Double Slit Interference or Interferenz am Doppelspalt is the reason for the lobing
The slit is a simplification here, it shows the problem in one plane instead of two. There is also an article in Wikipedia about "Acoustic Lobing".
Consider two drivers, each sending soundwaves. At some points in space the sound waves arrive with equal phase, they will add. This is constructive interference.
At some other points in space the sound waves arrive with a phase difference of 180 degrees, they will subtract, null each other. Tis is destructive interference.
There is plenty of articles about this.
Ruediger