Hearing - Inaudible Nuggets & Higher Frequencies

I've spoken to four people from different goldbearing areas of Australia with an interesting statement ... all of whom claimed something which I find VERY interesting.

Each of these people has told me that their children could hear signals "plain as day" through their earphones that the adults were unable to hear at all. One claimed that his own hearing was excellent yet he didn't believe his child when the kid was saying "can't you hear that?". When these signals were dug, they produced gold nuggets. I'd almost forgotten about this until I spoke to a chap just yesterday who had given his GPX-4000 to his son to use since his son could apparently hear signals that he was unable to pick up with his own ears. They dug over 800 grams in the span of a day with his son using the detector and he was doing all the digging. The nuggets looked to be less than the size of a 5c piece each. I do not know the size of the pieces dug by the other parties but one from Victoria was two and a half grams.

People under 30 years of age can hear a small range of higher frequencies that adults over this age cannot and it's to do with the way the bones in the inner ear change during the aging process. For example, there are ring tones for teenagers that are high frequency so that their parents and teachers cannot hear them.

If the signals can be heard and therefore detected, then surely they can be converted to other frequencies.

Could there be an untapped source of gold that only hits an inaudible (to some) frequency - and are we missing nuggets due to this?
Are the external speakers (often used) incapable of carrying the entire dynamic audio range that a good pair of earphones can?

Has anyone else heard of this?

Marco there is only one small problem with this train of thought, the Minelab machines are multi tonal or in other words their target response covers a very broad range of frequencies during the signaling process regardless of what Tone you set the detector at. I do not doubt however that children or younger people can hear faint responses better or more importantly can hear the variations in the responses from the detector and identify them as targets over ground noise or normal clatter from a detector.

JP

Gday

I know that I cant make any sense of targets if I operate my machine at a high tone level, and found that for me some responses seemed to be close in tone level to the threshold tone level and I was unable to decern one from the other.

What I did discover is that a low tone say at 1/4 turn on the gp extreme for instance was perfect for me and once I learned this I started to get more gold, so I think that if your hearing has deteriorated to the point that you can only distinguish signals in the lower tone range then you have to experiment with this until you find the level that best suits you.

This may not be a perfect solution , but the object of the exercise is to make any signal reponse from the detector stand out away from the chatter/threshold enough to be recognised by you, if the detector produces a signal of any kind their should also be a shift in the threshold, so having said that you may need to change your focus to this shift or waver in the threshold rather than a positive signal.

Very few deep pieces that I have gotten have ever been a definate, stop you in your tracks signal, but rather an iffy type, maybe or maybe not type of signal response, so the variations in hearing ability from one person to another would account for why bits of gold are still pulled out of areas that are seen to be flogged, as there seems to be a very fine line between recognising the signal and not recognising the signal in sone cases.

I have often wondered why there has not been any research into fitting these machines with some sort of meter that would give a visual representation as well as an audible signal, so that you could use both tools to decide whether you have a target to dig or not, as I would think that all elements like gold, lead, siver, copper, and steel objects would have a differing response value, just think that if you had a machine that was fitted with a meter and a vibrating mechanism in the handgrip then even the deaf or an "old fart like me that is almost past the use by date" could still successfully detect for gold.\

cheers

stayyerAU

You can test your hearing here http://www.freemosquitoringtones.org/

Very interesting topic....

DigDeep

Thanks for the link DigDeep... I just played some of the tones on the webpage to my younger wife and she was literally freaking out at tones that I couldn't even hear. If the detectors are outputting notes in ranges inaudible to the ears of many users, it may just be that there's a LOT of gold being missed.

8khz can be hear by everyone.
10khz can be heard by people under 60 years old.
12khz can be heard by people under 50 years old.
14khz can be heard by people under 49 years old.
15khz can be heard by people under 39 years old.
16khz can be heard by people under 30 years old.
17khz can be heard by people under 24 years old.
17.5khz can be heard by people under 24 years old.
18khz can be heard by people under 24 years old.
19khz can be heard by people under 24 years old.
20khz can be heard by people under 18 years old.
21khz can be heard by people under 18 years old.
22khz can be heard by people under 18 years old.

KOSS UR 30 headphones cover a range of 18hz to 20,000hz
Does this mean the range of the audio output of the KOSS (at 0.018khz to 20khz) exceeds the range of audio capability of older than 18y/o users? For me... I can't hear anything below the 15khz range. (EDIT: Below = Higher Frequency (<) .... ie: Below the figures given in the list and thus higher in frequency)

This brings me back to my original question: Are the KOSS earphones putting out audio signals that many of us are unable to hear? If so, what can be done to enhance these frequencies and convert them to an audible tone?

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well i might as well throw my damned machine in the river,the only one of those tones i can hear is the "everyone" tone.i`m 55 and can`t hear the 60 or younger tone.my lovely other other half, also 55, can hear the 49 and younger tone.
ok here`s the thing i don`t understand about this line of thought. when you set your machine up for detecting,you set the threshold up on your machine to a level that you can hear.if the other half and i swap machines (which we sometimes do.we have a 2200 a 3000 and a 4000),we have to adjust what ever machine we are using to our level of hearing.if when you are detecting you pass the coil over something that alters that tone , it may be a target. last winter,using the 4000 with a coiltek dd pro i got a piece of gold not much bigger than a grain of sugar.i kept losing it when i picked up handfulls of dirt,but after about 15 min i finally got the piece between my fingers so i could see it.
i don`t understand how not being able to hear different tones might effect your tally at the end of the day.my way of thinking is, if the tone that you can hear alters,that is good enough.
it is not my intention to say that any one is wrong,i`m just trying to understand.
good topic
cheers
dave

Hi Dave,
I think you're right: These detectors are supposed to respond with an audible tone when a target is within response range of the coil.

But what has me puzzled is the growing number of people who swear they can hear NO target yet their young son can clearly hear a signal. I believe the first time someone told me about this, they hinted that the sound was quite highly pitched (according to the kid reporting it to the parent holding the detector). I'm just curious to know if others have heard or experienced similar.

/My wife gets to lug the detector next time we go out since she's more than a decade younger than I am. I'm going to see if she notices any sounds that I miss.

Strange thing that I have noticed that may help the deaf.
I have my speaker mounted just below the handle and it points toward me, but there is something that has evolved from this that invokes another sense when concentrating hard. When the wind is blowing I can feel the audible signal in the hand grip and my hand. Strange as it sounds, I have felt sounds that have made me back up for a second listen. these have been targets that I wouldn't have audibly picked up on a windy day. Maybe I concentrate too much, but what I am saying is true. Combine both on a quiet day and there is very little that the senses wont pick up.
In case your wondering, I have 20/20 hearing and my eyes can see jungle drums 20 km's away.
I'm not joking about the findings from using a speaker.
Brett.

JP, i think what you wrote went over there heads, here's a tip folks, turn the volume up, im 41yrs old & could hear them all.

Yes Narrawa I think it must have. My point above is the detectors produce a very broad spectrum of tone when a target is found which as one poster has commented on disturbs the Tone of the threshold the operator has personally chosen as being a good sound they can hear audibly. I have friends who have major hearing loss and yet sometimes I struggle with keeping up with them in the numbers game, one guy in particular is a force to be reckoned with on the small stuff which flies in the face of his disability.

Bruce Candy has a fascination with all things audio (his amplifiers spring to mind here) and has designed his detectors accordingly so that they cover just about the hole spectrum of tonal response during signaling of a target, the headphones or speaker you use then reproduces that response in an audible sound that also covers that whole range.

As an aside generally speaking people with hearing damage can hear the higher tones produced by the GPX-4500 just that the sound is fainter due to the higher frequency, so they settle for a tone that sounds louder (usually between 35 and 50) to their ears, but once again the response still covers a very brood spectrum of tonal range during the signaling phase.

Hope this makes a little more sense,

JP

Thanks JP, that makes things a bit clearer. Good explanation too.

One question: I notice that the Coiltek coils seem to have a limited audio response to targets. By this, I mean that the Commander coils "warble" and cover a number of tones when a target is struck. You tend to get higher and lower tones too when depth and size comes into the equation. But I find the Coiltek coils seem to just "Bleep" by comparison. At least this is how it seems to be on the smaller coils.

With a reduction in the range of response, does this mean the Coiltek coils might suit users with hearing impairments?

Cheers,

Marco

Nero what you are noticing is the "Q" factor of the coil, Litz to my mind is more efficient so tends to be slightly more sensitive overall (although the latest Coiltek GoldStalker seemed to have improved a lot in this area). In some ground types the Coiltek coils will actually run quieter due to the slight differences in sensitivity to a Litz wound coil.

Regards

JP

G'day,
I can hear my standard 11 inch DD, directly without the audio turned on. My Goldstalkers don't do it just the standard coil. It seems my coil has become microphonic and is producing audible harmonics of the detector operating frequency of 1.26kHz. The weird thing is if I move a large target near the coil the audible frequency changes slightly. My daughter can hear it really well so it must have more power transfer in the upper harmonic range.

Interesting thread Guys, I have noticed that there is also another higher pitched component to the audio output when using the Koss phones, and it's apparent when you turn the threshold down so it's almost non-existent, the information those kids are hearing maybe superimposed upon that. Going by the mossies site it would be in the region of and above 10kHz. I think I'll attach a scope to the output and have a look.

Cheers
Grey.

The output does indeed contain a high frequency signal which is discrete from the threshold. Whether or not it contains target response information I’m yet to determine. When I get some spare time, I’m going to high pass filter, down-convert and amplify it and see.
It may explain Bogene's original settings, where an external amp utilises this higher harmonic component or audio processing undecoupled leakage.

Cheers
Grey.

i may have missed something here , but if you set up
your machine with a threshold you can hear, then
anytime that threshold wavers in anyway you investegate
whether you can hear a responce or not.

so even if there were tones you could not hear you
would still notice the threshold that you could hear change.

thats why you can get targets that don't give signals
they sometimes just null the threshold.

cheers fencejumper

Gday Fencejumper

Your absolutely right, very often the waver in the threshold is the only indication you will get that there is a target present, its not until you investigate further by scraping or removing overburden that you will get a more positive response.

I have referred to these wavers in the threshold in the past as being sub-signals ( for the want of a better name) you cant hear them clearly and be sure that you have something or not, but instinctively you sort of sense that you have something you need to investigate, and even when the signal developes into a positive response you are surprised thats its there, I think that these targets are on the very limits of your detectors capabilities and rather than producing a positive response they produce a negative response, such as a nulling effect of the signal that you mentioned.

So it seems even the nulling effect of the response is in itself a response as well, and is what causes the shift in the thresholsd that attracts your attention in the first place.

Any change in the threshold that you cant discount as ground noise, needs to be investigated, by that I mean if you scrape the ground and the signal disappears or weakens then you have a fair idea that its ground noise, if it persists and you have a signal that is improving and is still there using the 90 degree method, then you know that there is something there and you need to dig it.

Hope this makes some sense

cheers

stayyerAU

Quote StayyerAU

I have referred to these wavers in the threshold in the past as being
sub-signals ( for the want of a better name) you cant hear them clearly
and be sure that you have something or not, but instinctively you sort
of sense that you have something you need to investigate, and even when
the signal developes into a positive response you are surprised thats
its there, I think that these targets are on the very limits of your
detectors capabilities and rather than producing a positive response
they produce a negative response, such as a nulling effect of the
signal that you mentioned.


Is that found only when the unit is running in fixed tracking as I would expect if it wasn't, being such a light
response the unit would track it out and never be heard.
Mark

Gday Mark

I pretty much always run in "fixed" rather than "tracking", and this is because I think that there is always the chance that the machine might track out a signal that is very vague and it sees as ground noise, responses that are right on the extremities of its depth range or masked by high mineralisation.

The other reason I have always used "fixed" is that it makes you aware in changes to the ground conditions, as you enter more mineralised ground the machine starts to become slightly unstable and you have to re ground balance, this alerts you to the possibility of nuggets in that spot, just as the way you often find hot rocks in a nugget producing spot.

I also use the 4500 in fixed, even though they can handle the changing ground conditions better than the sd or gp machines as they are not effected by the magnetics in the ground, so the changes are very slight and hardly noticeable, the problem with the 4500 is that the changes that do occur are related to the interference it picks up from above ground sources rather than below ground sources.

cheers

stayyerAU

Hi,
Forget about the threshold you can hear and is adjustable with the control knob, there is another one that is completely independent, and doesn’t change when the threshold is adjusted. To hear it you need to lower the threshold so that it has almost gone. I can hear it on my 4500 but I’m using a pocket rocket battery system, I also run a fairly high target volume to compensate. if you use the 4500 battery there’s a possibility that the amplifier in the battery filters this other signal out. That being true, would explain why the 4000, not having the battery amp would have this background high pitched whine also.

I’m not sure yet if this bleed-through signal has any valid target info, I’m just too busy at present to fully investigate it. There is a possibility that it is just common mode noise bleeding through from the transmitter, and would thus not give any target indication. It’s a big problem keeping transmitter noise out of the audio on a metal detector, so much so that a lot of the old VLFs had a separate battery just for the final audio amplifier, which was AC coupled to the rest of the circuit.

Pulse induction detectors put immense demands on the battery when the transmitter is switched on. A Minelab PI at transmitter switch on is like a resistor of about 0.6 Ohms shorted across the battery, which would normally produce an instantaneous current of 13 or so Amps, however the inductance of the coil acts as a choke to impede the growth of the current. The battery has to fight this back EMF in order to start current flowing, whenever this occurs ripples appear in the battery voltage. If you’ve ever heard water pipes rattling in a house when you turn the tap on, this is a sign of poor plumbing design, and a good analogy of a poorly designed detector where this ripple or rattling will affect the audio output, in effect we hear the transmitter via the battery.

Electronics has come a long way since the old VLF days, and now we have very low series resistance capacitors. If we place some of these close to the transmitter and slowly charge them, they will store the needed charge so that when the transmitter is switched on it will draw current from these instead of the battery, which has a higher internal resistance. Thus if we run the audio circuit straight from the battery the ripple noise should be almost non-existent.

This may be why Minelab have placed the ancillary amp in the battery, and well away from the detector PCB. Any common mode noise should be easily rejected at the amp input giving a very clean threshold.
Sorry this is such a long winded waffle when I’ve not really had time to have a good look at that signal and determine what it is, but I like to think that it's not noise bleeding through from the transmitter, (faith in Minelabs’ expertise) but something coming from the audio processing, and if that’s true it may contain target information not evident in the audible threshold. This could be what stayyerAU is sub-consciously focussing on.

Marco, thanks for raising this subject, I’d heard this signal before, but dismissed it, now it’s going to be good to get to the bottom of it. You mention one person had a 4000, do you know what the other people were using?
Also do you know if they were using external amps or speakers etc?

Cheers
Grey.

Hi
My detector is a 3500 and it definitely give that null in the threshold when over a target at its extreme detecting limits, you can try this easily by just carefully raising your coil.
With the threshold turned down to just at the quiet point ie the "bogene settings" I can still hear the null in the background hum quite clearly with the amp turned up.
In fact I can even hear the faint EMI at times in the hum as well
I have tryed for a bit with this setting but on my machine the signal responce that breaks through is a bit broken and I am not confident that the detector audio is as sensitive , but then I cant increase the gain like the gpx machines to give more sensitivity like the original bogene settings called for.
Also it is hard to be sure you are ground balanced properly.
cheers Nvic

Thanks stayyerAU
I don't use fixed very often and that is a good example of deep targets which can be missed in tracking.
Mark

Gday Mark

Running in fixed will give you better depth than tracking in most cases, so if you can ground balance your machine effectively in the ground you are working and it stays reasonably well balanced and you only have to re balance every now and then then you are better off going that way.

In tracking if you hear a signal and swing over it several times you will more often than not track the signal out, particularly if its at the outer limits of the detectors depth capability, or sometimes in the case of a specimen nugget, say in iron stone where the mineralisation of the stone outweighs the quantity of gold in it.

If you have to use tracking due to the ground conditions then you will have to remember to switch it back to fixed to double check on something that you have heard, even if the ground conditions are bad once you have an inkling that you have a target there then going over it in fixed and scraping or digging the area will make the signal develope if it is in fact a target, if it does not become a solid and repeatable signal or has the tendency to move about while digging it then its is usually just ground noise.

Nvic, I am not familiar with "Bogene settings", but I do know that if you have the threshold turned below an audible range then you will not hear signals from small gold, you will pretty much hear only definate larger targets, as I said before you are in a lot of cases only listening for a subtle change in the threshold, if you have no threshold then many signal reponses will be lost to you.

And also I have had the experience of hearing an audible hum from below the threshold and I have just put this down to some sort of feedback from the signal enhancer/booster, as after trying several types I have found that some are worse than others, usually occuring when the enhancer/booster is turned up too high and the volume control and threshold on the detector are turned down to low.

cheers

stayyerAU

re stayyerAU
I'm heading off next week on a weeks detecting trip and tested out today what you said.
Put targets down till I could hardly hear them and switched over to fixed and the target responce was much better.
You were spot on and I wouldn't have thought there would be that much differance , Know what I will be doing from now on.
Regards Mark

DigDeep wrote:You can test your hearing here http://www.freemosquitoringtones.org/

Very interesting topic....

DigDeep

my god im deaf

Try this one for some that think they are going deaf which may not be the case

A lift in Volume may help with some frequencies

http://www.phys.unsw.edu.au/jw/hearing.html

goldslinger - with the mossie signal could hear all but the 22 at bottom - and i am 65 ???????

u308 - could hear all but the two right hand columns at equal volumes, but what does this mean??????
... kev (my wife reckons i am deaf because i like the tv up loud, who gives a stuff, i can still find nuggets)

Kev
nope i can hear 49 and younger no others younger and im 49/50 to many rock concerts when i was younger

I have now been waving my 4500 around for 18 months and even after
getting a new N/F mono coil I am
still collecting only bullets and bits of metal.
This thread has given me hope (in a way) as I can only hear
the 10khz for 60 and younger and 8 khz for everyone ring tones. I am 64
and thought until now, that I had reasonable hearing.
Given my track record of not finding any gold, and I might add
I have had two very experienced fellows, whom I trust, pointing me in
the right direction, with detailed map references, I am now trying to establish which settings I
should be increasing, to hear the signal better.
Please can someone help? Is there a control that is applicable in my instance to make a weak signal louder?
appreciate help
Thanks
John

Johnshares
I to went 15 months before finding and any nuggetts. I have hearing aids and was partly blaming them ( but like you finding heaps of lead shot etc etc) But the drought has broken and I now have 2 pieces ..... 1-5.9 grams and 1-.45 gram piece . I was absoulutely thrilled. It was like winning Tatts .. So hang in there , and you will find it soon.

John.

I can hear all the tones and ive just turned 28, ive worked as a welder for years and have worked with punchers and presses, grinding and saws brobo, ive had my hearing tested several times and have always come up tops as in what a teenage can hear, reason is i look after my hearing i always always have ear plugs in, once years ago at kardinia football ovel geelong i heard a seagull do a crap on the oval, and nigh one person believes me, that was nearly 15 years ago even i have doubts, i never listen to or ever have listened to really loud music, nor in the factory will i compromise my hearing never, hearing is an early warning system, and now ive learnt that good hearing can be good for finding gold im even more padantic, people i work with are grinding with no hearing protection what so ever and they wonder why they cant hear jack shite, even now i knock off ear plugs from work and use them if im going to let off a volley with the 12 ga or mauser, my gf can hear all the tones and the cat was pissed off big time.