Springs under turntable

Hello,
I was thinking of sharing the spreadsheet that I put together to design a spring with a targeted natural frequency with this group. You might already be doing it but just thought of sharing...

Item- Clearaudio Turntable

Total Load (3 Springs) = 23.79 lbs

Item No (Century Spring)-S942

Spring Rate (Lbs/Inch) = 2.75

Spring Rate (N/M) (k)= 612.94

Spring Outer Dia = 1.39 inch

Spring Wire Dia = 0.07 inch

Spring Total Coil = 5.75

Spring Free Length = 2.75 inch

Spring solid Height = 0.40 inch

Load (m)= 7.93 lbs

Spring height at the load 7.93 lbs = 0.48 inch

Spring Natural Frequency = 2.077 hz by using the below formula

Formula = 1/(2*Pi)*SqRt(k/m)

Excel Formula = =((0.5*(1/PI()))*SQRT(k/(CONVERT(m,”lbm","g")/1000)))

Another point that I wanted to highlight here is the importance of load and spring rate to get a spring natural frequency, something like 3hz. In this example, I needed to load each of the three springs to a compressed height of 0.48 inch leaving only (0.48-0.40) = 0.8 inch from the base to get a natural frequency of 2.1 hz. This also shows the degree of difficulty in arranging these springs under the turntable such that each one has a compressed height of only 0.8 inch from the base platform, something @mijostyn has pointed out earlier. 

Apologies for dumping a lot of numbers here but I thought this might be interesting to this audience.

Thanks.

Nice work Indranilsen, That is about as far as the Sota springs will compress before the chassis hits its stop. Remember the Sota subchassis hangs from its springs. This is the best picture I could find of it
https://hometheaterhifi.com/reviews/vinyl/turntables/sota-nova-turntable/.
If you hung a platform with springs you could put your turntable on it. If the springs themselves were hung from a threaded rod you could adjust them for turntable level and any mass configuration of the turntable.

This is why I use Delmonte Mandarin orange slices in water, in small cans, as my turntable isolation devices. I use three of them to support a slate slab containing a turntable chassis, either Denon DP80 or Lenco. I support the weight of the slate on the outer rim of the unopened can, and I support the base of the can at its center using a black diamond racing cone, away from the outer rim, so the outer rim never touches the shelf. The springiness comes from the flexing of the top of the can inside its stable outer structure. Someone gave me the black diamond racing cones, and I paid two dollars each for the cans of mandarin orange slices in water.

Mijo, I owned a Star Sapphire for 10 years, and I’ve had some experience with a Cosmos too. Based on my memory of these products only, I would have thought that the spring rate is certainly a bit higher than 3 Hz. In fact, I am now remembering that there was a modification to the springs that was performed by many owners, so as to reduce the spring rate. I can’t remember, but it had something to do with shimming the springs. Do you know anything about that?

Lewm, not at all but, people do funny things. Reducing the spring rate would be tough. You would have to replace all four springs with springs exactly the same size and length under tension. Some people may have added damping to the springs by stuffing them with foam. If you look at the link in my last post in the middle of that article is a plexiglass model of a Sota. The springs are hung from the top plate. Shims would just lower the sub chassis dropping the plater and tonearm relative to the motor.

Anyway, my resonance frequency is low enough that I can count it. With a record on it will take 7 bounces before it stops and I would have to say that it takes about 2 seconds but I have not tried to time it accurately. The idea is to get it below record warp frequency so they do not interact. Tonearm above, turntable below. I can play a severely warped record without difficulty.

The Sota's are not easy turntables to take apart and I would not want to risk damaging the wooden plinth.  IMHE the suspensions are tuned just fine as nothing in a normal environment bothers them. I have never felt the need to take one apart which is unusual for a guy who took his Divas apart to install new ribbons. 

Delmonte? During WW2 my deceased uncle made a fortune packing fruit which he sold to the military. That company was called the East Indies Fruit Packing Company. You know that company now as Delmonte. In the late 60's my uncle retired from his position as CEO and handed the Baton to his nephew, the nastiest SOB I have ever met. I banned Delmonte products until he passed. They do have the best Pineapples. In the mean while my uncle took his fortune and opened up Flagler Dog Track in Miami, FL and made another fortune. He gave at least 75% of it away mostly to educational institutions and Israel. In 1974 he started getting chest pains. His cardiologist begged him to go to the hospital. Instead,  he flew to LA for a meeting. At the end of the meeting he stood up and died on the spot. Age 60. I would think the spring rate of a Delmonte mandarin orange can would be just a little high:)