Well, it's pretty obvious the springs for the Linn are the wrong springs. Because if they were the right springs the turntable would not be affected by footfalls. There is a very simple relationship between resonant frequency, mass and spring rate. Most likely the folks at Linn didn't get the memo.
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One problem I have with mag lev suspension is that the heavier the object isolated the more powerful the magnets required. But we know that magnetic fields are bad for the sound especially in proximity to low level signals. For that reason I'm out. Of course the other objection is the very slippery nature of the opposing magnets doing the levitating. It is impossible to stop the top plate from moving laterally without putting uh stops in. |
As a designer of isolation devices since Jesus was a Boy Scout I would just say the spring rate in pounds per inch is related to the resonant frequency of the iso system by the equation, system resonant frequency Fr equals the square root of (total) spring rate over total mass. So the more springs employed the higher the total spring rate (the stiffer the suspension) and the higher the system resonant frequency. The way I obtained extremely low resonant frequency for my sub Hertz platform was use only one spring. Whaaaaat? Most spring systems are too stiff to be effective dealing with extremely low frequency vibrations that are the issue, the ones produced by footfall, traffic, the speaker feedback, Earth crust motion. Even iso systems that provide Fr of say 3Hz are not really that effective when it comes to dealing with extremely low frequencies since the iso system acts like a mechanical low pass filter and won’t attenuate very effectively much until the frequency of vibration reaches say 15 or 20 Hz. How to easily measure the Fr of the turntable suspension. Push up and down on the (suspended) turntable and time the motion with a stopwatch to obtain cycles per second. 3 Hz is a relatively slow undulating motion. A more rapid motion will be up around 8 Hz or whatever, which is too high to be effective against very low frequencies.
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Of course the spring can be an air spring, air being a compressible fluid, no? And designed just like steel compression springs to have a certain spring rate, which one selects for the load under consideration. Did I forget to mention my sub Hertz iso stand of yore was an air spring design? Of course, like everything else air spring designs are complicated by internal friction and damping. Some air springs have too much friction and or internal damping. And my single spring "Unipivot" Nimbus platform achieved 0.5 Hz resonance frequency in several directions. The Nimbus was also the only iso stand with six - count ’em! - directions of isolation.
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In fluid mechanics we consider air a compressible fluid. This is not to say it's a liquid.
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Frequencies above the resonant frequency get attenuated at a rate determined by the low pass filter so that if the resonant frequency is 3 Hz the effectiveness of isolation at 5 Hz is very poor say 5-10% but at 20 Hz the effectiveness is up around 95%. The iso system acts like a classic mass-on-spring mechanical low pass filter. |
You said, "Gases are compressible, too." I Never said they weren’t. Sheesh! Never said air is not a gas, either. Furthermore, I said air is a fluid, not a liquid. Hel-looo! Obviously liquids are not compressible, at least not generally speaking.
Education is what’s left after you forgot what you learned in school.
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Geoffkait
You said, "Gases are compressible, too." I Never said they weren’t. Sheesh! Never said air is not a gas, either.
Furthermore, I said air is a fluid, not a liquid. Hel-looo!
Obviously liquids are not compressible, at least not generally speaking.
google is my friend.
A fluid is any substance in which the molecules are free to flow. This includes both gases and liquids.
A liquid is any substance in which molecules are free to flow, and volume is fixed or nearly fixed. Liquids are a subset of fluids.
Thanks for validating what I said. So getting back to the the air spring device for a second it acts like a spring because air is compressible and the air inside the airspring is under considerable pressure, that pressure a function of the airspring and the load. I used one of my Nimbus platforms under my Very heavy Maplenoll turntable, so with the ballast (100 lb) plus the mass of the Maplenoll the air spring had to be pumped up to 80 lbs of pressure.
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- The subwoofer puts out what maybe 20Hz if you’re lucky. So the iso system doesn’t actually have to be too heroic for subwoofers. The resonant frequency of the iso system for the sub would only have to be what about 8 or 10 Hz to be effective at 20Hz and above? The idea of course is to prevent subwoofer cabinet resonance to feed back to the rest of the system via the floor. The Super Stiff Springs will provide between 2 and 4 Hz resonant frequency for the isolating system depending on total mass on springs. So, let’s say your subwoofer weighs 100 lbs. For the lowest resonant frequency of the system you would use three Super Stiff Springs but since the subwoofer’s lowest frequencies aren’t really an issue - as they are for components when seismic vibrations are involved - four springs are recommended under the subwoofer for stability. You still have to isolate the rest of the components from seismic, subways, footfall and tap, i.e., all sources of structureborne vibration. But by isolating the sub you eliminate one big contributor to structural vibration in the room.
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"Is there any TURNTABLE out there where I wouldn’t be able to hear the unintended taps, touches and bumps on the rack and sound/vibrations from my subwoofer?
Cheapest you can recommend please?"
For suspended turntables the reason vibrations like footfalls and other vibrations are audible is because the turntable’s suspension’s resonant frequency is not low enough to block or attenuate them. If the turntable is unsuspended it should be placed on an isolation stand of good design. For suspended turntables with issues remove the suspension and place the turntable on an isolation system of appropriate design. For turntables like Verdier and VPI and Raven and other big heavy turntables one need look no further than my new Super Stiff Springs, which are designed to isolate and support just about any heavy object under the sun. Just the ticket for subwoofers, heavy turntables and heavy amps; minimum weight 75-100 lb. For things like CD players, headphone amps, preamps and other moderate weight components I have a different softer spring, the Cryo Baby Promethean Mini Isolator, cryogenically treated high carbon steel compression springs.
Geoff Kait
Machina Dynamica |
"Every low level signal phono cartridge consists of key components: the stylus, cantilever, MAGNETS, coils and body. What are we going to now GK......you better go tell every cartridge maker about this."
Uh, it’s the size/strength of the magnetic field the mag lev systems produce that’s the issue. And the cartridge is in close proximity to the Verdier magnets, that’s the problem. Hel-loo! I’m not concerned about the Earth’s magnetic field any more than the cartridge magnetic field for that reason. Why do we have demagnetizers for LPs but not for the mag lev magnets? ;-) |
It would be a good idea to isolate both the subwoofer and the turntable and all components really. The attenuation of passive iso systems is around 6 dB per octave. But you’re right, the subwoofer’s lowest frequency will be almost entirely attenuated by the turntable’s iso system, assuming a 3 or 4 Hz iso system that’s 99% effective by the time you get up to 20 Hz. The most aggregious frequencies for the turntable are circa 10-12 Hz since they would excite the natural frequencies of the tonearm and cartridge.
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