Your choice of suspension material isn't quite right: It really needs to be elastic, stretchy. Thin bungie cords would be a way better choice. The trick is not to tighten the suspension too much or let it be too slack (which risks the HDD falling out).
The plastic cord that I use it quite elastic. Maybe not as much as bungie cord, but I would think elastic enough. And yes, I did experiment a bit how tight I should tie it. I made it quite lose. But I'll see if I can find bungie cord, and see if that improves things. As I said, seeking noises are completely gone. I copied a hundred gigabyte from one disk to another (and then deleting it), just because I enjoyed not hearing my disks rattle at all.
As for the "blue fill" recycled blue-jeans cotton batting, it is a fiberglass insulation alternative -- I used 8"x2 thick layers in my anechoic chamber. See -- http://www.silentpcreview.com/article876-page9.html
However, you're right that it too, does not really block noise, only absorbs it as it passes through, and the effectiveness gets much worse with decreasing frequency (below ~200Hz, its absorption falls dramatically).
Thanks for the link. I had missed that article. Impressive work.
I learned that the foam
does not do a lot of stopping noise going through. But now you are saying that also the cotton-based insulation doesn't work well ? I read that "ridig fiberglass plates" would be much better than the foam. And that cotton-based would be even better. But if it still block less than half the noise, maybe I shouldn't bother ?
Only one thing will block the noise -- walls of high mass/density.
One of my friends suggested that I should buy 2 boxes. Of slightly different size, and the biggest should fit in my cupboard. Then fill the space between them with sand. I'm not sure I like that idea. 1) it has the potential to become filthy, 2) getting my tubes/wires through the 2 boxes is not optimal. 3) I need to mess with a lid or door, where the hinges might become sound-bridges. 4) Will sand stop vibration-noise, or do I still need to suspend my pump ? A lot of work, for something that might not be effective.
Chances are, with a proper suspension of decently quiet HDDs, you will not need any acoustic foam to make them inaudible -- assuming a decent case.
I have a Fractal Design Arc Midi. It has not been designed to be quiet. (I think the R3 and R4 are for that). But with openings for fans, there is always room for noise to escape. I can't understand how one can claim a case is silent, when there are fans in it ? Even when the fans themselves don't make noise, but some component inside.
I might buy bitumen plates for noise dampening. And I have some of that foam still that I could put on top of the bitumen. That could maybe absorp some of the HDD spinning noise.
To contain the pump noise, I'd use something like a thick wall aluminum box to completely house it (with rubber gasket holes for the hoses & wiring), and float the pump in the box in a layer foam that will keep it from making direct contact with the metal box. The density of the foam should be chosen so it can stop mechanical vibration from getting into the box. Most foam also transfers some heat if it is not too thick/dense. Floating the whole encased pump assembly with elastic suspension will maximize the noise reduction.
Would foam be better than sand ? I guess 2 boxes with sand will be heavier, and are harder to hang in suspension.
My new SSD arrived this morning. Let's see if I can keep my HDDs spun down.
And hopefully my new fan controller will arrive tomorrow, so I can undervolt my pump.
If those things don't work, I will look at more drastic actions.
One other trick might be to buy a NAS, and put the 2 HDDs in there. The downside is, I see customer reviews claiming that their NASs do 60-25 MByte/sec. Old fashioned HDDs do 250-300 MBps, GbE is 125 MBps. So 25 MBps seems pretty slow. Not a problem when watching movies on my TV. But manipulating files and games around could take some time. (Copying 10GB takes 7 minutes. Painful when you were used to local storage).