Headphones may be used with stationary CD and DVD players, home theater, personal computers, or portable devices (e.g., digital audio player/MP3 player, mobile phone). Cordless headphones are not connected to their source by a cable. Instead, they receive a radio or infrared signal encoded using a radio or infrared transmission link, such as FM, Bluetooth or Wi-Fi. These are powered receiver systems, of which the headphone is only a component. Cordless headphones are used with events such as a Silent disco or Silent Gig.
Sensitivity is a measure of how effectively an earpiece converts an incoming electrical signal into an audible sound. It thus indicates how loud the headphones are for a given electrical drive level. It can be measured in decibels of sound pressure level per milliwatt (dB (SPL)/mW) or decibels of sound pressure level per volt (dB (SPL) / V).[12] Unfortunately, both definitions are widely used, often interchangeably. As the output voltage (but not power) of a headphone amplifier is essentially constant for most common headphones, dB/mW is often more useful if converted into dB/V using Ohm's law:

Sony’s technologically advanced WH-1000xM3 are the third generation of Sony’s flagship wireless headphones (following the excellent WH-1000xM2 and MDR-1000x models) that offer top-tier noise canceling, excellent quality wireless audio, and plush comfort. This enticing combination earned the model a rare five-star rating in our initial review, and — thanks to a few notable improvements — makes the latest version the best headphones you can buy.
Today they are typically used only in in-ear headphones and hearing aids, where their high efficiency and diminutive size is a major advantage.[20] They generally are limited at the extremes of the hearing spectrum (e.g. below 20 Hz and above 16 kHz) and require a better seal than other types of drivers to deliver their full potential. Higher-end models may employ multiple armature drivers, dividing the frequency ranges between them using a passive crossover network. A few combine an armature driver with a small moving-coil driver for increased bass output.

Preferences for the length of headphone cables vary for portable users, especially depending on where you prefer to wear your device: a backpack or a pants pocket necessitates a longer cable, while you'll opt for a short one when wearing a player on a neck lavalier or an armband. But a cable length at either extreme need not be a fatal flaw: extension cables can lengthen those that are too short, and cable wraps can tighten up ones that are too long.

Audiophiles generally agree that if you’re passionate about music, and you have a listening space that is relatively free of outside sounds, nothing beats a really good set of open-back headphones. As far as we’re concerned, you won’t find a set of open-back headphones that manage to combine superb sound quality and a reasonable price than the Sennheiser HD6XX/HD650. To be clear, these are not exactly the same models. The HD6XX is a run of the HD650 with a lower price from Massdrop, and a few physical changes, but when it comes to their audio chops, they’re identical.
However, most people won’t be able to hear the difference if they’re older than 24, have some form of noise-induced hearing loss, or are in the presence of outside noise. For this reason, we recommend wireless Bluetooth headphones for those commuting, or in noisy situations. If you’re listening primarily at home at the computer—get a set of wired headphones.

We’re totally convinced the Sony WH-1000xM3 will be the best pick for most people, but if you’re looking for some alternatives, we have you covered there, too. We identified seven other models that are more than worthy of your consideration, each with their own specific strengths, whether it’s for use during a workout — or merely to keep you from giving your credit card too much of a workout.
Garbage in = Garbage out (GIGO) is a popular phrase used to emphasize the importance of a good source. This can be the soundcard in your laptop, the quality of your portable audio player, or the CD player you’re using for music listening. Those fall into the “Source” category. The better your source is, the better the sound will be at the headphone end. This is why we are seeing more and more audiophile digital audio players (audiophile DAPs). They are expensive but they sound good.
The usual way of limiting sound volume on devices driving headphones is by limiting output power. This has the additional undesirable effect of being dependent of the efficiency of the headphones; a device producing the maximum allowed power may not produce adequate volume when paired with low-efficiency, high-impedance equipment, while the same amount of power can reach dangerous levels with very efficient earphones.
As the name gives away, these have an on-ear design instead of the over-ear design of most of Bose’s other offerings. The trade-off is that the On-Ear Wireless Headphones won’t be able to block out ambient noises as well, but some people might find them more comfortable. Plus they’re well cheaper than most other Bose wireless headphones. It should be noted that many reviewers, including Sound Guys, have praised the sound quality of these headphones.
We’re totally convinced the Sony WH-1000xM3 will be the best pick for most people, but if you’re looking for some alternatives, we have you covered there, too. We identified seven other models that are more than worthy of your consideration, each with their own specific strengths, whether it’s for use during a workout — or merely to keep you from giving your credit card too much of a workout.
Be sure to assess the build quality of your prospective headphones. Some earbuds and portable devices are relatively fragile, for instance. If the headphones fold up for easy storage, are the hinges robust, or will they fall apart in a month or two? Don't forget to consider that the earpads and earbuds will get extensive wear and tear over the life of the headphones.
Headphones are available with high or low impedance (typically measured at 1 kHz). Low-impedance headphones are in the range 16 to 32 ohms and high-impedance headphones are about 100-600 ohms. As the impedance of a pair of headphones increases, more voltage (at a given current) is required to drive it, and the loudness of the headphones for a given voltage decreases. In recent years, impedance of newer headphones has generally decreased to accommodate lower voltages available on battery powered CMOS-based portable electronics. This has resulted in headphones that can be more efficiently driven by battery-powered electronics. Consequently, newer amplifiers are based on designs with relatively low output impedance.
I tend to regard the M50 as the minimum for hi-fi listening with no apologies for limitations. But if you have to go cheaper than the usual $125 USD for the M50, the B&O Form2 with a simple bass boost gives a real hi-fi sound, and it should be available for about $100. The Beyer DTX-501P (similar to soundmagic P30) is good for $100, but needs a slight treble boost. The LSTN Fillmore with wood cups is somewhat colored, but still a good listen and good for $100. Below $100 are the Sennheiser PX series – not hi-fi by any means. There are several good IEMs below $100, and Apple Earpods with a Dirac or Accudio Pro player are very hi-fi, and cheap.

Dale: It’s really the same with any genre or sub-genre of music, that the sound from different artists and tracks can vary a lot, so having more than one headphone is a plus. When only one headphone is available at a particular time (portable use especially), one option is to use a headphone that can accommodate a wide range of genres, in which case there may be compromises to consider. Another option is to carry two headphones – one on the head or around the neck and another in a carry case. Some of the small headphones can make this easy to do.
In early powered radios, the headphone was part of the vacuum tube's plate circuit and carried dangerous voltages. It was normally connected directly to the positive high voltage battery terminal, and the other battery terminal was securely grounded. The use of bare electrical connections meant that users could be shocked if they touched the bare headphone connections while adjusting an uncomfortable headset.