The seminar Technical Acoustics is meant as a chance to explore specific aspects of acoustics in a broad spectrum of applications. The available subjects for this semester are divided in three main subjects: 3D Sound & Virtual Reality, Array technology and Digital Audio.
The seminar can be followed in both the German or English language and mainly consists off using scientific literature and discussions with your supervisor to understand your chosen project. This should result in a 30 minutes presentation as end product for both Bachelor and Master/Diplom students. Master/Diplom students must also write an additionally report.

Start: Tuesday 18 October 2011, Seminar room ITA Institute.
Credits: 3 SWS/ECTS (Bachelor), 4 SWS/ECTS (Master/Diplom).
More information can be found in the Campus system and the L2P learning system.

The following subjects are available to choose from, the exact details can be discussed and fixed with your supervisor:

3D-Sound & Virtual Reality

Human hearing system: Head-Related Transfer Function (HRTF)
A perfect 3D sound can be achieved by only a 2-channel (stereo-like) signal. The human ear demonstrates this by only having 2 eardrums but still has fully spatial localization abilities. The temporal and spectral differences of the perceived signal in the left and right ear can be evaluated to localize a sound source. Do you want to learn how this works? Or do you even want to put any sound into a desired direction by applying special digital signal processing that beats any known cinema 3D sound system?

Cross-talk cancellation (CTC)
The human ear needs only a 2-channel signal (“binaural signal”) to localize sound sources in the 3D space. This could easily be reproduced by a headphone. If you still want to listen to 3D sound via loudspeakers, but with full 3D sound, there is no need to buy a surround sound system with a lot of loudspeakers. A technique called “cross-talk cancellation” will make use of the interference of sound waves at certain positions in a room, to reproduce a desired sound pressure at these positions, with only 2 speakers. This enables a “virtual headphone” for 3D sound with a stereo system.

3D-acoustics reproduction systems (Ambisonics, WFS, Stereo etc.)
To enjoy real 3D sound in a multichannel loudspeaker setup, different techniques for signal conditioning are available. They mainly differ by the necessary amount of loudspeakers. It is still possible to reproduce 3D sound with a manageable number of loudspeakers such as in home-theatre systems. Starting with simple panning which is used in stereo or 5.1 systems (“vector based amplitude panning”), over to Ambisonics that considers the signal’s phases and has a unique and tight directional storage format, up to full Wave-Field-Synthesis that needs to cover the walls with hundreds or thousands of speakers.

Real-time room acoustics
Advanced modern tools are able to predict the way sound is propagating through rooms and enclosures. This way it is already possible to virtually sit down and listen to the acoustics of a concert hall that is not yet build (or maybe needs to be modified). To enable the user to walk through the hall or modify the shape or materials, it is necessary to simulate the acoustics in real-time, which is way more challenging compared to graphical real-time rendering. Do you want to know why? Or do you want to learn how to take this challenge and apply acoustics to a virtual reality system?

Psychoacoustics (human sound processing)
Why do we hear sound coming from the middle of two stereo speakers? Why is an MP3 file 10 times smaller than a WAV file but still sounds nearly the same? Why can some Mongolians sing way below or above the range of most professional singers? What is it that makes one chord sound harmonic but another not? You can find the answers to these questions in the magic of psychoacoustics.

Array Technology in acoustics

Circular microphone arrays in room acoustics
“The acoustics” of a room is built up by sound reflections from its boundaries, from many directions and with various arrival times. Why is this complex reflection pattern in some cases perceived as “good” acoustics and in other cases as “bad” acoustics? To find the answer, the reflection pattern can be analysed with a so-called virtual circular microphone array: one microphone slowly turning around along a circle. Are you interested to design and simulate – or even perform – a measurement with such an array in order to detect possibly disturbing ceiling reflections?


Sound source localization (“beam forming”)
Is it possible to make a recording of a music group and later on separate the individual instruments, e.g. in order to reproduce them separately in a surround format like Wave Field Synthesis? Yes, it is – when a special microphone array configuration is used: the so-called “logarithmic” array. Then, in the post-processing phase a “beam” can be formed in a direction at choice. Are you interested to explore the possibilities and limitations of this technique?


Acoustical imaging
Ultrasound is commonly used in medical diagnostics: “echoes” of unborn babies and “heart films” are well-known. Today, it is investigated if a woman-friendly “acoustic” alternative can be found for the usual X-ray method for breast cancer examinations, where the breasts have to be compressed in a rather painful way. Of course, transducer arrays should be used to make such a scan. Are you prepared to help designing such a method?


Better hearing with your glasses.
The goal of this project is to design two small microphone beam formers, which can be integrated in the temple arms of a pair of glasses to enhance the performance of a worn hearing aid. The beam former should be designed in such a way that the person who is talking to the wearer is elevated from the surrounding noise and still has to have the feeling of a ‘real world’ experience. Can you make the array work to handle this job?


Fire your message into a designated direction!
In this project a loudspeaker end-fire array should be designed, which is able to direct speech in only one direction and not omnidirectional. The purpose of such a system is to be able to designate announcements at train stations only on the platforms where the announcement is of importance. Similar situations can be imagined at airports or large stadiums. Are you up to fire the sound waves in the right direction?

Digital Audio

Audio coding (MP3, DTS, Dolby, MPEG, CD, DVD etc.)
To listen to acoustic recordings there is usually a storage-medium (Floppy disk, CD, DVD, blue-ray) and a playback system involved. To make this chain from recording to playback as efficient as possible there are hundreds of different coding techniques available. What makes the different coding techniques suitable for which playback purposes and which mathematical trick do they use? Do you want to dive into the mathematics behind audio coding?

Microphone technology
Microphones are everywhere around us and probably you are using one daily! But how do they actually work? What are the differences between a condenser and dynamic microphone? Besides air as a medium, there are also microphones for other media like water (hydrophones) or in the ground (geophones). Usually we think of microphones that are pressure sensitive, but what about particle velocities? Not to mention the different physical sizes. So there is a microphone for every specific purpose. Do you want to design a microphone for a specific problem or explain the different types with their advantages and disadvantages?

Loudspeaker technology
Loudspeakers can be big, small, have a lot of power, include multiple cones, consist of different materials, have different drivers (dynamic, electrostatic, magnetic) etc. What do all of those boundary conditions mean for the sound field that is generated by a loudspeaker? But what is often forgotten is that there is also a part that is not as visible on the outside as the things mentioned before. To make a loudspeaker work correctly there are also signal filters necessary, so what about their properties? Would you like to design the perfect speakers that resemble true sound?

Recording Technology
From analogue to digital recording, a lot has changed since Edison with his phonograph. There are several methods to store audio data: mechanical, magnetic, electrical or optical. In the latest years there is a focus on using the optical methods, creating higher information densities. By going from DVD to blue ray, the information density is increased by using a smaller wavelength. To go even further experimental optical storage systems make use of holographic methods. What are the advantages and of course difficulties of this new approach? Are you interested in the next generation recording media? With this seminar subject you can design the next generation multimedia data carrier!

Communication acoustics (Modulation techniques etc.)
In communications there is always a medium in between the sender and receiver. In between two people talking there is usually air and the speech is transferred by pressure waves. For the radio or mobile phones it is a bit different. To not affect the daily life, the audio (speech, music) is modulated on to a different carrier frequency and the whole package is transferred through the medium. There are several ways to do this (like amplitude or frequency modulation for radio). How does this process work and what are the limitations of using the different modulation techniques? Will you give a solution for the next generation mobile phones?