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The Association of Loudspeaker Manufacturers & Acoustics International presents
Dr. David R. Burd
Manager of Engineering and Technical Support
Free Field Technologies an MSC Company
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Tutorial – Actran for Loudspeaker Design
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What is Actran? • Actran is the most complete CAE tool for Acoustic, Aero-acoustic and
Vibro-acoustic modeling. • Actran is based on the finite and infinite element methods • Actran in a nutshell
– Material library: • Acoustic FE and IE (flow, temperature, visco-thermal effects) • Visco-elastic solid & shell (freq. dependent properties) • Poro-elastic (Biot model) and porous rigid (Craggs model) • Piezo-electric and composite materials
– Excitations & BC’s: • Structural (interfaced with Nastran, Ansys, Abaqus) • Turbulent boundary layer (Corcos), diffuse sound field • Aerodynamic Noise & CAA (Lighthill analogy) • Fan noise through incident spinning duct modes
• Actran is linked to many other CAE tools:
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The Actran Solver
• Acoustic FEM/IFEM approach • Multi-purpose toolbox: several computational sequences
– Direct Frequency Response – Modal Frequency Response – for interior problems – Hybrid Modal-Physical Response – the best of both worlds – Modal Extraction – for undamped structure or cavity
• Linux or Windows platforms • Direct & iterative solvers, multiple load & restart • Several types of parallelism available
FE domain
IE domain
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Actran Acoustics • Contains all acoustic as well as
weak vibro-acoustic coupling features of Actran – Finite elements – Infinite elements – Acoustic elements including visco-
thermal loss effects – Convected wave propagation
• Is a pre-requisite for all advanced Actran modules: – Actran Vibro-Acoustics – Actran Aero-Acoustics
• Applications: – Sound radiation from vibration
structures – Sound diffraction by rigid obstacles – Propagation in ducts – Acoustic resonances
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Actran Vibro-Acoustics • Contains all structural modeling
features as well as strong vibro-acoustic features of Actran – Structural finite elements – Modal representation of the
structure’s dynamic behavior – Mechanical excitations
(incl. random excitations)
• Requires Actran Acoustics as a pre-requisite
• Is a pre-requisite for: – Actran for NASTRAN
• Applications: – Strongly coupled
vibro-acoustic analysis – Acoustic transmission – Vibration of structures
in a heavy fluid – Multi-domain,
multi-physics applications
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ActranVI (Visual Interface)
• Provides a unified pre- and post-processor for all Actran modules
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Some Customers
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Actran for Loudspeaker Design
• The most complete tool for loudspeaker and other audio device acoustic simulation
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Case Study of a Ported Loudspeaker (1) Geometry Structure mesh
Pressure at 1400Hz Deformed membrane at 1600Hz
FRF transfer function: Power/excitation
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Case Study of a Ported Loudspeaker (2) Geometry
SPL at 1m
Pressure distribution at various frequencies
SPL at 1m with foam treatment
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Case Study of a Headset Geometry Finite element Speaker
Displacement on the membrane
Pressure distribution; 600Hz
Impedance with and without air
In air In vacuo
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Case Study of a Cell Phone Pressure at 4000Hz
Radiated Power/excitation
Pressure distribution at 500Hz
Directivity
Installation effects
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Tutorial – Radiation of a Horn Speaker
Actran Training - ACOUSTICS
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Pre-processing in ActranVI
Workshop - Radiation of a Horn speaker
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Workshop description • A horn loudspeaker is a loudspeaker element which uses a horn to
increase the overall efficiency of the driving element (diaphragm driven by an electromagnet). The horn itself is a passive component which improves the coupling efficiency between the speaker driver and the air.
• The objectives are: – To characterize the transfer function of the speaker at 1 m – To characterize the acoustic directivity of the speaker at different
frequencies
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Workshop strategy • The horn speaker is assumed rigid, only the acoustic part is modeled
A finite fluid component is defined
• The horn must radiate in free field baffled condition A infinite fluid component is also defined
• The driving element is only modeled by an acceleration boundary
condition An acceleration BC is applied
• The directivity of the speaker is assessed through virtual microphones
A field point post-processing component is created
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Mesh requirements • The following quadratic element sets are available in the mesh file(s):
– One 3D element set to model the Acoustic fluid – One 2D element set to support the surface excitation – One 2D element set to model the Infinite Elements – Two 0D element sets of field points to model a microphone array – Two 2D element sets of a BoxDomain for visualization
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Add Microphones • Actran can add arrays or custom microphone placements
automatically – Apply complex frequency response – Apply directivity patterns
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Materials • Many types of materials can be used
– Fluids (Air, liquid) – Solids (Plastic, wood, metal) – Porous (Polyfill, foam, fiberglass, grill cloth) – Composites – Laminates
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Check the Mesh Quality
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Post-processing with the PLTViewer
Workshop - Radiation of a Horn speaker
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Characterize the Transfer Function of the Speaker @ 1m
• As the excitation is a unit excitation (1 m/s²), the transfer function of the speaker at 1 m corresponds to the SPL (sound pressure level) at this microphone
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• The directivity of the horn speaker varies with the frequency, becoming less spread over the angle
Last microphones along YZ plane
First microphones along XZ plane
Characterize the Acoustic Directivity of the Speaker at Different Frequencies
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Post-processing of Maps in ActranVI
Workshop - Radiation of a Horn speaker
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Visualizing Maps 3 - Visualize Results (SPL maps in dB)
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Visualizing Maps 4 – Comparison with PLT results
• Directivity at the 16th virtual microphone (on the axis of the horn)
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Conclusions • Actran is very will suited to model and guide many aspects of
loudspeaker and loudspeaker enclosure design • Actran can model a variety of complex materials and structures • Post-processing is fast and easy using ActranVI
