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Feedback bronze wall

Discussion in 'General Electronics Discussion' started by IDontWantMyUsername, Apr 21, 2014.

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  1. IDontWantMyUsername


    Apr 21, 2014
    Hi people, I'm looking for some insights on a project where basically a bronze wall is going to work as a sound element in a feedback loop. I'm totally new to electronics, so bear with me! Quickly put - I'm here, and I'm eager to learn.

    Some details:

    The wall consists of two panels, both made of bronze; a front panel consisting of multiple smaller panels, and one solid inner panel. The inner and outer panels have a 10 cm gap or so in between (I'll get the specifics straightened out soon, and maybe have some pictures uploaded). The smaller panels making up the front have enough space between them to give access to the inner panel. Between the panels, we want to install a mechanism, causing constant feedback when a front panel is put into vibration. I will find out the dimensions and mass of the outer panels and announce them as soon as I can, but I would guess each is 3 m in height, and 1 m in width. I would guess the thickness to be about 1,5 cm. The walls are very resonant.

    The plan:

    1: Make an outer panel vibrate by hitting it once, and pick up the vibrations with a piezo element or contact microphone attached to its backside.
    2: Send the voltage from the piezo elements to a voltage amplifier attached to the inner panel.
    3: Send the voltage to motors which will be attached either to the outer, or the inner* panel, which will have a mechanism making the outer panels vibrate softly.
    4: The signal is sent in a feedback loop.

    *We have two suggestions as to how the motors could make the outer panels vibrate.

    1: A number of pneumatic motors attached to the inner wall hammer against an outer panel.
    2: A number of motors attached to an outer panel, working as g-force generators by rotating some kind of asymmetrical disk attached to them, make the panels vibrate.

    Some questions:

    - What power source would you recommend for such an installation?
    - What do you think of the two options for the execution of point 3? Are there better ways to do this?
    - What are your thoughts about the number of motors taken to make panels of such mass vibrate? Have our ambitions been set too high? If anyone would like to explain some formulas or just give me a hint about where to look into to get more understanding on this, that would be great. (As a notice, I must admit I do not have much experience with physics either.)
    - Any important details we haven't considered?

    Thank you very much!
  2. duke37


    Jan 9, 2011
    I await your pictures and maybe a diagram on what you intend.

    My initial thought is that it would be simplified if you used magnetic material i.e. steel. The panel could then be vibrated with a magnetic field, similar to a loudspeaker. With tight enough coupling the system could be made to resonate at its natural frequency.

    I think that efficiency will be low so power require dmay be high but at resonance, the main loss will be the sound output.
  3. IDontWantMyUsername


    Apr 21, 2014
    Thanks for the reply! It would be great if we could make it work by magnetism, but we're doing this on a very specific wall. I should maybe have added that we're aiming for a very weak sound, so we do not need very powerful motors. On the other hand, sustaining feedback with a low input (being the low output of the wall) will require much amplification.
  4. (*steve*)

    (*steve*) ¡sǝpodᴉʇuɐ ǝɥʇ ɹɐǝɥd Moderator

    Jan 21, 2010
    Glue powerful magnets to the rear of the wall and then use an electromagnet to produce a varying magnetic field (essentially connect it to an amplifier). This will place forces on the magnets which will in turn move the wall.
  5. IDontWantMyUsername


    Apr 21, 2014
    Hi, here are some pictures to illustrate what we're working with.

    I want to make some corrections as well:

    The wall consists of an inner part made of concrete, and an outer part made out of 14 instances of an inner and an outer bronze panel, with the outer panel having patterns carved into it. The wall is 288cm tall, and each inner bronze panel is between 85cm and 120cm wide, with the outer panels never exceeding the inner panels' dimensions. There's an approx. 10cm gap between each of the 14 bronze panel entities, I would suppose.

    We're not going to use all of the panels, but probably the ones with the least mass, to make it easier for ourselves. Between the concrete and the inner bronze panel, there's about 10cm of space. Between the inner and the outer panel, there's about 3.1cm of space. The inner bronze panel is 1cm thick, and the outer one is 1.2cm thick.

    With solution 1, the motor would be attached to the outside of the inner panel, hammering against the outer panel, or the concrete wall, hammering against the inside of the inner panel.
    With solution 2, the motor would be attached to the inside of either the outer or the inner panel.

    How this will be executed, I guess will be decided by the size of the motors.

    (The pictures were somehow tilted to the left when I uploaded them)
    IMG_1039.JPG IMG_1041.JPG

    Attached Files:

  6. (*steve*)

    (*steve*) ¡sǝpodᴉʇuɐ ǝɥʇ ɹɐǝɥd Moderator

    Jan 21, 2010
    I would seriously consider some of those surface resonance speakers. I'm sure you could find some less than 10cm in height. Many are even bluetooth, so you could connect to them wirelessly.
  7. IDontWantMyUsername


    Apr 21, 2014
    Hi! Thank you very much for the suggestion, that should make things a lot easier!

    So the chain I've described, only with surface resonance speakers instead of motors should work well then? How powerful do you think the amplifier will have to be to drive the installation? If we could use batteries as a power source, that would be best. Other suggestions for power sources are welcome.
  8. (*steve*)

    (*steve*) ¡sǝpodᴉʇuɐ ǝɥʇ ɹɐǝɥd Moderator

    Jan 21, 2010
    It's really hard to answer that question. I would advise you to see what's available and try some out.

    Since you're making several panels, you might consider making one to test various methods.

    The first step might be to find someone who uses one with their iphone (or whatever) and just place it on one of your brass sheets (preferably supported similarly to how it would be on a panel -- maybe supported only at the corners, for example).

    Based on your success or failure there, you should have some solid data to move forward with.
  9. IDontWantMyUsername


    Apr 21, 2014
    Hi, thanks again for the feedback, and for your patience with my horribly slow replies! Not so much electronics available here, we'll have to order it. The project is first of all for the sake of learning, and if things don't work optimally, that's fine. I'm very interested in building this from the bottom, and I've found some speaker elements with these specifications:

    Rated power 4W
    Maximum power 8W
    Nominal impedance Z4Ohm
    Frequency response90–20000Hz
    Mean sound pressure level
    79 dB (1W/1m)
    Resonance frequency fs158Hz
    Height of front pole-plate3mm
    Voice coil diameter17mm
    Height of winding4mm
    Cutout diameter45mm
    Net weight0,032kg

    I think I could remove the membrane and attach a metal plate to it to make it work like a resonance speaker. Seen lots of DIY's around the net.

    What do you think would be an optimal amplifier circuit to drive this? I've been looking at the TA2024, would it work well if I had two elements connected in series per amp channel to achieve a sum of 8 ohm impedance and 8w? Each channel works fairly well at 10w/8ohm if I don't misunderstand everything completely. I plan to run the amp with 9v batteries. Can it work? What have I missed? Are there other amps that would work better?

    How would it be to have two amplifier channels running one speaker element? Eg. 2 x 15w 4ohm amp channels driving a 30w 8ohm element?
  10. (*steve*)

    (*steve*) ¡sǝpodᴉʇuɐ ǝɥʇ ɹɐǝɥd Moderator

    Jan 21, 2010
    You need to be careful that the cone isn't part of the mechanism which keeps the voice coil from rubbing against anything.

    Also, in a regular speaker it's just the comparatively light voice coil which moves. You need to get that to vibrate the surface. I'm not sure, but I suspect, that surface resonant speakers have a fixed coil and a moving core (like a solenoid).

    Just a normal amplifier. For that speaker, a 4 or 5 watt amplifier..

    I'd be very careful trying to run an amplifier from 9V batteries. They won't last long. I doubt if they're really up to providing 5W for more than a very short time (if at all).

    I wouldn't worry about any of this until you find out if you can make your speaker work. Only then will you be able to judge the amount of power required.
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