because there is more to each of them than you copied and pasted to your response. Much more. Not wanting some of the newbies to be mislead, I have gone through each one again and will share the parts you left out, concerning audio response.
** any of the three will find silver, copper, gold, lead and brass, with very little difference in depth of detection. However, I do find that the 3 khz provides a very distinct audio response on deeply buried iron. As one who hunts in multiple tone, all metal mode, I listen to everything, ignoring the low tones of ferrous targets. What I have found is that iron gives a broken tone at the edges when using the 3 kHz coil. And, is far less likely to provide a consistent audio tone on deep iron. Especially when working the coil around edge of the target, listening for variances in the pitch.
**Again, I won't say that the 9-inch, 3 kHz concentric is any deeper than the 9-inch, 7.5 kHz concentric. But I will say that the distinct audio response of iron is much easier to decipher using the 3 kHz than it is the other two frequencies. It has saved me digging a ton of old farm implements!
**When I am hunting an old homestead, I'm convinced that the 3 kHz concentric provides a much more distinct "low iron growl" on those deep scraps of iron, than the other two freqs.
**Due to lower frequencies being more "in-tune" with higher conductive targets (such as silver and copper), it is LESS "in-tune" with lower conductive targets (such as iron and aluminum can slaw). Running the 3 kHz coil in all metal, with multiple tones, is the combination I use on old farmsites and open areas that allow the larger coils. It may not hunt any deeper than the other two frequencies. But it provides a very distinct audio tone on deep iron and other ferrous targets "bordering on" a high conductive reading.
**I like the 9-inch concentric at 3 kHz due to the distinct audio tone that the lower frequency provides me on ferrous targets.
**I won't say that the 3 kHz concentric will detect targets any deeper than the other two freqs at 9-inch concentric. But I use it for two reasons. One, it is very good at detecting old silver and copper coins. And two, it provides a more distinct audio signal on deep iron and modern trash, (than the other two freqs) when running in all metal mode.
**In my opinion, not only is the 3 kHz coil "hotter" on silver and copper. I think the 3 kHz coil does a better job of "ignoring" those smaller bits of low condutive trash. Iin all metal, it still detects them. But they provide an audio response that allows my ears and brain to determine whether I want to dig or not.
**my choice for wide open spaces is the 9-inch concentric at 3 kHz. I have been using it for well over a year now and find that it is not only very sensitive to the silver and copper coins I find. But it also provides less sensitivity to ferrous targets that are frequently found in the sites I hunt. When I am hunting in the 4-tone, all metal mode, it makes a more distinct "low tone" audio response to iron targets, helping me to make a decision whether to dig, or not.
**I won't say the 3 kHz hunts any deeper than my 9-inch concentric at 7.5 kHz. But I can sure tell a difference in the audio tones of ferrous targets. Your results may vary, depending on your soil conditions and the sites you hunt.
**I like the 3 kHz coil. I hunt in 4-tone, all metal most of the time. And I simply ignore the low tones. I am convinced that the 3 kHz coil provides me a more definite audio response to low tone iron than even the 7.5 kHz coils. And far better than the 18.75 kHz coils. This more defined audio response allows me to separate targets better and spend less time checking and rechecking those "iffy" signals. With that said, if someone took the tags off of my LF and MF coils, based on depth, sensitivity and separation characteristics, I'm not sure I could tell them apart.
**Having all 3 frequencies of concentric coils, as well as the 10.5 DD at 18.75, I use the 3 kHz concentric coil most of the time. In all metal, I can differentiate the masking sounds of iron better than with the 18.75 coils.
**you will find very little difference in the detection depth or the ability to detect coins, or coin sized targets, with the three various frequencies. I say this because the difference between 3 kHz to 7.5 kHz to 18.75 kHz is not very much. I have convinced myself that the 3 kHz coil will allow me to hear the low tone created by iron, when adjacent to a coin, better than the other two frequencies.
**I haven't found any coins using the 3 kHz that I couldn't have found with the 7.5 kHz due to depth. But I have dug less iron using the 3 kHz, due to the audio differences I mentioned before. And, I am convinced I was able to "unmask" several old IH cents from iron infested ground that I wouldn't have with the 7.5 kHz. So as to not leave any frequency out, I don't use the 18.75 kHz much because the sensitivity is too hot for the types of places I hunt. If I have to lower the sensitivity of the detector to compensate for a "hot" coil, then what is the point if I am coin shooting for silver and copper? When the X-50 and X-30 were introduced, all I used were the 7.5 kHz coils. In fact, if you search the first 12 months of posts, you will likely find some posts I made saying that I preferred the 7.5 and couldn't tell much (if any) difference in comparing detection depth between coils or detector models. For the most part, I still feel that way about the three detector models. However, just as with the X-70 itself, the more I use the 3 kHz coil, the more I like it. Theoretically, the 3 kHz coil should be more sensitive to copper and silver. And, I swear I can hear a subtle difference in the audio produced by iron targets with the 3 kHz coil than I can the other two. So, to "not really" answer your question again, I guess it is just my preference based on my hearing the tones and interpreting them. That and I want that low freq/high conductivity theory on my side!
HH Randy
