Specifying a Spring

[5v333]

Lb/inch = mass/length
While k = mass x gravity / length
They left out the acceleration due to gravity for some reason.
This and not using units from si system seems strange/stubborn.
The SI system is like the greatest gift that man gave to the gods.

I think the big diff between springs and sorbothane is that sorbo has a very high damping coefficient. But springs are cool

 

[5v333]

Paul i hope you have fun from some experimenting and hopefully you do some kind of measurments. Please Come back with your results, pics and thoughts.

 

[Gold]

Paul i hope you have fun from some experimenting and hopefully you do some kind of measurments. Please Come back with your results, pics and thoughts.

This is two or three projects down the line. It might be a year or so but I’ll get to it.

I don’t know if I can make credible measurements. I have no experience with accelerometers and making measurements with them. I can jump up and down and look at audio meters.

 

[ccaudle]

Lb/inch = mass/length
While k = mass x gravity / length
They left out the acceleration due to gravity for some reason.

Maybe the abbreviation is wrong, and it really should have been lbf, i.e. pound-force, 4.45 newtons. I don't know if that is the most likely explanation, or if it really is pound (mass)/length, and so you have to convert to appropriate units to find the spring constant in force/length in metric. Because of the ambiguity with English measurements I guess you would have to measure for yourself and confirm.

 

[abbey road d enfer]

They left out the acceleration due to gravity for some reason.

I guess it's because lb is a unit for both mass and weight.
It used to be the case in the old MKSA system (Meter, Kilogram, Second, Ampere), where a mass of one kilogram exerted a downward force (weight) of one kilogram-force, but was correct only for a specific gravity of 9.81m/s².

 

[5v333]

I just wrote and asked them.

 

[5v333]

First answer was a cut/paste from their website.

Then i got this with an example:

"The only information we have is that the rate is lbs/in. For the .19" length spring (9657K236) the rate is 14.5 lbs/in (14.5 pounds to compress this spring 1 inch). The maximum load for this same spring is 1.07 lbs and this will make the compressed length of the spring .12" (because the spring is only .19" in overall length).

We do not know or understand this to be calculated any other way or with any other unit. "

 

[Gold]

First answer was a cut/paste from their website.

Then i got this with an example:

"The only information we have is that the rate is lbs/in. For the .19" length spring (9657K236) the rate is 14.5 lbs/in (14.5 pounds to compress this spring 1 inch). The maximum load for this same spring is 1.07 lbs and this will make the compressed length of the spring .12" (because the spring is only .19" in overall length).

We do not know or understand this to be calculated any other way or with any other unit. "

That might not be a satisfying answer if you know the math. For my pea brain it simplifies things.

 

[5v333]

Knowing what is what gives us the ability to do the math.

 

[ccaudle]

That might not be a satisfying answer if you know the math. For my pea brain it simplifies things.

How will you go from that information to determining the resonance frequency and Q?
What frequency range do you want to begin isolation? Do you have a way to verify whether the isolation platform makes things better or worse?

I just noticed in your first or second post in the thread you wrote "they did the engineering work" but it was not really clear who "they" referred to. Is this exercise because you need to buy springs at McMaster-Carr, or you already bought springs from somewhere else, that place did the engineering work to determine which springs to sell you, and now you are trying to work backwards to determine how they decided which springs to sell you?

 

[abbey road d enfer]

How will you go from that information to determining the resonance frequency and Q?
What frequency range do you want to begin isolation? Do you have a way to verify whether the isolation platform makes things better or worse?

I just noticed in your first or second post in the thread you wrote "they did the engineering work" but it was not really clear who "they" referred to. Is this exercise because you need to buy springs at McMaster-Carr, or you already bought springs from somewhere else, that place did the engineering work to determine which springs to sell you, and now you are trying to work backwards to determine how they decided which springs to sell you?

Indeed I have serious doubts about the capability of the spring supplier to oversee the whole evaluation process.
In order to make it right, a solid understanding of tone arm/cartridge is necessary.
Ideally, the resonance frequency and amplitude should be known.
The elastic suspension is a LPF, where the spring is the inductor, the total suspended mass is the capacitor, and some king of solid or liquid friction the resistor.
The input of the filter is the displacement due to noise or schocks; it is variable, could be a permanent sinewave or a step/pulse.
The lower the resultant corner frequency, the higher the attenuation. That would suggest using a very heavu cradle and very soft springs, but that would be impractical since it could result in large displacements not compatible with the space limitations.
It is essential that the resonant frequency of the suspension be significantly lower than the tonearm/cartridge resonance, which is usually about 7-12Hz. IINM, Paul mentioned less than 1Hz, which is about 3 octaves below the tonearm/cartridge resonance, which would result in about 36dB attenuation of this crucial band, eve, if the damping is not very ggod.
Now, I believe the supplier, given just a few elements, like corner fequency and suspended mass (which he would probably translate as load ), should be capable of giving a plausible answer.

 

[5v333]

I think inductance relates to mass, capacitance relates to 1/k and yes, resistance relates to the damping coff.

 

[5v333]

Angular velocity gives:

 

[Gold]

How will you go from that information to determining the resonance frequency and Q?
What frequency range do you want to begin isolation? Do you have a way to verify whether the isolation platform makes things better or worse?

I’m asking about these springs to design a turntable QC/transfer cart. I don’t have a way to measure and publish results. I’ve done some reading on accelerometer measurements and like most things you have to know what you are doing to get accurate and repeatable results. I don’t think it would be a good use of my time and money to do good accelerometer measurements.

I just noticed in your first or second post in the thread you wrote "they did the engineering work" but it was not really clear who "they" referred to.

That was in reference to the inertia base for my lathe. I started a separate thread for that. I bought spring isolators from a company that makes industrial vibration isolation and seismic construction products.

Is this exercise because you need to buy springs at McMaster-Carr, or you already bought springs from somewhere else, that place did the engineering work to determine which springs to sell you, and now you are trying to work backwards to determine how they decided which springs to sell you?

No. I have an idea for a spring isolated turntable plinth. The McMaster springs are cheap so its not necessary to get it right the first time. Hopefully it will work but the isolation properties aren’t the only criteria that will determine success. It also has to be ergonomically pleasing. Since its a QC station it can’t feel like the plinth is moving around too much.

i think I can come up with some methods to test the isolation properties that will satisfy me. I can record tones on a lacquer to check tonearm resonance. I can jump up and down for impact isolation. I can record unmodulated groove and measure the results.