reliability of the equipment which is most appropriate, after which experimental results illustrating the performance of this approach are presented. The experimental data show a direct correlation between the reduction in enclosure surface vibration and the reduction in noise radiation.

Currently there has been and is a lot of discussion generated by articles in the popular press concerning the possible future hearing loss developed by individuals who listen to personal stereo players (PSP). How much of this concern is real and how much is unreal perception from media publicity? In this work PSP users were approached in their natural environment and questioned about their use while the equivalent at ear LAeq was measured. From this information an LAeq,8h was calculated for comparison to the workplace noise exposure regulations commonly in place in New Zealand and Australian jurisdictions. The results indicate that approximately 25% of a cross section of typical users could be considered to be at risk. Is this significant and how does this compare to workplace noise exposure?

There is a general lack of confidence in the noise barrier industry in the design and specification of effective noise barriers. There is also a need for clear guidance in the application of appropriate standards. The aim of this paper is to enable informed choices to be made using best practice in the detailed design and specification of noise barrier systems both for industrial and transport noise and to give an update of the latest developments in noise barrier design standards and technology to the benefit of the future Australasian Market.

The third in a series of articles taken from a paper entitled “Factors Affecting Outdoor Sound Propagation“,

In industry, noise can cause damage to hearing. However, it can also cause a range of non-auditory effects. In industrial environments noise can be reduced by purchasing quiet equipment, locating noisy equipment away from workers, ensuring appropriate vibration isolation is used, enclosing noisy equipment where necessary, attenuating noise through ducts and louvres, and by providing adequate shelter from noisy environments. Although noise in office environments does not generally pose a risk of hearing damage, there are a range of factors to consider that may reduce the non-auditory effects of noise on health. This article gives some guidance on how to set and achieve appropriate noise criteria.

According to data given by the Australian Council of Trade Unions there are about 1.5 million Australian children under the age of five. Every year 250,000 new babies are born and by the time a child is in his or her second year, 57% of mothers are back in the workforce and by the time children turn three, 68% of mothers are back in the workforce. Many new childcare facilities have recently been constructed in the built environment in many parts of Australia and New Zealand to cater for this growing demand. The proposed location of childcare facilities is highly important because of the noise impact they will have on the surrounding neighbours. However, in many cases childcare facilities are being proposed in normal residential roads with as many as five neighbouring residential properties at their boundaries. Often childcare proprietors would like to accommodate as many children as practicable. This can be as many as 50 to 60, or even 90 children in the age group 2 to 5.

The fourth in a series of articles taken from a paper entitled “Factors Affecting Outdoor Sound Propagation“

The wind energy industry is booming in New Zealand and presents a new set of challenges to the acoustics industry. The NZ Standard NZS 6808:1998 ‘Acoustics – The Assessment and Measurement of Noise from Wind Turbines’ provides guidelines on the way in which sound from wind turbines should be measured and assessed and the levels of sounds that are acceptable. As part of its resource consent conditions for a New Zealand designed and manufactured 500 kW wind turbine at Gebbies Pass near Christchurch in July 2003, Windflow Technology offered to do better than the guidelines and be no louder than 30 dBA at the boundary (including tonal penalty). This paper outlines the process of estimating the sound levels in the area, determining the sound source when the turbine was found to be over the limit, and the results from implementing the solution. The paper also raises other unique issues in measuring sound levels in different wind conditions and topography, and low frequency/infrasound concerns that are arising.

The reliable field measurement of airborne sound insulation between rooms in the very low frequency range (20 Hz – 100 Hz) presents a substantial challenge for several reasons. Sound source and microphone placement can have a strong effect on the transmission, and diffuse field conditions are usually not possible to establish in medium-sized rooms. In this study we compare three methods that have been proposed previously for transducer placement with each other, and with mass law theory. Our results show that substantially different values may be obtained from each method of measurement. Furthermore, we examine the influence of the test signal on the measurement, and find that non-linearities in the building fabric can also substantially affect the apparent sound reduction index in the very low frequency range. We discuss how measurement techniques might be refined to increase their reliability.