For those of you using springs or spring based devices, or thinking of it, here’s a heads up! You can get better isolation, at least on paper, by mass loading the springs as much as possible. Springs can be loaded to the point where the coils almost start to touch. This usually means compressing the springs about half their uncompressed height. On the other hand, depending how soft the springs are and how tall, you might need to observe center of gravity issues. So, keep additional mass COG as low as possible.
Since resonant frequency is a function of the square root of MASS if you can double the mass you can lower the resonant frequency by about 30%. Remember that the total spring rate in the equation for Fr is the number of springs x spring rate per spring. For springs, as a general rule, the way things work out is the best you can do is about 2 Hz. Even when you minimize the number of springs and maximize the mass. Which is actually very good, indeed. But you won’t be able to get down to 1 Hz without resorting to more uh, severe methods. Since a lot of seismic energy is in the region 0-2 Hz, the lower the better rule applies.
Of course how the component is interfaced to the top plate and how the top plate is interfaced to the floor or rack is something worth pursuing. And damping the top plate is another area for investigation.
Pop quiz - Anybody ever construct a double layer mass on spring platform?
Since resonant frequency is a function of the square root of MASS if you can double the mass you can lower the resonant frequency by about 30%. Remember that the total spring rate in the equation for Fr is the number of springs x spring rate per spring. For springs, as a general rule, the way things work out is the best you can do is about 2 Hz. Even when you minimize the number of springs and maximize the mass. Which is actually very good, indeed. But you won’t be able to get down to 1 Hz without resorting to more uh, severe methods. Since a lot of seismic energy is in the region 0-2 Hz, the lower the better rule applies.
Of course how the component is interfaced to the top plate and how the top plate is interfaced to the floor or rack is something worth pursuing. And damping the top plate is another area for investigation.
Pop quiz - Anybody ever construct a double layer mass on spring platform?
