1).The size of the objects.
The size of the object is bigger, the sound is louder, the depth is deeper; The size of the object is smaller, the sound is not
louder, the depth is shallow.
2).The Material of the objects.
The gold metals like the Iron and stainless steel, the depth is deep; And the Non-ferrous metals of aluminum and brass, the depth is shallow.
3).The influence of the soil
a. The hardness or thickness of the soil.
The thickness is larger, the penetrating power is smaller, the depth is shallow; The thickness is smaller, the penetrating power is larger, the depth is deeper.
b. The moisture of the soil. The moisture is larger, the value of resistance is larger, the depth is shallow; The moisture is smaller, the value of resistance is smaller, the depth is deeper.