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Thread: De-coupling woofer from baffle

  1. #1
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    De-coupling woofer from baffle

    Recently I have become concerned about mounting a woofer (in my case a 15 inch 2216nd) to the baffle. The concern is obvious: transfer of motion of the woofer frame to the baffle of the cabinet.

    I am using specs and diagrams for the M2 and the S4700 as my "best practices" guide. What I am seeing so far is the the woofer is simply attached via eight 10-32 bolts going into T-nuts on the baffle. I assume there is a slightly compliant speaker gasket in between the back of the woofer frame and the front of the baffle.

    Is that it? Are there any "hidden" dampening or de-coupling tricks in there (eg, rubber washers or shoulder washers etc between the bolt head and the frame, well nuts or whatever)?

    Is the gasket behind the frame relatively "squishy" or relatively hard. I appreciate that the gasket is there both to dampen and to prevent air leaks.

    Were more exotic techniques used in the K2 and E2 models. Or, perhaps, with adequate internal bracing, the issue of coupled vibration (woofer to cabinet) is already minimized?

    Your collective thoughts are appreciated.

    Thanks,
    -Tom

  2. #2
    Senior Member grumpy's Avatar
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    I believe that's it. The topic of coupling or uncoupling drivers gets very quickly to: What problem are you attempting to solve?
    You want a good seal. You don't want loose bits vibrating (buzzing), or a resonating frame (or cabinet) sucking energy away at frequencies you want emanating from the cone.
    How that gets solved (mass, bracing/stiffness, dampening material(s), ...) is a system designers job to take seriously or ignore, and less a yes/no question.

    In this case, unless you're using unconventional construction methods or materials (in which case, you're on your own), I'd humbly suggest either going with the nominal JBL driver attachment method or experimenting a bit, perhaps with a thicker baffle and/or bracing from a stiffened rear panel to the back of the 2216 (can get complicated quite easily, but with DIY, the sky is the limit ). Of course, you may end up with a box that has horrible resonant modes if you're not careful... Hence the known recipe suggestion. Very nice driver, BTW.


    Quote Originally Posted by withTarragon View Post
    Recently I have become concerned about mounting a woofer (in my case a 15 inch 2216nd) to the baffle. The concern is obvious: transfer of motion of the woofer frame to the baffle of the cabinet.

    I am using specs and diagrams for the M2 and the S4700 as my "best practices" guide. What I am seeing so far is the the woofer is simply attached via eight 10-32 bolts going into T-nuts on the baffle. I assume there is a slightly compliant speaker gasket in between the back of the woofer frame and the front of the baffle.

    Is that it? Are there any "hidden" dampening or de-coupling tricks in there (eg, rubber washers or shoulder washers etc between the bolt head and the frame, well nuts or whatever)?

    Is the gasket behind the frame relatively "squishy" or relatively hard. I appreciate that the gasket is there both to dampen and to prevent air leaks.

    Were more exotic techniques used in the K2 and E2 models. Or, perhaps, with adequate internal bracing, the issue of coupled vibration (woofer to cabinet) is already minimized?

    Your collective thoughts are appreciated.

    Thanks,
    -Tom

  3. #3
    Senior Member christo's Avatar
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    Quote Originally Posted by withTarragon View Post

    Were more exotic techniques used in the K2 and E2 models. Or, perhaps, with adequate internal bracing, the issue of coupled vibration (woofer to cabinet) is already minimized?
    Here's a picture of the K2s woofer mounting plate - notice there is no gasket. But the cabinet is heavily braced.
    Attached Images Attached Images  

  4. #4
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    Quote Originally Posted by grumpy View Post
    I believe that's it. The topic of coupling or uncoupling drivers gets very quickly to: What problem are you attempting to solve?
    You want a good seal. You don't want loose bits vibrating (buzzing), or a resonating frame (or cabinet) sucking energy away at frequencies you want emanating from the cone.
    How that gets solved (mass, bracing/stiffness, dampening material(s), ...) is a system designers job to take seriously or ignore, and less a yes/no question.

    In this case, unless you're using unconventional construction methods or materials (in which case, you're on your own), I'd humbly suggest either going with the nominal JBL driver attachment method or experimenting a bit, perhaps with a thicker baffle and/or bracing from a stiffened rear panel to the back of the 2216 (can get complicated quite easily, but with DIY, the sky is the limit ). Of course, you may end up with a box that has horrible resonant modes if you're not careful... Hence the known recipe suggestion. Very nice driver, BTW.
    ----------------

    You are correct. I will add that the terms coupling, dampening, and MDF vs plywood, will always cause a thread to deteriorate.

    I try and keep it simple in my mind. I am working on the assumption that the majority (not all) of cabinet vibration is caused by the direct coupling of the speaker frame to the baffle. While the air oscillating inside would contribute substantially less. This second effect is, of course, best handled by mass (thicker walls), fiberglass, dampening (eg, Constrained layer techniques, and to a lesser extent cabinet material itself) and bracing.

    I am also assuming that the worst offender for vibration is the baffle (it is the first piece "shaken") and to a lesser extent the other walls vibrating. So I will certainly double up on the baffle thickness at the very least and then add some CLD when bracing the baffle to the side walls and especially the rear wall.

    My hope was some sort of trick to stop the conduction of vibration at the baffle ("nip it in the bud"). Logical choices would be the speaker gasket and the mechanical attachments (bolts or clamps). The question of whether vibration sucks out the energy over some bandwidth is interesting. Obviously, if the energy is vibrating the walls then it is not going to cone motion. That is my intuition, but when I think it through the energy transmission has to be so far down relative to the cone motion, that I end up thinking that this must be a minor third order effect. On other days I can argue myself out of that one....

    Yes, I am quite taken with the 2216nd woofer. It has plenty of bandwidth, low distortion, etc. What is not to love. Frankly, given the R&D costs, tooling etc, I am surprised that it only seems to used in the M2 and S4700.

    The eventual cabinet will be two way ported system (probably the same cabinet and port geometry as the S4700) and CD horn (JBL driver). DSP will be used for crossover and EQ. I hate to say it, but the planning and learning is half the fun. The luxury of the DIYer .....

    -Tom

  5. #5
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    "....
    Here's a picture of the K2s woofer mounting plate - notice there is no gasket. But the cabinet is heavily braced.
    ...."

    Thanks for the picture. I am surprised.
    Even if it wasn't for decoupling vibration, I assume something would be there for possible air leaks.

    I guess, once again we learn that bracing is our friend. Apparently, a very good friend.
    -Tom

  6. #6
    On Holidays Ian Mackenzie's Avatar
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    Quote Originally Posted by withTarragon View Post
    Recently I have become concerned about mounting a woofer (in my case a 15 inch 2216nd) to the baffle. The concern is obvious: transfer of motion of the woofer frame to the baffle of the cabinet.

    I am using specs and diagrams for the M2 and the S4700 as my "best practices" guide. What I am seeing so far is the the woofer is simply attached via eight 10-32 bolts going into T-nuts on the baffle. I assume there is a slightly compliant speaker gasket in between the back of the woofer frame and the front of the baffle.

    Is that it? Are there any "hidden" dampening or de-coupling tricks in there (eg, rubber washers or shoulder washers etc between the bolt head and the frame, well nuts or whatever)?

    Is the gasket behind the frame relatively "squishy" or relatively hard. I appreciate that the gasket is there both to dampen and to prevent air leaks.

    Were more exotic techniques used in the K2 and E2 models. Or, perhaps, with adequate internal bracing, the issue of coupled vibration (woofer to cabinet) is already minimized?

    Your collective thoughts are appreciated.

    Thanks,
    -Tom
    If you read the user manual it refers to the enclosure supports that couple the enclosure to the floor.

    The 2216 driver kicks hard so the enclosure needs to be stable.

    On the woofer. The frame is designed to be rigid do it does not resonate. Itís only the cone diaphragm that is moving, not the frame.

    When the woofer is running itís like an engine that pumps air with the~ signal inward and outward.
    While the enclosure is ported for air to flow in and out of the port the stiffness of the air loads the cone diaphragm.

    The goal of the front baffle to be form a solid rigid platform for the driver. Because the baffle has a hole for the driver itís thick to improve rigidity. So the goal is to clamp the driver to the baffle.

    Back to your question l would use a cork gasket which is relatively hard but will form a seal under pressure.

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    Quote Originally Posted by Ian Mackenzie View Post
    If you read the user manual it refers to the enclosure supports that couple the enclosure to the floor.

    The 2216 driver kicks hard so the enclosure needs to be stable.

    On the woofer. The frame is designed to be rigid do it does not resonate. Itís only the cone diaphragm that is moving, not the frame.

    When the woofer is running itís like an engine that pumps air with the~ signal inward and outward.
    While the enclosure is ported for air to flow in and out of the port the stiffness of the air loads the cone diaphragm.

    The goal of the front baffle to be form a solid rigid platform for the driver. Because the baffle has a hole for the driver itís thick to improve rigidity. So the goal is to clamp the driver to the baffle.

    Back to your question l would use a cork gasket which is relatively hard but will form a seal under pressure.
    ______________

    I understand the goal of a rigid frame, however I am still trying to get my mind around the notion of "where is the energy going"? The major portion is of course going to the cone, but doesn't Newtons 3rd law tell us that there will be a force in the other direction. I assume this is ultimately going to the frame I thought. If there is not resonance, that simply means the reaction (motion) is not preferential for certain spectral regions (i.e., a resonance). So is the idea that the reaction would not be able to vibrate the various elements when they are all coupled tightly together (frame to baffle to side wall to back wall to the various braces etc)?

    That would suggest that lots of good solid bracing, plus the extra mass in the cabinet walls are the cure (IOW, don't bother with trying to dampen it with some squishy material). Perhaps I have just answered my own question.

    Thanks,
    -Tom

  8. #8
    Senior Member jmpsmash's Avatar
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    Quote Originally Posted by withTarragon View Post
    ______________

    I understand the goal of a rigid frame, however I am still trying to get my mind around the notion of "where is the energy going"? The major portion is of course going to the cone, but doesn't Newtons 3rd law tell us that there will be a force in the other direction. I assume this is ultimately going to the frame I thought. If there is not resonance, that simply means the reaction (motion) is not preferential for certain spectral regions (i.e., a resonance). So is the idea that the reaction would not be able to vibrate the various elements when they are all coupled tightly together (frame to baffle to side wall to back wall to the various braces etc)?

    That would suggest that lots of good solid bracing, plus the extra mass in the cabinet walls are the cure (IOW, don't bother with trying to dampen it with some squishy material). Perhaps I have just answered my own question.

    Thanks,
    -Tom
    you have to differentiate between force and energy. newton 3rd law says equal and opposite force, not energy. Energy is only used when something is moved by that force. Putting a 10kg block on a table has 98 Newtons of force acting on it, but no energy is used since it is stationary.

    In case of a loudspeaker, if the cabinet is perfectly rigid, then it won't move even with a huge force on it. then no energy is loss there. However, if the cabinet vibrates along then vibration movement leads to energy loss through the vibration.

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    Quote Originally Posted by jmpsmash View Post
    you have to differentiate between force and energy. newton 3rd law says equal and opposite force, not energy. Energy is only used when something is moved by that force. Putting a 10kg block on a table has 98 Newtons of force acting on it, but no energy is used since it is stationary.

    In case of a loudspeaker, if the cabinet is perfectly rigid, then it won't move even with a huge force on it. then no energy is loss there. However, if the cabinet vibrates along then vibration movement leads to energy loss through the vibration.
    --------
    I understand what you are trying to get at and I understand the concepts of force and energy (I like to think of energy as work or force x distance). But we are getting away from the interesting stuff and going elsewhere. So maybe we should stop.

    I thank everyone for their thoughts. I will rely on cabinet mass and bracing and not try and prevent the transmission of vibration using dampening (using squishy" stuff") to decouple the woofer frame's motion to the cabinet. However, I do remember that KEF used "well nuts" when they attached their woofers to the baffle. This put a layer of rubber between the frame-to-bolt-to-baffle connection. I am digressing again .....

  10. #10
    On Holidays Ian Mackenzie's Avatar
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    If the driver was infinitely low in mass and not bolted to the front baffle it would in theory fly across the room.

    My advice is donít over think anything related to Audio. It leads to an obsession which leads to spending huge amounts of money.

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    Yes, any possible vibration of the magnet/basket assembly results from the VC's reactive forces. To yield maximum control over the cone movement, you have to keep any reactively induced movements as low as possible. Hence, you'd be aiming at mounting the basket as close and as tight as possible to a as stiff as possible baffle and box.

    Best regards!

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    Quote Originally Posted by Kay Pirinha View Post
    Yes, any possible vibration of the magnet/basket assembly results from the VC's reactive forces. To yield maximum control over the cone movement, you have to keep any reactively induced movements as low as possible. Hence, you'd be aiming at mounting the basket as close and as tight as possible to a as stiff as possible baffle and box.

    Best regards!
    There have been several notable uses of decoupled, Linkwitz (RIP) has some work on his site, KEF, and several others. Many believe (and have measured) that the tiny movements of the driver frame as excited by the moving mass are less important than the potential for exciting the large surface areas of panel resonances via rigid coupling.

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