Aircraft Sound Research Articles

Real-time identification of aircraft sound events

Metropolitan airports constitute an environmental nuisance, mainly due to noise pollution originating from aircraft landings and takeoffs, affecting the wellbeing of the airports’ neighboring populations. Noise measurement is considered the fundamental means to evaluate, enforce, validate, and control noise abatement. Noise measurements performed by sound monitors located close to urban airports are often disrupted by urban background noise that interferes with aircraft sounds. Detecting aircraft noise, classifying, identifying, and separating it from the residual background noise is a challenge for unattended aircraft noise monitors. This paper suggests a simple and inexpensive methodology, based on ADS-B (Automatic Dependent Surveillance-Broadcast), which can facilitate isolating aircraft noise from background noise. Experiments showed that using ADS-B driven noise monitors is at least as accurate as the commonly used radar–driven noise monitors, in terms of true positive, false positive, or false negative detection during the examined periods.

Spectral and Spatial Multichannel Analysis/Synthesis of Interior Aircraft Sounds

A method for spectral and spatial multichannel analysis/synthesis of interior aircraft sounds is presented. We propose two extensions of the classical sinusoids+noise model, adapted to multichannel stationary sounds. First, a spectral estimator is described, using average information across channels for spectral peak detection. Second, the residual modeling is extended to integrate two interchannel spatial cues (i.e., coherence and phase difference). This approach allows real-time synthesis and control of sounds spectral and spatial characteristics. It finds applications for multichannel aircraft sound reproduction, and more generally for musical and environmental sound synthesis. The ability of the model to reproduce multichannel aircraft sounds is assessed by a numerical simulation.

Perceived quality features of aircraft sounds: An analysis of the measurement characteristics of a newly created semantic differential

The increasing air traffic in the past has led to the fact that and more and more people were affected by aircraft noise. Since the potential of reducing noise level of current aircraft will be limited in the future after recent developed techniques have been realized in practice. Therefore, additional efforts are necessary to improve the sound quality of aircraft noise and give hints to aircraft manufactures concerning components that have to be acoustically optimized. The present study describes the development of an item list for a semantic differential (SD) that is appropriate for the determination of different perceptive features of aircraft sound quality and focuses on the estimation of the reliability of this new instrument. The selected 10 SD items have relation to the sound components emitted by the different technical devices of airplane engines. The analyses of the measurement characteristics of the different items were based on G-theory. This method presupposes data possessing interval-scale-level characteristics. Therefore, the used rating scales were examined with respect to this attribute. The results verified that the data fulfill this precondition. The results gave evidence that the judgments show large inter-individual differences. The proportion of variance which can be traced back to the factor “aircraft sound” amounted to at most one-fifth of total variance indicating that the differences between the aircraft sounds are rather small. Nevertheless, the findings demonstrate that it is possible to measure not all but several decisive aspects with sufficient reliability and expense.

Model-based synthesis of aircraft noise to quantify human perception of sound quality and annoyance

This paper presents a method to synthesize aircraft noise as perceived on the ground. The developed method gives designers the opportunity to make a quick and economic evaluation concerning sound quality of different design alternatives or improvements on existing aircraft. By presenting several synthesized sounds to a jury, it is possible to evaluate the quality of different aircraft sounds and to construct a sound that can serve as a target for future aircraft designs. The combination of using a sound synthesis method that can perform changes to a recorded aircraft sound together with executing jury tests allows to quantify the human perception of aircraft noise.

Perceptual representation of aircraft sounds

This study is part of a research program supported by the European Commission through the Sixth framework program: “Sound Engineering For Aircraft”. This program is devoted to the acoustic features of aircraft noise which could be improved by aircraft manufacturers from a sound design point of view. The present study focuses on aircraft sound perception. Fourteen different aircraft sounds are studied and correspond to seven take offs and seven landings. Preference tests are carried out in order to assess the sound agreement using a seven-point scale, each stimulus being compared to a reference sound. For each pair, subjects have to justify their answer in their own words. Their descriptions are analysed in a linguistic way. Dissimilarity tests are also carried out using the same stimuli. Four perceptual factors, which explain the distance between aircrafts sounds, are extracted thanks to INDividual multidimensional SCALing (INDSCAL) analysis. They correspond to the temporal evolution of the sound level (one factor for the slope of the increase and another factor for the regularity of the increase) and to the timbre aspect (one factor for tonality and one factor for the texture of noise). The verbalisation helps to understand and interpret these dimensions. Objective classical criteria are tested to characterize these perceptual effects using correlations between objective and subjective measurements.

Affective Reactions to and Preference for Combinations of Interior Aircraft Sound and Vibration

Affective reactions to the interior aircraft environment are a basic constituent of perceived ride quality. This study addresses affective reactions to combinations of interior aircraft sound and vibration. In agreement with findings from environmental psychology, it was found that the combinations of six interior aircraft sounds and vibrations (no vibration, 16 Hz, and 95 Hz) gave rise to affective reactions described by two dimension s: valence (unpleasantness-pleasantness) and activation (activated-deactivated). Moreover, preferences for the affective reactions induced by the sound-vibration combinations were related to both of the affect dimensions. Taken together, these findings suggests that (a) different combinations of sound and vibration induce different affective state and (b) by measuring preference in addition to affective reactions, ride quality optimization may be facilitated.

AIRCRAFT SOUND AND DISTURBANCE TO BOWHEAD AND BELUGA WHALES DURING SPRING MIGRATION IN THE ALASKAN BEAUFORT SEA

AbstractShort‐term behavioral responses of bowhead whales (Balaena mysticetus) and beluga whales (Delphinapterus leucas) to a Bell 212 helicopter and Twin Otter fixed‐wing aircraft were observed opportunistically during four spring seasons (1989–1991 and 1994). Behaviors classified as reactions consisted of short surfacings, immediate dives or turns, changes in behavior state, vigorous swimming, and breaching.The helicopter elicited fewer detectable responses by bowheads (14% of 63 groups) than by belugas (38% of 40). Most observed reactions by bowheads (63%) and belugas (86%) occurred when the helicopter was at altitudes ≤150 m and lateral distances ≤250 m. Belugas reacted significantly more frequently during overflights at lateral distances ≤250 m than at longer lateral distances (P= 0.004). When the helicopter was on the ice with engines running, 7 of 14 groups of belugas reacted, up to 320 m away, sometimes with small‐scale (≤100 m) diversion; only 1 of 8 groups of bowheads reacted.For the fixed‐wing aircraft, few bowheads (2.2%) or belugas (3.2%) were observed to react to overflights at altitudes 60–460 m. Most observed reactions by bowheads (73%) and belugas (70%) occurred when the fixed‐wing aircraft was at altitudes ≤182 m and lateral distances ≤250 m. However, the proportions reacting, especially to low‐altitude flights (e. g., ≤182 m), were underestimated for both species because observation opportunities were brief. Even so, reactions were more common when the aircraft was low (≤182 m): P= 0.009 for belugas, P= 0.06 for bowheads. There was little if any reaction by bowheads when the aircraft circled at altitude 460 m and radius 1 km.Aircraft sounds measured underwater at depths 3 m and 18 m showed that a Bell 212 helicopter was 7–17.5 dB noisier than a Twin Otter (10–500 Hz band). Bell 212 sound consisted mainly of main rotor tones ahead of the helicopter and tail rotor tones behind it. Twin Otter sound contained fewer prominent tones. Peak sound level as received underwater was inversely related to aircraft altitude, and received levels at 3 m depth averaged 2.5 dB higher than at 18 m depth. The dominant low‐frequency components of aircraft sound are presumed to be readily audible to bowheads. For belugas, these components may be inaudible, or at most only weakly audible. Mid‐frequency sound components, visual cues, or both, are probably important in eliciting beluga reactions to aircraft.

Affective judgment of aircraft sound quality

Emotion is an important feature of the description and evaluation of sound quality, but this fact has often been treated as a ‘‘nuisance variable’’ in sound quality. The objective of this study was to investigate sound quality descriptors of aircraft sounds. The approach to descriptors in this case originated from the need for consideration of emotion in sound quality research. Thirty-two participants (n=32) rated eight recorded sounds from turboprop aircraft binaurally replayed over headphones. Subjects rated 21 descriptors designed to capture the subjective dimensions of aircraft sounds. The descriptors were commonly used sound quality adjectives, which have emotional/affective connotation. The principal component analysis resulted in two main components. The first factor was interpreted as pleasantness and the second factor as stimuli intensity. These results indicate that affective descriptors can model perception of aircraft sound, i.e., emotional evaluation is important to aircraft sound quality. This study indicates that both description and judgment/decisions about sounds can be based on emotions. One approach to understand and improve sound quality modeling is to investigate the subjective emotional impression of sounds. [Work supported by NFFP Grant No. 232.]

Annoyance caused by different simultaneous environmental sounds.

To prevent or reduce the annoyance in residential areas with two or more different sound sources, it is relevant to develop a quantitative model in which the sound exposure levels from the separate sources are combined into one overall sound exposure measure that adequately represents total noise annoyance. The literature shows that many field studies have had difficulty obtaining valid total annoyance ratings, and that the more persuasive data are too rough to model total annoyance. In the present laboratory experiments, (total) annoyance ratings were obtained for various combinations of impulse, road-traffic, and aircraft sounds. Separate dose-response relationships for the three isolated sounds were also determined. The results support a relatively simple model in which the impulse and/or aircraft sound exposure is expressed in the A-weighted Leq of equally annoying road-traffic sound by applying level-dependent penalties, and the total sound exposure level is obtained by a summation of the corrected Leq’s of the various single sources. Advantages of the method used and applications of the present model will be discussed.

Light Aircraft Sound Transmission Studies: The Use of the Two-Microphone Sound Intensity Technique

Light Aircraft Sound Transmission Studies: The Use of the Two-Microphone Sound Intensity Technique

A time history algorithm for aircraft noise

In the course of the development of a comprehensive computer airport noise model offering a choice of noise metrics (see previous paper), the ASDS metric (“Aircraft Sound Description System”) required the computation of the time noise levels from aircraft flyover exceed specified thresholds. A package of subroutines was developed that performs a noise level time history simulation by tracking aircraft position and orientation along a three‐dimensional flight path using variable time steps depending on the rate of noise level change. The A‐weighted noise levels at observer positions are calculated for each time step from two three‐dimensional models: a three‐component jet engine noise emission model (front fan, rear fan, jet) where each component varies with engine thrust at a different rate; and a propagation model describing the excess attenuation of A‐weighted levels as a function of distance. Both models use aircraft specific empirical parameters determined from measured spectral data, and calibrated by comparing calculated and measured maximum A‐weighted flyover levels for a range of practical distances. The subroutine package is capable of calculating threshold exceedance times, cumulative distributions of noise levels, and the time‐integrated energy equivalent noise level from an aircraft flyover. [Work supported by the U. S. Department of Transportation.]

Development of an integrated airport noise model

A set of computer programs, called Integrated Noise Model (INM), has been developed to compute noise exposure values due to aircraft at various locations around airports. The INM evolved from an earlier computer model used for investigating noise around 23 U. S. airports in terms of NEF. The INM consists of three independent routines: (1) Contour Analysis Model, (2) Grid Analysis Model, and (3) Contour Plotting Pack.age. INM will compute noise exposure values for the following: Noise Exposure Forecast (NEF); Day—Night Average Sound Level (Ldn); Community Noise Equivalent Level (CNEL); Aircraft Sound Description System (ASDS); and Daily Overall Sound Exposure (DOSE, an experimental noise metric). The calculations are sensitive to details of fleet mix data and flight operational procedures. The Contour Analysis Model develops points on curves of equal noise exposure. The Grid Analysis Model computes exposure levels at user‐specified points. Optional output allows examination of the noise contribution from each flight. The Contour Plotting Package retrieves contour point locations from mass storage and plots them. [Work supported by U. S. Department of Transportation.]

Subjective measurements of the relative annoyance of simulated sonic bangs and aircraft noise

Experiments were conducted on a total of seventy-nine subjects, in which they were asked to estimate the relative annoyance of the sound of a jet aircraft, a piston-engined aircraft, and sonic bangs, each of which was reproduced electronically at various levels. For the sonic bangs, a sound typical of that received inside a building was chosen. The results are generally consistent with those of earlier experiments using different scaling techniques, and in the case of the jet and piston aircraft sound broadly support the method of calculating perceived noise levels. The increment necessary to double annoyance is about 13 PNdB. The rate of increase of annoyance with level is greater in the case of the sonic bangs, about 10 dB for doubling. By relating the reproduced noise levels to their original values it is concluded, with some reservations due to experimental limitations, that the upper limit of acceptable sonic bangs (as heard in domestic interiors) is about 1·9 lb/ft 2 initial pressure jump measured on the ground in the open. This figure is based on the value of 110 PNdB for conventional aircraft sounds.

Developments in Aircraft Sound Control

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Developments in Aircraft Sound Control

This paper describes present requirements for sound control in larger airplanes from the viewpoints of the operator, the passenger, and the manufacturer. It presents a new method of approach to the problem of satisfying these requirements, showing measures being taken toward their solution on a new aircraft project, and giving anticipated results.