Marion Burgess

Noise prediction for urban traffic conditions—related to measurements in the Sydney Metropolitan Area

Abstract A method for the prediction of the noise levels from road traffic, developed at the National Physical Laboratory (NPL), has been used for comparison with measured values of road traffic noise in the Sydney Metropolitan Area. As the comparison was not good, multiple regression analysis, using the basic format of the NPL formula, was performed. A better comparison was obtained from a formula in which the term relating to the average road speed of the vehicles was excluded. This new formula permits a simple graphical representation for the determination of L 10 for urban traffic. A similar formula and graph for the determination of L eq is also provided.

Radiation efficiency of acoustic guitars

The transfer functions between acceleration and force (‘‘accelerance’’) at the driving point and radiation efficiencies for the top plates of guitars have been investigated. A vibration exciter was used for driving the guitar at the bridge and the transfer functions and cross‐power spectra were measured at the driving point with the aid of an impedance head. The frequency spectrum of the accelerance function determined in this manner showed good agreement with those reported for the same guitar using a different excitation and measurement method. The output acoustic intensity was measured with a sound‐intensity probe and the radiated sound power from the top plate was determined. The radiation efficiency, determined from the ratio of the top plate radiated sound power and the input power, is presented for different guitars and for a guitar with a modified top plate.

The effect on recognition memory of noise cancelling headphones in a noisy environment with native and nonnative speakers

Noise has the potential to impair cognitive performance. For nonnative speakers, the effect of noise on performance is more severe than their native counterparts. What remains unknown is the effectiveness of countermeasures such as noise attenuating devices in such circumstances. Therefore, the main aim of the present research was to examine the effectiveness of active noise attenuating countermeasures in the presence of simulated aircraft noise for both native and nonnative English speakers. Thirty-two participants, half native English speakers and half native German speakers completed four recognition (cued) recall tasks presented in English under four different audio conditions, all in the presence of simulated aircraft noise. The results of the research indicated that in simulated aircraft noise at 65 dB(A), performance of nonnative English speakers was poorer than for native English speakers. The beneficial effects of noise cancelling headphones in improving the signal to noise ratio led to an improved performance for nonnative speakers. These results have particular importance for organizations operating in a safety-critical environment such as aviation.

Using the effect of alcohol as a comparison to illustrate the detrimental effects of noise on performance

The aim of the present research is to provide a user-friendly index of the relative impairment associated with noise in the aircraft cabin. As such, the relative effect of noise, at a level typical of an aircraft cabin was compared with varying levels of alcohol intoxication in the same subjects. Since the detrimental effect of noise is more pronounced on non-native speakers, both native English and non-native English speakers featured in the study. Noise cancelling headphones were also tested as a simple countermeasure to mitigate the effect of noise on performance. A total of 32 participants, half of which were non-native English speakers, completed a cued recall task in two alcohol conditions (blood alcohol concentration 0.05 and 0.10) and two audio conditions (audio played through the speaker and noise cancelling headphones). The results revealed that aircraft noise at 65 dB (A) negatively affected performance to a level comparable to alcohol intoxication of 0.10. The results also supported previous research that reflects positively on the benefits of noise cancelling headphones in reducing the effects of noise on performance especially for non-native English speakers. These findings provide for personnel involved in the aviation industry, a user-friendly index of the relative impairment associated with noise in the aircraft cabin as compared with the effects of alcohol. They also highlight the benefits of a simple countermeasure such as noise cancelling headphones in mitigating some of the detrimental effects of noise on performance.

Reverberation times in British living rooms

Abstract Reverberation time data obtained by the BRE in furnished rooms in dwellings over the last twenty years are reported. It is shown that reverberation times have decreased over the period and are now well below the value of 0·5 s found in the 1950s, particularly at high frequencies. It is shown that the reduction in reverberation times could have resulted from changes in the room furnishings. An attempt to predict the reverberation times of a furnished room from information about the absorption of the bare room and typical furnishings was not successful because of a lack of information about the absorption characteristics of certain items of furniture.

Application of the sound intensity technique to measurement of field sound transmission loss

Abstract In newly completed buildings, or following modifications and alterations, it is often necessary to determine if the dividing wall meets the required acoustic specifications. The conventional methods for the determination of the field transmission loss are complex and time-consuming and normally only the measurement of noise reduction is attempted. The sound intensity method can be used for determination of the field transmission loss and offers the advantage of providing the transmission loss data for elements of walls, such as doors and windows. The acoustic characteristics of the receiving room are not critical—if necessary, absorption can be added and this is much easier than providing a reverberant space. The sound intensity method has shown good correlation with the conventional methods for laboratory test procedures. The results from some field sound transmission loss measurements of composite partitions using the sound intensity technique are presented. Comparisons are made between results obtained by the sound intensity technique and the conventional method. The importance of the experimental procedure is discussed.

Resonator effects in window frames

Abstract Measurements of the traffic noise reduction of facades comprising casement windows showed dips in the performance at frequencies below the critical frequency. The application of the Gomperts theory on the resonance of slits was found to require unrealistic assumptions for the dimensions of the transmission paths around the windows. An alternative explanation based on the theory of Helmholtz resonators is proposed, and tested empirically by carrying out a series of measurements using a metal casement window. Changes in the gap widths and volume of the cavity within the frame produced changes in the frequency for the dip in agreement with the assumption of a Helmholtz resonator effect.

Selling safety: the use of celebrities in improving awareness of safety in commercial aviation.

Abstract The aim of this study was to investigate the influential power of a celebrity to convey key safety messages in commercial aviation using a pre-flight safety briefing video. In addition, the present research sought to examine the effectiveness of subtitles in aiding the recall of these important messages as well as how in-cabin aircraft noise affects recall of this information. A total of 101 participants were randomly divided into four groups (no noise without subtitles, no noise with subtitles, noise without subtitles and noise with subtitles) and following exposure to a pre-recorded pre-flight safety briefing video were tested for recall of key safety messages within that video. Participants who recognised and recalled the name of the celebrity in the safety briefing video recalled significantly more of the messages than participants who did not recognise the celebrity. Subtitles were also found to be effective, however, only in the presence of representative in-cabin aircraft noise. Practitioner Summary: Passenger attention to pre-flight safety briefings on commercial aircraft is poor. Utilising the celebrity status of a famous person may overcome this problem. Results suggest that celebrities do increase the recall of safety-related information.

Traffic noise and the open window

Natural ventilation is often the only means of providing fresh air in domestic buildings and it may become the preferred method for other buildings as well, in order to conserve energy. The simplest way of achieving natural ventilation is to open a window or door, but the sound attenuation of the building envelope may be severely reduced. The effect of an opening on facade attenuation may be predicted, if the sound transmission loss values of the facade elements are known. The accuracy of such predictions has been investigated by measuring the traffic noise attenuation of the facades of an experimental building. Various percentages of open window area were examined, and the effect of staggering the opening sashes in a spaced double window was measured. [Work supported by A.R.G.C. and S.P.C.C.]

Investigation of the role for noise canceling headphones to assist speech recall in noise

There are many situations where it is necessary to hear, comprehend and be able to recall spoken information in less than ideal listening conditions. For example within an aircraft cabin where, despite improvements in modern passenger aircraft, noise generated from aircraft engines and aerodynamic airflow makes it difficult to hear important on-board safety announcements such as the preflight safety brief. The benefits of headphones that incorporate active noise control in such environments are the focus of a series of research studies. In this paper, we discuss the techniques developed to investigate the use of active noise control headphones on the intelligibility and recall of speech generated outside the headphones in noise typical of that in a commercial aircraft cabin. The initial studies were directed towards assessing the effects on the recall for safety announcements. These studies have been extended to investigate if there are any benefits for those for which English is a second language. The results suggest that the use of active noise control headphones can minimise communication errors in a range of situations and this paper will discuss the methodology adopted and summarise the outcomes.