Here is a short story. I have these nasty neighbours playing loud music almost every night. They are located in an adjacent building, so we are only separated by a thick wall, which carries over all low-pitch vibrations. The vibrating sensations in my head are unbearable and I cannot sleep properly. I have also exhausted all "legal" and "common sense" options in dealing with them, so please do not offer any advice on resolving such a situation. Do not mention ear plugs either, I had ear inflammation because of them. My question here is technical merely. For some time I have been thinking of building/using a sound wave device/speakers that could penetrate the wall and cause those neighbours discomfort. An example here would be a very loud, high frequency "mosquito" sound, say 17000 Hz. However from what I heard, such high frequency sound would not penetrate a thick wall. Basically I am looking for anything that could generate very unpleasant sound able to move through that wall. I would use it when they turn up their volume, so they realise that it is not worth it :-). Any suggestions would be greatly appreciated, I really wanna sleep more than 2 hours a night ! Thank you for help.

I certainly sympathize. What about those devices they use to get rid of bugs and other pests that uses a sound of some kind?

Is moving an option?

The problem there is that if you use a subwoofer to send back at them the low frequency sound they send to you when they are listening to their music then they probably won't even hear it. If it is that loud to you then imagine how loud it must be to them. All you would end up doing is introducing an even louder sound into your side.

From what I know is that the more dense the material the better sound travels through it. Things like Styrofoam make decent insulators against sound while a vacuum would be the best but of course how do you put up a vacuum space between you and your neighbor without spending a fortune? So some sort of foam would be good although it would not work as good as it would if up on their wall. Something is better than nothing right?

I really don't know enough about it but you may want to try looking up acoustics and the physics involved because their may be a way that with the right material, shaped the right way, to create a wall cover that could bounce the sound back to them.

Just some things to think about...

You said, "cause those neighbors discomfort" ...

That's perhaps borderline assault. I sympathize with your plight but come on ... moving is your best option. Carefully choose your next domicile with protection for your sensitive hearing in mind.

There are more than a few people studying the use of sound as a non-lethal weapon (crowd/insurgent control applications). Since any and all of their techniques are quite likely well beyond your reach I don't feel guilty recommending a google search. You might also take a look at the Mythbusters website as they had at least one segment dealing with such topics.

Could you argue that it is in some way self defense, rather than assault, as the noise is causing bodily harm of some sort?

Anyways, unless you can implant the device into their building, i don't think low frequencies sound waves would do much but irritate you along with them (but less to them). Now if your willing to bring yourself to a greater discomfort to give them a minor discomfort, you need more help than just finding a way to retaliate .

Now if you could find a way to introduce a frequency of 95GHz to them, that would shut them up real quick, but probably land you into some sort of hole never to see daylight again in some government facility , well or a military contract depending on how good your device is!

Best bet, set up some sound proofing in your house unfortunately. If they aren't breaking any sound bylaws, what can you do... Bake them a pie, buy them a six pack, i don't know.

Perhaps you should look up the inventions of Nikola Tesla. He used a mechanical oscillator that shook a whole building and part of the neighborhood. Perhaps you should look up people who are big fans of this inventor and like to tinker.

But beware...some stuff could be more lethal than you would really want.

Of course, you cold try this: No doubt these people stay up half the night. Why not wake them up early with your tunes or perhaps talk radio.

...or...get an authentic Indian drum and do drumming. I have a friend who has a drum of this sort. It is louder than any regular music and penetrates walls easily. (I am assuming that if your neighbors are allowed to keep everyone awake with noise that no one can come after you for doing it.)

I know you are thinking of a technological noise maker, but a primitive one may do just as well...like a high pitched whistle for example....

Thank you guys for your input. I am researching my options, also the ones you presented. Moving out is not an option, if I played them drums, I am sure that would make them even happier. Spending a fortune on isulation is not viable. They are the cause of the problem and they should pay, hehe. So, as funny as it sounds I would be happy to spend some cash in order to punish them, rather than a new home. Bullies all over the world should be made aware that there is a price to pay for their wrong doing. What do you think of the mentioned mosquito 17khz loud buzz ? I could simply buy an amplifier and play it from my PC, but before I do it, I need to know if the sound will travel through the wall.

High frequency sounds will not penetrate a concrete block or brick wall. The anti-mosquito thing wouldn't work even if they could, because it's outside of the normal range of human hearing (17kHz wouldn't do much to dissuade mosquitoes, from what I understand these systems operate more in the 30-40kHz range).
If you want to get back at them, I would suggest some other method, rather than simply competing with their stereo system (it would cost a bit of money to do so, if their music is loud enough for you to hear and be disturbed by). Try ordering several pizzas to their house from different restaurants every time they turn up the music. At first, they might think it's cool, but after the 200th or so anchovy pizza they're being expected to pay for, it'll get old. Make sure not to admit to anything, and make sure to block your phone number before placing the order, so as not to be traced.
If you insist on competing with them, I would recommend a very bassy album in a genre that's a polar opposite of what they play (for instance, if they play hip hop or rap, play death metal, if they play country music, play jazz) and putting it on whenever they put their own music on. You will end up suffering more because of it, but you will get your revenge. (I live in a predominantly mexican neighborhood, and since the neighbors like to hang around outside listening to loud mexican music and are good at turning it down before the cops arrive, I tend to play death metal on my car stereo until they get the hint. However, I don't mind extremely loud music, as long as it's music I like.)
Your best and most reasonable option is to approach them and explain your situation politely. If they don't care, you can invest in cheap soundproofing. The internet abounds with reasonable and expert advice on how to soundproof a wall on a budget, and if you're determined, you can achieve expert results for less than a hundred dollars, assuming the wall is about 8X16 or smaller.
If that's still not an option, purchase a pair of noise canceling headphones, and either wire the speaker wires through an amplifier or wear the headphones yourself. The former option might be more appealing, as you might be able to get enough volume to effect them, as well.

Expensive but .. see http://en.wikipedia.org/wiki/Active_noise_control.

A fun alternative might be to hire the loudest mobile PA within a hundred miles .. park up where you can't be seen .. announce (need the right voice for this) "This is God - turn the f******g volume down" and drive away rather smartly. Naturally they're going to rush out with all their knives and guns and stuff .. the good bit is that they're going to spend the next six months waiting for it to happen again. Maybe you like it .. maybe you don't.

-C2.

Perhaps use multiple nearby pay phones.

Take up learning to play the drums and buy a set.