Hole underneath Piezo

[tomrbland]

Hi,

Does everybody put a hole underneath their piezo on DIY's to let the piezo bend as you should? or does this turn out to be too sensitive?

I was thinking of making mine out of and wooden cross with a slight hole in the middle (a fem mm deep/all the way through haven't thought about this bit yet.) which was just a few mm smaller than the piezo then glue the piezo round the edge of the hole.

What does everybody else think?

Cheers

[bogiesbad]

Az you probably already know, flexing the piezo by pushing down on the center will reverse the polarity as opposed to flexing the edge down as with foam tape under the ceramic. I would imagine the hole need be only a few mm's deep.

[badnomad]

I think that the foam tape method is still the best.......you basically want the vibration transmitted through the cone to the piezo, and, as the output is a waveform, polarity is not crucial.......it will still trigger. The only time you want a lot of free play in the piezo is if you are using it as a speaker, otherwise you can fracture the ceramic.

Myke C.

[tomrbland]

Interesting,

I think I will have a go with a small hole as this seems to have given the best results in testing. Ill keep you up dated.

Cheers

[mikejl46]

I have made a few drums using this method. It would be like having a hole under the piezo, because only the outer edges of the sensor are supported. They work great for drums used to trigger the Rock Band game. They also work great with my TD-3 and TD-6.

[tomrbland]

Thanks mike,

Nice site very interesting.

Cheers

[racer52]

Hi,

Does everybody put a hole underneath their piezo on DIY's to let the piezo bend as you should? or does this turn out to be too sensitive?

I was thinking of making mine out of and wooden cross with a slight hole in the middle (a fem mm deep/all the way through haven't thought about this bit yet.) which was just a few mm smaller than the piezo then glue the piezo round the edge of the hole.

What does everybody else think?

Cheers

I came up with a similar discovery about the piezos too. I used a dual trace oscilloscope to measure the trigger signals from a real Roland pd125, as well as some trigger mounts I was trying. I found I did not need a ‘hole’; however the placement of the mounting tape acted as one. I was able to obtain a signal that was 20 times larger than the Roland. Time will tell if the ceramic will hold up.

As you noted, flexing the edge of the piezo relative to the center produces a much stronger signal than compressing the crystal directly against the back. The direction of flex controls the polarity of the first (and strongest) oscillation.

I die cut a round piece of mounting tape (3M-VHB tape) slightly larger than the ceramic portion of the piezo. This is not applied to the ceramic side, but if it were, it would cover the ceramic as well as a slight portion of the brass edge around the ceramic. This piece of tape is applied to the solid brass side, centered so that an even amount of brass shows all around. I then stick the piezo to my solid metal cross brace in the drum.

At this point all you have is the bare trigger attached to your cross mount via the circular spot of tape on its underside. The ceramic side has nothing applied to it yet.

I cut a ring of Poron foam to set over the top of the piezo. This foam ring has an outside diameter that matches the outside (largest) diameter of the piezo's brass backing. The inside diameter is smaller than the diameter of the white ceramic section of the piezo. When this is set on the white side of the piezo it should cover the brass completely and should also cover a small portion of the white ceramic.

A cone is then set over the ring to complete the assembly. I am experimenting with both foam cones and solid silicone cones for this section of the trigger.

The foam ring on top and the tape on the bottom now have an effective overlap area. The larger the overlap, the less 'bend' resulting in a less sensitive trigger signal. This overlap area may be increased (thus decreasing sensitivity) by making the bottom circle of tape larger and/or by making the top foam ring inner diameter (the hole in the ring) smaller.

This setup causes the first oscillation to swing negative. The Roland TD-20 seems to like that signal. Reversing the placement of the tape circle to the ceramic side and the foam ring to the solid brass side of the piezo will result in the first oscillation being positive.

My DIY pads are all set as pd-125's on the Roland TD-20. Sensitivity is set to around 0 to 6

I also have a modified mounting method for the rim piezo. I use only one rim piezo and can trigger it from any place on my DIY pad. More on that later - I am now about 1/2 hour late to work. gotta go

[tomrbland]

Racer52, That was fantastic!

Any chance of some pictures?

Here is what I was planning to do:
cut a hole a few mill smaller than the brass rim, then glue the brass side to the hole with the ceramic side facing up. I figured that I should have the ceramic side facing up as if is faced down it could part from the brass plate given the direction it would bend. i was then going to stick my foam cone straight on top of the piezo. Simple and hopefully should work. What do you think?

Also height of the cone? What is best?

Thanks
Tom

[racer52]

Hey there Tom,
Disclaimer: This is all new to me too. What I know of this has been learned only recently – From this site as well as others, and from my own experiments.

I’ll need to get some pictures of the parts – later on that one.

I looked at your piezo research doc - nice scope display! Mine does not display the settings. You will find that once the trigger is mounted in the drum the resulting wave form will be noisier and not as smooth looking. Head vibrations will induce this look.

Mounting it as you described would work – the question is for how long. I do not know if the piezo will tolerate being hard mounted to the wood – it does seem like a high stress producer. The direction of bend will dictate the polarity of the trigger pulse. What you are describing will produce a positive going pulse., ie: same waveform type as seen in your research link.
Another consideration is that your trigger is now solidly mounted to the wood, so the wood needs to be very well isolated to prevent false triggers from the shell of the drum.

The waveform I got from the Roland pd125 was a negative going pulse. The Roland TD20 works fine with this, so that is what I shot for.

Anyway, I do not know what your drum module is looking for as far as trigger polarity. I am rather ignorant on what is needed. If that is what you need, then you can obtain the same signal pattern (positive pulse) by placing the foam ring I mentioned, between the wood and the brass side of the piezo. Then mount the foam cone to the ceramic side using a round piece of foam tape cut to fit the ceramic ( I would make it a bit larger than the ceramic). You would not need to cut out a hole in the wood. And the piezo will have some protection from shock.

As for cone height.. ahh, well, I have no clue what is correct. I just cut my cone to a height that allows it to protrude above the rim of the drum. It ends up a bit over 1 inch. Too little height will produce secondary triggering when the head vibrates off the top of the cone. Head needs to be fairly tight.

Other notes- I saw that there is someone selling some really nice piezos, with cone attached, here on this site. It looks like he has the base of the cone completely covering both the ceramic and the brass outer edge on the ceramic side and then uses a ceramic sized foam tape on the solid brass underside. This will produce a negative trigger. It seems that it would produce a better trigger (better flex) than those that use the same sized foam tape circle on both top and bottom (only compresses the piezo).

I'll get pics later for you

[bogiesbad]

It is widely(?) accepted that reversing the leads will reverse polarity...is that what you see with your Scopes?

The layer or two of foam tape cut to the size of the ceramic beneath the piezo is the method used by many of the DIY'ers around here.

[tomrbland]

It is widely(?) accepted that reversing the leads will reverse polarity...is that what you see with your Scopes?

The layer or two of foam tape cut to the size of the ceramic beneath the piezo is the method used by many of the DIY'ers around here.

Yeah if you swap the wires you reverse the polarity so it doesn't matter which you are achieving with your DIY really!

(by the way racer52, i am going to have a think about what you have said in that at orchestra practise tomorrow (give me something to do in 96 bars rest!) Interesting stuff)

[racer52]

It is widely(?) accepted that reversing the leads will reverse polarity...is that what you see with your Scopes?

The layer or two of foam tape cut to the size of the ceramic beneath the piezo is the method used by many of the DIY'ers around here.

Good point Chris!
Flipping the piezo only really matters after you have already soldered up the piezo to the connector mounted in the drum. As they say - It only matters when it matters

As for the ceramic sized tape issue. It seems that most are mounting both the top and bottom side of the piezo with the same size double face tape (ceramic sized). I too did that. I had to set my trigger levels pretty high in the TD-20 while trying a variety of pad types in the menu. Then I noticed, as Tom has too, that a bigger signal could be made by not just compressing the crystal portion, but by causing some flex to occur. My first post to Toms question talks about the construction concept I tried. I'll make some pics and post them.

Tom - Glad to keep you busy during those long rest counts. I could never keep count anyway. Hey, try your idea and let us know what you discover.

Another idea: I had also tried yet another concept I saw here. This version is where I cemented the complete brass side to a 12.5" sheet metal disc (picture in your mind, a piezo with a 12.5" brass bottom). Then suspended the disc in a Remo Dead Ringer hoop with the Dead ringer foam. This worked amazingly well untill my center cone (attached to the ceramic only) lost its tension and the drum started to double trigger and/or miss trigger. I'll revisit that concept now that I know about Poron memory foam - I like the idea of not altering the donor drum.

The point is,Tom, to try your idea, if you have the time, and see what you can learn from it. Or, do like I did, and use something from everyone here and build an even better mouse trap! well maybe mine is not better - just different. I seem to enjoy the tinkering.

-wayne

[bogiesbad]

As for the ceramic sized tape issue. It seems that most are mounting both the top and bottom side of the piezo with the same size double face tape (ceramic sized). I too did that. I had to set my trigger levels pretty high in the TD-20 while trying a variety of pad types in the menu. Then I noticed, as Tom has too, that a bigger signal could be made by not just compressing the crystal portion, but by causing some flex to occur. -wayne

The very simple concept of mounting a piezo atop a layer or two of double side foam tape (3M works best) sized to the ceramic and placing a foam (Poron very soft works best) cone directly on top (I and many use the adhesive backed foam and simply stick it to the piezo) has been used for quite some time. Your "discovery" of piezo flex producing better and stronger signals is not new to seasoned DIY'ers. As DIY has become more popular I have seen more people stray from this very simple recipe...although they get trigger response I doubt their results are really very good. High sensitivity and great positional detection...ability to do buzz rolls and use brushes...those are the results I get with this method. I made my drums in mid-2005 following Jman's and feefer's posts on their success with this method and have been enjoying excellent results with almost no failure since. All the credit goes to Michael Beatnik Bandit who was the first to my knowledge to introduce this method.

[tomrbland]

Thanks Chris,

Its just a learning curve for all, I am waiting on some old toms at the moment, when they arrive I can start my building . 2 10" and 1 12" for £28 inc postage happy me!! But it is proving hard to get in touch with the drum shop :s I am at school during office hours and they're not very good at emails!

Ill keep you all informed as to how it goes but for now I am having to plan everything theoretically!

I figure to stop cross talk from the shell I need a really heavy bit of wood as my cross piece. This should stop it.

Talking of the rim, how do you mount a flat piezo on to a round drum :s

[racer52]

I have had the best results by applying tape to only the top and bottom portions of the brass backing. and when I stuck it to the drum I positioned the disc as close to the head as possible with out touching the head. this got the top strip of tape near the top of the drum shell. the bottom strip of tape was furthest from the rim of the drum. this left the compete middle/cross section of the piezo with no contact to the shell at all. My guess at why this worked so well is that the vibration from a rim strike would progress from top to bottom down the shell of the drum. First passing thru the top tape then thru the bottom tape and allowed a shock wave to flow across the piezo. Hey - this worked for me and I have no clue why it really does. But I am using only one rim trigger and I can just let my stick fall lightly on the rim and can trigger my tamborine sound on my tom. Hope that helped