Another Diy Plate Reverb

[saint gillis]

  Here is a small video showing the process state :
https://youtu.be/1WkJ4rLzJGE

  Now when I see the photo of an EMT, as mentioned by someone in another forum, I realise that the driver is not as the center of the plate :

  Likely as he said to avoid comb filtering...

 

[vinyvamos]

Just spotted these, maybe useful?

http://cpc.farnell.com/visaton/ex-45-s/exciter-46-x-46mm-10w/dp/LS03718

I also just came across these Visaton drivers and wondered whether I should consider it for my plate reverb project, and MrClunk has already mentioned it . Any thoughts on these? Could be an easy off the shelf solution eh!

 

[ubxf]

i don't know what piezzo you are using but i've been using this contact mic with decent results http://barcusberry.com/product.cfm?ProductID=9
and for the other side this looks interesting
http://www.feonic.com/vibration-speaker-technology#products

 

[Jarno]

Send sound to the plate wirelessly!
Damson Cisor

Now someone make a bluetooth contact microphone, and you can put the plate in the garage and simply stick these two on.

 

[abbey road d enfer]

The Ecoplate II is made with Stainless steel, & sounds very good.  It has more high frequency than an EMT.

The concern about stainless steel is that it is not very efficient magnetically, so using guitar pickups would result in very low output.

 

[abbey road d enfer]

Having experimented with all sorts of transducers, I ended up with a combination of exciter and guitar pickups as the most satisfying. There is no issue with the weight of the exciter, which is much less than the weight of the plate, nor with the frequency response of guitar pickups and neither the level. You need to choose pickups with the highest self-resonance; humbuckers are often below 4kHz; you need to select the ones with the lowest impedance - you would better rewire them in parallels instead of series. An EMT plate does not have much HF beyond 8 kHz.
The only significant issue is the plate itself and its mounting. You can't use just any stock of cold-rolled steel. That's the secret ingredient in EMT plates. Ecosonic opted for second best, stainless. Beware that guitar pickups won't work with stainless, so you may want to fix a steel pole piece or a magnet on the plate near the pickups.
Piezo pickups are not such a good idea since they are optimized for vertical pressure sensing; in a plate the pressure propagation is longitudinal.

 

[saint gillis]

I ended up with a combination of exciter and guitar pickups as the most satisfying

Hey thank you! This looks like very valuable information!
What is an exciter?

 

[abbey road d enfer]

Hey thank you! This looks like very valuable information!
What is an exciter?

http://www.daytonaudio.com/index.php/loudspeaker-components/loudspeaker-drivers-by-series/exciters.html
http://www.ebay.fr/itm/like/152411097427?lpid=97&chn=ps
http://www.digikey.com/en/product-highlight/p/pui-audio/audio-sound-exciters
http://www.visaton.de/downloads/pdf/visaton_exciter_principles.pdf

 

[saint gillis]

Ok I got it, I thought you were only talking of capturing the sound.
So you recommend to use an exciter to make the plate vibrate and guitar pickups to record the sound of the plate!

 

[saint gillis]

Beware that guitar pickups won't work with stainless, so you may want to fix a steel pole piece or a magnet on the plate near the pickups.

This sounds interesting! Why not with stainless?

 

[L´Andratté]

Check this
http://sound.whsites.net/articles/high-z.html

 

[saint gillis]

Piezo pickups are not such a good idea since they are optimized for vertical pressure sensing; in a plate the pressure propagation is longitudinal.

This is another good thought Abbey!
I did notice when I made some tests with a piezzo that the sound was not really rich, but when I put a little pressure on the piezzo with my finger the sound became a lot more deep and I thought of putting a soft element making some kind of gentle pressure on the piezzos... well it was just a thought

 

[PRR]

> Why not with stainless?

Good stainless is nearly non-magnetic. (I think the Chrome breaks-up the Iron magnetic domains.)

Bad stainless is slightly magnetic but nowhere near plain iron/steel.

But try it. I just stuck a magnet on two different spoons, a chromed steel wrench, and back on the icebox, did not feel as major a difference as I would expect from published numbers.

 

[abbey road d enfer]

This sounds interesting! Why not with stainless?

Abstract:
"Magnetic and non-Magnetic Stainless Steel

There are several families of stainless steels with different physical properties. The magnetic properties of stainless steel are very dependent on the elements added into the alloy. A basic stainless steel has a ‘ferritic’ structure and is magnetic, formed from the addition of chromium – it can be hardened through the addition of carbon, making it ‘martensitic’. However, the most common stainless steels are ‘austenitic’ – these have a higher chromium content and nickel is also added. It is the nickel which modifies the physical structure of the steel and makes it theoretically non-magnetic."

 

[Jarno]

Apart from the chemical composition, the degree of cold work also determines the "magneticness".
This causes most types of stamped or cold rolled materials to be magnetic, at least magnetic enough for "us" (development of MRI equipment) to be of interest.
Also, a lot of electric guitar and bass strings are stainless steel (and those strands are cold drawn, hence magnetic).

 

[PRR]

> It is the nickel which modifies the physical structure of the steel and makes it theoretically non-magnetic."
>  the degree of cold work also determines the "magneticness".

Thanks for the added info.

 

[saint gillis]

Having experimented with all sorts of transducers, I ended up with a combination of exciter and guitar pickups as the most satisfying. There is no issue with the weight of the exciter, which is much less than the weight of the plate, nor with the frequency response of guitar pickups and neither the level. You need to choose pickups with the highest self-resonance; humbuckers are often below 4kHz; you need to select the ones with the lowest impedance - you would better rewire them in parallels instead of series. An EMT plate does not have much HF beyond 8 kHz.
The only significant issue is the plate itself and its mounting. You can't use just any stock of cold-rolled steel. That's the secret ingredient in EMT plates. Ecosonic opted for second best, stainless. Beware that guitar pickups won't work with stainless, so you may want to fix a steel pole piece or a magnet on the plate near the pickups.
Piezo pickups are not such a good idea since they are optimized for vertical pressure sensing; in a plate the pressure propagation is longitudinal.

Hey Abbey!
I didn't go forward yet, but I'm still in for finishing the plate.
So you advise to choose humbuckers with a high self resonance and a low impedance. The problem is that these informations are  rarely provided in guitar pickups datasheets or specs.. do you have any models suggestions?

 

[abbey road d enfer]

So you advise to choose humbuckers with a high self resonance and a low impedance. The problem is that these informations are  rarely provided in guitar pickups datasheets or specs.. do you have any models suggestions?

Indeed manufacturers don't generally publish these figures, but many people have done measurements on guitar p/u's. Just google "guitar pick up impedance".

 

[saint gillis]

What about self resonance frequency, is it directly related to impedance?

 

[abbey road d enfer]

What about self resonance frequency, is it directly related to impedance?

Self resonance is the result of the nominal inductance reacting with the parasitic capacitance. Both increase with the number of turns, so yes, for a given structure, the higher the impedance, the lower the self-resonance frequency.