Actran for loudspeakers design
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Key Features for Loudspeaker
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Key features of Actran
 Rich library of materials:
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Visco-elastic
Porous & poro-elastic
Membranes
Piezo-electric
…
 Infinite elements
 Axi-symmetric and 3D computation
 Rich Post-processing
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Material library
 Actran contains a rich library of materials:
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Fluid
Visco-thermal fluid
Porous material (Biot & Craggs model)
Piezo-electric materials
Shells and solids (pre-stressed effect can be treated)
Membranes
Springs
 Frequency dependent properties
 Damping effect can be easily included into the materials
 All standard structural and acoustic excitations and boundary conditions
are available
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Boundary Conditions
Acoustic Infinite Elements
 Objective:
 Create a non reflective boundary condition (free field modeling)
 Allow for sound pressure levels calculation even far from the source ->
directivity plots
 Capable to simulate baffled structures
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Axisymmetric Computation
 If axi-symmetry (i.e. no variation with ) of the geometry
 Possibility to perform axisymmetric computations of different orders
 Advantages
 3D results at (almost) the cost of a 2D computation!
 Meshing is easier
 Post-processing is faster
 Quarter and half-model can also reduce the computation time
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Piezo-electric material
 Piezo-electric materials can be used to simulate:
 Acoustic radiation of a piezo-electric material
 Structural response through actuation and sensing
 Force at the voice coil induced by an electrical signal can be simulated
through distributed loads, depending on the electric signal
Radiation of a piezo-electric material
Main vibration modes and shapes
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Voice coil
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Damping effects
 The damping due to viscous effects in air can be modelled accurately
 Equivalent transfer admittances functions allows modeling perforated
plates
 The dissipated energy can be retrieved from the results database
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Visco-Thermal Effects
 Visco-thermal effects occur when sound waves travel through thin air
layers or narrow channels :
 Effects are due to the boundary layer created by viscosity :
The fluid is not allowed to slip on the plate’s
surface and the velocity profile across the layer
thickness is not uniform
 References:
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 M. Beltman, Viscothermal wave propagation including acousto-elastic
interaction, PhD Thesis Universiteit Twente, 1998
 Tom Basten, Noise reduction by viscothermal acousto-elastic interaction in
double wall panels, PhD Thesis Universiteit Twente, 2001
 Vincent Decouvreur, Evaluation of visco-thermal acoustic effects in thin air
layers. Comparison of experimental and theoretical approaches, Student
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Thesis, DTU/ULB
Post-processing
 Actran/VI offers a wide variety of tools to post-process your results:
 Maps, contours, cutplanes...
 Energy balances
 Spectrums
Maps + Deforms + Cutplanes
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Cutplanes + Contour
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Multiple Maps + Deforms
Application Examples
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Case Study: Loudspeaker with
bass reflex - Actran Model
 Key ingredients
 Visco-elastic shells finite elements for the loudspeaker
 Acoustic finite elements for the interior air and near field exterior + viscothermal
 Infinite elements for the far field
 Realistic symmetric excitation at the voice coil + symmetric geometry  Half
model for CPU time sparing
 Performance
 Size of the box: around 40cm high
 Resources: 2 hours on a standard Linux PC with 4GB of RAM for up to 2kHz
Geometry
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Structure mesh
Vibro-acoustic mesh
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Case Study: Loudspeaker –
Results
FRF transfer function: Power/excitation
Deformed membrane at 1600Hz
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Pressure at 1400Hz
Case Study: Loudspeaker for cell phones
 Key ingredients
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Visco-elastic shells finite elements for the membrane + copper + cover
Acoustic finite elements for the interior air and near field exterior
Infinite elements for the far field
Visco-elastic solid finite elements for the rubber protection
 Distributed constant excitation on the copper layer attached to the membrane
 Performance
 Resources: 4 sec / freq on a Windows64 PC with 2GB of RAM for up to 10kHz
Loudspeaker
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Interior mesh
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Free field model
Case Study: Loudspeaker for cell phones - Results
Pressure distribution at 4000Hz
Radiated Power/excitation
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Pressure at 4000Hz
Case Study: Cell phone
 Key ingredients
 Visco-elastic shells finite elements for the membrane + copper + cover
 Acoustic finite elements for the interior air and near field exterior
 Infinite elements for the far field
 Visco-elastic solid finite elements for the rubber protection
 Same loudspeaker as previous, embedded in a realistic model
 Performance
 Resources: 8 sec / freq on a Windows 64 PC with 2GB of RAM for up to
10kHz
Geometry
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Exterior mesh + Speaker
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Cell phone mesh
Case Study: Cell phone - Results
Pressure at 4000Hz
Pressure distribution at 500Hz
Radiated Power/excitation
Directivity
Installation effects
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Case Study: Portbox
 Key ingredients
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Visco-elastic shells finite elements for the membrane
Acoustic finite elements for the interior air and near field exterior
Infinite elements for the far field
Adding porous material in the back
 Symmetric excitation + symmetric geometry  ½ model for CPU time sparing
 Performance
 Resources: 2 sec / freq on a Windows 64 PC with 2GB of RAM for up to 1kHz
Geometry
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Finite element Speaker
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Case Study: Portbox - Results
Pressure distribution at various frequencies
SPL at 1m
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SPL at 1m with foam treatment
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Headphone Membrane
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Finite Element Model
Acoustic infinite
elements (coupled to
finite elements)
Thin membrane
(0.1mm)
Axisymmetric
Model
Holes = rigid walls (default
acoustic boundary
condition)
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Results
Axisymmetric model of the headphone’s
(SPL, 600Hz)
Grandwill in air velocity at diaphragm center, no back
or front cavity
Axisymmetric model of the headphone’s membrane, radiating into 2 semi-infinite medium.
Comparison of ACTRAN with measurements: velocity at the diaphragm center
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Results: Fluid-Structure Coupling
Grandwill in vacuo, with and without added mass (0.11gm)
In vacuo
In air
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IEC711 Coupler
Real Live Demo, Viscothermal Effects
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IEC711 Coupler - Model Description
A Combined BEM/FEM Acoustic Model of an Occluded Ear Simulator
Bin L. Zhang, Søren Jønsson, Andreas Schuhmacher, Lars B. Nielsen, Internoise 2004
« It represents the human ear canal from app. 10 mm behind its
opening to the concha cavity. Its acoustic impedance and
volume approximates that of the actual human ear canal. »
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IEC711 Coupler - Finite Element Model
Four different materials in Actran
model
Piston is modeled
as an acoustic
velocity BC
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Helmholtz resonator 1.3kHz
(orange = narrow slit)
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IEC711 Coupler - Results
Transfer impedance (dB)
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IEC711 Coupler – Viscothermal Effects
Transfer impedance (dB)
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IEC711 coupler – Losses Only for Helmholtz « 5kHz »
Helmholtz resonator 5kHz:
the viscothermal effects are
accounted for only in the
narrow slit (magenta).
Second mode is damped
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IEC711 coupler – Losses only for quarter wavelength
Quarter wavelength: the
viscothermal effects are
accounted for only in the tube
(yellow).
No major effects
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Acoustic Evaluation of a Loudspeaker
Yasuo Shiozawa, Sound Technology Department Yamaha
Presented at the 2011 RCCM conference in Tokyo
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Contents
 Bass Reflex Speaker
 Characteristic Evaluation of the Sound Quality at Low Frequency
 Application
 Conclusion
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Speaker Lineup of YAMAHA
HiFi
Home Theater
PA
Musical instrument
Desktop Audio
Digital Sound Projector
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Acoustic Simulation
Motion Electric Cone Speaker
Evaluation of Acoustic Characteristics
Electric- Structure– Acoustic Coupling
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Analysis of Speaker
Solid= Analysis
Dash = Experiment
Solid = Analysis
Dash = Experiment
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Bass Reflex Speaker
Helmholtz
Resonator
MCK Model
Neck
Cavity
Helmholtz Resonator
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LC model
Damping coefficient “h”
Viscosity + Thermal
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Visco Thermal Elements
Without Loss
With
Loss
Helmholtz Resonance Characteristics
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Experiment
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Analysis vs Experiment
■Cavity
Same SPL
High SPL
■Neck
Same Velocity
High Velocity
Mark: Experiment
Line: Analysis
Sound Pressure
Particle Velocity
Spatial Distribution of Helmholtz Resonance
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Influence of Neck Length
Evaluation Point
Normalized in L=0.010
Resonance Frequency
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Q Ratio
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Influence of Neck Diameter
Evaluation Point
Normalized in R=0.018
Resonance Frequency
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Q Ratio
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Control of energy properties
When resonance frequency and cavity capacity are known, the
Q Ratio can be controlled at the neck head and neck diameter.
Wave Length of
Resonance Frequency
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System of Bass Reflex Speaker
Resonance of
Speaker
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Resonance of
Helmholtz
Analysis Results
SPL Characteristics of Bass Reflex Speaker
Total SPL
In front of port
In front of speaker
Electric Impedance
Sound radiation from the
speaker and the port are
reverse phase
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Helmholtz Resonance
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Sound radiation from the speaker
and the port are same phase
Sound Quality
Solid: Bass Reflex
Dash: Ordinary
Without Visco Thermal
With Visco Thermal
There is a clear
difference of the sound
quality.
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Conclusion
Acoustic analysis can be widely applied in the development of loudspeaker
systems since it allows to predict the different design characteristics of the
system
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Actran
Customer list
Presentation Subtitle
December 17, 2014
Some of our Automotive Customers
MSC Software Confidential
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Some of our Aerospace Customers
MSC Software Confidential
3
Some Other References
MSC Software Confidential
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