Saving you ears and getting the most from a detector

[Jackpine Savage]

Here's my setup procedure before I start swinging.

Detector volume= Max
Headphone volume turned all the way down. Now lay a couple coins on top of the ground and sweep the coil 5-6" over them while increasing the headphone volume. Stop when the signal from the coins gives a comfortable discernable response. Reset threshold if neccessary.

Why start with the headphones volume off rather than all the way up? Well, its all to do with how human hearing works. If you start with high volume and reduce it you will always end up with a higher overall volume setting than neccessary. Human ears are fairly sensitive to low volume sounds, they just need a chance to hear them! Too high of an overall volume setting results in fatigue so they never get that chance! My hearing isn't that great anymore but this system works better for me on long hunts... mo' betta!!

JMHO

Tom

 

[I a thr]

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[Elton]

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[Jackpine Savage]

to my original post. Maybe obvious to some but worth mentioning. Depending on the detector and conditions don't be afraid to alter the volume as neccessary. If you are getting lots of loud responses from shallow trash of course lower the volume to reduce fatigue. Also, volume settings can vary depending on the detector design. Some are more modulated (lower volume) on deeper targets and some boost the audio response on faint targets. My original post was not meant to be an end all.

Have fun and protect your hearing!

Tom

 

[Digger]

I agree with trying various combinations to find one that meets individual requirements. But if and when I do adjust the volume levels, I prefer to do it at the detector and keep my headphones at max. It may not make a significant difference. But it seems the battery life might be longer if the detector volume was adjusted instead of the headphones. The audio output (volume) of the detector is powered by the detector's battery pack. Therefore, more current would be required as you increase the volume level. On the other hand, most headphones are not battery operated, and simply vary the resistance of (pad down) the signal being received from the detector. So if it requires less power to amplify a "lower volume" signal from the detector (by using max headphone volume), wouldn't making the volume adjustment at the detector be the "more economical" manner of adjusting the volume? Granted, it might take longer. (you'd have to press the keypads on the detector to change those settings, compared to turning the knobs on your headphones). But if it ends up with the same results, and adds some "hunt time" to a set of batteries, it might be worth trying. Like I said, just thinking out loud. HH Randy

 

[Jackpine Savage]

Digger,

Detector audio circuits aren't all that complicated. My edjumacted guess is that audio power drain is not affected by turning down detector volume. ie: the audio section is operating full blast all the time and the volume control simply does what it says without saving any power just like adjusting the pads on you phones. On an entertainment system with pre-amps and amps, ya it probably saves a tiny bit on your bill. You did make think of something else and that is circuit noise. At max detector volume is their more internal noise or does lowering the detector volume (pad resistance) cause some circuit noise? OK maybe, this is getting kinda like angels on the head of a pin!

Where's BB for the real skinny??

Tom

 

[John LA]

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[Digger]

in that the audio section is operating full blast all the time. But if that is the case, why does the use of headphones extend battery life? Is that simply the difference between the impedance of the speaker, compared to most headphones? Where is that darn BB?

Randy

 

[BarnacleBill]

Well lots of variables. The internal speaker used will probably be between 8 to 32 ohms impedance depending on brand & model. On older detectors the most commonly used amplifier class would be an AB class. This is the typical amp design used in most stereo systems in the last 40 years, providing good fidelity and decent power consumption. Efficiency runs at about 60% at best but with a big caveat. The greatest heat loses occur when the amplifier is adjusted to about the 1/3 of it's operating level. Guess where most people end up setting their home stereo level to?

On the newer detectors my guess is that they are converting to the use of Class D amplifiers which are a digital amplifier class and have efficiencies up to 90%. This would save battery power, but could increase costs as many of these designs require additional filtering components to remove the digital portion of the signal and leave the analog audio.

Since most of these amplifiers are designed to drive the internal loudspeakers, there is a bit too much signal for most types of headphones. Headphones can be a real pain in the arse to provide an output for as the impedances can be anywhere from 8 ohms up into the 600 ohm range. Most manufacturers use the down and dirty method of just putting a limiting resistor(sometimes called a build out resistor) in the headphone output circuit. Well those resistors do limit, but once again they are wasteful because they generate heat in varying amounts depending on the impedance of the headphones(and where you have them adjusted), in conjunction with how high the detector volume is set to. The resistor values I've seen are in the 100 to 200 ohm range, with my own preference being to use a 220 ohm in my own designs. A better solution would be to use an auto-former, but the cost and weight factor is just not practical in a metal detector.

Therefore using headphones will use less power by the simple fact you are wearing the speakers on your ears and not suffering the air loses over the distance of ears to loudspeaker, all other things being equal. You are also cutting was down on ambient background noise, another mechanical factor in your favor.

So how do you know for sure what settings are most efficient? Measure! Insert an amp meter in the battery supply, use a calibrated microphone to measure SPL(Sound Pressure Level) at the headphone cup and vary the detector and headphone settings.

And how do I do it? I put batteries in that sucker and go detecting!


HH
BarnacleBill

 

[Boris]

OK well there you have it. I carefully read every word you typed and I agree, I am just going to put energisers in and swing my coil.

 

[Jackpine Savage]

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