If not the most frequent, this is one of the most frequently asked questions we get about metal detectors. However, it’s not as simple as you may assume to respond to this question. There are other factors at play. First, of course, there are metal detectors designed expressly for deep target detection. Some people can discern a depth of several metres beneath. Specific smaller detectors detect only external objects. The detector’s frequency and sensitivity are two parameters. However, there are other more factors to consider.
I have a canned solution for those of you who only read the first two paragraphs of an article:
A standard handheld metal detector can detect an object the size of a small coin at a depth of about the same distance as the detector coil’s diameter.
A detector with an 8 “coil, for example, would detect a small coin-sized object at 8” +/-.
This is not, however, the detectors’ maximum depth capabilities. For example, with my Garrett AT Pro, which has an 11″ coil, I can get a signal within 10 feet of my car.
Factors involved in the depth to which a metal detector can detect metals:
When it comes to deciding how deep a metal detector will detect an object, the size of the thing is crucial. So, whereas a single coin may only be detectable at a depth of around afoot, a large box of cash may be detected twice as much, depending on the detector settings.
Metal detector coil size
Size Matters. This applies to both the size of the object and the coil. Many detector brands offer alternative coils to the ones that come with the detector. For example, Minelab provides a 15 “DD smart coil for the Equinox series of metal detectors instead of the 11” DD coil that comes standard. Do not be fooled. When detecting metals, bigger is not always better. When you see debris areas, more giant waves give you a much larger detection pattern. This means that it will detect many more targets at the same time. This can be not only a hindrance but also a nuisance. Most companies make small “sniping” like Minelab’s 6 “DD Smartcoil for this very reason.
A “box” style metal detector like the Garrett GTI 2500 with the Eagle Eye coil connected will be a good alternative if you’re looking for a large and possibly intense target. With these detectors, particular massive objects can be spotted several feet deep.
Metal detector frequency
Another aspect that determines depth is the metal detector’s operating frequency. According to the general rule, the lower the frequency, the better a metal detector will be at finding massive, deep objects. Conversely, a metal detector’s ability to detect tiny shallow targets improves with increasing frequency (5 kHz-10 kHz). The majority of gold prospecting metal detectors have higher frequency settings (40 kHz-100 kHz). This is why most detectors operate between the frequencies of 12 and 18 kHz, which effectively locate a wide range of artefacts such as coins, jewellery, and relics.
There are stipulations in the example of a typical detector that can detect a coin at the approximate depth of the coil size. If, for example, the currency is tilted on its edge instead of being flat, the detector may not detect it as profoundly as the pattern of the radio waves sent to the sensor will be read differently due to the orientation of the coins.
When the earth is wet, it is general knowledge that detectors gain more depth. However, the water content of our soil varies significantly from season to season in the Midwest. You may lose a few inches in the hot, dry summer, but you should expect your detector to reach its maximum depth in the moist spring and fall. On second thinking, perhaps this isn’t such a horrible thing. Digging a 12-inch hole in rock-hard dirt is a chore that no one enjoys.
Metal detector sensitivity
To get the maximum depth from a detector, the frequency should be set to “high”. However, under normal conditions, the sensitivity should be set to approximately 3/4 to 2/3 of the detector’s maximum. Having the sensitivity set to max all the time can result in the detector acting erratically and picking up even the most miniature unwanted objects, such as small pieces of wire.
I hope this clears up the question for most people. Good luck and happy hunting!