Plate Reverb pickups

[joaquins]

Nice progress!

Just enough level to deal with the noise, the schematic I attached earlier used 20W power amp, that should give you a ballpark number, they wouldn't use 20W amp if they needed one and with that was enough, so, I guess should be around that number, at least to start. 20W amp, the power for the driver shouldn't be too off, maybe is a little too much but we never pissed off by a little too much headroom...

JS

 

[gato]

Just wanted to chime in on the driver question.
I've used the Vidsonix Ghost and it works well! Its been years but I remember there were rolen star drivers that were supposedly better but I couldn't source them at the time. Also I've used piezo elements that I pulled from Radio Shack piezo buzzers. There was a time when I would go buy up the buzzers as they arrived. You can do all kinds of fun stuff like coat them in liquid plastic for underwater microphones. I once froze one of those mics in a block of ice to record the sound of ice melting. There is a sound but its not terribly exciting.
To use a piezo as a driver you need really high voltage (but low current). I haven't tried it with something as big as a 2m by 1m plate reverb though since I already had the driver.

 

[pitol678]

Just wanted to chime in on the driver question.
I've used the Vidsonix Ghost and it works well! Its been years but I remember there were rolen star drivers that were supposedly better but I couldn't source them at the time. Also I've used piezo elements that I pulled from Radio Shack piezo buzzers. There was a time when I would go buy up the buzzers as they arrived. You can do all kinds of fun stuff like coat them in liquid plastic for underwater microphones. I once froze one of those mics in a block of ice to record the sound of ice melting. There is a sound but its not terribly exciting.
To use a piezo as a driver you need really high voltage (but low current). I haven't tried it with something as big as a 2m by 1m plate reverb though since I already had the driver.

Those are some cool sounding experiments!! Particularly the one with the meting ice, too bad it didnt have a more exciting result. very cool

I have heard of the Vidsonix Ghost but based on what another person said above in this thread, Im wondering about the amount of surface area that is in contact with the plate. i may try it just as an experiment though because it seems that a few people have used them. Do you have a ghost on a plate reverb? If so, do you have any sound samples or a website? Thanks!

 

[pitol678]

I have a 3" speaker which says that it is "4-6 ohms" and can handle an amplifier from" -10 to 80W."  However, when I take it out of its enclosure it seems to have very little volume. How can I determine how much volume it takes to drive the plate? Does it need a lot of volume to have the desired effect? Thanks

 

[joaquins]

If you don't have enough driving capability you will need too much amplification after and will have problems with S/N ratio. If you have too much excursion of the plate it could generate some artifacts but I think you will be able to tell if that's happening and could try for simply lowering the driving level. You could try with the one you have and you will find out if it works for you or not.

JS

 

[abbey road d enfer]

Although, I have no clue as to how much sound the driver needs to put out.

Typically an EMT140 with tubes was hardly capable of 2W. When they went to solid-state, the power was increased to about 4W. The latecomers took advantage of the availability of cheap and reliable monolithic power chips that were capable of delivering a few dozens Watts, but there is no need for that. When you listen to an EMT140, you hear almost nothing from the plate, unless you're in complete silence.

 

[pitol678]

Although, I have no clue as to how much sound the driver needs to put out.

Typically an EMT140 with tubes was hardly capable of 2W. When they went to solid-state, the power was increased to about 4W. The latecomers took advantage of the availability of cheap and reliable monolithic power chips that were capable of delivering a few dozens Watts, but there is no need for that. When you listen to an EMT140, you hear almost nothing from the plate, unless you're in complete silence.

Thats great to know! I was wondering about that because even as I'm testing my driver, I can hear it but just barely. However, I can only hear a faint bit of reverb (I think) coming from the plate. I received my pickups in the mail yesterday and am planning on a test run of the whole thing this weekend! Looking forward to it

Edit: Seeing as how I can solder but not follow a schematic in order to build an input amp yet, would something like this be any better than a simple headphone amp?
http://www.ebay.com/itm/Fender-Pawn-Shop-Special-Greta-2W-8ohm-1x4-Tube-Amp-/281524712597?pt=LH_DefaultDomain_0&hash=item418c2e3495

 

[LeeYoo]

Anybody tried a surface transducer?

https://www.sparkfun.com/products/10975

Leo..

 

[mr coffee]

@ pitol678 -

May I suggest you consider these

http://www.parts-express.com/dayton-audio-daex25-sound-exciter-pair--300-375

as they are meant to be attached to a surface to cause it to emit sound, like a wall, panel, etc.?

They are not expensive, but they are wideband (up to 20 khz), can handle quite a few watts, and use the magnet as a moving mass to impart vibration into the attached panel, i.e., your suspended echo plate. More likely to do the trick than a bunch of low mass piezo transducers.  For output, piezo is fine; to drive, you need something wideband with guts.

Seems like a good choice for a good quality DIY plate on a budget.  A chip audio amp with eq ought to drive it nicely.

Let us know how it's going...

mr coffee

 

[abbey road d enfer]

Edit: Seeing as how I can solder but not follow a schematic in order to build an input amp yet, would something like this be any better than a simple headphone amp?
http://www.ebay.com/itm/Fender-Pawn-Shop-Special-Greta-2W-8ohm-1x4-Tube-Amp-/281524712597?pt=LH_DefaultDomain_0&hash=item418c2e3495

I doubt it has any advantage over a simple headphone amp, and the voicing may not be optimum for the application. The only processing that's needed on the input side is a high-pass filter and a treble boost. A guitar amp does not do it well.

 

[abbey road d enfer]

Anybody tried a surface transducer?

https://www.sparkfun.com/products/10975

Leo..

These are very convenient because they require no adjustment whatsoever, except finding the right position on the plate, but they have a larger contact surface, which may tend to damp the plate. I guess it would be possible, after having found the right position, to install it permanently via a short rod screwed on the plate. Or maybe the additional damping would be to your taste...

 

[abbey road d enfer]

@ pitol678 -

May I suggest you consider these

http://www.parts-express.com/dayton-audio-daex25-sound-exciter-pair--300-375

as they are meant to be attached to a surface to cause it to emit sound, like a wall, panel, etc.?

They are not expensive, but they are wideband (up to 20 khz), can handle quite a few watts, and use the magnet as a moving mass to impart vibration into the attached panel, i.e., your suspended echo plate.

I think one should take the 20kHz spec with a large spoonful of salt, because it depends on the nature of the plate it is attached to and the coupling via 3M adhesive pads certainly introduces a mechanical LPF. But it should be ok. Probably less so than the other that attaches in a single point. This one with 3 points of adhesive is likely to introduce more damping, which one may or may not appreciate.

More likely to do the trick than a bunch of low mass piezo transducers.

Indeed. The mass ratio, which is a direct parameter in the mechanical  transfer efficiency, is definitely not good for piezo discs.

  A chip audio amp with eq ought to drive it nicely.

+1

 

[thomasdf]

I have used these speaker / transducer with great results!

http://www.vidsonix.com/vidsonixnew/info_vxgh72.htm

They are quite cheap. My problem was with the pickups.
I ended up using large piezos and boost their level with Shure SM57 transformers (I guess it changed the frequency response a bit but well... ) and then used good line amplifiers.
It sounded great except that my plate was too small and not properly tuned.

Anyways, you should give those a try

 

[abbey road d enfer]

I have used these speaker / transducer with great results!

http://www.vidsonix.com/vidsonixnew/info_vxgh72.htm

They are quite cheap. My problem was with the pickups.
I ended up using large piezos and boost their level with Shure SM57 transformers (I guess it changed the frequency response a bit but well... ) and then used good line amplifiers.
It sounded great except that my plate was too small and not properly tuned.

Anyways, you should give those a try

In my last experiments (1984), I used single-coil guitar pick-ups. They are extremely apt at picking the steel plate vibrations, the mounting is relatively easy (make the magnets 1/8th inch from the plate) and they don't damp the plate. Their impedance is lower than piezos; the only drawback is they pick hum from equipment near them. I could have experimented with humbuckers if it had been an issue.

 

[pitol678]

@ pitol678 -

A chip audio amp with eq ought to drive it nicely.

As Im trying to get the electronics portion of the plate sorted out, I am wondering if my headphone amp is powerful enough. The one I have is here: http://www.musiciansfriend.com/pro-audio/behringer-microamp-ha400-headphone-amp?pfm=sp

When I drive the headphone amp very hard, I get distortion and still not much in the way of volume. I can hear the reverb but the volume is so low. If I turn up the preamps enough to somewhat accomodate, I also get distortion as well as more noise. At the risk of asking a dumb question, what is a "chip audio amp"? Can anyone recommend one for this application?

FYI, I purchased piezo pickups and have them installed and used the specs provided in an earlier post by Mr Flinn, I believe

 

[joaquins]

The level needed will depend on many factors, I wouldn't take as a reference hearing or not if the plate sounds.  The noise on your output should be your main concern, if you are comfortable with the noise level on your output without getting much distortion then your amp is powerful enough.

The audio chip amp I guess is referring to an integrated power amp, like the 20W driver I quoted in the schematic. Is an opamp with few watts output capability, as it it may need a heat sink but you just should look at it as a conventional opamp only is much bigger and capable of doing that task. The 20W it's shown on the scheme should be big enough or you are having other problems in the chain, maybe the noise on the pre you are using for the piezo elements. In that case is an LM1875 but you should go for a parametric search in your desired provider since the exact same chip may not be available and it doesn't worth a headache for a easily replaceable chip, then you go to the data sheet and a typical application is all what you need, where you'll find the schematics and maybe even the board and BOM for the amp. Then you need to add the filter and treble boost required, but that could be in a separate board or even in your DAW.

JS

 

[emrr]

I can only add that my Ecoplate III which is beside the client couch can scare the client if the monitors are turned down low.  If they are up, maybe the person sitting right next to the plate will think there's a ghost in the corner.  That sounds like more volume than an EMT possibly.  I don't know how they compare for metal thickness, tension, etc. 

 

[pitol678]

I can only add that my Ecoplate III which is beside the client couch can scare the client if the monitors are turned down low. 

Do you mean that even if they are low, the volume is startlingly loud, or that it sounded as if there was a ghost in the room?

 

[emrr]

If the control room is quiet, it can scare the client.  Otherwise it's only the person sitting next to the plate that might hear it when the control room monitors are up at normal volume. 

 

[pitol678]

So here is a sample of the plate if anyone wants to check it out. Obviously it needs some work, but Im trying to narrow down the variables in order to fine tune everything. Feel free to point out anything that jumps out at you and make any suggestions. Ive added a bit of EQ, cutting below 100hZ and dipped out some mids. Right now Im using a Marantz 2020 to drive the plate because my Behringer headphone amp just doesnt have enough power so Im not sure how much bearing this has on the sound.

The tune is my friend covering Leonard Cohen's version of Tennesee Waltz recorded with an SM7b>CAPI/VP28> CAPI553>Reaper

https://soundcloud.com/eric-davidson-2/plate-reverb-demo-vox-and-verb
https://soundcloud.com/eric-davidson-2/plate-only