Well, there's no getting around it; low frequencies travel through this building like poop through a duck. A cupboard door being closed in the other unit's kitchen is an audible thump in my bedroom.
I can filter out the higher-frequencies -- like talking -- with a somewhat noisy fan, but I can't think of anything to stop the fact that when one of my neighbours comes home at 10pm, makes herself some food, and takes a bath...well, I can hear (and FEEL) her thumping around until she retires to her room. Which may be anywhere from 11pm to 1am.
Right now this is keeping me awake.
What's my solution? Bear with me here, there's a lot of variables. And I want to make it clear that this is me "trying to understand and solve the problem," not "whining."
I can hardly tell people not to move around after 10pm; if I worked nights and somebody asked me not to open cupboards and doors when I got home...well, I'd think they were nuts. Though my neighbour could stand to be a bit more CAREFUL with her movements after 10pm -- pushing the cupboards shut instead of knocking them shut, for instance -- I don't want to suggest such a thing right now. It would seem like a demand or a lecture (unless I can find some way to speak with them long enough to "ease" the suggestion in, rather than just march over and say "stop it").
I don't think that BLOCKING the sounds is feasible; a big box fan might work (my old one is so rattly by now that I'll need to get it replaced), or maybe some other kind of polite noise-maker could cancel out the thumps. Structural soundproofing isn't something I can do without landlord initiative, and even if they would do it I think it's hopeless: the structure of the house itself is a conduit for these noises, it seems.
I could change my schedule. Normally I try to get to sleep by 9:30pm, and get up by 7am. I've spent a lifetime trying to figure out how to sleep properly, but I HAVE heard (and garnered some evidence) that people can manage just as well (if not better) with 6 hours of sleep. Though that might not be me.
Strangely, my last apartment suffered a different structural problem: the ceiling creaked horribly. I could hear every footstep in the apartment above me, and I can remember many late nights being unable to sleep -- or being woken up -- by the folks upstairs walking around late at night or (worse) having vigorous, regular sex.
But somehow THIS noise is affecting me more, either because it's a DIFFERENT sort of noise -- maybe it's vibrating my bed, slightly -- or because I'm not fully "at home" yet.
All of which forces me to acknowledge that I have a lower threshold for noise than some people do. For that reason I have no idea if THIS degree of noise is abnormal and therefore "something which MUST be stopped or fixed." This also means that I might be able to get used to the noise...and for what it's worth, my neighbours are so far SAINTS when it comes to making noise. I just wish they worked 9-5 like I do...
The other variable is blood sugar (as always). My blood sugar often rises as I'm sleeping, which happens to certain diabetics. If it rises (or lowers) to a certain point I become edgy, sensitive, and I have a lot of trouble sleeping. This is difficult because if I fall asleep at an ideal blood sugar, chances are my neighbour coming home will wake me up...at which point I'll have a higher blood sugar, and I'll need to lower it again before I can reach a good "sleep state." This is my problem right now: my neighbour's been silent for half an hour but I'm still "wound up." Not to mention I'm afraid to try to sleep, begin to drift off, and then be thumped awake again.
It's always good to have a plan, so here is mine. I'm going to just keep on and see how it goes. Chances are I'll get used to it eventually, the same way I (sort of) got used to the creaking ceiling. If this situation disrupts my life to the point where I'm a total wreck, well, I'm paying rent by the month so I can always find another place. Which would suck.
In the meantime, maybe I could get a foam pad for under the futon, to dull any vibrations that might be making it sound worse. Or try a box fan. Or earplugs. Or yoga!