(Created 2009-08-11.)

ENGINEERING ACOUSTICS, INTRODUCTORY COURSE | VTA030 |

**Aim**

- To give knowledge of acoustic signals and waves in different materials and components (the hearing frequency range) and of methods for generating sounds, acoustic regulation and noise limiting and measuring techniques in these areas.

*Knowledge and understanding*

For a passing grade the student must

- Be able to interpret and describe the fundamental concepts such as acoustic effect, intensity and wave impedance.
- Be able to describe the physical foundation for waves in a gas, and using the law of continuity, equation of motion and ideal gas law deduce the wave equation.
- Be able to recall the harmonic solutions to the wave equation for a one dimensional, as well as spherical field.
- Be able to describe the cause for sound reflection, and -transmission at an interface.
- Be able to describe the directional impedance and directional properties of a piston.
- Be able to describe the components representing the acoustic mass, compliance and resistance and their correlates in mechanical and electrical systems.
- Be able to describe the four most common principals of electromagnetic transformation.
- Be able to recall and interpret the wave theoretical expression for sound pressure from a point source in a rectangular room with sound hard walls.
- Be able to describe what signifies a wavetheoretical, geometrical and diffuse model of the sound field in a room and in with situation the respective model is suitable for usage.
- Be able to describe when the statistical properties of a room becomes dominant and what implications that has.
- Be able to explain properties and functional principals of resonance- and porous absorbers and the influence of material parameters and dimensions on the absorption.
- Be able to explain and describe the most important psycho acoustic concepts, including subjective and the corresponding objective room acoustic measures.

*Skills and abilities*

For a passing grade the student must

- Be able to deduce the expression for reflection factor within and in front of an interface with acoustically different medium for a plane incident wave, prependicular or inclined to the interface.
- Be able to calculate the sound pressure in the free field and exited sound effect from an array of point sources.
- Given a distributed acoustic system with a one dimensional wave propagation, be able to reproduce and model this in a combination of one- (i.e. lumped components) and two-ports, described by two-port matrices.
- Given a loudspeaker element and its mechanical parameters, be able to design a closed loudspeaker box and bass reflecting box such that the loudspeaker has a, in the bass area, frequency independent transfer function.
- Be able to derive the mechanical parameters of a loudspeaker element from measurement of the electrical impedance of the element.
- Be able to apply Thevenins theorem on acoustic systems.
- Be able to calculate eigen frequencies, eigen modes and mode density in finite systems with simple geometries and boundary conditions.
- Be able to present the solution of an acoustic problem in a technical report.

**Contents**

Acoustic concepts. Effect, intensity, wave impedance and level. Sound waves. Sounds in different medias, above all in air. Plane and spherical wave damping. Sound excitation. Round emitting and directed sound sources and corresponding recievers, plane oscilator. Exponential horn. Acoustical resistances and reactances treated as electrical quantities in equivalent configurations. Resonators and absorbents, transformers. Principals for reciprocial transformers. Electrodynamic loudspeakers. Condens microphone and piezoelectric vibration pickup. Sound in rooms. Transfer functions in rooms. Statistical properties, effect balance and reverbation. Absorption and regulation. Sound isolation. Hearing and psychoacoustics. Sensitivity for different tone heights and subjective sound level. Masking of critical bands. Directional hearing and influence of phase difference of sources. Acoustic components at noise reduction. Porous absorbents. Mufflers. Vibration insolation, bending of plates.

**Literature**

Lindblad S: Akustik III, Compendium.

Collection of examples. Manual for laboratory work.