If you don't mind, 'beest', let me clarify the statements you made.
It's not a theory, but detector producers more then once confirmed that a detector performs "best" with his original coil while that is were the detector (box) is adjusted on.
Actually, that is incorrect if applied as a whole. A metal detector AND coil combination will perform 'best' if they are designed well, properly adjusted, and are able to handle different search site conditions better.
FACT: Some search coil
'sizes' and/or search coil
'types' might NOT work well if they are not a good match for the existing site conditions. Site conditions include the Ground Mineral make-up as well as the amount of, and proximity of, discarded trash and desirable targets.
FACT: Some search coils might be a proper size and shape and type, but the detector they are used with might not be well designed to handle more challenging trash, such as too much junk close-together or a lot of Iron Nails or other nearby ferrous debris.
Now, let's go back to "proper settings." generally the operator has control of such things as Sensitivity and Discrimination. But your statement really applies to metal detectors that rely on a factory designed or preset Ground Balance. The so-called
"turn-on-and-go" detectors where the operator doesn't have easy control of the GB setting which has been 'preset' in design or at the factory prior to shipping.
Ground Balance is an often less-understood adjustment function by most metal detecting Hobbyists, and back in the early to mid '80s we saw a big trend for many detector manufacturers to product more 'preset GB' models then the more controllable units with an Automated GB or Manual GB.
EXAMPLE: Because they have been so well known, let me refer to a Tesoro Silver Sabre model. It is an easy-to-use detector and they came with an internally 'preset' Ground balance. That was done at the factory in final production when the employee hooked up a 'standard' search coils and 'calibrated' it. "Calibration' was the term meaning adjusted the internal Ground balance. Then, tht specific detector was then shipped with that specific search coils and was 'calibrated' of Ground Balanced with that coil. The GB was done, typically, using a piece of ferrite.
THE GOOD NEWS: That specific detectors with that 'standard' search coils that came with it were 'tuned' or 'calibrated' so that they would work OK in most 'typical' or possibly 'average' ground mineral environments w/o falsing.
THE BAD NEWS: The detector user might select a hunt siste that has more intense mineralization and the "turn-on-and-go" detector with a preset GB might not be able to handle it, and that can also cause false signals.
Another problem could be the user wanted to change to a larger-size search coil, or a smaller-size search coil, ... or even change to a different but same-size search coil and that particular coil was not first 'calibrated' or 'tuned' to the detector and the result was maybe a too-negative the GB or a too-positive GB. In some cases that could cause falsing, a loss of detection depth, or even be so positive with that coil that the detector will not respond to a bigger-size high-conductive coin.
Of course another coil can have more benefits were it finds deeper, or smaller ... and be "better" (for you).
But the detector (box) performs best with the original manufactory coil.
All that was implied what that the system control box and the originally supplied search coils should have been properly 'tuned' or 'Ground Balanced' or average search conditions.
In my current Detector Outfit, I only have three models that lack an external Ground Balance control, and in one case, my Tesoro Silver Sabre microMAX, I keep a 6" diameter Concentric coil mounted to it 'full-time' so I am not changing search coils. And, I made sure it was properly 'calibrated' as I have all my "turn-on-and-go" detectors by adjusting the internal GB trimmer for the more mineralized ground where I will grab it for use.
My Tesoro Bandido II microMAX also keeps a 6" Concentric coil mounted, but I do have a 'standard' 8" Concentric coil on-hand, but that doesn't matter. The Bandido II microMAX features an external manual Ground Balance so I can properly 'tune' or 'calibrate that unit' system box and the attached search coil for whatever the existing conditions might be, and THAT will provide me the 'best' or peak performance and be better than a factory calibrated 'best guess' setting.
I never buy "bigger better" coils. I always hunt with the manufactory coil (even 8 inch). And i always found nice, good enough, never less or worse then my huntingbuddies (among some with the "best" detector and coils).
As long as YOU are satisfied with the detector's performance and the results you achieve, then that's fine. But I can assure you, most detectors that are sold are NOT going to provide the 'BEST' performance all-around. Actually, with the trend the past several years to keep offering a bigger-size coil on even the lower-end models, those detectors with a supplied coil are going to operate worse than 'normal' simply because the 'standard' coil is now too large to work well in confined spaces or amongst a lot of discarded trash.
That's why I prefer and recommend a serious detector operator invest in a better designed or more controlled model that provides Ground Balance control.
Monte
But from the detector manufacturers.
