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SP ACOUSTICS CORE AREAS
- Measurement technology and calibration
- Building and room acoustics
- Machine and vehicle acoustics
- Environmental noise
SP ACOUSTICS Sound & Vibration Krister Larsson SOUND - - PowerPoint PPT Presentation
SP ACOUSTICS Sound & Vibration Krister Larsson SOUND - - PowerPoint PPT Presentation
SP ACOUSTICS Sound & Vibration Krister Larsson SOUND ENVIRONMENT 2012 SP ACOUSTICS CORE AREAS Measurement technology and calibration Building and room acoustics Machine and vehicle acoustics Environmental noise SP ACOUSTICS
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SP ACOUSTICS LABORATORY
Sound transmission suit Large Reverberation chamber Hemi-anechoic Smaller reverberation chambers
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SP LISTENING LABORATORY
Auralisation Listening tests Product development
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CALIBRATION AND MEASURMENT TECHNOLOGY
National Metrology Centre, sound and vibration Calibration services
- Sound level meters and microphones
- Vibration meters and transducers
- Dynamic force
- Sound analysers and fft analysers
- Sound and vibration calibrators
- Reference sound sources
- Tapping machines
- Artificial ears and mastoids
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BUILDING AND ROOM ACOUSTICS Sound insulation in buildings Impact and drum noise Building service equipment noise Structure borne sound Absorbers Smart textiles Standardisation
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MACHINE AND VEHICLE ACOUSTICS
Sound insulation in complex structures Damping materials Absorption Tyre – road noise Noise and vibrations in ships Vibrations
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ENVIRONMENTAL NOISE Sustainable cities Transportation noise Wind energy Energy production
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SP Shipping and offshore acoustics
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Problem description
- Noise and vibration sources
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Problem description
- Transmission paths
– Air borne – Liquid borne (water) – Structure borne
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Sound – Energy and information
Acoustic efficiencies Normal electric motor: 2 10-7 Jumbo jet aircraft: 1 10-6 Low pressure fan 1 10-6 Human voice 5 10-4 Loudspeaker 5 10-2 Information: wanted and unwanted We have to deal with the management of Energy!
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Noise control engineering
- Management of energy
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Sound propagation in structures
Longitudinal waves Rotational waves, transversal waves Flexural (bending) waves CSteel=5000 m/s, Crubber=400m/s Stiffness, density Stiffness, density, geometry
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Dispersion of bending waves
Force acceleration frequency Speed bending waves
B < B >
fc
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Sound, structures and their interaction
- Sound radiation from vibrating structures (bending waves)
<fc >fc
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Critical frequency
- Influencing parameters
– Mass per unit area – Bending stiffness
- Lightweight stiff structures are normally
good sound radiators
frequency Speed bending waves Increasing mass-stiffness ratio
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Finite structures, modes and resonances
12 Hz 112 Hz 243 Hz 387 Hz
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Reduce sound at a receiver
Isolation
- Block the transmission path
- Structure borne sound
– Blocking mass – Blocking stiffness – Joints – Vibration isolation (eg Sylomer or Sylodyn) – Dynamic stiffness
- Air borne sound
– Sound insulation – Wall panels, enclosures – Reduction index Damping
- Dissipation of energy, convert sound energy to
heat
- Structure borne sound
– Damping layers (eg bitumen) – Loss factor
- Air borne sound
– Absorption, Suspended ceilings, curtains, textiles – Absorption coefficient
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Isolation, insulation Transmitted wave field Reflected wave field Block the transmission path Incident wave field sudden impedance change
Impedance: reaction force due to a given motion Reduction index R: Relation of transmitted power to incident power
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Air-borne sound insulation of simple panels
stiffness first resonances mass controlled bending stiffness, mass, damping Reduction index R
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Measurement examples
Single panels Air-borne sound insulation
6 dB/octave
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Double wall design
If you want to reduce weight you have to spend space
10 20 30 40 50 60 70 80 100 1000 frequency [Hz] Reduction [dB]
Heavy layer Spacer Steel Double wall resonance
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Porous absorbers
Viscous friction
Absorption
Panel absorber Resonance absorber Membrane absorber Absorption coefficient
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Measurement of absorption in an diffuse field
the equivalent absorption area reverberation time T is a measure for S, A=S
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Measurement of absorption in the Kundt’s tube
Advantage: small samples Disadvantage: samples have to be fitted very accurately into the tube
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Damping layers
damping layer has to do work! right spot, sufficient stiff Damping layer steel
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