An interesting discovery

Hackmaster

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Maybe not a discovery, as I doubt I'm the first in the history of hackdom to happen upon this phenomonon.
But before I get ahead of myself here, this all started with me making a cigar box instrument with some left over bits & pieces.

I've made many over the years as a hobby and a sideline to pedal at craft fairs. They also make unusual and bitchen' gifts.
So I was making a resonator type instrument using a gallon tin can bottom for the resonator itself.
I've made a few of these before. Unplugged they sound like a banjo on acid.
This is what they generally look like....
DSC07646.JPG
You'll notice that it has a magnetic pickup.
It works that way, it pickups the vibrations of the strings in proper fashion, but looses the rasp and bite of that scientifically designed resonator in the process.
In other words, plugged in it sounds like any other cigar box guitar with a mag pickup.

I've tried a few ways to get more snarl and sass. I've epoxied piezo discs directly to the underside of the resonator.
It was closer, it picked up the rasp, but had the annoying piezo tone and was painfully bright.
Due to the odd impedance of the piezo, a tone pot is useless.

So today I was testing a donor single coil for the project at hand, and had it connected direct to the amp via clip on jumper wires.
It was connected and on when I picked up the can bottom.
As soon as the can came in close proximity to the pickup, the can bottom turned microphonic... o_O
So like an excited kid I started tapping on the can bottom with different objects while moving the pickup around.
Even sticking the poles directly to the can, and the sounds were getting encouraging.

Several beers later I found a happy distance @ 3/16" for the air gap between the pickup and the can bottom for the raspiest and raunchiest tone.
This was getting interesting for me as now I had a way to bring out the banjoish character & sassy rude tone amplified.
So now it sounds like a banjo on acid thru a ring modulator plugged in.
A very metallic sound with clanking overtones.
A huge plus is that the pickup is now hidden under the "resonator".

DSC07629.JPG
Much cleaner look.

Anyway, the whole reason of this rambling post is to ask if anyone knew exactly how this works?
A magnetic pickup is mounted 3/16" away, underneath a thin steel can bottom.
The strings are a full inch over the can bottom,
DSC07631.JPG
So the pickup isn't picking up the strings in a way we normally think of. It's picking up the can bottom.o_O
The whole surface of the can bottom is alive. It pickups up the rasp of the steel resonator along with the sound of the strings.
Tapping on the surface also produces different tones.

Oh, it also feeds back like a banshee when gained up.
Touching the can bottom squelches it, like touching the soundboard on an acoustic guitar when it feeds back.
The tailpiece is grounded to the back of the volume pot as per common sense, as well as the can bottom resonator for good measure.

So how does the pickup manage to couple with the can, to make what in effect seems to be a crude microphone?
Inquiring minds want to know.

This seems to be what's happening. Am I on the right track?

.
 
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Cross-Section of a Typical Condenser Microphone
Condenser Microphone



Dynamic Microphone
 
Alright Professor Hackmantis - I hope you've got a cot in your workshop since I'll be needing a place to sleep while you teach me all this cool :poo:.


...and I'm only half kidding.

And I like my eggs scrambled. :pound-hand:
I appreciate your input. It gave me an angle to research.
Those picture get the idea across in an easy to understand way.
Now I need to investigate this further. Talk about a rabbit hole...

Oh, scrambled eggs are fine with the dog & I, but the wife has fruit for breakfast.
Your offer to cook will be greatly appreciated . :rolf:
 
Yeah I guess I was picturing it as if the can lid was the front plate and the pickup was the back plate so as the lid moves closer to the pickup while vibrating it generates the fluctuations in the field.
Exactly....but the diaphragm is super thick....and there’s a magnet and coil involved for motivation...so...I can see deferring to the dynamic concept...especially since there is no power applied, and it’s purely mag field reacting to ferrous diaphragm movement. But I am just a silly human...
 
Exactly....but the diaphragm is super thick....and there’s a magnet and coil involved for motivation...so...I can see deferring to the dynamic concept...especially since there is no power applied, and it’s purely mag field reacting to ferrous diaphragm movement. But I am just a silly human...
Hmmm, Part of my surprise is from the fact that the string moves a huge amount to generate the current. You can see the pattern as it vibrates.
That can lid can't be moving more than a thousandth of an inch from the vibrations.

The speaker cone moves a good deal in the magnet as well.
 
Basically creating eddy currents


Its what makes Tele bridge pickups have so much bite. The brass plate on the bottom alters the field in a unique way
Great link, thanks.
 
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