why choose that frequency range for ic5

[loannguyen]

I'm a beginner,

I am making a pulse induction metal detector based on Hammerhead Pulse Induction Metal Detector by Carl Moreland Rev D1. But I don't understand why IC5 oscillation frequency is chosen to be around 900-2500Hz. Metal detectors (PI) on the market usually have oscillation frequency in the range of 100-1000Hz.
Is there any special reason to choose the 900-2500Hz frequency range?

[Carl-NC]

PI detectors can range from 25 Hz up to 20,000 Hz. It all depends on what you want to do. 100-1000 Hz is on the lower end typically used in cache hunting. 1000-2500 is typically used in beach hunting. 2500-20000 would be used for gold nuggets.