Acoustics and sound systems Part 1

Acoustics :

Establish a structured link between an auditory experience and the physical reality of sound production.

To achieve this: presentation of the various existing models of sound sources and their radiation, the specific acoustic and electroacoustic characteristics of microphones, the objective characteristics of the transformations undergone by acoustically propagated signals, as well as the perceptive effects of these transformations.

The aim is to enable students to predict, at least qualitatively and if possible quantitatively, what will change in their listening when they modify certain physical parameters of the sound production conditions;

A 1: Elementary acoustics

Intuitive understanding of the acoustic phenomenon and the propagation of sound: Origin of the force of pressure,

Distinction between the speed of molecules, the acoustic speed of air and the speed of the acoustic wave,

Orders of magnitude in acoustics,

Framework of linear acoustics,

Interdependence between spatio-temporal variations in pressure and acoustic velocity,

Propagation laws,

Notion of acoustic energy and acoustic intensity,

Concept of sound level and its summation rules.

A 2: Basic perception

How do we perceive levels and timbres?

Zones of auditory perception

Physiological ear

Concept of loudness and its summation rules

Spectral distortions as a function of listening level

Pitch perception

A 3: Acoustic basics

Elementary types of sound propagation and production :

Plane wave and spherical wave ;

Notion of harmonic wave and complex notation

Ideal diffuse field model; notion of absorption quantity, equations for sound level and critical distance

Two velocity terms for the spherical wave: propagation and proximity effect

Taking account of source directivity

Introduction to Green's function; interpretation of impulse responses

Simulation of acoustic propagation in a room: image sources and ray tracing

A 4: Room acoustics

Links between physical parameters and characteristics of the propagated signal

Reflection of plane waves in the case of a "local reaction", concept of acoustic impedance of a wall

Acoustic impedance of an acoustic membrane, interpretation as a resonator

Absorption coefficient as a function of the direction of arrival of the plane wave, Paris formula in a diffuse field

Sabine and Eyring formulae, use of absorption tables

Eigenmodes: introduction to the theory, interpretation in resonators, simple forms in dimensions 1 and 2

Notions of scattering and diffraction

Laws of isolation and coupled rooms

A 5: Quality of room acoustics

Link between objective criteria and perceptual factors:

Notion of perceptual factor, methodology of perceptual tests

State of the art on the explanation of perceptual factors by objective criteria

Impact of listening conditions on perceptual factors

Speech Transmission Index as a measure of speech intelligibility

A 6 : Microphones

Technologies and their acoustic and electrical characteristics :

Electromechanical models of electrodynamic and electrostatic microphones,

Technical characteristics,

Directivity of microphones, proximity effect,

Diffraction and phase effects

A 7: Radiation

The main sound production models for musical instruments and loudspeakers:

The dipole and the flute: the different modes of interference for the propagation of even and odd harmonics; the case of the forced regime

The circular plane piston, loudspeakers and brass instruments: directivity diagrams as a function of the ratio of wavelength to piston radius

Plate eigenmode radiation and stringed instruments

FSMS 1

Continuous assessment, followed by the submission of a personal report on the design of a system adapted to the constraints of the room and the project.

2 Written tests:

- Acoustics

- Sound