2mo ago

If I know the frequency and magnitude of a high pitched continuous sound, how can I calculate the potential effects of damping materials?

I have a small hard drive that is making a constant high pitched sound that is typical of the drive, and not very noticeable to the average person, but I have pain induced noise sensitivity. I am curious about how to calculate damping potential. As an initial guestimate, the frequency is very near to my maximum audible range and likely around 12kHz-16kHz. It is a little higher than the switch mode power supplies that I can also hear if it is dead silent in the room, although the drive is a higher amplitude. Addressing the noise with a solution is probably beyond the scope of anything I would actually do, but knowing how to solve it is far more interesting to me. (ELI15 )

17 comments

You might be overthinking this. Frequency is inverse of wavelength, so to answer your question, you need material with no gaps larger than the wavelength to block the sound.
The distance of the sound depends on the energy of the sound and your hearing. So imagine your drive is a tiny light bulb. Turn off the light in your room, wherever you see light, or reflection of light, you'll hear the noise.
My suggestions:
First is to cover your drawer opening with cloth, or foam and see if that reduces enough sound. I know this might over heat your drive.
If that doesnt work, mount the drive under your desk with velcro, or mount the drive that is not directly line-of-sight to your ears.
I don't think there is a way to block out all of the sound, especially at night when it's very quiet. I turn off all electronics in my bedroom at night, otherwise I can't sleep.

High pitch noise like from hard drives, typically in the 5 to 15k hz frequencies generally can be dampened quite a bit with pretty simple solutions like accoustic foam. Since it's probably not that loud you won't need much material to achieve a bit of reduction. Only thing I'd worry about is temperature management, keep an eye on it. Afaik there are also special desktop PC cases that are insulated, for like sound studios and such.

If it's stable, then could you create the opposite sound and cancel it out?
- I don't think so. The thing is on my laptop bed stand. So it is always in arm's reach and I don't have a controlled environment because I move around within the room. I was thinking more like some kind of specific sound damping material to line the interior of the box for the external HD but the thing is small.
  Two things here, the cover could be lined with something thin. Or I could shove it inside the box I made originally for my laptop PSU brick but had to mount the latest one underneath (mess of a cord visible on the other side of the HD). I'd need to do the new PSU plug differently to get the HD all the way into that box. Still all I can do is brute force an empirical damping solution. I can't even ballpark about material properties and sound in this space. It would be a handy abstract skill.
  
  I think my point is being missed.
  If you were to take two identical waves and line them up with each other, matching up the peaks and troughs, the two waves are said to be “in-phase,” which, when summed, results in an even larger wave (louder sound). But what happens if you delay one of the waves by exactly one-half wavelength, matching up the troughs with the peaks of the other like in the picture below?
  Imagine illustrating noise cancelling by adding two identical but opposite soundwaves.
  Source: https://www.soundguys.com/how-noise-cancelling-headphones-work-12380/

Absorption coefficient depends on material.
In your case, literally any enclosure at all will make a big difference. If you want to truly eliminate it, the most effective way would be to replace the drive.
- But is there a direct rule of thumb (or more) about the relationship between density, thickness, and frequency?

I would look up DIY sound dampening/absorption panels. The sound you're hearing isn't just from the source to your ear, it's also bouncing off everything in the room. If you make those surfaces "break up" the wave, they will be attenuated sufficiently by the time they reach your ear.
But also, as yourself if the materials and effort you go through to solve this is worth more than the cost of a different hard drive that doesn't make the noise.

17 comments