Learning objectives
Knowledge and understanding:
For students of all branches of engineering this is a key course, it is practically the only opportunity to see (or, rather, hear) the techniques learned in previous courses, in which the purely theoretical foundations of modern advanced mathematical methods are taught. When the "numbers" are transformed into sound, abstruse and difficult mathematical procedures (such as differentiation and integration) quickly become very clear and immediate, and the possibilities offered by sound editing systems on the PC, used extensively both during lectures and during laboratory exercises, make it possible to listen immediately (usually in real time) to the "effects" of filters or other devices (compressors, gates, convolvers, denoising, etc.).
Applying knowledge and understanding:
The course is tailored to practical application, not to theoretical knowledge. Great emphasis is given to measurement methods, simple computations performed in Excel, and solution of practical problems. The student will learn to use the decibel scale, to “think in decibels”, and to perform the common math operations on dB values.
Making judgments:
In the whole course the judgment method is always based on human listening experience, not on numerical evaluation of the results. Acoustics is a perceptual science, and the final judgement can only by given by our hearing system, and not by means of “objective” numerical quantities. The students are consequently trained to listen and evaluate perceptually the most relevant acoustical effects, such as frequency-domain filtering, reverberation, echo, noise contamination, etc.
Communication skills:
The goal of this course is not, definitely, to train the students to perform as actors on stage. However, a significant part of the course is devoted to the study of the verbal and musical communication between performers and audience. In this part of the course, the students learn some tricks employed by professional actors and musicians, and become skilled in diagnosis and correction of communication problems due to room acoustics, improper design of the electro acoustical systems, or improper use of them by the performers and the audience.
Prerequisites
None
Course unit content
The course of Applied Acoustics is an introductory course to a scientific and technological field undergoing a very rapid development, which offers great employment opportunities, and which involves disciplines apparently very different: architecture, structural engineering, physiology, psychology, statistics, physics, electronics, vibration mechanics, fluid dynamics, digital signal processing, telecommunications, measurements, hygiene of the workplace, music, musicology, virtual reality.
Obviously in a course of 6 CFUs we can only provide the methodological basis of the topic, which must then be furthered in more in-depth courses, such as courses for Competent Technicians in Environmental Acoustics or Master Courses available at some Italian or foreign universities (for example Perugia , Naples , Florence , Rome), or even dedicated post-graduate degrees (these are usually abroad, but in Italy it must be evidenced the post-graduate (advanced) degree in Sound and Music Engineering of Politecnico di Milano, taught entirely in English, delivered at the Como Campus).
Because of its multidisciplinary and transversal nature, the Course of Applied Acoustics is attended by students from various degree programs (almost all branches of Engineering, but also some Architecture students, and even the students of the course in Techniques of Prevention in the Environment and at the Workplace of the Faculty of Medicine, for which attendance is compulsory only to the first part of the course, with the exclusion of the final part dedicated to electroacoustic and musical applications).
Full programme
Physical Acoustics: definition of quantities, propagation of mechanical disturbances in an elastic medium, sound pressure, particle velocity, speed of the sound wave. Equation of the acoustic waves.
Energetical Acoustics: sound propagation seen as energy transport. Definition of Sound Intensity and Sound Energy Density. Active and Reactive energy, propagating and stationary sound fields. The Reactivity Ratio (or index).
Psychoacoustics: physiological and psychological mechanisms of sound perception by humans. The logarithmic scale of decibels (dB), elementary operations on quantities expressed in dB. Frequency weighting curves, methods of Loudness assessment, frequency analysis with constant bandwidth, with constant percentage bandwidth (octaves, etc.), with critical bands (Bark). Masking phenomena in time and in frequency. Use of psychoacoustics for encoding "lossy" and "lossless" audio signals with large reduction of the "bitrate" required (MP3, WMA, AAC, FLAC, OGG, etc.).
Sound Propagation: plane waves, spherical waves, standing waves. Reflection and absorption. Specular and diffuse reflection . Definition of sound absorption coeff. and scattering coeff. . Measurement techniques of the absorption coeff. and of the scattering coeff. .
Propagation outdoors: ground absorption, effect of temperature and wind gradients, of air absorption, of shielding or obstacles. The Maekawa and Kurze-Anderson formulas for the estimation of shielding attenuation.
Propagation indoors: the phenomenon of multiple reflections, stationary reverberant field. Formulas of the reverberant field and of the semi-reverberant field. Transients when a sound source is switched on and off: sound tail, impulse response of a room, Schroeder backward integration. Definition of Reverberation Time T60 and other quantities related to the acoustic transients. Sabine formula for the estimation of the reverberation time. The apparent sound absorption coefficient, and its measurement by tests in reverberation room.
Propagation through building structures: insulation of partitions, windows, tapping noise. Measurement techniques and Italian law.
Digital Signal Processing applied to audio and acoustics. Sampling sound, artefacts due to limited amplitude resolution and temporal discretization. Basic algorithms for digital filtering (FIR, IIR): a complex theory made easy. The FFT algorithm, fast convolution, partitioned convolution. Effects of nonlinearities and of time variance.
Advanced method for impulse response measurement (MLS, ESS, etc.). Sound quality in concert halls and opera houses. ISO3382 acoustical parameters. Temporal and spatial parameters. Use of directive microphones for assessing the spatial properties of the sound field inside a room.
Speech intelligibility in classrooms, auditoria and over telecommunication systems. The signal-to-noise ratio, effect of reflections and reverb. The Speech Transmission Index (STI) and its measurement.
Electroacoustics: transducers (microphones, loudspeakers). Devices for processing analog and digital acoustic signal: amplifiers, equalizers, reverbs, compressors, etc... Applications in the audio/electronics industry, in the field of telecommunications and broadcasting, in the recording industry and in entertainment industry automotive, in aviation and marine sectors.
Techniques for numerical simulation of sound propagation: finite element models, boundary elements, ray tracing, beam tracing. Using simulation programs, with hands-on practice in the laboratory.
Instrumentation and equipment for acoustical measurements: sound level meter, spectrum analyzer, impulse response measurement system. Virtual Instrumentation on PC, software for acoustical measurements, with practical exercises in the laboratory.
Numerical processing of the acoustic signal: from general theory to practical applications on PCs. Auralization, virtual acoustics reality. Outline of modern applications in the entertainment industry, and future uses for "live" real time applications. "Plugins" for digital processing of acoustic effects; FIR and IIR filters, fast convolution, calculation of Inverse numerical filters, active cancellation of sound.
The 4 modern methods for measuring absorption coefficients: ISO 354 (reverberation room), ISO 10534 (standing wave tube), the Intensimetric Method (Farina/Torelli), the Impulsive Method (EN 1793/5).
lab sessions : measurement of impulse response and other major acoustic parameters employing Aurora, numerical simulation of the sound field inside a room by making use of two calculation programs (Ramsete, Comsol).
Bibliography
The official textbook for the Applied Acoustics course is:
P. Fausti: Acustica in Edilizia , Rockwool Italy, Milan (2005) - in Italian - free download in PDF format, you can also request for a free hardcopy to Rockwool. Thanks Rockwool!
The books RECOMMENDED (not required) for thorough preparation of the exam are:
R. Spagnolo: Manuale di Acustica Applicata - Citta' Studi Editore, Milano (2001/2007).
S. Cingolani, R. Spagnolo : Acustica Musicale ed Architettonica , Citta' Studi Editore, Milano (2004/2007)
Thomas D. Rossing (ed.): Springer Handbook of Acoustics , Springer Science + Business Media, New York (2007).
The support material for the course used during the lessons is available in the "Public" section of this website:
http://pcfarina.eng.unipr.it/Acoustics-2014-Lessons.htm - It is recommended to download especially Powerpoint slides and Excel spreadsheets containing the exercises done in the classroom.
Teaching methods
The "theory" of the lessons is administered by computer tools, avoiding traditional "lectures" in the classroom. The teacher posts on the website a variety of media (slides, handouts, videos of lectures), indicating to the students to which of them they should access before each "lesson" in the classroom.
During these lessons, the classroom activities will be of "workshop" type, with problem solving and execution of project sizing, partly carried out by the teacher as an "example", and then replicated by the students.
This type of activity also includes systematic verification of the progress gradually achieved, resulting in building an individual assessment profile for each student, and therefore with the possibility of establishing aids and supports for those who are falling behind.
Assessment methods and criteria
The assessment consists of two separate tests:
1) a written examination, consisting of a number of exercises to be solved in numerical form. The use of pocket calculator, notes, handouts, charts and graphs is allowed. Some students may be exempted from the written test, on the basis of the results obtained during in-class tests.
2) Oral examination, which focuses mainly on theoretical topics, and which can be accessed only after passing the written test. Again some students may be exempted from it, on the basis of in-class test results.
Other information
http://pcfarina.eng.unipr.it/Acoustics-2014.htm
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