Speakers and Earphones on a Metal Detector

[PeterInSa]

We have a Metal detector that has an internal speaker when you go over a small piece of metal the sound is reasonably loud, however on windy days this sound is dispersed. When you connect headphones to the detector you can hear the signal quiet plainly. However I have tinnitus and if you go over a horse shoe I do not wish to have a big bang in my ears, so the alternative is twin speaker mounted on the backpack straps on your chest, connected to the detector by a stretch cable. or....

However using and Amplifier at its max with the twin speakers the sound out of the speakers is not as loud as the sound out of the built in internal speaker.

I put this down to one or 3 things,
. The plug that the speaker/earphones connect to has a lower signal than that is sent to the internal speaker, ie the detector is designed for earphones or the internal speaker.

. There is an impedance mismatch with the speaker a different impedance to the earphones.

. The earphones work as mono and the twin speakers are wired as stereo and pick up the mono signal ( on both speakers?) or vice a versa.

What I would like to do is have a Blue Tooth Transmitter into the audio output plug of the detector going into a blue tooth receiver, into the AMP and into the twin speakers ( all on the chest backpack straps) and able to adjust the volume up, not just run it on max for a lesser volume than the internal speaker.

Comments to resolve the challenge appreciated

Peter

[tristen]

Simple!

Such bluetooth devices for metal detectors are available.

Do a Google SEARCH, i.e. and check the various links which appear for a description supplier details.

[hinekadon]

is your detector one of the ones that get louder on size of the object ???? if so there is an easy way , connect a zenner diode and a pot across the speaker and this will only allow a certain volume ( volts ) across the speaker and never get too loud , have built this into a ear muff on one ear works well

[PeterInSa]

Re ( Such bluetooth devices for metal detectors are available.)

Have Tried 3 types 2 were designed for detectors and the 3rd I purchased off ebay all with the same result.

re (is your detector one of the ones that get louder on size of the object ???)
Yes, Not a problem with the in built speaker, anyway cannot touch the circuit its under warranty.

However using and external Amplifier at its max with the twin speakers( with direct cable connection or Blue Tooth setup to the Amp) the sound out of the speakers is not as loud as the sound out of the built in internal speaker.

[hinekadon]

but dont you have a 3.5mm plug for audio out ????

[loopyloo]

My thoughts here would be to use something like a simple colour organ (I think that's what they're called) plugged into the headphone socket, to turn audible signals into visual signals.

[hinekadon]

yep loopy could be ? what are they like in the sun ????

[Uncle Fester]

... When you connect headphones to the detector you can hear the signal quiet plainly. However I have tinnitus and if you go over a horse shoe I do not wish to have a big bang in my ears,

Hinekadon is on the mark here, kind of.

Forget the external speaker.
If you want to do some serious metal detection you need to use headphones to pick up the faintest noise changes and learn how they respond to different target depths.
I can often tell roughly how deep a target is, how large and if it is ferrous or non ferrous simply from variations of the audio signal by scanning with consistant speed.

Get a pair of cheap 'over the ear' passive noise cancelling headphones with about 35Ω impedance. Really no need to spend more than $40.
Take them apart and attach(preferably solder) two universal diodes like the 1N400x series, anti-parallel to each of the headphone transducers(speakers if you like to call them).
Anti-parallel means both soldered parallel to the speaker but one in reverse.
If it still can get too loud, use 1N5819 or similar schottky diodes.
Do not use a resistor or potentiometer to dampen the signal as you will lose the important low signal sensitivity.

If your detector has a high impedance head phone output >600Ω, should be in the specs, then get back to me first.

[hinekadon]

getting old eh! yes schottky diodes.is what i meant quite a few years ago i built one for a mate that was looking for his wifes ring on a gold coast beach ,think he still uses it now , havent heard from him in the last ten years but his son sees me occasionally

[PeterInSa]

Re (If you want to do some serious metal detection you need to use headphones to pick up the faintest noise changes and learn how they respond to different target depths.
I can often tell roughly how deep a target is, how large and if it is ferrous or non ferrous simply from variations of the audio signal by scanning with consistant speed.)

Totally agree

I use an expensive gold detector with a variable noise limited and still use external speakers.

My wife uses the detector in my original comment ie the detector with inbuilt speaker, and at this stage I do not want to suggest/push her towards headphones, but in the event of getting twin speakers with more amplification the noise limiting diodes across the speakers may be an option.

We have been detecting since the mid 80's and only in the last 5 years have gone to speakers and realise there are many downsides.

Peter

[Uncle Fester]

My wife uses the detector in my original comment ie the detector with inbuilt speaker, and at this stage I do not want to suggest/push her towards headphones, but in the event of getting twin speakers with more amplification the noise limiting diodes across the speakers may be an option.

Looks I need to correct some confusion there.
The diodes are not noise limiting they limit the maximum sound pressure.
From your OP I thought a sudden volume increase using head phones was your concern.
The suggested diodes are ONLY suitable for head phones connected to the headphone socket which has a higher impedance.

However using these diodes over actual loudspeakers connected to an amplifier that have a low impedance can overload the amplifier or fry the diodes.

I see no point limiting the volume this way using external speakers, you wanted more volume and ambient noise, wind, birds, crickets will always interfere with the audiable dynamic range.
...unless of course you don't want to disturb/attract bystanders, where headphones again would be much better.


Maybe a tiny guitar amplifer with speaker like this can solve your problem as it will have a higher and adjustable sensitivity to match the signal better than a bluetooth system on your headphone socket and a more penetrant frequency response. This model also seems to have a switchable overdrive function. This means it will have a very high sensitivity for low signals and when it reaches a certain volume the sound seems compressed. Because the audio from your metal detector is already a square wave the distortion won't matter, just emphasize that is is a louder signal by adding a few odd harmonics without actually getting much louder than what you set with the volume control. This should be the perfect solution:

[hinekadon]

Is there something else in play here ???? perhaps the headphones might mess up her hair ???or other reasons

[PeterInSa]

I use the 2 speakers( 60mmx60mmx20mm ea) on my upper chest, connected to the detector via an Amp/ Blue Tooth setup. The Detector can amplifier the signal ( Target Volume) and adjust the Target Volume Limit. Her machine at a 1/3 of the price and the best detector on the market for small gold for the price has neither. We both have Tinnitus.

Not all downsides with speakers:
Headphones are hot in the summer,
Detecting at dusk or dawn and someone walks up behind you with headphones on, its been known to give the wearer a fright.

The above are not the reason for us using speakers.

[hinekadon]

hi peter: we were just wondering why speakers . I understand tinnitus as ive had it since I had it for too many years , the mate that i was reffering to on the coast complained about the heat so he put cable ties over the headphones ear piece and this allowed him to hear it well but not get a hot /sweaty ear as it held it off his ear slightly . Hope this helps regards don

[PeterInSa]

Hi Don,
When I drive to WA with the caravan, the road noise makes my Tinnitus worse, last year did a couple of days with the Headphones on with the detector and my Tinnitus to me is louder, I enjoy detecting and known that I will find significantly more faint signals with headphones than speakers but I don't want my Tinnitus to get any worse. As an aside a friend's Tinnitus gets worse if he has to many coffees.

[hinekadon]

Yes Peter I sympathise with you and your tinnitus etc but allowing no difference in air pressure seems to help road noise is a nightmare but having the back windows down helps front up . The cable ties were just to hold the headphones off his head and he could hear well with them cheers don

[Uncle Fester]

last year did a couple of days with the Headphones on with the detector and my Tinnitus to me is louder,.

That is strange, I use headphones to mask my Tinnitus. I can't even hear what is said on movies with out headphones because of the tinnitus.
I keep the volume just barely so high that I can understand what they say.
I also have a hearing aid which helps a bit in some converstions but do not work as well as the head phones.

I would think that a detector signal producing a constant freqency and only changes in volume when it approaches a target could be real a problem with tinnitus.
I built my own PI detector, probably almost 20 years ago. It is a graveyard of cmos timer chips and so it was childsplay to design one as a VFO for the audio.
That means it just ticks when there is no signal and squeals at full signal, everything inbetween has a different frequency but the volume stays the same, so I can set it at a comfortable level. Our ears are much more sensitive to frequency changes than volume changes.

I always wanted to redesign it using PIC micros, but I never get to do any gold hunting anymore, therefore pointless. My wife and kids are not interested and nothing nearby anyway.

[Uncle Fester]

allowing no difference in air pressure seems to help road noise is a nightmare but having the back windows down helps front up . cheers don

I can't even drive(at higher speeds) with the windows open at all. The variable wind pressure drives me nuts. Ceiling fans, don't even ask.
I put extra capacitors in normal pedestal fans to spin them ultra slow and noiseless.
It sucks to get old, but I had tinnitus already before I was 40y/o because I spent 10 years in a hard rock/metal band in the 80's. Was the best time of my life but now I have to pay