Keynote Lectures

Binaural Models and their Technological Application
Jens Blauert

The Institute of Communication Acoustics,
Bochum, Germany

The human binaural system, using input from only two sensors on a movable holder, has a number of astonishing capabilities, such as precise localization of sound sources, analysis of auditory scenes and segregation of auditory streams, suppression of reverberance, noise and coloration, enhancement of desired talkers against undesired ones, providing spatial impression and the sense of immersion. To simulate these capabilities, models of the binaural system using digital signal processing have been built and are constantly being improved. Modern models have a bottom-up, signal-driven part, complemented by a hypothesis-driven, top-down part. While the bottom-up part evaluates sound fields regarding the positions and the perceptual attributes of sounds, it takes further processing steps to interpret the binaural activities, to assign meaning to them and to initiate proper actions. To this end, a transition from signal processing to symbol processing, following a process of object building, has to be accomplished. Finally, the sets of symbols have to be interpreted by cognitive processes. In this lecture, a special focus will be laid on technological application of binaural signal processing. To this end, reference will be given to recent activities of AABBA, an open international circle of researchers with a special interest in the application of binaural models. Generic application can be found in the fields of, for example, aural virtual environments, hearing aids, cochlear implants, assessment of product-sound quality, machine listening, room acoustics, speech technology, audio technology, robotic ears and tool for research in auditory physiology.

Jens Blauert
Ultrasonic Measurements and Imaging in Extreme Conditions
Rymantas Kažys

Ultrasound Institute
Kaunas University of Technology

Ultrasonic methods are often used for measurement and monitoring of various non-electric quantities, including distances, pressure, displacements and properties of materials. In many cases these measurements must be performed in extreme conditions- in high temperature and corrosive environments and/or under a high pressure and a strong nuclear radiation.

In this presentation a review of ultrasonic measurement and imaging methods in extreme conditions is given. As examples measurements of static and dynamic displacements and vibrations, on- line monitoring of materials properties during manufacturing process and ultrasonic imaging inside accelerator driven sub-critical fission reactors are discussed.

The last case is extremely complicated because the core of accelerator driven nuclear reactors is cooled by means of a heavy liquid metal, for example, lead-bismuth eutectic alloy. The imaging system used for such purpose must operate in very harsh conditions including high temperature (160 – 450 °C), strong g and neutron radiation, high pressure and chemical activity of the hot liquid metal.

In the presentation the high temperature ultrasonic transducers and visualization methods developed at the Ultrasound Institute, Kaunas University of Technology, are presented. The 3D acoustic computer model, which enables to simulate ultrasonic visualization of the core of a nuclear reactor with the heavy liquid metal coolant, is discussed.

Rymantas Kažys
On the Interaction Between Ultrasound and the Living Cell
Eitan Kimmel

Biomedical Engineering Department
Haifa, Israel

Noninvasive manipulation of cells in vivo by ultrasound for therapeutic purposes (e.g. opening the blood brain barrier for the introduction of drugs) is a field that has a great potential but is not fully understood. We have provided last year a comprehensive explanation for the generation of sub-cellular-level forces by an ultrasonic pressure wave. Using a physical model that incorporates molecular forces with bubble dynamics and gas diffusion, we predicted that ultrasound induces a pulsating bubble in the intra-membrane space between the two lipid leaflets; by periodically pulling the leaflets away from each other, while pockets of dissolved gas accumulate in the hydrophobic zone located between them. The main reason that such membrane response to ultrasound irradiation was not previously observed is that it involves both very tiny displacements of a few nanometers and very rapid movements of less than one microsecond. At this stage “intramembrane cavitation” is not yet a common knowledge and investigations of membrane behavior under ultrasound are needed as well as direct experimental validation of the theory. Current optical methods (e.g., Fluorescence Resonance Energy Transfer – FRET) that are sensitive to nanometric displacements will be discussed, and compared with acoustic and dynamic methods.

Eitan Kimmel
Contemporary Vibration Isolation: Theory and Applications
Leif Kari

Department of Aeronautical and Vehicle Engineering
KTH Royal Institute of Technology
Stockholm, Sweden

Vibrations generated by machines or other sources frequently cause unwanted effects while transmitting to a receiving structure. As a general rule of thumb, structure-borne sound, that is vibrations in the audible frequency domain, radiates sound, while low frequency vibrations may cause structural fatigue and failure. A simple vibration transmission reduction is attained when decoupling the source from a receiving structure by mounting it upon vibration isolators. Traditionally, a vibration isolator provides insulation designed to meet low frequency requirements, while its structure-borne sound property remains arbitrary. However, increasing interest in noise abatement has heightened the need for effective isolation within the audible frequency domain, requiring structure-borne sound property data from the source, the vibration isolator and the receiving structure. In this paper, contemporary vibration isolation is focused upon, covering measurements and theoretical modeling, energy flow and stiffness data, practical and more academic vibration isolation issues as well as novel solutions such as magneto-sensitive vibration isolators.

Leif Kari
Traditional and Innovative Concepts for the Noise Control of Outdoor Machines
Eleonora Carletti

IMAMOTER Institute
Italian National Research Council
Ferrara, Italy

Considerable research effort has been spent in the automotive industry to develop high quality vehicles which combine low noise emissions with acoustically pleasant and comfortable passenger cabins.

The situation for outdoor machinery is totally different, even if effective noise and vibration control technologies are now well established. For many families of outdoor machines several studies have been carried out referring to the limitation of noise and vibration. Some effective acoustic criteria have been introduced already at the machine design stage. As a consequence, the environmental noise impact by these sources has been increasingly reducing in the last decade. Some milestones of the author’s researches will be presented, concerning the acoustic characterisation of these complex sources and the implementation of some effective noise control solutions.

Unfortunately, all the noise control technologies currently available for outdoor machines are based on the reduction of the sound pressure level. This parameter has proved to be an inadequate indicator of the subjective human response to noise. For this reason, despite the fact that noise levels at the operator position have been greatly reduced and nowadays they comply with the legislative requirements, these noise reductions are not connected to a real improvement in the operator acoustic comfort. Some results of the researches carried out by the author in recent years will be presented to show how these limitations could be overcame by tailoring the innovative noise control criteria based on Sound Quality to this specific field.

Eleonora Carletti
Vortex Sound Interaction and Its Application in Aerospace Propulsion System
Xiaofeng Sun

Beijing University of Aeronautics and Astronautics

It is found that vortex sound interaction can result in the energy conversion between pressure wave and vortex wave, and there are some possibilities to exploit such mechanism to suppress various instabilities in aerospace propulsion system, including cascade flutter, rotating stall and combustion instability. To realize these objectives, one of key issues is to give more accurate vortex sound interaction models. The speech will firstly review the recent development of vortex sound interaction models, and then discuss the relevant physics with emphasis on the effect of non-linearity and grazing flow on the impedance of a perforated plate. Finally,a hybrid control strategy for the suppression of combustion instability, including theoretical and experimental results, are introduced based on the active change of wall impedance condition through vortex sound interaction.

Xiaofeng Sun