Nobsound springs - load range

@hm9001 appreciate the confirmation. Perhaps the springs in my Nobsounds are different, which is certainly weird if that’s the case. Or perhaps there is error in my calculations. My amp weighs 28.4 kg in the spec sheet, and it takes a total of 18 springs to achieve 50% compression (~7mm gap). 28.4kg ÷ 18 = 1.6kg per spring. The gap with 1 spring and 1.6kg load is ~7mm in my system.

Ignoring the discrepancies in the compression of the springs, I presume ~50% compression of the springs is the sweet spot. Perhaps not for all systems as some have settled with 1-2mm gap (>90% compression). The type of component may be a factor too ie. DAC or CD players requiring higher spring compression while amps requiring lower compression, an assumption on my part.

I’ll be testing the 2nd set of Nobsound on the DAC and another pre/power amps soon to find out myself.

The Rate I calculated for @hm9000 was right at 20lb/inch of travel for the spring measured.

Based on your specs, @ryder I calculate about 12.6lbs per one inch travel for the Rate of Compression.

As I understand it, so long as you are in the travel range (not fully compressed) then no matter how large the gap is, the force to move the object further remains the same or constant. I'd guess leave it in the middle but no one seems to have any idea why. Can the 'different audible results' be identified other than 'pre-knowing' how many springs are being used...  

I'd still love a thought on best Rate of spring to use. I ordered 100 springs .75" long with a 9.3lb/inch compression rate. These will allow a lot more travel of the component (or more soft 'floating'). 

Of course I do not know whether one wants one's equipment on a very stiff, barely springy bed, or on a highly springy and very flexible bed (assuming stability). This is the question I'd love someone to weigh in on with knowledge of resonances.

Is there any difference in spring tension between silver or blue end caps

@musicaddict I try to put in some physics about spring mass systems (have to dig a little since this is long ago since I had to deal with that in my engineering study).

A spring extends or contracts in a linear relation with the force you are applying, or the other way round, the force F the spring excerts is proportional to the distance x that you are forcing the spring from its neutral (unloaded) position:

F = kx , where k is the spring constant. Your assumption that the force stays the same is wrong, the force gets higher the more you compress the spring. That is the reason why it settles in at a compression that depends on the mass you put on top.

From the formula above I can calculate k for my springs: k = F/x. Putting 2.5kg and 7mm gives me:  k = 3500 kg/s^2 (sorry for international units, but as continental European I cannot get used to imperial ;-)

Now let's calculate the resonance frequency, it is given by formula

f = 1/2Pi  sqrt(k/m), where m is the mass you put on the spring. You can see that for the same spring (or amount of springs), the frequency gets lower with higher mass. At the same time if you put two springs in parallel, you double the effective spring constant, and, with the same mass, increase the resonance frequency.

Putting the values for my DAC and spring configuration in the equation (mass ~3kg per spring), I get a resonance frequency of a little more than 5Hz, which is about what I would estimate when exciting the DAC and watching it swing.

Which resonance frequency does one want to get? The springs should decouple/isolate the component from its base, so that no vibrations are transmitted either way. The spring mass is a low pass system, it decouples above the resonance frequency, but kind of transmits vibrations below. What you want to avoid is transmitting vibrations for audio frequencies, so the resonance frequency should be below the audio band.

@hm9001, I think we agree but that I did not state it clearly enough. If a single spring has a 4kg rate per 4cm, then from the resting point of a 1kg wt at 1cm, it would take another 1kg of weight to depress 1 more cm additional. It's what I have heard referred to as a 'constant rate' compression spring.

(Different is a 'progressive rate spring' where the rate changes, and increases as you depress. A common example was fork spring replacements in motorcycles for a nicer ride.)

Thanks very much for the above info on frequencies. It makes sense and I will work to further digest the resonant frequency issue. This sure gets me started. It will be interesting, after I do the math conversion to see where the 9.3 lb springs may get me or not.  Thanks again.