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Permalink Reply by matt g on June 16, 2014 at 9:14am

Sounds like this should help.  I'll give it a go and see if it's better! 

Here it is now. Piezzo is currently at the bottom.

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• 20140616_131603.jpg, 1.2 MB

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Permalink Reply by Dan Sleep on June 16, 2014 at 9:31am

I may be way off base here, and if I am, I am sure someone will set me straight. But:

It seems to me that a standard disk piezo may not react to a human voice sufficiently like it does when it is attached to a cigar box. Maybe what is happening is that you have to crank the volume up too high to compensate for the lack of output signal, thus causing it to feed back. Granted, as you speak into the can, your voice should make the sides and bottom of the can vibrate, but maybe it just does not vibrate enough to put out enough signal.

I am just guessing though, and I would be interested in the feedback (pun intended) from those more knowledgeable than I am.

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Permalink Reply by The Phrygian Kid on June 16, 2014 at 9:42am

If you look inside a modern microphone (there are several types, but basically...)  you'll find a very thin metal 'membrane', this is the thing that excites by sound passing it. To get our primitive cigar box guitar brains around this lets call that 'the string'.  Movement in the string is captured and turned into current by a centre tapped coil, which is very similar to a humbucker by virtue of the 'centre tapped' business.  The string (membrane) is housed inside and mechanically decoupled from the chassis, so that sound can only approach the string from one direction, through an opening in the top (the meshy bit that you sing into).

Now if you use a tin can on its own for a microphone then the string and the chassis are one unit, there is no decoupling, so this thing will amplify sound from every which direction, (it is omni directional in microphone speak).  Best thing i can suggest is stuff the tin inside something bigger and shock mount it with elastic bands or springs or whatever..

after that you can begin to assess whether a piezo is up to the job and consider stuffing a guitar pickup in there, pointed at 'the string'

good luck  

Ps as mr sleep observed, the piezo is not going to get singing on its own.  So its taped to the tin right ??

dude this is always gonna feedback, think about it

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Permalink Reply by Marcus Darwell on June 16, 2014 at 10:37am

...but the funny thing is, one of my earlier cookie tin CBG builds (with a disk piezo under the bridge and well insulated) could be sung into!!! Yeah, you had to stretch your neck a wee bit to sing into the sound holes but....it actually worked...quite we'll.....
All sorts of devices have used piezos effectively as mikes so a can should work....my idea is insulate the can on all sides with thin foam and put a lid on it with an orifice (love that word) that funnels the vibes down to the piezo....

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Permalink Reply by JL on June 20, 2014 at 3:10am

soft fluffy material is good for stopping sound from reflecting off the surface it is covering, but does nothing for stopping sound from penetrating through it.  hard dense material is good for stopping sound from penetrating (credit to my child's 4th grade science fair project). Home sound booths have 2-3 layers of dry wall to stop outside sound from coming in and then the inside walls are covered with foam egg-crate to stop sound reflecting around inside.  So I'd suggest using cork, perhaps the cheap stuff from the home improvement center for making your own bulletin boards should work.  Another idea is several layers of paste-board coasters. 

since the bottom disk in the can is acting as a diafram, gluing some of this to the outside bottom should help diminish outside sound coming in, and will likely deaden the diafram's response to higher frequencies.

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