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The Nail Board Test And Sensitivity


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I just watched a video of a guy comparing the new legend to the equinox on Monte’s nail board test.  Sorry, but I don’t have a link to it, but I think I saw it over on the friendly forum.  In the video he is using the nox and says he has the recovery speed set at 8 and sensitivity at 23.  Then he also mentions that recovery speed is what’s important on this test, not sensitivity.  I have to disagree.  Running 23 sense on what is basically an air test with an 11” coil only a few inches above the targets seems like way too much power to me.  Monte has confirmed that this test of his was developed from surface finds.  So I’m thinking this guy would have gotten better results (with both nox and legend) by lowering the sensitivity dramatically.  Like maybe down to 10 or 12 on the nox.  Am I correct in my assumptions?   I have a site near my house that’s loaded with old iron.  Most finds are 3-5” deep or less.  I’ve actually compared non ferrous signals with low sensitivity and then bumped the sense up to 20 or so and the signal is more muddled and much more iffy to define than on the lower setting of around 12.  I’m just curious why these guys doing the nail board tests aren’t at least trying a lower sensitivity setting?

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Sensitivity being too high is one thing to consider.  So is swing speed.

In real world, bed of nails situations there is absolutely no way that I would ever swing my coil in such a fast and haphazard way as the tester in the video you referenced. The same goes for many other testers that I have seen lately who think that swinging a coil really fast over nails and coins is a true representation of what these detectors can actually achieve in real world situations or that the one that can be swung fastest is the best for all ferrous/non-ferrous situations. I certainly will swing fairly quickly in tiny 1 to 3" swings when I have isolated a non-ferrous target in a high iron or high aluminum trashed site to zero in and center the target under the coil. I would never do that while walking a site to try and find a quality non-ferrous target in a densely trashed area which Monte's Nail Board test recreates.

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High sensitivity/gain levels will give more falsing on rusty undisturbed Iron & make small Aluminum bits appear bigger, especially when they are shallow.

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31 minutes ago, Jeff McClendon said:

Sensitivity being too high is one thing to consider.  So is swing speed.

In real world, bed of nails situations there is absolutely no way that I would ever swing my coil in such a fast and haphazard way as the tester in the video you referenced. The same goes for many other testers that I have seen lately who think that swinging a coil really fast over nails and coins is a true representation of what these detectors can actually achieve in real world situations or that the one that can be swung fastest is the best for all ferrous/non-ferrous situations. I certainly will swing fairly quickly in tiny 1 to 3" swings when I have isolated a non-ferrous target in a high iron or high aluminum trashed site to zero in and center the target under the coil. I would never do that while walking a site to try and find a quality non-ferrous target in a densely trashed area which Monte's Nail Board test recreates.

This is a great point. But to defend the "fast swingers," it's also possible that they normally use a fast swing speed. And since that's their hunting style, that's the testing approach they use.

When I know I'm in a high trash environment, I do slow down my swing speed a little bit. But I don't always know I'm in a high trash environment, especially at a new permission. So I use my "default" swing speed...which may or many not be faster compared to other metal detectorists. When I do my own nail board tests, I'm doing it using my personal default swing speed to see if, had the test actually been a real world hunt, would my detector have given me enough indication to dig or at the very least, take different action, ie slow down my swing, shorten the arc of my swing, swing from a different angle, adjust my sensitivty or other settings, etc.

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1 hour ago, NCtoad said:

I just watched a video of a guy comparing the new legend to the equinox on Monte’s nail board test.  Sorry, but I don’t have a link to it, but I think I saw it over on the friendly forum.  In the video he is using the nox and says he has the recovery speed set at 8 and sensitivity at 23.  Then he also mentions that recovery speed is what’s important on this test, not sensitivity.  I have to disagree.  Running 23 sense on what is basically an air test with an 11” coil only a few inches above the targets seems like way too much power to me.  Monte has confirmed that this test of his was developed from surface finds.  So I’m thinking this guy would have gotten better results (with both nox and legend) by lowering the sensitivity dramatically.  Like maybe down to 10 or 12 on the nox.  Am I correct in my assumptions?   I have a site near my house that’s loaded with old iron.  Most finds are 3-5” deep or less.  I’ve actually compared non ferrous signals with low sensitivity and then bumped the sense up to 20 or so and the signal is more muddled and much more iffy to define than on the lower setting of around 12.  I’m just curious why these guys doing the nail board tests aren’t at least trying a lower sensitivity setting?

I agree that lower sensitivity is better. But to possibly defend/explain the person who made the video (Iffy Signals?), they might conduct all tests using the highest sensitivity reasonably possible on their machine. This could be one way they try to keep different tests from different days/machine as consistent as possible.

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24 minutes ago, mh9162013 said:

I agree that lower sensitivity is better. But to possibly defend/explain the person who made the video (Iffy Signals?), they might conduct all tests using the highest sensitivity reasonably possible on their machine. This could be one way they try to keep different tests from different days/machine as consistent as possible.

It was this guy:  

 

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What the coil transmits is normally fixed, with transmit boost being a rare exception, where you can boost the voltage applied to the coil.

Sensitivity or gain controls are therefore filters applied after the fact, that amplify or filter the signal from the coil in various ways. Most detectors have a single control that you actually don’t know what’s really going on, unless you experiment with it to see what happens. It’s a possible blend of functions in one control. The White’s V3i gives you direct access to several possibilities, the preamp gain (RX Gain), all metal sensitivity, and discrimination sensitivity. Reading the White’s V3i manuals can teach you a lot about detectors, especially the V3i Advanced User Guide. A basic circuit flow chart from page 4-1:

0B8833BE-FD7E-4695-A1ED-A7C2BFFBF012.jpeg
The manual has excellent discussion of the sensitivity and threshold audio controls.

My point here is the controls do not affect masking effects per se, as the coil properties are fixed. You are not increasing or reducing the field size or strength, but in general simply doing an audio amplification process. Reducing gain or sensitivity will suppress some signals to where they will not be heard, allowing only the strongest signals to break through. If you primary desired target signal is stronger than the undesirable signals, reducing sensitivity can suppress or totally eliminate the undesirable signals. If the primary target becomes fainter, as it often will, increasing volume can offset this.

Long answer to say yes, reducing sensitivity and possibly increasing volume can save your mind and sanity, and produce cleaner results. But note that when striving to reach the deepest, faintest signals, this is not a good idea, for what I’d hope are obvious reasons. However, what they can’t do is actually modify what the coil is doing in something like the Monte test, as that part of the equation is fixed. What may work however is actually raising the coil. Being too close can create overload situations from the targets being too close to the the coil, and since the coil field is globular is shape, raising the coil can reduce extraneous edge i.e. masking effects, by working a smaller “tip” of the field.

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3 hours ago, Jeff McClendon said:

In real world, bed of nails situations there is absolutely no way that I would ever swing my coil in such a fast and haphazard way as the tester in the video you referenced. The same goes for many other testers that I have seen lately who think that swinging a coil really fast over nails and coins is a true representation of what these detectors can actually achieve in real world situations or that the one that can be swung fastest is the best for all ferrous/non-ferrous situations. I certainly will swing fairly quickly in tiny 1 to 3" swings when I have isolated a non-ferrous target in a high iron or high aluminum trashed site to zero in and center the target under the coil. I would never do that while walking a site to try and find a quality non-ferrous target in a densely trashed area which Monte's Nail Board test recreates.

Jeff, you have exactly nailed my biggest 'peeve' concerning all these separation tests: they simply don't reflect a realistic hunting style. I mentioned this in a video Calabash did showing coin/bottle cap separation. Using super-fast super-short sweeps he showed that the Deus II would ignore the BC and detect the coin. But right at the end of the video he inadvertently did a couple of normal sweeps over the combination and the Deus barely made a chirp. If, using normal hunt sweep, you don't get a good enough response to say, "Hey, what was that?" then it's a fail.

I'm not picking on Calabash, it seems that everyone is doing these tests like this. But nobody does normal hunting with a 3" sweep at a blistering speed. Yes, it might be used for zeroing in on a suspected target, and for that these test results are useful, but you need the normal hunt results first.

When I test separation I use a 1 meter sweep at 1m/s set by a metronome. My preferred target arrangement is a silver quarter placed between 2 transverse-oriented 16p nails, all at a 3-1/2" depth. I reduce spacing until the detector can no longer issue 3 distinct target responses. A lot of people test by placing the nails longitudenally but this becomes a test for a co-located composite response instead of a separation response. If you understand why nails give a double-beep when swept longitudenally then you will understand the mechanics of this test.

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Monte's Nailboard test ..I consider one of the excellent tests for surface separation of the type / 2D / non-ferrous shallow object in the surface climbing iron ...

such a "Monte nailboard" test revealed very quickly whether you have a correctly set detector for this type of separation ... but they also revealed such a test .. how the tested detector and coil ... can handle a given situation ...
 The size of the coil also plays a big role in such a test .... a smaller coil allows to achieve better results in such a test ..., on the other hand to achieve good results in the test using 11 "coil size requires a separation good detector, together with optimal we set up for such a 2D separation test ..

The important settings in this test are:
1. high Frequency used /  weighted multifrequency / is better ..
2. High recovery speed is better..
3 .. Very low settings  Iron bias / silencer / is better..

In this test of Equinox vs Legend, I'm concerned that Equinox used a high Iron bias setting, which was a sign of the Equinox separation.

In my tests Equinox achieves better results ....

 

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5 hours ago, Geotech said:

Jeff, you have exactly nailed my biggest 'peeve' concerning all these separation tests: they simply don't reflect a realistic hunting style. I mentioned this in a video Calabash did showing coin/bottle cap separation. Using super-fast super-short sweeps he showed that the Deus II would ignore the BC and detect the coin. But right at the end of the video he inadvertently did a couple of normal sweeps over the combination and the Deus barely made a chirp. If, using normal hunt sweep, you don't get a good enough response to say, "Hey, what was that?" then it's a fail.

I'm not picking on Calabash, it seems that everyone is doing these tests like this. But nobody does normal hunting with a 3" sweep at a blistering speed. Yes, it might be used for zeroing in on a suspected target, and for that these test results are useful, but you need the normal hunt results first.

When I test separation I use a 1 meter sweep at 1m/s set by a metronome. My preferred target arrangement is a silver quarter placed between 2 transverse-oriented 16p nails, all at a 3-1/2" depth. I reduce spacing until the detector can no longer issue 3 distinct target responses. A lot of people test by placing the nails longitudenally but this becomes a test for a co-located composite response instead of a separation response. If you understand why nails give a double-beep when swept longitudenally then you will understand the mechanics of this test.

You “nailed” it Carl. :smile: The test itself just is what it is. But one of the most important factors in real world detecting is coil control and technique, which largely separates the real pros from everyone else, not the particular machine in use. Coil technique varies so wildly on Monte tests as actually performed, so as to render them almost useless for comparative purposes between different operators.

I always imagined the perfect detector test is one that takes a person out of the loop. A adjustable mechanical sweep arm arrangement for the mechanics. And a digital meter reading to replace the audio, so that exact numeric audio output levels are compared, rather than poorly recorded audio on videos. These tests measure the people involved every bit as much as the detectors.

Thats not to say they are a waste of time, and that one can’t glean good information from them. It just helps a lot if the eyeballs watching the videos have some knowledge of how easily the results can be manipulated just by varying the speed of the swing, or the often impossible to determine coil height as seen from the camera.

Personally I like to include hot rocks in my own tests, plus various ferrous items that read non-ferrous, as I usually am more concerned with false positives than anything else. I therefore make my own test setups as required for my purposes alone, and only share the results in a generalized sense via my “opinions.”

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