Homemade headphones 1

[scarecrow55]

I'm trying to make a pair of big headphones for my metal detector. I've got a couple of small 49mm cone speakers Mylor 8 ohms 0.5W but they don't seem to want to work. I've also tried it on a sterio set without success. The cable I'm using is sterio but I've tried all combinations of wiring. Can anyone help a non electics guy
Cheers

 

[BrianG]

How many combinations of wiring can there be? If you can't get any sound out of these speakers even on your stereo then I would expect that they are defective (I assume we are talking a regular mains powered one here, not something like an i-pod with maybe high impedance phone output?) .

Can you at least measure the speaker coil continuity with a test meter?

 

[analogkid2digitalman]

Have you plugged a known good set of headphones into the detector to verify that the detectors headphone output is is working?

Personally I like to use walkman style earbuds just in one ear only so I can also hear warnings from rattle snakes. And yes, I have encountered them while treasure hunting.

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"It's the questions that drive us"
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[scarecrow55]

Thanks guys, my no1 headphones are OK, so's the sterio etc. I bought 2 brand new speakers at the weekend, it would be a coincidence if they are both duff.
When I put a battery across the terminals I get the usual clicks

 

[bklauba]

My guess would be an impedance mismatch. Many headphones are higher impedance than the usual 4 - 16 ohms that speakers typically are. This trend started when Sennheiser starting using microphone elements (running "backwards") for headphone drivers (back in the late 60's?).

An ohm meter reading on your phones that work might well come up with a DC resistance (which will be significantly lower than impedance) of 200 - 1200 ohms. If that is the case, the amp driving the phones might well be designed for something in this range. Putting an 8 ohm load across the amp is almost like putting a short across it; maybe some current will flow, but zippo in the way of voltage, hence no wattage, and no audible signal.

 

[OperaHouse]

The old headphones may not meassure any resistance (open) if it is an older high impedence ceramic type ear piece that used to be supplied with transistor radio. You may need to provide a one IC amplifier to drive the low ohm headphones.

 

[scarecrow55]

Thanks guys, it seems I have got the wrong type of speakers then? these are they.

http://www.maplin.co.uk/module.aspx?ModuleNo=3275&doy=19m10

 

[analogkid2digitalman]

Why not just purchase a set of large cup headphones that are compatible with the detector? Will probably be much more comfortable on your ears when using for extended periods of time.

Just a thought...

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"It's the questions that drive us"
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[scarecrow55]

at £60 ? - I live in Yorkshire with a smattering of Scottish blood.
Mind you it seems I've wasted £5 now with those speakers

 

[analogkid2digitalman]

You need to go to playgrounds with sandy bottoms and find some of mom and pop's gold and silver jewelry that they have lost while pushing the kids on the swings!
Not to mention all the coins that fall out of the kids pockets while playing about.

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"It's the questions that drive us"
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