The Association of Loudspeaker Manufacturers & Acoustics International presents. Dr. David R. Burd

Transcription

1 The Association of Loudspeaker Manufacturers & Acoustics International presents Dr. David R. Burd Manager of Engineering and Technical Support Free Field Technologies an MSC Company

2 Tutorial Actran for Loudspeaker Design

3 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:

4 The Actran Solver IE domain 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

5 Actran Acoustics Contains all acoustic as well as weak vibro-acoustic coupling features of Actran Finite elements Infinite elements Acoustic elements including viscothermal 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

6 Actran Vibro-Acoustics Contains all structural modeling features as well as strong vibroacoustic 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

7 ActranVI (Visual Interface) Provides a unified pre- and post-processor for all Actran modules

8 Some Customers

9 Actran for Loudspeaker Design The most complete tool for loudspeaker and other audio device acoustic simulation

10 Case Study of a Ported Loudspeaker (1) Geometry Structure mesh FRF transfer function: Power/excitation Deformed membrane at 1600Hz Pressure at 1400Hz

11 Case Study of a Ported Loudspeaker (2) Pressure distribution at various frequencies Geometry SPL at 1m SPL at 1m with foam treatment

12 Geometry Case Study of a Headset Finite element Speaker Pressure distribution; 600Hz Displacement on the membrane Impedance with and without air In air In vacuo

13 Pressure distribution at 500Hz Case Study of a Cell Phone Pressure at 4000Hz Radiated Power/excitation Directivity Installation effects

14 Tutorial Radiation of a Horn Speaker Actran Training - ACOUSTICS

15 Pre-processing in ActranVI Workshop - Radiation of a Horn speaker

16 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

17 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

18 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

19 Add Microphones Actran can add arrays or custom microphone placements automatically Apply complex frequency response Apply directivity patterns

20 Materials Many types of materials can be used Fluids (Air, liquid) Solids (Plastic, wood, metal) Porous (Polyfill, foam, fiberglass, grill cloth) Composites Laminates

21 Check the Mesh Quality

22 Post-processing with the PLTViewer Workshop - Radiation of a Horn speaker

23 Characterize the Transfer Function of the 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

24 Characterize the Acoustic Directivity of the Speaker at Different Frequencies The directivity of the horn speaker varies with the frequency, becoming less spread over the angle First microphones along XZ plane Last microphones along YZ plane

25 Post-processing of Maps in ActranVI Workshop - Radiation of a Horn speaker

26 Visualizing Maps 3 - Visualize Results (SPL maps in db)

27 Visualizing Maps 4 Comparison with PLT results Directivity at the 16 th virtual microphone (on the axis of the horn)

28 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