Stressful noise from neighbors
Unwanted music, especially in the very low (/ bass) frequencies, is stressful because its beats disrupt the rhythms of the brain and heart (because the music beats have a periodicity similar to the heart beat), of the activity that people are focused on (including relaxing). Music has about one beat at every second, which means that during a few hours of listening there are many thousands of them. By its very design, a (very low frequency) beat is a very rapid compression of air which is meant to whip the air. When exposed to unwanted music, people can't think normally.
Normally, sound only affects the eardrum and is therefore heard by people. If the sound's power is high enough, it can also affect the rest of the body and will be felt. Very low frequency sounds, like those from music bass, even at a low perceived intensity, both affect the eardrum and are felt (like hits) by the entire body.
Tiny science lesson: A wave (electromagnetic, sound or tsunami) is a disturbance that carries energy without transporting matter, and disturbs the matter it interacts with. Waves can cause resonance inside the objects they interact with, resonance which amplifies the effect of the waves inside the objects. Mechanical waves, like sound, travel only through matter (including gases like air), disturbing it but not carrying it with them. There is no sound particle and yet you can still hear sound and it can still rip your eardrum or even clothes apart given enough power. The smaller the frequency of a wave is, the larger its wave length is, and the less it is absorbed by obstacles; this is true for both sound and electromagnetic waves.
Very low frequency sounds are not absorbed by walls, they make the walls vibrate and go further right through them with virtually no attenuation. Medium and high frequency sounds are easily absorbed by objects (like walls), so they don't normally go further (unless they have enough power). Also, the bass has a much higher power than the satellite speakers because people are less sensitive to very low frequencies (so more power is required to be heard). Moreover, the music beats generated by a subwoofer are produced with the peak power of the subwoofer; as an example, the average room-filling satellite speakers pair has an RMS of 40 W, while a subwoofer's peak power is 500...1'000 W. However, objects (like walls) don't have sensitivity, so they are affected by the entire power of the sound. However, objects (like walls) don't have sensitivity, so they are affected by the entire power of the sound.
Music bass (produced by a subwoofer) is a pulsating very low frequency sound. It's a repetition of beats that form shock waves which feel like a hammer hitting the body at every second. The very low frequency sound has the capacity to make heavy objects (like walls), not just air, vibrate, while its pulsating pattern has the capacity to make objects pulsate with the beats of the music. In the same way, bass makes the internal organs pulsate, starting with the most delicate part, the brain, causing distress of an intensity that depends on the intensity and duration of the bass. People can't think normally at such times.
Unwanted music beats, especially in the very low (/ bass) frequencies, have an effect similar to the Chinese water torture, where the beat is the water drop and the need to stay in the home (to sleep, rest or perform various activities) is the restraints.
The long-term physiological effects of bass include lack of energy and of will to do things, high blood pressure, heart fluttering (which feels like a butterfly's touch), stomach and esophagus burning sensations, low libido.
A radio set can't normally generate low frequencies, which is why it sounds tiny / thin. It's unlikely for a radio set to be heard by neighbors, unless its volume is very high or the walls are very thin. But the more power the speakers can give to low and very low frequencies (that music beats are made of), the more stressful the percussions of the beats get.
Silence promotes brain development. This is because silence frees the brain from being busy handling external situations, frees it for introspection, allowing it to follow its own rhythm.
Why is bass felt whereas "normal" sound heard?
Bass beats are shockwaves with a period of about 1 second, which pass through the walls, forming wall-sized waves that hit the people on the other side, and are felt (not just heard) as percussions / impacts / shock waves, just like a firing cannon is felt. Beats literally feel like someone is hitting you every second. It feels like being inside the subwoofer.
The very low frequencies of the bass are not absorbed by walls, they are actually amplified by walls through resonance. The walls and the body resonate at very low frequencies (those from bass), and this amplifies the power of the waves.
High frequencies are absorbed by walls much easier, so they are absorbed before they reach the other side. For example, for each doubling of the frequency, a brick wall provides more sound insulation with about 5 dB; for each halving of the frequency, the wall provides less sound insulation with about 5 dB.
The human ear is much less sensitive to low frequencies than to high frequencies, so a subwoofer's volume (= output power) is increased much more than the volume of the satellite speakers. Moreover, the music beats generated by a subwoofer are produced with the peak power of the subwoofer; as an example, the average room-filling satellite speaker has an RMS of 20 W, while a subwoofer's peak power is 500...1'000 W. However, objects (like walls) don't have sensitivity, so they are affected by the entire power of the sound. This means that the air pressure created by a subwoofer (which generates the audible low frequencies of bass) is much higher than that created by the satellite speakers (which generate the audible high frequencies). Satellite speakers can also produce very low frequencies, in particular those that have a bass knob.
When you feel the music / bass, so you don't simply hear it, the inside of the body (starting with the most sensitive part, the brain) is literally compressed by the music beats. When these beats are unwanted and they happen for hours, it's torture. If a very low frequency sound is not pulsating (= has no beats), it's perceived as a pressure wave (= hum) instead of a beat.
Feeling the bass is an indication that every beat makes the internal organs pulsate, not just the eardrums.
Sound patterns make sound perception very different. The difference between sound in general and bass beats, which is a pulsating very low frequency sound, is like the difference between speech (which is called airborne noise) and hitting a wall (with a hammer, or even a hand; which is called impact noise), or between a hammer pressing on a wall and hitting the wall. In short, the difference is that an impact noise is a shockwave during which the noise is produced in a very short timeframe; the fast alternation between silence-noise-silence can be stressful to people. Bass is a shockwave which hits walls like a hammer, at every second / beat, making them pulsate with the beats of the music. It is virtually unstopped by walls. It has the same effect on the internal organs, starting with the most sensitive part, the brain.
When trying to find out from where sound is coming, especially in the form of low volume pulsations without a clear cause, be aware that simply listening from inside of your home is pointless. Sound, especially bass, can appear to come from one place but actually comes from the opposite direction. To find out the source, you have to listen to doors because they have the lowest sound insulation.
If you ever feel the need to ask a neighbor to turn the music down, instead of this, depending on your situation, you should tell the neighbor any of the following:
Don't ask the neighbor to turn down the music. If you do, you'll likely still hear it and you will have to ask again and again until you can't hear anymore.
If the neighbor only turns the volume down, you can try again by saying:
Most subwoofers which come with satellite speakers can't be turned off independently from the satellites. Even if the subwoofer's volume is turned to the minimum, you would still feel the bass. Some satellite speakers, from audio systems that come without a subwoofer, can also can generate bass, although its frequency is not as low as a subwoofer's.
If the neighbor has a habit of slamming doors, try this:
If you argue with the noisy neighbor, he will continue making noise. Don't tell a noisy neighbor that you know the law; some people feel threatened by the law.
Instead of talking to the noisy neighbor, you could print (one of) the above bullets and, if you live in an apartment building, you could try to display it where everyone can see it (you need the approval of the home owner association), or you could put a printed copy in the mailbox of each (nearby) neighbor.
During your conversations, some neighbors might start defending themselves with fallacious arguments. People use fallacious arguments in order to pretend that they are the victim of that situation.
Here are possible answers to some fallacious arguments.
I can do what I want on my property.
Not if you're hurting other people.
I can't even flush the toilet because it disturbs you.
Flushing the toilet takes a few seconds of low volume noise that has no beats or bass. Music has beats which feel like a hammer for hours, with a beat at every second.
I can't make any noise because of you.
I am complaining about impact noises which can be avoided, noises which feel like a hammer is hitting me. Everyday household noises are rare, random and can't be avoided, so I'm not complaining about them.
For example, the beats from loud music, especially the bass (generated by a subwoofer), make the walls pulsate and feel like a hammer is hitting me every second.
This way you can say that any sound bothers you.
Most sounds (in a home) don't have a beat every second, and don't make the walls pulsate for hours. Also, you can avoid using a subwoofer, you can keep the music volume at the level of a normal conversation, and you can use (wireless) headphones, but other sounds (like cleaning or renovating) can't be avoided.
Why don't you complain when people renovate their home and bang with the hammer all day long?
Because there is a construction law which makes it explicitly legal to build and renovate a home. Also, the noise made during construction / renovation can't be avoided, and people do these things only once every few decades.
Why don't complain to other people about their noise?
I did but you didn't see me doing it.
I am stressed and I need to relax.
Everybody has problems, everybody is stressed, but most people don't hurt others.
I listen to music only once a year.
If everyone around would do the same, we would listen to unwanted music every week / day. Please do not use a subwoofer and keep the music volume at the level of a normal conversation, or use (wireless) headphones.
I will turn the music down.
If the subwoofer has power, it will make the walls pulsate even at the lowest volume because the very low frequencies of the bass are not absorbed by walls, they are actually amplified by walls through resonance. Please do not use a subwoofer and keep the music volume at the level of a normal conversation, or use (wireless) headphones.
You have a problem. You are old.
Okay, I have a problem. That doesn't give you the right to make me suffer.
Let's be good neighbors.
Sure. When someone tells you that you're doing an action which is directly hurting them, you should stop doing it (regardless of what the law says).
Is that a threat?
Using the law is not a threat, it's a way to help you understand that you are hurting others and you should stop. Doing illegal things would be a threat.
This is life in an apartment building.
Life is made by the choices of people. Since this noise can be avoided, you can choose to make life quieter or noisier.
Studies show that music has beneficial health effects.
Those studies are performed on people who are willing to listen to (specific types of) music, and listen in the same room as the speakers, not through a wall that's vibrating. I want to listen to music when I feel the need, but now I'm forced to listen to the vibrating walls, and this feels like a hammer is hitting me every second.
Is there a right to have quiet? What about a right to listen to music?
Most likely you'll not find any law around the world that explicitly gives people the right to either have quiet or listen to music (specifically, to disturb other people's quiet with music). In the absence of something explicit, how is a right established?
Generally, people believe that they have a right to anything they like to do (and is not expressly illegal). In legal language there is a subtlety which escapes colloquial language. When an action is not expressly forbidden it means that it's not expressly illegal, so it's possible, but it's not expressly legal either. This means that listening to music isn't necessarily a right.
A right may be expressly given by a law. For example, construction law gives the right (perhaps based on a permit) to build and renovate, while a permit which is issued by the city hall can give the right to hold a public music concert.
(Even someone who has a permit to make noise on a regular basis may be fined, or have the permit revoked, especially if the noise breaks environmental laws.)
It's possible to argue that the right to listen to music exists because of the Universal Declaration of Human Rights (UDHR). Specifically, article 24 states "Everyone has the right to rest and leisure". The word "rest" could mean "quiet", while "leisure" could mean "listen to music". The critical distinction between these potentially conflicting rights is that the effects of Alice exercising her right to listen to music enter Bob's property and actively obstruct his right to have quiet, and may actively degrade his health (see Studies).
In a legal system where Alice's rights must respect Bob's rights (article 29.2 from UDHR), this means that Alice is legally responsible for the direct degradation of Bob's health. To make a parallel, some people may consider beating other people to be leisure (and therefore a right), but because this action directly degrades the health of the beaten, it must be (and is) illegal.
A right may also arise from custom. For example, because most people make some form of household noise during cleaning and other activities, and listen to radios and TVs (which are usually not enhanced by subwoofers), these actions become a right. However, few people make so much noise that it disturbs their neighbors, so it's customary to have a rather quiet environment instead of a very noisy one.
When does sound / music become a disturbance? What should the law say (but usually doesn't)? Disturbing sound is sound that's produced by an activity that can be avoided or can be performed so that it doesn't produce sound, with reasonable financial costs for most people, when any component of the sound is perceptible enough to make it difficult for someone to relax, and when there is no law which makes the activity explicitly legal. Sound components can be: volume / intensity, periodicity of beats (especially around 1 second), low and very low frequency beats.
What happens when a neighbor disturbs you with music? You become unable to rest, to think, to perform activities that require mental concentration, and directly degrades your health (see Studies). If you were to leave your home in order to get away from the noise, you would become unable to use your property. Making someone unable to use their property is illegal.
People who listen to music do it for hours, whereas various household activities which may cause disturbing noises last for seconds or minutes, have no beats and don't make the walls pulsate. Flushing a toilet takes a few seconds, but think about flushing it thousands of times, one after another. That's what the beats of music do, every second, thousands of times, while the subwoofer makes the walls pulsate during this time. Home renovation does involve powerful noises, but one family does this only once every few decades (maybe years, for smaller renovations).
People who want to listen to music at a volume higher than that of a normal conversation could use (wireless) headphones. This would let everyone enjoy either quiet or high volume music, without obstructing each other's right.
What can you do if you have a noisy neighbor?
First, you might want to talk to the noisy neighbor, maybe he'll stop. If not, check if the noisy neighbor rents the place, and if so, try complaining to the owner. Next, try calling the police to see if their intervention can stop the noise; maybe even make a written complaint (perhaps signed by more neighbors).
If the problem isn't solved, search for laws that penalize the people who make disturbing noise. You may want to check the public disturbance law, or start here. Some governments have extensive understanding and protection of people against noise, such as UK (see Noise policy statement for England), while others might have none.
Then, once you know your rights (with approximation), go to a lawyer to see what can be done through the legal system. Ask the lawyer about:
First, try to obtain an injunction which expressly forbids the neighbor to disturb you with music. The injunction informs the neighbor, in a legally authoritative way, what your and his legal rights are. If the neighbor breaks the injunction and you prove this with witnesses, like police or other neighbors, the punishment will be more than a small fine. There were cases of people who were sent to jail for breaking an injunction order that forbade them to disturb their neighbors with music.
If you own the home, you could try to sell it and if the buyers refuse to buy because they don't want to live in a noisy place, you can sue the noisy neighbor for devaluation of property or material loss, in order to recover the price (difference).
If selling your home is not an option (because you could end up in the same situation), you could try to rent it. If the renters leave because of the neighbor's music, or if the renting agency blacklists your home from being rentable, you can sue the neighbor for loss of income (for example, to be paid monthly every time a renter leaves before the end of a month because of the music).
The lawyer should be able guide you through the process of choosing witnesses and, possibly, how to get medical evidence of the noise's effect on your health. Witnesses could be other neighbors, previous owners or renters of the home, potential buyers and renters, and the real estate agency that's trying to sell your home.
The lawsuit is not conditioned by the existence of a public disturbance law. Besides, you can't (normally) sue someone based on a law whose punishment is only a small fine.
A lawsuit is a long, expensive and complicated procedure. But, maybe the idea of a lawsuit is enough for the noisy neighbor to think at the consequences and stop.
Before a lawsuit, you should make sure to inform the neighbor, in a legally provable manner (like mediation), that you suffer because of his noise. This way, the noise that the neighbor makes after being informed becomes intentional, something which will have impact in a lawsuit.
Alternatively, you could try to sue that neighbor for causing extreme stress. In this case, you will likely have to prove that music that comes through walls, bass in particular, degrades your health. For this you will likely have to provide the court a medical evidence, like a medical certificate, regarding the effects of that kind of noise. You could start by reading this.
The noisy neighbor might argue that there are no studies which show that noise degrades people's health, and that there is no known mechanism through which noise would have such an effect. While such studies would make your case easy, they are not necessary. You don't have to prove what the noisy neighbor is arguing for.
You should argue that you are the one suing the neighbor for the effect the noise has on you, not on the general population, not on the subjects of a study. Whatever the trigger mechanism is, physical or psychological, the neighbor's music has physical effects on your body. Medical evidence can prove that once music starts, your body responds as if it's under extreme stress.
Psychological evidence isn't very useful because people react differently when subjected to noise. Some people are less sensitive and are not affected, some people can cope with the stress, some people become depressed, and some people handle the stress for a while until they snap and become instantly violent.
If you decide to sue for torture, the defense might claim that since there is no permanent (physical or mental) damage then it can't be called torture. Torture doesn't require permanent damage, it requires pain to be inflicted; an example is torture with electrical shocks.
To get the medical evidence, you will have to reproduce the noisy conditions (like music coming through walls) in a controlled environment, and have medical doctors measure various biological characteristics, like pulse, blood pressure and levels of stress hormones (like cortisol, adrenaline and norepinephrine). While brain scans are also useful to show the activation of the same locations as in the case of pain, it's virtually impossible to get them in this scenario. It might be useful to try to perform a task that you normally do when the neighbor's noise affects you.
You will need to include baselines before the noise starts and after the noise ends (allow some time to pass), to show that only the presence of the neighbor's noise produces extreme stress in your body.
The stress that the controlled environment may cause you would be lower than that produced by the real environment, because in the controlled environment you can stop the experiment whenever you want (so the mental pressure is much lower).
If the neighbor makes noise at predictable times, you can collect the required medical information in your home.
Pulse and blood pressure that are elevated for long periods of time have been associated (in medical studies) to an increased risk of cardiovascular disease, to the point of a severe risk of cardiovascular arrest and stroke.
Cortisol is meant to produce the "fight or flight" response in case of danger, but in the absence of a choice, its effects are physically destructive.
What kind of physician would be most qualified for the collection of this medical evidence? One that deals with stress would likely be best; the next best choice would probably be an endocrinologist.
Noise can even lead to temporary insanity. There were cases of people who were (shot and) killed because they wouldn't stop playing loud music, and because the police either couldn't or wouldn't do anything about the noise.
How do you prove the noise levels? Aside from the police reports, there are the rest of the neighbors and the renters. There are also some accredited governmental agencies (like the Environmental Agency) and private companies that can perform accredited noise measurements on request.
In front of a judge, emphasize the facts below and say that the law should take them into consideration because they make all the difference:
If the noise is coming from a neighboring public place, like a park, you can ask the city hall (who probably administers it) to make specific changes to the park, like dismantling the park furniture (like tables) around which the noise makers gather. If the city hall doesn't respond to your request (check the legal time limit in your country) or refuses to make the changes you requested, you can try suing them for facilitating the noise and therefore your suffering.
WHO - Burden of disease from environmental noise: "The total burden of health effects from environmental noise would be greater than one million years in western Europe, even with the most conservative assumptions that avoid any possible duplication."
The Ghost in the Machine (Vic Tandy, 1998): Infrasound can cause hallucinations.
Effects of infrasound: High intensity infrasound has been observed to cause: changes in blood pressure, changes in pulse rate, changes in respiratory rate, vibration of internal organs, resonance in inner organs (such as the heart), pressure in the ears, fatigue, apathy, depression, loss of concentration, drowsiness, vertigo, imbalance, incapacitation, disorientation, nausea, vomiting, bowel spasm.
Are audio systems without a subwoofer any good?
Yes. Such systems can't use a subwoofer to hide the fact that the satellite speakers are of low quality.
An integrated subwoofer is used by manufacturers to cover the weakness of the satelite speakers in reproducing a perceptually balanced sound, by overpowering all other frequencies with bass, especially the mid ones.
The integrated subwoofer will make the music sound powerful in the very low frequencies, but will further reduce its clarity. Because the music lacks clarity and sounds muddled, people will turn the volume up to hear better (but this won't improve the clarity).
Cheap speakers usually have an overemphasized bass because (it's cheap to do and) people don't like to buy speakers that sound tiny / thin (like radios). However, they might have a "Bass" knob that you can use to change the amount of bass they output.
To see if your speakers use bass to hide a reduced clarity in the mid to low frequencies, deactivate the subwoofer and turn off any bass effect (from the "Bass" knob on the speakers). Now listen to voice (with no music); the average YouTube voice-only clip is more than enough for this.
If the voice sounds tiny / thin, similar to that of the average radio or smart TV, but possibly less clear than a radio / TV (because the radio / TV is designed to output clear voice), you have evidence that the speakers lack mid to low frequencies. If you add bass effect, the voice will start to sound boomy instead of getting fuller; this is because bass adds very low frequencies, not mid to low frequencies that voice needs to resemble human voice.
Why can a radio / TV be designed to output clear voice, while a speaker used for music can't? Because the radio / TV doesn't actually improve the mid to low frequencies of voice, it decreases the power for other frequencies that would normally cover the voice. If you were to do the same with a speaker used for music, the music would sound bad / underpowered.
Why then do humans have such full / deep voices? Because when humans speak, their chest resonates, and because the chest is very large compared a to speaker's driver, it powers a lot more the mid to low frequencies, giving voice its fullness.
Measuring noise volume
If you want to measure the noise yourself (which has no legal relevance), you need a sonometer that can detect sound with frequencies below 20 Hz and volumes below 20 dB.
There are many types of dB, but all measurements have to be performed with the same type. For human perception, dBSPL and dBA are usually used (including in legislation).
The sonometer must be multiband, meaning that it has to be able to show the sound volume for separate frequency bands.
Don't waste your money on a sonometer which doesn't have these features, but note that the ones that do have them are extremely expensive.
How is noise volume perceived?
The lowest volume of sound that the average healthy and young person can hear is about 0 dB for a continuous tone of 1'000 Hz. You can read details here.
Sound can still be present even at volumes lower than 0 dB, but humans can't normally hear it. This is because 0 dB is not complete silence, but a threshold for normal human hearing.
Because dB is a logarithmic scale, each subtracted 6...10 dB are perceived as a sound that's half as intense. Each added 6...10 dB are perceived as a sound that's twice as intense. Each 3 dB represent a doubling / halving of the energy of the sound.
All around, there usually is background noise which covers a lot of faint sounds; for example, an empty broadcast studio has a background noise around 20 dB. However, a persistent and percussive noise, like bass, might be heard or just felt through the background noise (especially because this is not necessarily continuous), and this may be disturbing.
A refrigerator usually produces about 40...45 dBA of noise (only high frequencies, no bass), at 1 m distance, in the noisiest stage.
Most people should be able to sleep well even if in the room there is a fan (like from an air purifier) which generates a continuous noise with a volume below 30 dBA. If the noise has beats, especially in the very low frequencies, the volume has to be much lower, as close to 0 dB as possible, because there is no background noise which can cover the beats. A deep, regenerative sleep requires the complete absence of very low frequencies, and an almost complete absence of the higher frequencies.
Does sound insulation help?
If very low frequencies (bass) is what's stressing you, then sound insulation can't help. To be able to relax, you would have to eliminate the bass, not simply reduce it. Very low frequencies can't be stopped even with professional sound insulation. You would literally need a home inside a home, with mechanical dampeners and tens of centimeters of professional sound insulation in between them. Save your money for moving elsewhere.
Even worse, sound insulation would block all higher sound frequencies, so the very low frequencies, even if at a low volume, would remain the only thing that your ear focuses on, so they would be more stressing.
Where to move?
If you want move and build a house which is as quiet as possible, see this.
Wireless headphones, WiFi or Bluetooth, can provide a sound clarity which is much better than that of most (standalone) speakers. On top of this, since they are on the ears, you can hear every sound from the music.
Some headphones have both WiFi and Bluetooth.
Headphones can only make you hear the thumping bass, they can't make you feel it on your body (like subwoofers can), but they also don't stress the neighbors.
The headphones whose ear pieces completely surround the ears, called "over ear", are usually the best for comfort (because they don't press your ears, unless the earcups are not deep enough) and sound quality (because they have the space to contain better technology).
For the same sound quality, wireless headphones are much more expensive than wired headphones. Also, you can't find audiophile-level wireless headphones, but for wired headphones you can go as high as you can afford.
Headphones make room acoustics irrelevant, while for speakers it's very important.
Open and closed
There are open and closed headphones. Open headphones allow the air (and sound) to circulate between the inside and outside of the headphones, through the outer side of the earcups.
Because the sound exits from the open headphones, they can disturb the people in the same room.
Closed headphones don't allow the air to circulate, and because of this their sound has a very faint echo (you will not be aware of it) which may make some types of music (like rock) more interesting.
Because the air doesn't circulate in closed headphones, the ears get hotter than in open headphones.
Headphones with noise canceling are closed because they need to be as insulated from the outside as possible.
Unless you want closed headphones because you don't want to bother people in the same room, you should get open headphones.
Soundstage is the size of the area from which sound appears to come, when listening to headphones or speakers.
A wide soundstage means that the sound feels like it's coming from a wide area around the listener, while a narrow soundstage means that the sound feels like it's coming from a narrow area (like listening through a hole).
A narrow soundstage makes sound perception less clear, so listeners feel the need to turn the volume up to hear better.
Open headphones have a wider soundstage than closed headphones. Large and deep earcups increase the soundstage.
Because the headphones with noise canceling are closed, their soundstage is limited.
See Rtings for headphone ratings of technical parameters like soundstage.
WiFi headphones come packaged with a base station. The base station has to be connected through a cable to the 3.5 mm headphone output of a TV, portable radio, computer or standalone music player. The headphones themselves connect to their base station through WiFi, to receive the sound, and this wireless connection lets you move around from room to room, while the base station and the sound playing device stay in the initial room.
Proper headphones don't have a problem if between the base station and the headphones there is one wall made from reinforced concrete, but two such walls will likely be.
There are models of headphones which allow you to connect several of them to a single base station, so that several people can listen to the same sound, at the same time. Usually, you can't buy a single base station and several headphones, you have to buy as many headphones as you need, each packed together with its base station.
The headphones can be placed on the base station to recharge the batteries. When the batteries are new and full, they can let you listen to music even for 20 hours.
Bluetooth headphones are usually made to work with a music playing device which contains a Bluetooth emitter, like a smartphone, so, unlike WiFi headphones, the base station of the Bluetooth headphones doesn't connect to the music playing device, but is used only to recharge the batteries of the headphones.
Because Bluetooth headphones are mostly made for portable devices, some models have a noise reduction (/ canceling) feature which significantly reduces the noise that comes from the outside into the headphones, so that your music listening experience is not degraded by the the surrounding noise. Be very careful with such a feature because it will also limit your ability to hear incoming cars and other potential dangers. Activating noise canceling will likely degrade the sound quality.
Bluetooth headphones are likely to have a microphone will lets you answer phonecalls, but privacy oriented people might prefer to avoid that.
For the same sound quality, Bluetooth headphones are more expensive than WiFi headphones, but have more features.
If you hear short interruptions in the sound of the headphones, increase the volume of the source (PC or smartphone). The emitter is optimized to cut power when sound volume drops to near silence, so the headphones don't receive anything during very quiet periods.
Some headphones have rechargeable batteries, usually one in each ear piece, which can be replaced when their charge lasts too little time (like just a few hours). For some headphones, in order to open the compartment of the batteries you have to rotate (in opposite directions) the outside and the inside halves of each ear piece.
When you buy wireless headphones, in order to test their sound quality, make sure to disable any effects (like noise canceling) on the emitter.
Using a very expensive instead of a cheap cable between the sound source and the base station of WiFi headphones makes a clear difference in sound quality.
If you are interested in wireless headphones with good sound quality, a good soundstage (compared to most headphones) replaceable batteries, and with additional heaphones without the base station, look into Sennheiser's open WiFi headphones (current model RS 185).