Aircraft noise-monitoring according to ISO 20906: Evaluation of uncertainty derived from the human factors affecting event detection

One of the most important issues in aircraft noise monitoring systems is the correct detection and marking of aircraft sound events through their measurement profiles, as this influences the reported results. In the recent ISO 20906 (unattended monitoring of aircraft sound in the vicinity of airports) this marking task is split into: detection from the sound level time history, classification of probable aircraft sound events, and the concluding identification of aircraft sound events through non-acoustic features.An experiment was designed to evaluate the factors that influence the marking tasks and quantify their contribution to the uncertainty of the reported monitoring results for some specific cases. Several noise time histories, recorded in three different locations affected by flyover noise, were analyzed by practitioners selected according to three different expertise levels. The analysis was carried out considering three types of complementary information: noise recordings, list of aircraft events and no information at all.Five European universities and over 60 participants were involved in this experiment.The results showed that there were no significant differences in the results derived from factors such as the participant’s institution or the expertise of the practitioners. Nonetheless, other factors, like the noise event dynamic range or the type of help used for marking, have a statistically significant influence on the marking tasks. They cause an increase of the uncertainty of the reported monitoring and can lead to changes in the overall results.The experiment showed that, even when there are no classification and identification errors, the detection stage causes uncertainty in the results. The standard uncertainty for detection ranges from 0.3 dB for those acoustic environments where aircraft are clearly detectable to almost 2 dB in more difficult environments.     

Acoustic comfort in large dining spaces

This study carried out a questionnaire field investigation in two typical large dining spaces. The results suggest that the acoustic comfort of diners has an influence on the comfort evaluation of the overall dining environment, and background noise is an important factor affecting the acoustic comfort evaluation of diners. The role of various individual sound sources in background noise has been investigated, considering general background music, speech sound, activity sound, and mechanical noise, and it has been revealed that background music, other diners’ speech sound and tableware’s impact sound has a dominant impact on the acoustic comfort evaluation of diners. Compared with the existence of background music in background noise, diners’ acoustic comfort evaluation is higher than that without background music. The loudness, articulation, noise level and preference degree of various individual sound sources are factors which affect diners’ acoustic comfort evaluation on sound sources. In terms of demographic and social factors, gender and the frequency of dining out have a significant impact on diners’ acoustic comfort evaluation.     

Estimation of directivity and sound power levels emitted by aircrafts during taxiing, for outdoor noise prediction purpose

Integrated noise model (INM) is the most internationally used software to calculate noise levels near airports. Take off, landing or pass by operations can be modeled by INM, but it does not consider aircrafts taxiing, which, in some cases, can be important to accurately evaluate and reduce airports’ noise assessment.Aircraft taxiing noise emission can be predicted using other prediction tools based on standards that describe sound attenuation during propagation outdoors. But these tools require data inputs that are not known: directivity and sound power levels emitted by aircraft during taxiing.This paper describes methods used to calculate directivity indexes and sound power levels, based on field measurements made in Madrid-Barajas Airport (Spain). Obtained results can be used as inputs for general purpose outdoor sound prediction software, which will be able to evaluate noise at airports vicinity as industrial noise.Directivity and sound power levels have been estimated in octave and third octave band terms, for several aircraft families.     

Interactive simulation of aircraft noise in aural and visual virtual environments

This paper describes a novel aircraft noise simulation technique developed at RWTH Aachen University, which makes use of aircraft noise auralization and 3D visualization to make aircraft noise both heard and seen in immersive Virtual Reality (VR) environments. This technique is intended to be used to increase the residents’ acceptance of aircraft noise by presenting noise changes in a more directly relatable form, and also aid in understanding what contributes to the residents’ subjective annoyance via psychoacoustic surveys. This paper describes the technique as well as some of its initial applications. The reasoning behind the development of such a technique is that the issue of aircraft noise experienced by residents in airport vicinities is one of subjective annoyance. Any efforts at noise abatement have been conventionally presented to residents in terms of noise level reductions in conventional metrics such as A-weighted level or equivalent sound level L_eq. This conventional approach however proves insufficient in increasing aircraft noise acceptance due to two main reasons – firstly, the residents have only a rudimentary understanding of changes in decibel and secondly, the conventional metrics do not fully capture what the residents actually find annoying i.e. characteristics of aircraft noise they find least acceptable. In order to allow least resistance to air-traffic expansion, the acceptance of aircraft noise has to be increased, for which such a new approach to noise assessment is required.     

Impact of aircraft sound quality combined with the repetition of aircraft flyovers on annoyance as perceived activity disturbance in a laboratory context

This study focuses on perceived activity disturbance evaluated by participants who are subjected to the repetition noise of current aircraft and modified aircraft in regard to tonal quality. A previous study devoted to the sound quality of aircraft noise revealed that one of the most important perceptive features is the emergence of Doppler shifted tones. Six 20-min sound sequences were created combining two variables: number of aircraft (N₁ with six aircraft and N₂ with 10 aircraft plus one sequence without aircraft N₀) and tonality (sequences with current aircraft, sequences with +5 dB-amplified tonality and sequences with −5 dB-attenuated tonality). For all sequences, the equivalent sound level and the peak level of the loudest event are constant, except for the sequence without aircraft. Sixty-three subjects, attending two different sequences in one session, rated on a category scale the level of activity disturbance due to the noise environment when carrying out memory and concentration tasks. The order of presentation was controlled as an additional variable in the variance analyses. The perceived activity disturbance is significantly influenced by the equivalent sound level. The influence of the number of aircraft flyovers is statistically significant at the 5% level. High tonal components have no effect on perceived disturbance. Memory and concentration performances, measured by number of incorrect or correct answers, are influenced only by the order of presentation, revealing the importance of the learning effect. Reaction time, which is influenced by the equivalent sound level, seems better adapted for measuring the effect of noise on task achievement. These results are discussed in regard to related research.     

Determination of the sound energy level of a gunshot and its applications in room acoustics

In some cases an impulsive noise source such as a gunshot can be a preferred alternative when investigating building acoustics, including sound insulation measurements, when compared to conventional steady state noise sources. A gun equipped with blank cartridges is an impulsive noise source that is lightweight and small enough to be easily transported. The differences in the noise characteristics between individual cartridges for the same gun are usually small, so the impulsive source can be replicated to a high degree. This paper is focused on the practical application of the sound exposure levels produced by a gunshot with a known sound energy level in the rooms under investigation. In this way, the equipment and methods required by the conventional method are simplified significantly. Furthermore, reverberation times need not be measured, since the equivalent absorption area can be directly obtained from the measured sound exposure levels. Using Green’s theorem, the roles of the sound source and measuring microphone were exchanged, which simplified the determination of sound insulation as it was easier to change the position of the gun than the microphone. The results obtained using the impulsive noise source were in good agreement with those obtained using the conventional method. Above 100 Hz, their difference in any frequency band of interest was less than 1 dB.     

Aircraft noise annoyance estimation: UK time-pattern effects

An improvement appears to be possible in estimating UK aircraft noise annoyance. This is based on a more detailed analysis and modelling of the data supporting the present UK aircraft noise policies. There is empirical evidence that people’s real-life annoyance at aircraft noise is in part determined by its time-patterns. People benefit from Heathrow’s regular and predictable alternation cycles on westerly operations, equivalent to an effective dB(A) Leq value for that operational mode some 2-dB less than the measured dB(A) Leq. This correction is statistically controlled for people whose work/business is connected with Heathrow. The implications of a time-pattern correction would be significant for UK airport noise contours.     

Calibration of subjects with master scaling: An application to the perceived activity disturbance due to aircraft noise

The aim of this study is to assess whether or not rating perceived activity disturbance using magnitude estimation scale and using master-scaling transformation is more relevant than rating disturbance with category scale to reveal the influence of the number and the sound quality of aircraft flyovers. The master-scaling transformation is intended to reduce the inter-individual differences between people. Thirty participants were subjected to six sound sequences. They attended the test in two different sessions separated by a week at least, and had to evaluate the level of activity disturbance due to the noise environment when carrying out memory and concentration tasks. During each session, participants first went through a calibration phase and were then subjected to one 20-min sound sequence. The calibration phase, which can be also considered as a training phase at the beginning of each session, allows subjects to built their own annoyance scale. As expected, the perceived activity disturbance depends on the equivalent sound level and on the number of aircraft. But the master-scaling transformation did not succeed in reducing the variability between subjects. This transformation which calibrates the subjects on only one aspect of the sound (which is the equivalent sound level in this experiment) could emphasis the difference between subjects who have been more or less sensitive to other aspects of the sound (the tonality or the repetition of events in this experiment) than to loudness. Nevertheless, this experiment confirms that Stroop reaction time, which is influenced by the number of flyovers, seems to be adapted for measuring the effect of noise on task achievement.     

Effect of background noise levels on community annoyance from aircraft noise

A study of community annoyance caused by exposures to civil aircraft noise was carried out in 20 sites around Gimpo and Gimhae international airports to investigate the effect of background noise in terms of dose-effect relationships between aircraft noise levels and annoyance responses under real conditions. Aircraft noise levels were mainly measured using airport noise monitoring systems, B&K type 3597. Social surveys were administered to people living within 100 m of noise measurement sites. The question relating to the annoyance of aircraft noise was answered on an 11-point numerical scale. The randomly selected respondents, who were aged between 18 and 70 years, completed the questionnaire independently. In total, 753 respondents participated in social surveys. The result shows that annoyance responses in low background noise regions are much higher than those in high background noise regions, even though aircraft noise levels are the same. It can be concluded that the background noise level is one of the important factors on the estimation of community annoyance from aircraft noise exposure.