Source with Directivity
Use the Source with Directivity 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.
Coordinate System Selection
By default, Global coordinate system is selected from the Coordinate system 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.
There are two main reasons to choose a transformed coordinate system for this feature:
1
When using a Hemispherical distribution of rays (see the Ray Direction Vector section), the first basis vector of the selected coordinate system defines the hemisphere axis. However, if the Specify local coordinates check box is selected in the Local Coordinates section, then the Forward direction ef defines the hemisphere axis. (This Forward direction can be defined in either global coordinates or in a transformed coordinate system.)
2
The Source with Directivity node defines built-in variables for the azimuthal and polar angle. For a physics interface with the default name rac and a Source with Directivity 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 Global coordinate system 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 Ray release position (see the Initial Position 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.
Release Times
This section is only shown if the Allow multiple release times check box is selected in the physics interface Advanced Settings section. Furthermore, this Advanced Settings section is only shown when Advanced Physics Options are enabled (click the Show More Options button in the Model Builder toolbar).
Enter Release times (SI unit: s) or click the Range 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.
Initial Position
The rays are released in a spherical or hemispherical distribution of directions emanating outward from a single point. Here, enter the components of the Ray release position vector q0 (SI unit: m). By default the ray release position is at the origin.
Ray Direction Vector
Select an option from the Ray direction vector list: Spherical (the default) or Hemispherical. If Hemispherical 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 Coordinate System Selection section) or the Forward direction ef specified in the Local Coordinates section.
Intensity and Power
This section is shown when either ray intensity or ray power, or both, are solved for, meaning that any option except None has been selected from the Intensity computation list in the physics interface Intensity Computation section.
Select an option from the Directivity list: Specify spatial directivity (the default) or Specify total source power.
For Specify spatial directivity, enter a value or expression for the Spatial directivity Dθ) 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 Reference level Lref in dB (default 65 dB) and the Reference distance 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 Spatial directivity and the Reference level, evaluated for that ray’s initial direction, when the ray reaches a distance from the source equal to the Reference distance.
For Specify total source power, enter a value or expression for the Total source power Psrc (SI unit: W). The default is 1 W. Enter a Power weighting factor 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 Power weighting factor evaluated for that ray, normalized such that the sum of the power over all rays equals the Total source power. Much like the Spatial directivity, the Power weighting factor 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.
Initial Ray Frequency
This section is shown when the Allow frequency distributions at release features check box is selected in the physics interface Ray Release and Propagation list. Unlike some other ray release features, only a single value of the Initial ray frequency f0 (SI unit: Hz) may be entered, not a distribution or a list of values. The default is 1 kHz.
Initial Phase
This section is shown when ray intensity is solved for, and in addition the Compute phase check box is selected in the physics interface Intensity Computation section. Enter a value or expression for the Initial phase Ψ0 (SI unit: rad). The default is 0.
Local Coordinates
The Specify local coordinates check box is cleared by default. When it is selected, enter the components of the Forward direction ef and the Transverse direction et (dimensionless). By default these directions are the first and third basis vectors, respectively, in whichever coordinate system was selected from the Coordinate System Selection section. These vectors are used to set the hemisphere axis (if Hemispherical is selected from the Ray Direction Vector 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.