Research in the Room Acoustics Group
Applied Acoustics : Research : Research in the Room Acoustics Group
(revised 20090112 MK)
Architectural acoustics is usually taken to deal with two branches: building acoustics and room acoustics. Building acoustics is concerned with sound insulation and sound propagation in the building structure, whereas room acoustics deals with the behavior of sound waves in and between rooms (due to air-borne coupling).
This, modified, Lindsay's 'Wheel of Acoustics' shows the interplay between different areas of science, engineering, and art.
Current Research Areas
The focus of the research inside the Chalmers Room Acoustic group is on the interaction between the human, architecture and technology, and communication beween humans in an environmental setting. Chalmers Room Acoustics Group is involved in the following research areas:
Emoacoustics
Emoacoustics is a new term used to describe the interaction between emotion, hearing, and vibration sensing. The concept of Product Sound Quality is becoming an integral component of product development and design. Affective reactions, i.e. emotions, are a major factor determining the perceived sound quality. Also additional modalities such as vision and tactile sensing are influenced by and influence emotional status.
Daniel Västfjäll's work is at the very forefront of research into Communication Acoustics and Product Sound Quality. (GP, December 2007)
Auditory Quality of Systems
Including systems for transmission of signals such as voice and music, acoustics of musical instruments particularly organs, as well as product sound quality of technical devices such as cars, trucks, aircraft etc as well as household goods such as white goods, vacuum cleaners etc.
In the INTEL fan noise project our research was focussed on the interference of computer fan noise on performance and relaxation.
Technology of and human response to Virtual, Mixed and Augmented Environments
Including audio virtual reality, enhancement of visual virtual reality systems by audio, sound field prediction and calculation by ray tracing, image source methods etc (auralization), as well as multi-modal and affective aspects of virtual environments including vibration. We are also partners in the exciting FP6 project called PRESENCCIA concerning multi-sensory perception.
The importance of sensory interaction was investigated in our part of the PFF project in cooperation with the Volvo Technology and Volvo Truck companies.
Architectural Acoustics
Including subjective and objective characterization of small, medium, and large rooms for voice and music, prediction of the acoustical characteristics of rooms by scale model (ultrasonic) and software based modeling for general room acoustics prediction of metrics as well as audible sound field simulation, auralization, stage acoustics.
The wavelet/scalogram toolbox developed by CRAG offers a convenient way of analyzing room impulse response and head-related transfer function measurements.
Audio, Electroacoustics and Sound Reproduction Technology
Including active systems, sonar by airborne ultrasonics and associated transmitters and sensors, electroacoustics of sound recording and reproduction systems such as microphones, loudspeakers, headphones etc, as well as arrays of such devices and associated digital signal processing systems.
The setup for automated measurements of individual Head-Related Transfer Functions (HRTFs) is a valuable addition in achieving maximum performance in the use of Auralization.
What we have been doing over the years:
The history of room acoustics research at the department dates back to the 1940's. Chalmers Room Acoustics Group builds on this teaching and research experience. In the 1960's, Dr. Tor Kihlman, Dr. Sven Lindblad, Dr. Bertil Nordlund, and other researchers at the department, were among the first to study speech intelligibility in lecture halls and classrooms using modulation based instruments, mimicking the transmission properties of speech, thus preceding for example the development of the Speech Transmission Index invented a decade later.
The Thorsson speaker used in the early speech intelligibility research (ca. 1960).
With the addition of Dr. Mendel Kleiner, Dipl. Ing. Jakub Kirszenstein, and Dr. Elizabeth Stangham to the staff, a new era started in the architectural acoustics research at the department ca 1970. With his long experience in architectural acoustics, working in Poland, Jakub Kirszenstein managed to focus on the important outstanding issues in room acoustics: namely the prediction of the physically and subjectively measurable properties of sound fields in rooms for listening to natural and man-made sounds such as amplified and non-amplified speech and music. Together with Jakub Kirszenstein, Mendel Kleiner developed a digitally controlled, sound field simulation system for audible prediction of the room acoustic quality of auditoria. Elizabeth Stangham developed new and important models for the prediction of sound levels in large spaces with sound scattering objects, such as factories and offices. T.Lic. Alf Berndtson was the first to use auralization to investigate the influence of the acoustic environment on speaker's talking comfort.
Prof. Mendel Kleiner listening to the hemispherical loudspeaker array used for auralization in the anechoic chamber (ca. 1974).
The Chalmers Room Acoustics Group (CRAG) was formed in 1989 to unite both senior and junior researchers, and to create a body of critical mass for excellence. With support from the Swedish Council for Building Research (BFR), it became possible to rapidly develop the work in this field, and the department's research in this field soon became cutting-edge. Work was done in the areas of:
- Metrics for room acoustics,
- Numerical prediction of sound fields in rooms,
- Electronic reverberation enhancement, and
- Audible simulation of room acoustic response (named Auralization by Dr. Kleiner).
The basic principle of fully computed auralization (ca. 1990).
The doctoral students, graduating from the CRAG group, have been able to achieve their professional goals and obtain good positions in the field. Under the leadership of Dr. Mendel Kleiner, the CRAG group quickly became famous particularly for its work concerning numerical prediction and auralization. Dr. Bengt-Inge Dalenbäck developed the world's first professional, generally available software for room acoustics metrics prediction and auralization, and now successfully runs his own company specializing in this field. Dr. Peter Svensson developed the theory and prediction of electronic reverberation enhancement and now is professor at NTU, Trondheim, Norway. Dr. Rendell R. Torres developed criteria for the audibility of diffracted and scattered sound. Rendell Torres became professor at the Rensselaer Polytechnic Institute, Troy, NY, USA.
The sound diffracted from the edges of objects forms an important part of the early reflections in an auditorium (ca. 2000).
Dr. Vincent Rioux developed a unique library of terms used by organ voicers, and is now project leader at IRCAM the well known research institute for sound at Centre George Pompidou in Paris, France. Dr. Daniel Västfjäll showed mood as a determining factor in product sound quality decisions in his Ph.D. research and has two Ph.D. exams, including one from Chalmers and another from Göteborg University. Dr. Västfjäll also carried and continues to carry out important work on the interaction between aural and visual stimuli in the built environment and studies in particular the concept of presence as applied to both stimuli separately or in combination.
The CRAG Air aircraft proved that the balance between vibration and sound is important to passenger well-being (ca. 2002).
The influence of visual stimuli on what is being heard in rooms can be used to great advantage in architectural acoustics. Additional work on the interaction between vision and hearing in virtual reality environments was done by Dr. Pontus Larsson. Larsson showed that visual impressions can influence the auditory perception in rooms and that virtual reality fidelity can act as a modifier. Larsson is now an assistant professor at the department and also employed at the WSP consultancy in Gothenburg, Sweden.
The quality of the virtual reality rendering will influence the perceived acoustic quality (ca. 2001).
Dr. Matthias Scholz researched the sound generation mechanisms of metal, flue organ pipes and the determining factors for the sound quality of such organ pipes. Matthias Scholz is now at Bruel & Kjaer, Naerum, Denmark.
The sound intensity pattern, at the fundamental frequency, of an sounding open flue organ pipe (ca. 2003).
Dr. Aleksander Väljamäe in his dissertation showed that multi-sensory motion simulators often lack in convincing sound rendering, and also showed indicating that one should strive for thinking about space, time, objects, and events rather than in terms of optimizing cues for different modalities separately in virtual reality simulators. Dr. Aleksander Väljamäe now has a postdoc position at the Laboratory for Synthetic Perceptive, Emotive and Cognitive Systems of the Institute of Audiovisual Studies in Universitat Pompeu Fabra, Barcelona, Spain.
Dr. Aleksander Väljamäe proving that reality still is more convincing than virtual reality (ca. 2005).
Interior truck cabin sound is of great concern to truck manufacturers and drivers. Reasonably low sound pressure levels can be achieved using passive sound absorption. However low frequency sound is difficult to absorb and will dominate the truck cabin interior sound scene. The question is then: "How can we make the sound better if we cannot, or do not want to, lower the level further?". The aim of Dr. Anders Genell's dissertation work was to use a sound quality approach to the interior sound and vibration environment in truck cabins by investigating the meaning of sound and vibration in the truck cabin. Continuously reduction of prominent sounds contributing to a negative impression will change the sound so that it finally ends up as a noise-like sound lacking meaning. How people react to sounds depends on experience and hence measurement of emotional reactions and grouping listeners according to their emotional reactions can be a useful way of creating focus groups for expert ratings, defined by common emotional responses to key reference sounds and vibrations.
Drs. Pontus Larsson and Anders Genell testing out the truck sound lab.
