DIY spring suspension feet for Chassis?

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Hi gurus,

Does anyone know how to make feet for a chassis which are audio isolating? I am thinking of the Solid Tech brand.

I am trying to source some thick anodized aluminium tubing, then I thought I could use a tube cutter for nice cuts; though I don't have access to a machine shop, the final finish especially on the edges would be difficult.

Three small springs drilled to the inner rim, and finally a small foot on the inside as seen in the photo.

Or maybe someone knows of a source for said feet but without a heavy price tag...
 

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I have an idea but I did not come to the realization yet: using two neodymium disc magnets that push each other. They should be fixed in two telescopic aluminium or brass tubes. The tubes should fit tight but with minimal friction. I measured the pushing force between two 10 mm diameter, 5 mm thick magnets by a kitchen scale, it is about 2 kg weight at 2-3 mm distance (measuring the attraction force would have been difficult). Four legs could hold 8 kg weight.
 
oshifis said:
I have an idea but I did not come to the realization yet: using two neodymium disc magnets that push each other. They should be fixed in two telescopic aluminium or brass tubes. The tubes should fit tight but with minimal friction. I measured the pushing force between two 10 mm diameter, 5 mm thick magnets by a kitchen scale, it is about 2 kg weight at 2-3 mm distance (measuring the attraction force would have been difficult). Four legs could hold 8 kg weight.

Good idea in principle.

Except

There will still be contact and friction between the magnets and each leg.
So there will still be noise & vibration transmission.

Andy
 
(Not that I know why any of this might be necessary, but...)

Yes, even if you used some more magnets, so the telescoping tubes wouldn't even touch each other, there would still be transmission of motion from the base.

And, in fact, it might be almost a worst-case for airborne pressure waves affecting the motion of the 'suspended' unit. Spring suspensions would suffer similarly. There would also be some nasty resonant modes, in either case.

The solution would appear to be adding damping (like small 'shock absorber' cylinders, or just the right amount of friction), and maybe some mass. Additional damping would also be needed for both horizontal modes. Sounds 'messy'. But the filter equations would be straightforward.

Either that or create an active-feedback motion-cancelation mechanical-stabilization system. That might be a fun project, using some MEMS accelerometers, and maybe some speaker motors as actuators, plus some feedback-control amplifier systems.

Any type of vertically-oriented 'suspension' system seems like it would create many more problems than it would solve, if it solved any at all.

And it seems much simpler, and probably much better as well, to just use a very massive base, to rest the unit on, or to which to firmly attach it, unless you need protection during earthquakes as well.
 
If you suspend something from a spring or springs, say a bungee cord, or you support it on a spring suspension, the resonant frequency depends only on the amount of deflection between unloaded and loaded conditions. All the other terms drop out. So if you set your turntable on some sort of spring suspension (and we have to assume linear springs here), the resonant frequency can be calculated from a single number- how far it compresses the springs.

The formula is Frequency=0.15915*SQRT(386.22/Deflection in inches). "SQRT" is the Excel square root function.

So, if your suspension compressed 1", the resonant frequency of the system will be 3.128Hz.

I just find it intriguing that the result comes from such a simple measurement. Naturally some damping is needed, lest things get out of control.

Do some research on "minus k" and "zero length springs". There are some patents to watch out for, but the technique saves a lot of space. Useful to anybody? I dunno.
 
Conrad Hoffman said:


Do some research on "minus k" and "zero length springs". There are some patents to watch out for, but the technique saves a lot of space. Useful to anybody? I dunno.



I am sitting right next to a piece of equipment based on the zero-length spring. So it is useful in that it provides me with employment!!

Most gravity-measuring meters use the zls. There's even a company called ZLS


Andy
 
Conrad Hoffman said:
If you suspend something from a spring or springs, say a bungee cord, or you support it on a spring suspension, the resonant frequency depends only on the amount of deflection between unloaded and loaded conditions. All the other terms drop out. So if you set your turntable on some sort of spring suspension (and we have to assume linear springs here), the resonant frequency can be calculated from a single number- how far it compresses the springs.

The formula is Frequency=0.15915*SQRT(386.22/Deflection in inches). "SQRT" is the Excel square root function.

So, if your suspension compressed 1", the resonant frequency of the system will be 3.128Hz.

I just find it intriguing that the result comes from such a simple measurement. Naturally some damping is needed, lest things get out of control.

Do some research on "minus k" and "zero length springs". There are some patents to watch out for, but the technique saves a lot of space. Useful to anybody? I dunno.

Hi Conrad,

That IS interesting. I seem to vaguely recall having something about that pointed out to us (re the other terms dropping out), in Physics class, during my first year as an EE undergrad.

I guess I was thinking more about what might happen at higher, non-resonant freqencies, and was imagining that having something so 'loosely' suspended might make it much more vulnerable to having vibration induced in it.

Then again, I am still not sure what the goal is, here.
 
i was working at a stereo shop in NC back in the 70's and we tried to make a magnetic isolation table for turntables. nice idea, except that magenetic fields are "lossless" springs, and the mass of the table against the lossless spring makes a very high Q resonance. you may want to add an aluminum vane as a damping element (aluminum is an antimagnetic material). since we didn't think of this at the time, we ended up with a turntable stand that oscillated uncontrollably at something like 5 hertz, and so was not such a great idea.
 
unclejed613 said:
i was working at a stereo shop in NC back in the 70's and we tried to make a magnetic isolation table for turntables. nice idea, except that magenetic fields are "lossless" springs, and the mass of the table against the lossless spring makes a very high Q resonance.

That's actually not such a bad thing. Since such devices isolate above their resonant frequency, having such a high Q resonance actually increases the isolation in the vicinity of resonant frequency than if you were to damp the resonance.

In other words, with the Q well damped, you'd need to lower the resonant frequency in order to get the same amount of isolation you'd get with a higher Q resonance at a higher resonant frequency.

se
 
There are many ways you can do a proper sub sonic suspension. There are a lot of scientific tables around for not a lot of money (~1K) , compared to the prices of those toys of anti-vibe legs that float around clamimg superior sound.

Here is a link for some reading

http://www.newport.com/BenchTop-Compact-Pneumatic-Vibration-Isolation-Pl/139761/1033/catalog.aspx

What I think would be very efficient is a magnet idea with the twist. Two neodium magnes oppsoing each other. One magnet fixed the other mounted on a piston like inner cylinder that has a soft rubber seal and oil inside the tube. Playing with ammount and viscosity of the oil one can tune dampening. Rubber attenuates side vibrations and vertical vibrtions are dead completely. The problem is magnetic field around the legs that can pose some problems to MC cartridges.
 
DECKY999 said:
What I think would be very efficient is a magnet idea with the twist. Two neodium magnes oppsoing each other. One magnet fixed the other mounted on a piston like inner cylinder that has a soft rubber seal and oil inside the tube. Playing with ammount and viscosity of the oil one can tune dampening. Rubber attenuates side vibrations and vertical vibrtions are dead completely.

How 'bout the damping feet on some of the Japanese turntables back in the 70s? Had a Pioneer table back in the 70s that had viscous damped feet. They used mechanical springs instead of magnets, but with ultimately the same principle.

Another thing that might be cool would be the shock absorbers made for RC cars. My sister's boyfriend had one many years ago and what really amazed me about it was that you could drop the thing from six feet and it'd just go *thoomp!* on the floor and not bounce at all.

se
 
They can be useful as well. I don't now about the spring stiffness.

General problem in vibe-absorption using coil springs is their linearity - more weight carying capability = more stiffness = high resonant freq. Generally coil springs have to be quite soft to have system resonant frq below 10Hz. That is why most people in this business like rubber and its non-linear response. Or no springs at all. Magnets have similar problem - more wight = distance between magnets is smaller = magnetic force is higher and therefore aparent stiffness of the system. However, they are very effective in suppressing vertical vibrations of small magnitude.
 
DECKY999 said:
Magnets have similar problem - more wight = distance between magnets is smaller = magnetic force is higher and therefore aparent stiffness of the system.
The stiffness (1/compliance) is constant as far as the magnetic field is homogenous. The force is inversely proportional with the compliance and the distance, just like in loudspeakers. The resonance will be determined by the compliance and the mass of the suspended equipment.

Actually I tried neodymium ring magnets for suspending the platter in my turntable. In this case the suspension is well damped, because the shaft is still in brass sleeve lubricated by oil. The magnets are far enough and the field is static so they no not disturb the cartridge.
 
The stiffness (1/compliance) is constant as far as the magnetic field is homogenous. The force is inversely proportional with the compliance and the distance, just like in loudspeakers. The resonance will be determined by the compliance and the mass of the suspended equipment.

Actually I tried neodymium ring magnets for suspending the platter in my turntable. In this case the suspension is well damped, because the shaft is still in brass sleeve lubricated by oil. The magnets are far enough and the field is static so they no not disturb the cartridge.
Hi OSHiFiS!
I trying of make a magnetic suspension in a MS RX1500 VG, i tried before with a thorens but when i puted a magnetic ring (ceramic one) i found a force that atract the headshell and interact with the cartridge. I discovered to late the problem but now i looking for an a magnetic isolation with many sustances but at this time i couldn't find anything.
I will like to know how squematic of your magnetic suspension and wich you propose for isolate eficiently. The only i couldn't do is use bismut but next month i will go to Argentina (i came from there) and i found a place to get 50%purity of that diagmanetic element. Cu++, Al+++, Fe++, not work, sandwiches of many sustance, not work.
Distance i have 40mm under the platter and over the plinth.
Best Regards
Esteban Bikic
 
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