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I have a treadmill desk and my downstairs neighbour is complaining about the noise. Specifically the noise made by the impacts of my walking. Unfortunately the floor of my flat is not concrete but made of wooden beams topped with a laminate floor: not a lot of mass to absorb the impacts and not much dampening either. So, I have to do that myself. Ideally I'd have a big slab of marble and a length of open/closed cell foam of just the right density and dimension and would sandwich that underneath the treadmill. I don't have and couldn't carry a big slab of marble, so as a stand-in I'm going with a large wooden board as thick as they come (or can be glued together). Say a kitchen countertop. What I can't figure out is: How dense does the foam need to be?

Given

  • a treadmill with a weight $m_t = 26\mathrm{kg}$ that occupies an area $a = 8555\mathrm{cm^2}$ ($59\mathrm{cm} \times 145\mathrm{cm}$)
  • a human with a weight $m_h = 70\mathrm{kg}$ walking at a steady speed $v = 3 \mathrm{km/h}$ with decent shoes for runners
  • a wooden board with the dimensions of the treadmill used to evenly distribute the impacts across the foam
  • open or closed cell foam occupying the same area as the board / treadmill

Arrangement

  1. Human
  2. Treadmill
  3. Board
  4. Foam
  5. Floor

Unknowns

I don't know the force of my impacts caused by the walking nor how much the shoes mitigate.

Resources

Reducing 3D Printer Noise

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  • $\begingroup$ Have you got a specific type of foam in mind? Polysterene, PP foams would have different properties and ultimately behaviour at the same density. $\endgroup$
    – NMech
    Mar 3 at 10:35
  • $\begingroup$ @NMech Good point! No, I don't have any specific type of foam in mind. I don't know a thing about foam materials so I wouldn't know which one would be best for this. Strictly speaking it doesn't even have to be foam. An air mattress might work, too. But to limit the scope of this question I think it's good to stay with one material / family of materials. $\endgroup$
    – phdoerfler
    Mar 3 at 11:04
  • $\begingroup$ Interesting question. Maybe might try mounting the treadmill on a base that is a sandwitch of a 4x8 plywood board on 4 underinflated mountain bike inner tubes, perhaps repeated, for the low frequency damping, and strapped down with nylon webbing to keep it from falling apart. In addition, on the outside of the plywood, a layer of camping sleep mat or yoga mats might be a material for damping midrange acoustic frequencies $\endgroup$
    – Pete W
    Mar 3 at 16:04
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Its more the noise of the entire floor resonating with your jogging rhythm and vibrating as an echobox.

Even if you manage to soften half of the impact by a clever system of plywood and foam you delay the resonance by just a few steps.

Ideally you would need your treadmill in an enclosure on an expensive suspensions system.

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  • $\begingroup$ Yes, this is correct. The floor acting as a speaker is the problem. $\endgroup$
    – phdoerfler
    Mar 3 at 20:57
  • $\begingroup$ And, yes, I might need a lot of foam or a big air mattress or bicycle tires. And maybe a lot of plywood. I might even have to cast a slab of concrete in place. But I fail to see how it would be infeasible. Surely there has to be a way to calculate the necessary spring / dampening force and get some numbers out to know what ballpark of mass and springiness we're talking about. Then we know if it's impossible. $\endgroup$
    – phdoerfler
    Mar 3 at 21:03
  • $\begingroup$ You probably can't do much about the ~10Hz components (deep bass component from footsteps, and structure vibrations that can be felt, if applicable), but I think you could significantly reduce the 100-1000Hz components before they couple to the floor frame and resonate from there $\endgroup$
    – Pete W
    Mar 3 at 23:58
  • $\begingroup$ i jog endurance. put in 8 to 10 miles daily. my pace which is average is 5 miles per hour. appoximately 2 steps per second. unfortunately this is very close to natural frequency of common residental structures, or a hormonic of it. its really hard to insulate it. $\endgroup$
    – kamran
    Mar 4 at 0:12
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Your proposed arrangement will probably not be ideal.

putting a wooden board between the treadmill and the foam might make the board act as a speaker phone and make the noise more significant (in the room). This will be more evident if the mass of the board is small.

To give you a more intuitive example, think of taking a sheet of metal with certain weight and width (but different thickness) and vibrating it (across the thickness). As the thickness decreases (therefore mass also ) the noise will become much louder. There are some products that you can use for increased damping.

Additional problems you might encounter:

  • tilting of the board (if the foam is thick), when the center of gravity of man-treadmill changes.
  • if the board is not strong/stiff enough, having the treadmill on the board will probably create bend or break the board pretty quickly under daily use.
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  • $\begingroup$ Good points! Let me clarify: By "wooden board" I really mean: Anything stiff and heavy that is about the shape of a thick wooden board. Say a slab of marble or concrete or steel. However it somehow needs to get into my flat and sheer weight rules out a lot of materials. I assumed some sort of thick plywood or kitchen countertop would be a good compromise. I shall add that info to my question. $\endgroup$
    – phdoerfler
    Mar 3 at 13:03
  • $\begingroup$ Addressing the remainder of raised points in your answer: I already got a few small and stiff foam blocks underneath the treadmill (However, no additional slab of some stiff and dense material) and according to my downstairs neighbour the noise is "a little better". These foam blocks hold up very well to shifts in the centre of gravity. How would this be different with one large piece of foam + something heavy on top to distribute the load? $\endgroup$
    – phdoerfler
    Mar 3 at 13:15

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