Products AxiDriver - Examples - Cone

Simple Cone

File: (Default after start-up)

The first example is already available at start-up. The example demonstrates the simulation of a 250mm diameter cone speaker.

In the sketch the blue lines are parts of the vertical and uniform moving diaphragm. The red lines indicate suspension-rings, which are moving also vertically but here the velocity distribution is such that the velocity is zero at the frame from where it increases linearly. The width of the outer suspension is given by the value of ws2. The other suspension is the spider, which holds the voice-coil in place, and its width is ws0. Black lines indicate reflecting boundaries. The gray lines indicate the infinite baffle. The little dot shows the rotation point for spectral sound pressure analysis.

In AxiDriver the simulation has two steps: Solving Observation The BEM is based on the Helmholtz-Integral, which can be regarded as a spatial transfer-function with multiple sources. Initially some of these sources are unknown but can be solved for. In AxiDriver we have to start the solver whenever we alter the acoustic structure. The solver parameters are controlled on page Solver. Sampl Frequ ensures that the size of the finite elements are smaller than λ/6 for the specified frequency. The solver sets the system up for the given frequency range and the number of points. Once AxiDriver solved the Helmholtz-Integral, it allows for calculating the sound field at arbitrary points in space, and at frequencies the system has been solved for. We can view the sound-pressure field at a specified frequency, or frequency response functions at dedicated spatial points. The field can be observed with the help of the right hand contour plot. In order to view frequency response curves we would need to install the graphing server Vacs. The link is automatic. AxiDriver updates the spectra after changing motor parameters or after enabling observations on page Vacs. You can switch this automatic-mode off in the preferences. In this case you would need to explicitly trigger the Vacs-output by clicking the Vacs-symbol in the top-panel (or see menu Processing).

The motor system is modeled with the help of lumped elements in the standard way. "Lumped" indicates that only one rigid body mode of the mechanics is taken into account. The motor parameters can be obtained from Vacs - Dyn Driver Parameter Identifier, or from Klippel Distortion Analyser, for example with the help of copy and paste (see external link www.klippel.de).

AxiDriver couples the acoustic field to the motor system through the radiation impedance of the diaphragm. Because in AxiDriver the radiation is independent of the mechanical system (no modes) the motor system parameters can be altered without the need for resolving the acoustic system.

The two plots above display the radiation resistance and reactance. The red curve is produced by the cone and the blue is added for comparison with the radiation impedance of an equivalent disk. The cone-cavity emphasizes the radiation in the proximity of 1kHz. In contrary to flat or convex shaped diaphragms, which exhibits only mass-like reactance curves, has the cone also a frequency range with stiffness-like properties, as can be seen by the negative reactance in the range 1k...2kHz.

AxiDriver lets you also calculate the motion of the voice-coil and the electrical driving point impedance.

There we run into a small problem, which effect is that the fundamental resonance might not be visible in the resulting curves. The cause is the coarse frequency-resolution in the lower frequency band. If we want to investigate the fundamental resonance then the only way is to change the frequency range on page Solver, say fmin = 10Hz, fmax = 200Hz and Num frequ = 50, and then to re-solve the total system. The result should look like the following graph:

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