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speaker driver damping
speaker driver damping
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Old 2nd December 2017, 12:27 AM   #1
Discopete is offline Discopete  Canada
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speaker driver damping
Default speaker driver damping

I'm wondering why I don't see any references to physically damping drivers with serious weight instead of novel vibration damping materials like duckseal etc.

Predictably, how would adding a 20lb steel/lead puck to the magnet of a driver affect it's performance? Would this not serve to significantly improve/increase the kinetic energy of the vc/cone? Would it not extend to reduce cabinet resonance also?
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Old 2nd December 2017, 01:33 AM   #2
Andrew Eckhardt is offline Andrew Eckhardt  United States
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Adding damping material to the basket controls basket resonances. Adding mass to the motor slows it down. Physically connecting two opposed motors can nearly stop them from moving if the drivers are well matched. Even in the latter most condition box internal sound pressure will flex and resonate the walls. With fairly beefy ceramic magnet designs you're almost at the point of diminishing returns mass-wise, while lighter duty neodymium based motors are so light that they could use a brick glued on for good measure. I've built "small" speakers that weighed over 80 pounds and the enclosure still vibrated. Sufficient to say that if just the woofer motor weighed 80 pounds alone, the box would still move.
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Old 5th December 2017, 10:16 PM   #3
Discopete is offline Discopete  Canada
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speaker driver damping
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Originally Posted by Andrew Eckhardt View Post
Adding damping material to the basket controls basket resonances. Adding mass to the motor slows it down. Physically connecting two opposed motors can nearly stop them from moving if the drivers are well matched. Even in the latter most condition box internal sound pressure will flex and resonate the walls. With fairly beefy ceramic magnet designs you're almost at the point of diminishing returns mass-wise, while lighter duty neodymium based motors are so light that they could use a brick glued on for good measure. I've built "small" speakers that weighed over 80 pounds and the enclosure still vibrated. Sufficient to say that if just the woofer motor weighed 80 pounds alone, the box would still move.
How/why would it slow it down? If the motor was held against an unmovable substrate, it's performance would be compromised?

I had another thought, could you attach an arm on the back of a cab and on that a suitable sliding weight in order to cancel cab vibration? How would this affect driver performance?
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Old 5th December 2017, 10:53 PM   #4
Ron E is offline Ron E  United States
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Kind of seems like a solution looking for a problem.

Adding mass reduces the resonant frequency, it doesn't "damp".
Exactly how do you think it would "significantly improve/increase the kinetic energy of the vc/cone"?

You can successfully reduce cabinet vibrations with bracing with a lot less than 20lb of material.
Adding large mass to the driver will stress the driver and the panel it is mounted to.

Some have made a magnet cradle that supports the motor with sort of rubber isolators. Others go out of their way to decouple the driver from the cabinet. For the most part, all of these are also solutions looking for a problem and are often more about marketing.
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Old 5th December 2017, 11:25 PM   #5
W0J0 is offline W0J0  United States
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I'm not sure what your end goal is. A chunk of steel on the basket of a driver is not going to do much to damp resonance, afterall even anvils ring. That's why blacksmiths wrap the base of them with a chain; to absorb and dissipate the energy transferred into the anvil. In theory, that is why ductseal works; it absorbs the energy transferred to the basket and damps the basket. If you want to attach "pockets" of lead bird shot to the basket, it would have the same effect but I'm not sure I've ever experienced a basket ringing in all my years of listening to speakers professionally. If I have, it wasn't apparent.
If you're trying to keep a cabinet from vibrating, try trapping a dense material between two layers... Heavy, limp mass (maybe vinyl) between layers of foam, attached to the cabinet walls. Or build a box inside a box with a layer of sand in between. That will dissipate any energy that would transfer through cabinet walls. Alternatively, concrete could be used instead of sand for brute force stiffening of cabinet walls.
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Old 6th December 2017, 04:59 AM   #6
planet10 is offline planet10  Canada
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speaker driver damping
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Originally Posted by Discopete View Post
Predictably, how would adding a 20lb steel/lead puck to the magnet of a driver affect it's performance?
You’d have to worry a lot about it pulling the magnet off the basket.

When we build most of our speakers we tightly couple the speaker magnet via a holey brace to at least 4 of the box panels. This would effectively be adding the mass of the box in the same manner as your steel weight without its issues. Not the reason we do it, but… We also use ductseal to damp “local” basket ringing.

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Old 6th December 2017, 05:07 AM   #7
planet10 is offline planet10  Canada
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speaker driver damping
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"small" speakers that weighed over 80 pounds
Mass is not an asset when you are trying to avoid resonance unless it is because of intelligent bracing or, as in the case of stranded bamboo plywood, it brings a significant increase in stiffness.

dave
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Old 6th December 2017, 05:11 AM   #8
planet10 is offline planet10  Canada
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speaker driver damping
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...tightly couple the speaker magnet via a holey brace to at least 4 of the box panels...
And if the opposite side just happens to be another baffle with the same driver wired in the same acoustic polarity you create a stystem with active vibration cancelation.

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Old 6th December 2017, 09:41 AM   #9
Discopete is offline Discopete  Canada
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speaker driver damping
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Originally Posted by Ron E View Post
Kind of seems like a solution looking for a problem.

Adding mass reduces the resonant frequency, it doesn't "damp".
Exactly how do you think it would "significantly improve/increase the kinetic energy of the vc/cone"?

You can successfully reduce cabinet vibrations with bracing with a lot less than 20lb of material.
Adding large mass to the driver will stress the driver and the panel it is mounted to.

Some have made a magnet cradle that supports the motor with sort of rubber isolators. Others go out of their way to decouple the driver from the cabinet. For the most part, all of these are also solutions looking for a problem and are often more about marketing.
My logic is clearly misplaced by ignorance. I guess there's a difference between Fs and vibration. But if Fs was 0hz, does that not describe a fully damped driver? Stopping the motor from moving in the opposite direction of the vc would increase the vc's potential acceleration, no?
I suppose I was suggesting a sort of active vibration cancelling with the sliding weight..I mean until the right spot is discovered and then fixed in place.
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Old 6th December 2017, 10:50 PM   #10
Andersonix is offline Andersonix  Sweden
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speaker driver damping
If you accept Newtonian physics, conservation of momentum means m1v1=m2v2, where in our case m1 is the cone and m2 is the simplified(!) mass of everything else (basket, motor, cabinet). So if you hang your loudspeaker from a string and shoot off your cone at v1, the reaction in the cabinet will be to move at velocity v2=m1v1/m2. And if you decide to make m2 twice as big, then v2 (cabinet reaction) is halved.
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