I'm thinking of building a pair of high end to me MTM 2 way speaker in a 1.1 ft3 box with 3/4 inch thick plywood or particle board.
Having read some long discussions about box materials and bracing technique in these forums , I have a question if my idea might work or not . I plan to make H shaped brace on the center inside the box but instead of the wood material connecting the left part to the right part of the H brace , I replace it with a mini shock absorber like the ones used on small atv (please refer to the link below), To add stiffness and damping at the same time . Any idea it might work as effectively as I like it to? Any idea guys?
Thanks 🙂 https://www.google.com.ph/search?q=shock+absorber+as+speaker+box+damper&tbm=isch&tbo=u&source=univ&sa=X&ved=0ahUKEwjdg-TkzKbSAhVEV7wKHT2KCG0QsAQIHA&biw=1280&bih=603#tbm=isch&q=atv+mini+shock+absorbers&imgrc=ppCBPZ-Ckfko1M:
Having read some long discussions about box materials and bracing technique in these forums , I have a question if my idea might work or not . I plan to make H shaped brace on the center inside the box but instead of the wood material connecting the left part to the right part of the H brace , I replace it with a mini shock absorber like the ones used on small atv (please refer to the link below), To add stiffness and damping at the same time . Any idea it might work as effectively as I like it to? Any idea guys?
Thanks 🙂 https://www.google.com.ph/search?q=shock+absorber+as+speaker+box+damper&tbm=isch&tbo=u&source=univ&sa=X&ved=0ahUKEwjdg-TkzKbSAhVEV7wKHT2KCG0QsAQIHA&biw=1280&bih=603#tbm=isch&q=atv+mini+shock+absorbers&imgrc=ppCBPZ-Ckfko1M:
Yes that works! KEF LS50 uses this technique. There is a Youtube video explaining more about it (and other stuff): https://www.youtube.com/watch?v=E2fFz_S_v2o (at 51 min). I am not sure whether the shock absorbers are directly usable or that you have to use some other damper.
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damping bracing - since the frequency is higher and stroke so low its usually just made with a soft, lossy glue line in shear connecting overlapping pieces from each wall
Damping Bracing
much older idea than this patent, but it was easy to find: https://www.google.com/patents/US7270215
much older idea than this patent, but it was easy to find: https://www.google.com/patents/US7270215
perhaps, but should be easily to fix by rotating the one 90dg - my own approach is to never locate such bracing members at exactly the middle of panels
the material composition of the damping layer is not specified in the quoted text, but isn't the current consensus some type of non hardening adhesive - Sikaflex silicone, GreenGlue, etc?
the material composition of the damping layer is not specified in the quoted text, but isn't the current consensus some type of non hardening adhesive - Sikaflex silicone, GreenGlue, etc?
Another older approach to controlling resonance,
BBC-style thin-wall cabinets. Why so special? - Harbeth: For 40 years - the world's most natural sounding loudspeakers
Looking at the other design made me think of using magnets in some way. The magnets would provide the "friction", the control resistance, a centre point would be established where there peak strength while the speaker is not being fed power.
BBC-style thin-wall cabinets. Why so special? - Harbeth: For 40 years - the world's most natural sounding loudspeakers
Looking at the other design made me think of using magnets in some way. The magnets would provide the "friction", the control resistance, a centre point would be established where there peak strength while the speaker is not being fed power.
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The hysteresis, stiction and dead zone of a hydraulic damper make it unsuitable for the vibration amplitude and frequency of a panel resonance.
A damper is ineffective for amplitudes below 1mm and frequencies above 40Hz. Fortunately, the tyres are effective at damping out these frequencies.
Also the rubber bushes at the ends of the damper are used to attenuate these frequencies where the hydraulic damping is insensitive.
"Lossy" flexible compounds in shear are much more sensible for this. As described by the other posts.
Cheers,
Mike
A car shock absorber is an exceedingly smart device today. The car suspension is a whole bunch of elements that act like resistors (minimally), inductors, and capacitors that pass or block or deaden the various impingements from the pavement and passing or not passing them on to the riders depending on frequency.
Very low frequencies are passed to riders while high are converted to heat. A good quality motorcycle or a Maserati will flow the riders right across speed bumps ("sleeping policemen") as if they weren't there.
If you were making a space-station subwoofer, you might well design a very very light box and control parasitic vibrations using L, C. and R elements. (Or you might use motional feedback.)
But on earth, prolly not sensible.
Ben
Very low frequencies are passed to riders while high are converted to heat. A good quality motorcycle or a Maserati will flow the riders right across speed bumps ("sleeping policemen") as if they weren't there.
If you were making a space-station subwoofer, you might well design a very very light box and control parasitic vibrations using L, C. and R elements. (Or you might use motional feedback.)
But on earth, prolly not sensible.
Ben
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You are correct with the LCR analogy. And frequencies below 1Hz are not significantly attenuated by the dampers.
However a passive car damper is inherently sensitive to velocity, not frequency.
As stated, frequencies above 40Hz are mainly dissipated by the tyres and bushes.
The damper behaves like a bass driver (2-40Hz), the tyres like a midrange (40-100 Hz), and the bushes and other lossy elements like a tweeter.
Crossover design applies to car suspension too!
https://en.wikipedia.org/wiki/Mobility_analogy
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What if one would use a metal rod fixed to one side and a tube to the opposite side with the rod sticking into the tube with a large longitudinal overlap. They need to be of very close tolerance and the remaining small space is filled with silicone grease. This would give quite a lot of friction.
I guess vehicle shock absorbers of even the most high-mech variants will not be able to properly damp very small movements properly because of the valves and stuff involved.
Regards
Charles
I guess vehicle shock absorbers of even the most high-mech variants will not be able to properly damp very small movements properly because of the valves and stuff involved.
Regards
Charles
I've been using the Diversitech anti-vibration pads here -- for audio components, washing machine, etc. They're cheap and very effective. Might be worth considering for this application.
Just a matter of trading off cost, complexity, maintainability, weight, ability to teach people how to fix 'em, manufacturer's liabilities, aesthetic car design........ Similar to issues raised by OP post.
But, the latest generation of automobile suspension is active and "smart". Hey, isn't that like "motional feedback" in speakers?
Ben
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We would not need any adaptive thing here. We just want to damp resonances and we want to do this constantly with the same amount of damping applied.
I bet even the most advanced shock absorbers would not be able to effectively damp the veeeerry small excursions caused by box vibrations.
Regards
Charles
I bet even the most advanced shock absorbers would not be able to effectively damp the veeeerry small excursions caused by box vibrations.
Regards
Charles
Is anybody really thinking of buying Koni shocks for their boxes?
Damping has a place in box construction and a long history of sand-filled panels, etc testifies to that.
Adaptive or smart systems are, well, smarter than brute solutions. The tradeoff is between cost, etc all the kind of stuff I mentioned earlier. Again, prolly makes no sense except extra-terrestrially.
Funny, nobody has looked up and cited the research on how bad a problem is box vibrations. That's where this discussion needs to start.
I like the idea of active damping. Bentoronto, you also talked about "skyhook" technology. It should be possible to use the principles from noise cancelling headphones, you think?
Even tennis racquets have piezoelectric motional feedback embedded in them.
There's a material whose name I forget that has a high force/low amplitude response to an electric current, it can be used for vibration control.
Any of the speaker "exciter" technologies used for turning a resonant panel into a speaker can also be used for cancellation.
Exciting stuff!
Even tennis racquets have piezoelectric motional feedback embedded in them.
There's a material whose name I forget that has a high force/low amplitude response to an electric current, it can be used for vibration control.
Any of the speaker "exciter" technologies used for turning a resonant panel into a speaker can also be used for cancellation.
Exciting stuff!
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I think there is a misunderstanding of panel vibrations. Start with understanding that, like a room, a panel vibrates with different modes. When you add cross bracing what you are doing is preventing the panel to vibrate in certain modes. If you replace the cross brace with a damper then you are still allowing the panel to vibrate in those modes but with reduced amplitude. However, for modes which exhibit a node at the point where any type of bracing or damping is attached, neither the brace or damping will have any effect since at a node there is not displacement of velocity of the panel. Cross bracing is most effective at eliminating or controlling a mode which would otherwise exhibit an anti-node at the place of attachment. A point where displacement an velocity of the panel would otherwise have maximum displacement. The more effective way to eliminate panel resonances is by some type of constrained layer damping which provides damping over the entire surface of the panel, thus controlling all the possible panel modes.
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