Auralisation of airplanes considering sound propagation in a turbulent atmosphere
Doktorsavhandling, 2017

Aircraft noise is a major issue in urban areas. Due to a rising level of urbanisation and the continuing growth of air traffic more people are exposed to aircraft noise than ever. Methods currently used for assessing the impact of aircraft noise on humans consider mostly energetic quantities, and not the dynamic character of the sound. Therefore, in order to obtain a more accurate picture of the impact of aircraft sound it may be helpful to assess how the audible sound is perceived. Auralisation is a method for rendering audible sound fields and may be used to create audible aircraft sound. A tool was developed to auralise the sound of jet airplanes and consists of an outdoor sound propagation model and an emission synthesiser. The emission synthesiser computes an emission signal consisting of tonal components and broadband noise. The spectral components vary over time and take into account directivity. An inverse propagation model was developed to compute back from a receiver to source in time-domain. An automated procedure was developed to extract features from the resulting signal. These features were then used to directly synthesise the emission as function of time, and this signal was propagated to the original receiver resulting in an auralisation that should reproduce the recording it is based on. To validate the auralisation tool, a listening test was conducted where participants were presented with recordings and auralisations and had to rate their similarity. Results indicate that differences exist between the auralisations and recordings. Improving the synthesis of the blade passing frequency is expected to improve the similarity between auralisations and recordings. Finally, fluctuations can typically be noticed when listening to sound from a distant aircraft, and one cause of these fluctuations is atmospheric turbulence. A computationally fast algorithm was developed to take into account the amplitude and phase modulations that arise as the sound propagates through the turbulent atmosphere. According to the author the method results in improved plausibility of the auralisations.

Auralisation

Aircraft noise

Outdoor sound propagation

Atmospheric turbulence

SB-L516, Sven Hultins Gata 6, Chalmers.
Opponent: Dr. Stephen Rizzi, Aeroacoustics Branch, NASA Langley Research Center

Författare

Frederik Rietdijk

Chalmers, Bygg- och miljöteknik, Teknisk akustik

Rietdijk, F.R., Heutschi, K., Auralisation of aircraft with a synthesised emission signal based on features determined from recordings

Cities are expanding and more people than ever live close to an airport. An
airport nearby can be convenient, but there is also a strong disadvantage:
noise. Aircraft are loud, and while modern aircraft are quieter, the amount of
people exposed to aircraft noise has gone up significantly.

Aircraft noise is known to cause stress, annoyance, and sleep disturbance. In
order to determine how many people are affected by aircraft noise, we first need
to investigate when they are affected. Let us consider for example annoyance.
When is the aircraft noise causing annoyance and what is making it so annoying?
We need to find out what factors play a role, and then try to quantify their
contribution, because that gives the possibility to develop aircraft that sound
less annoying, or could cause less sleep disturance.

In order to investigate these aspects, experiments need to be conducted. This
thesis describes a tool that simulates the audible sound of aircraft in order to
investigate aspects like annoyance. A listening test was done in order to
evaluate the tool. The outcome was that the auralisations did not sound
sufficiently similar to the recordings yet, and improvements are therefore
needed before the tool could be used for investigating aircraft noise impact.

How realistic auralisations sound, can depend on many factors, and one factor that is
thought to be important is the impact of atmospheric turbulence on sound
propagation. When you listen to distant aircraft you can hear strong
fluctuations in the loudness. Earlier aircraft sound simulators did not include
this effect. An algorithm that would account for these fluctuations was
developed and implemented in the simulation tool.

Drivkrafter

Hållbar utveckling

Ämneskategorier

Rymd- och flygteknik

Strömningsmekanik och akustik

Signalbehandling

ISBN

978-91-7597-620-4

Doktorsavhandlingar vid Chalmers tekniska högskola. Ny serie: 4301

Utgivare

Chalmers tekniska högskola

SB-L516, Sven Hultins Gata 6, Chalmers.

Opponent: Dr. Stephen Rizzi, Aeroacoustics Branch, NASA Langley Research Center