The Interior Lumped Speaker Boundary is used to model a loudspeaker (dust cap, cone, and surround assembly) or another transducer using a lumped representation with a coupling to an Electrical Circuit interface. The mechanical and electric properties of the speaker can, for example, be described through a Thiele-Small representation and associated lumped parameters. Add this node from the Interior Conditions submenu. The interior version of the Lumped Speaker Boundary includes the effects of the fluid domains on both sides of the speaker boundary explicitly. For microtransducer applications it may be necessary to use the Lumped Speaker Boundary or Interior Lumped Speaker Boundary of The Thermoviscous Acoustics, Transient Interface.

In the time domain, nonlinear effects can be included in the lumped model through parameters that depend on the axial position x or velocity v of the speaker. These are, for example, the typically measured BL(x), CMS(x), or RMS(v). Predefined variables exist for the axial velocity actd.ilsb1.v_ax and an ODE is solved for the associated axial position actd.ilsb1.x_ax (use the appropriate physics and feature tag). These variables can be directly used in expressions in the electric components in the Electrical Circuit model as they are globally defined.

Define how the Speaker area (projected) of the speaker is computed by selecting either Selected boundaries (the default) if all boundaries are present, or Use symmetries if the speaker surface is only partially represented.

When Use symmetries is selected, select the Speaker area multiplication factor Ascale as Automatic (the default, the model is analyzed for the presence of symmetry conditions); or User defined and enter a value (default is 1). The settings are required in order to compute the effective area of the speaker which is used to compute the acoustic load and radiated power.

Define the Speaker axis direction eax by selecting Automatic (the default) or User defined. For the automatic option, the axis is computed as the average of the surface normals; this option is valid if a full speaker surface is selected. The User defined option should be used if the speaker surface is only partially represented and is the only option when Use symmetries is selected.

For the Automatic option select Reverse automatic speaker axis direction if necessary. The axis orientation can be visualized by plotting the axis components actd.ilsb1.e_axx, actd.ilsb1.e_axy, and actd.ilsb1.e_axz. (using the proper item and physics scope).

Enter the initial value of the force Fc and axial speaker position xax, used when solving the associated ODEs. The default value is 0 for both and is typically correct, except if the simulation is started, for example, with an initial excursion of the driver.

This section gives information about the state of coupling/connection to an Electrical Circuit interface. If the Interior Lumped Speaker Boundary is not connected, the text Connect to ‘External I vs. U’ in the Electrical Circuit interface text will be displayed. Once connected, a reference with a tag to the associated External I vs. U node, in the Electrical Circuit interface, is displayed.