anchor: Source:setCone
  Sets the Source's directional volume cones. Together with Source:setDirection, the cone angles allow for the Source's volume to vary depending on its direction.
  Source:setCone( innerAngle, outerAngle, outerVolume )
  innerAngle number The inner angle from the Source's direction, in radians. The Source will play at normal volume if the listener is inside the cone defined by this angle.
  outerAngle number The outer angle from the Source's direction, in radians. The Source will play at a volume between the normal and outer volumes, if the listener is in between the cones defined by the inner and outer angles.
  outerVolume (0) number The Source's volume when the listener is outside both the inner and outer cone angles.