literal stompbox

[theMinister]

some old-timey, mountain-music friends of mine asked if i could build a stompbox for them.  literally, a box that amplifies their stomping/foot-tapping.  i made a prototype using an old 6" speaker wired to a jack and mounted in a 16"x16"x5" box.  it rang pretty bad so i drilled a couple of 2" holes in the bottom, which worked alright in my garage with my little practice amp.  through a pa, however, feedback was a major issue.   stomping on it was fine.  when it was pushed high enough that foot-tapping could be heard feedback was soon to follow.  position was not the issue.  i'm wondering if anyone has any suggestions to reduce the ringing and feedback.  speaker size?  contact mic?  something in between the jack and speaker/mic?  i'd like to keep it passive if possible.
thanks in advance.

[sponge]

use a small contact mic, made from a piezo speaker.

bugbrand sells them on his site: http://http://www.bugbrand.co.uk/pages/shop.htm

and if you prefer to DIY, you can make them really easily (and i mean REALLY easily) : http://http://home.earthlink.net/~erinys/contactmic.html

[theMinister]

i tried out a contact mic made from a crappy toy i had laying around.  sounds good but there is still a lot of ringing.  would a cap in line help at all?  i'm gonna hit ratshack tomorrow but i don't have the time to experiment too much.  i have another chance to hear it through a pa on sturday night, maybe i'll build a box with a few different options in it.  
thanks again.

[para]

i’d say take just a piezo disc ( no plastic case) and epoxy it to the backside of a sheet of metal ( score the metal so it sticks). you could even use a “for sale” sign, or anything metal, not too thick though. then attach that to the top of the box and drill a hole down for the leads to run into the box. mount the 1/4 on the side of it for ease of use and keep the box away from the amp. whether you want to believe it or not the feedback is all about position ( and sensitivity of the mic). if the mic didn't pick up the amps signal then there wouldn’t be any feedback. as for just setting a mic inside of a box. you are just micing the acoustic space in there and the ringing, aside from the feedback, will be the boxes natural acoustic resonance ( which you changed by drilling holes). removing the space of the box ( having the mic outside instead of inside) and affixing it to the sheet of metal should give you a more natural sound and also use the acoustics of the room its used in, instead of the inside of the box. and you are making the mics surface huge with the extra sheet of metal so it will be more sensitive.


make sense?


you might want to build a simple little preamp or booster for it too. maybe add some clipping diodes in there to help shape and control the sound and compress the output a bit, with a switch of course. i can imagine the attack will be a bit loud so having options might be nice for the guy.  

and experiment! this is pretty new (or extremely old) territory. i’m sure its been done before but i have never seen it out side of like tap i guess?

steven

[theMinister]

well, version 1.2 was worked out tonight.  basically a 14" piece of 2"x6" with a shallow hole drilled to mount the piezo disk in and a hole just large enough for a 1/4" jack to be mounted.  it worked great.  there was no ringing, it had a great tapping/stomping on the floor sound.  now i just have to work out the details (make it pretty).  
you wouldn't think such a seemingly simple project would turn out to be so damned time consumming.
thanks for the help.
josh

ps-i did a little more searching, and this guy gets $150 bucks for these!  what a crock!

[Timoty777]

ps-i did a little more searching, and this guy gets $150 bucks for these!  what a crock!

wow that is ridiculous.

all the more reason to go the DIY route.  

[para]

$150.00  WTF?   maybe $15.00 and leave out the sanding and varnish for me.


sorry to go the complicated route. simple is (almost) always better.

cool that you are getting good results.

if you had the space, maybe add a passive tone control too. pot + cap to roll off the highs, instead of worrying about using a bass cab of e.q. like the article suggests


post photos when your done

[theMinister]

if you had the space, maybe add a passive tone control too. pot + cap to roll off the highs, instead of worrying about using a bass cab of e.q. like the article suggests

yeah, i have some small pots that are about 200k.  i looked at some schematics but am still a little confused.  i think the cap should be parallel with the jack, right?  and the pot would go before the cap?

any suggestions are greatly appreciated.

[para]

it should be + of the piezo to the pot, then to the cap, then the cap to ground. but you will then take the same out of the pot and send that to the + of the jack. and the pot will also control the volume or you can just take it straight off of the piezo and leave it full volume which is probably better in this case.


different caps will give you a different final cutoff freq and a different slope rate. so try a couple different values if you can. like with guitars they vary from  .02u to .047u but something else in this case could work well

 http://en.wikipedia.org/wiki/Lowpass_filter