COMSOL 6.2 - Source with Directivity

	This feature is only available in 3D.

Use the node to release rays with initial intensity or power following a spatial directivity function. This is useful for modeling loudspeakers or human talker sources in a room acoustics context. The rays will emanate outward from a point in either a spherical or hemispherical distribution. Predefined variables for the azimuthal and polar angles within this distribution can be used to define the spatial directivity function, either as a sound pressure level or in terms of absolute power.

By default, is selected from the list. Other user defined coordinate systems can also be selected from the list. However, boundary coordinate systems are not included in the list because there is no requirement for the ray release position to be on a boundary.

When using a distribution of rays (see the section), the first basis vector of the selected coordinate system defines the hemisphere axis. However, if the check box is selected in the section, then the ef defines the hemisphere axis. (This can be defined in either global coordinates or in a transformed coordinate system.)

The node defines built-in variables for the azimuthal and polar angle. For a physics interface with the default name rac and a node with the default name swd1, these variables are called rac.swd1.phi (azimuthal angle) and rac.swd1.theta (polar angle). These angles are defined with respect to the selected coordinate system; for example, if the is used, then rac.swd1.theta is the angle between the ray direction vector and the positive z-axis, while rac.swd1.phi is the angle of the projected ray direction vector in the xy-plane, measured counterclockwise from the positive x-axis.

No matter which coordinate system is selected, the (see the section) is always specified in global Cartesian coordinates. Thus the selected coordinate system controls the orientation of the source while the global Cartesian system always controls its position.

This section is only shown if the check box is selected in the physics interface section. Furthermore, this section is only shown when are enabled (click the button in the toolbar).

Enter (SI unit: s) or click the button (

) to select and define a range of specific times. At each release time, rays are released with initial position and ray direction vector as defined in the following sections.

Select an option from the Ray direction vector list: (the default) or . If is selected, the hemisphere axis is not defined in this section; the axis is either the first basis vector in the selected coordinate system (see the section) or the ef specified in the section.

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For , enter a value or expression for the D(φ, θ) in dB. The default expression is 0[dB]*cos(rac.swd1.phi)*sin(rac.swd1.theta). The expression is a placeholder that shows the variable names for the two polar angles. The directivity will typically be defined by an interpolation function that represents a given source like a loudspeaker. Also specify the Lref in dB (default 65 dB) and the Rref (default 1 m). The ray intensity or power is initialized such that the sound pressure level of each ray equals the sum of the and the , evaluated for that ray’s initial direction, when the ray reaches a distance from the source equal to the .

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For , enter a value or expression for the Psrc (SI unit: W). The default is 1 W. Enter a Pwt, which can have any unit. The default expression is 1. The initial intensity and power of each released ray will be proportional to the evaluated for that ray, normalized such that the sum of the power over all rays equals the . Much like the , the can be a function of ray variables such as the azimuthal and polar angles. For this option the reference distance is assumed to be 1 m. The total power divided with the surface area of the sphere/hemisphere at 1 m is used when computing the intensity along rays. Remember that the intensity is a local sound field quantity.

This section is shown when the check box is selected in the physics interface list. Unlike some other ray release features, only a single value of the f0 (SI unit: Hz) may be entered, not a distribution or a list of values. The default is 1 kHz.

This section is shown when ray intensity is solved for, and in addition the check box is selected in the physics interface section. Enter a value or expression for the Ψ0 (SI unit: rad). The default is 0.

The check box is cleared by default. When it is selected, enter the components of the ef and the et (dimensionless). By default these directions are the first and third basis vectors, respectively, in whichever coordinate system was selected from the section. These vectors are used to set the hemisphere axis (if is selected from the list). They also control the definition of built-in variables for the azimuthal and polar angles, which can be used to define a spatial directivity function for the released rays.