Quote:
Originally Posted by Craig Sawyers
If it does not move to its unloaded position, you get the same result by using the ratio of cylinder pressure to atmospheric pressure. So if the cylinder pressure is 3 bar, the relevant ratio is B = 3 and hence the resonant frequency is about 0.3Hz. That will be quite high Q and hence legs have quite careful viscous damping using oil and orifices, which means that the legs start to operate (ie to attenuate) at about 1Hz.
It is more complicated than that, because they have to deal with horizontal excitation too, so the legs also have pendulum mechanisms too (also damped) to handle that.
|
I'm not sure about that, at least not in the terms I'm thinking of.
If we have some sort of air suspension system supporting a mass and the piston has some area and there is some pressure in the cylinder so the pressure times area balances the gravitational force of the mass.
If I move the pass up and down a little, the pressure in the cylinder changes due to the change in volume of the space the gas has to occupy. This creates a restoring force which acts to put the piston and mass back to its equilibrium resting position once I've stopped poking it. The proportional to deflection restoring force (for small deflections) and the mass create the classical mass-spring resonator and the resonant frequency is now set by the mass and the spring coefficient.
If I now connect or add a large air reservoir to the pressure side of the cylinder, and ump it all up to the same pressure as before. I have the same pressure, I have the same mass, I have the same piston area.
What has changed is that when I poke the mass and deflect it a little, I change the volume of the pressure side of the piston by the same amount, but due to the much greater connected volume the change in pressure is now far less, and that means the restoring force is far less and therefore the springiness is far more compliant. This drops the resonant frequency of the the system.
If I took the mass off of the piston and the cylinder was long enough, the piston would move far higher to its new equilibrium position than it would have before I added the air reservoir, because there is more air that needs to expand before the pressure comes down to the rest position.
The resonance is controlled not by the spring force, but by the slope of the force/deflection curve at the operating point.
I think we're just visualising different things in different terms.
It would be one heck of a preamp with air sprung valve sockets with say a 1Hz natural frequency and little dampers. Don't tell the audiophiles - they'd only argue over which gas sounds best.
David