Assigning Spatial Directivity to a Source
The Source with Directivity node can be used to release rays in a distribution with user defined spatial directivity. This node sets up a point source where rays emanate outward in a spherical or hemispherical distribution.
When the ray intensity or power is solved for, you may either specify the spatial directivity in terms of sound pressure level or enter the total source power. When specifying a spatial directivity function, the intensity of each released ray at a distance r (SI unit: m) from the release point is
where pRMS is the root mean square pressure at a distance r = Rref from the source,
•
ρ (SI unit: kg/m3) is the density of the surrounding fluid,
•
c (SI unit: m/s) is the speed of sound in the medium,
•
Rref (SI unit: m) is the reference distance,
•
D(ϕ,θ) is the spatial directivity in dB, and
•
Lref is the reference level in dB.
Strictly speaking, the ray acoustics approximation gives infinite ray intensity for a spherical or hemispherical wavefront as it is first released from an infinitesimally small point source. In reality, diffraction effects would make the ray acoustics approximation inaccurate within a few wavelengths of the release position.
If the ray power is solved for, then the total power of all released rays is
where Ω (SI unit: rad) is the total solid angle subtended by the released rays: 2π for a hemispherical release or 4π for a spherical release.
Alternatively you can specify the total source power Psrc directly, along with a power weighting factor Pwt. Then the intensity and power of each released ray is proportional to the value of Pwt evaluated on that ray, while the sum of the initial power over all rays is Psrc.