# APPLIED ACOUSTICS

## Learning outcomes of the course unit

The objective of this course is to introduce the fundamentals of a broad variety of topics related to acoustics, with a balanced combination of theory, experimental measurements, numerical simulations and computer programming.

Students who will successfully complete this module will be able:

- To explain the theoretical fundamentals of a number of topics related to acoustics, as listed in the extended programme above

- To understand and be able to use the technical language used in scientific literature of acoustics

- To apply engineering acoustic knowledge and calculation formulae to the solution of a number of simple acoustic problems

- To design and to apply a number of signal processing algorithms to acoustic and audio signals (using MATLAB)

- To use (at a basic level) a number of commercial software packages for acoustic simulations and signal processing

- To perform some acoustic measurements

- To interpret results of acoustics measurements and of plots and graphs related to acoustic phenomena

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. But this is a “postgraduate” course, so it will be extremely difficult for students choosing it during their undergraduate program.

## Course contents summary

Physical Acoustics:

Definition of quantities. Propagation of mechanical disturbances in an elastic medium.

Sound pressure and particle velocity. The speed of sound.

The wave equation.

Sound intensity and sound energy density. Active and reactive intensity. Propagating and stationary sound fields.

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.

Masking phenomena in time and in frequency. Audio compression algorithms based on psychoacoustic principles.

Sound Propagation:

Plane waves, spherical waves, standing waves. Sound reflection and absorption.

Sound propagation outdoor.

Room acoustics: reverberation, sound quality in concert halls and opera houses, ISO3382 acoustical parameters.

Advanced methods for impulse response measurement.

Digital Signal Processing applied to audio and acoustics.

Fundamentals of spectral analysis and Fourier transform.

Sampling of signals.

The DFT and the FFT algorithms. Convolution.

FIR and IIR filters, calculation of Inverse numerical filters.

Active control of sound.

Auralisation.

Virtual acoustics and 3D audio.

Electroacoustics and instrumentation for acoustic measurements:

Acoustic transducers (microphones, loudspeakers).

Devices for processing analog and digital acoustic signals: amplifiers, equalizers, reverbs, compressors, etc...

Sound level meters, spectrum analysers, impulse response measurement systems.

Virtual Instrumentation on PC and software for acoustical measurements, with practical exercises in the laboratory.

Techniques for numerical simulation of sound propagation:

Fundamental of finite element methods, boundary element methods, and ray tracing.

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).

## Course contents

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.

Because of its multidisciplinary nature, the Course of Applied Acoustics is attended by students from various degree programs (almost all branches of Engineering, but also some Architecture students).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.

Lesson 0 Course introduction, program, web page

Lesson 1 Nature of sound, fundamental physical quantities

Lesson 2 Energy & Sound, scale of decibels

Lesson 3 Human auditory system, loudness evaluation, weighting curves

Lesson 4 The Sound Level Meter, equivalent level, calibration, time history with different time constants (slow, fast, etc.)

Lesson 5 Sum and subtraction of values in dB, examples of dB summation, Spectral Analysis, FFT, octave bands, Bark bands

Lesson 6 Free Field sound propagation, point sources, spherical divergence, directivity

Lesson 7 Linear sources, cylindrical divergence, excess attenuation

Lesson 8 Noise screens, Maekawa formulas, examples

Lesson 9 Indoor sound propagation, semi-reverberant field, critical distance

Lesson 10 Reverberation time, definition and Sabine's formula

Lesson 11 Environmental correction factor K2, sound propagation inside not-Sabinian rooms.

Lesson 12 Digital sampling of sound, digital filters, FFT, convolution in time and frequency domain

Lesson 13 Measurement of impulse response: impulsive sources, microphones

Lesson 14 Measurement of impulse response: loudspeakers, MLS and ESS methods

Lesson 15 ISO3382 standard, acoustical parameters: T20, T30, EDT, Clarity, Definition, Center Time, IACC, Jlf, G

Lesson 16 Speech Transmission Index: measurement and calculation

Lesson 17 Sound absorbing materials, typical products. Example of measurement of Alpha Sabine according to ISO 354 (reverberant room)

Lesson 18 Sound insulating materials, typical products. Frequency dependence of the Sound Reduction Index R, the Mass law, resonances and coincidence.

Lesson 19 Italian law about building acoustics (DPCM 5/12/1997), experimental assessment of compliance

Lesson 20 Italian law about environmental noise (L. 447/1995), acoustical zoning, the new EC standards based on Lden - Results

Lesson 21 The Single Event Level (SEL) and its usage for evaluation of transportation noise

Lesson 22 Examples and exercises regarding environmental noise

Lesson 23 Examples and exercises regarding noise at the workplace

Lesson 24 Digital Sound Processing, FIR and IIR filters, FFT, aliasing, windows, spectrogram

Lesson 25 Fast convolution by FFT, partitioned convolution, computation of FIR coefficients for inverse filters, the Kirkeby inversion

Lesson 26 Measurement of the absorption coefficient: reverberant room, standing wave tube, sound intensity method, impulsive method

Lesson 27 The Hour of Code - writing small programs (plugins) for audio

Lesson 28 The Hour of Code - using visual programming for audio processing

Lesson 29 The Hour of Code - examples of coding

Lesson 30 Techniques employed for sound recording and reproduction, mono, stereo, multichannel, 3D, the Soundfield microphone, Ambisonics

Lesson 31 Wave Field Synthesis (WFS), loudspeaker arrays, the Casa del Suono lab in Parma

Lesson 32 Microphone arrays, virtual microphones, the RAI project

Lesson 33 Simulation of sound propagation outdoors employing the DISIA/CITYMAP software package

Lesson 34 Simulation of sound propagation indoors employing the RAMSETE software package

Lesson 35 Auralization of the results with the AURORA software package

## Recommended readings

The recommended textbooks for an introduction to this topic are:

P. Fausti: Acustica in Edilizia , Rockwool, Italy, Milan, 2005 (free download in PDF format)

In Italian

R. Spagnolo: Acustica: Fondamenti e applicazioni, UTET Università, 2015, ISBN: 9788860084460

T. D. Rossing (ed.): Springer Handbook of Acoustics, Springer Science+Business Media, New York, 2007

L.E. Kinsler, A.R. Frey, A.B. Coppens, and J.V. Sanders: Fundamentals of Acoustics, Wiley & Sons, 2000

F. Fahy: Foundations of Engineering Acoustics, Academic Press, 2000,

ISBN: 9780122476655

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:

ACUSTICA

Fondamenti e applicazioni

Autori: R. Spagnolo

Marchio: UTET Università

Anno: 2015

ISBN: 9788860084460

Thomas D. Rossing (ed.): Springer Handbook of Acoustics, Springer

Science+Business Media, New York (2007)

Online Notes:

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-2015-Lessons.htm - It is recommended to download especially Powerpoint slides and Excel spreadsheets containing the exercises done in the classroom.

## Teaching methods

The course includes a combination of frontal lectures and workshop/laboratories.

The theoretical background of the material covered by this module will be explained during frontal lectures. Computer-based and practical demonstrations will often be used during lectures to demonstrate the practical aspects of this discipline.

Hands-on workshop or laboratories, with the aid of computers or measurement equipment, will also be carried out to allow students to familiarise themselves with numerical simulations and signal processing and with experimental measurements.

Class tests will be carried as formative or summative assessment to monitor and evaluate student progress.

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. 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.

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.