void detector

[nasiri1977]

what is the best void detector?

[Mike(Mont)]

They all work pretty good at finding empty holes.

Okay, joking aside. I've heard people talk about how the frequency generators can detect the magnetic field of an empty chamber. I know even a steep-walled gully can give a signal.

You might want to study about resonance in a closed cylinder. The length of the chamber affects the resonant frequency.

[Mike(Mont)]

Here's something for you to try--I've heard people with a locator rod baited for silver finding empty bottles. I suspect the end of the bottle probably plugged with dirt so to make a sealed chamber, but don't know that for sure. So maybe try a silver frequency.

[nasiri1977]

as a matter of fact we are dealing with an issue here. the map says that at the northern part of the agiven spring located under a cliff lies a tunnel which leads to a chamber . there were originally signs on a rock right above the expected tunnel. but now it has been eroded completely due to the passage of the time. now with the door of the tunnel closed we can not even enter into the chamber. due to depth issue pulse indection can not be used to detect gold. how can we find the entrance now?

[Mike(Mont)]

I would use a frequency generator type device. Not much use if you can't use L-rods. Some would say still no use. Something else might try is one of those IR cameras to find the opening. There is an inexpensive one that attaches to a smart phone. I paid $200 but don't know what they have now but certainly better than what I got. Telephoto lens etc. SEEK Thermal (Thermal.com) is the name and I'm not sure what countries they sell to . Those expensive ones Kellyco sells cost thousands and they are not even a camera.

BTW, a cheap smartphone will run much slower, a time lag of a couple seconds but it still works. I don't know if this will work for you if the entrance is deeply buried.