Open-back headphones have pads which rest on the outer ear. They're designed such that the outer shell of the ear cup has perforations usually with horizontal cutouts. The Open back headphones design of the ear cup enhances better natural sound because of less coloration as compared to the Closed back headphones.
Closed back headphones have much larger earpads which encircle the ears. They are designed such that there's a big pad which cups the ears, and it features an insulated outer shell of plastic which covers the ears. The Closed back headphones actually have a very solid outer shell which doesn't have any sort of perforations such that the outer shell effectively cups/encircles the entire ear. The Closed back headphones are excellent at isolating noise. They block most of the ambient noise, but they've a smaller sound stage, which gives the user the perception that the audio/sound is originating from within their head. Closed back headphones also tend to produce much stronger low frequencies as compared to Open back headphones.
Low Impedance vs High Impedance
Headphones normally come in various different impedance levels, such as 8 ohms, 16 ohms and 32 ohms. The power that's supplied by an audio source may be at varying levels because of a variety of factors including being limited because of being battery powered. Generally, as the impedance of the headphones increases, much more voltage will be required in order to drive it, and the audio loudness of headphones for a particular voltage decreases.
The determination of impedance is usually disregarded by many headphone buyers, however, the truth is it's one of the most important factors to consider when choosing the best headphones for your particular needs. Impedance is basically just how much power the headphones can put out so that it can overcome resistance to move the headphones' diaphragm.
Low impedance headphones (that is, less than 25 ohm), usually require little power in order to deliver high audio levels. Low Impedance headphones play well with devices which have weak amplification. These can include; mobile phones, portable music players and various other portable devices. This type of headphones can be used at home and also while jogging with your mobile phone; this is one of the reasons why most of the on-, in-, and over the ear headphones, are low impedance. Low impedance headphones are normally designed to get plugged directly in to a single (one) source, and generates sound more efficiently from a lower level input signal. This headphones tend to be much louder and much more efficient, however, they will also require a much more capable amplifier.
High impedance headphones (25 ohms and above), generally require more power in order to deliver high audio levels. As a result, they're protected from damages caused by overloading. High impedance headphones are typically designed for studio like applications where there might be multiple phones/devices wired in parallel and receiving input signals from a single source. High impedance headphones are more tolerant of the amplifier limitations, however, they will produce less volume for a particular output level. They are also a little more durable (that is, electronically), however, they require much higher signal levels in order to produce the same level of output level of the low impedance headphones. This type of headphones can be used with a wider range of audio equipment.
Passive Headphones vs. Active Headphones
Passive (noise cancelling) headphones are made of materials which help in blocking out sound waves from the surrounding environment. The same way ear muffs soften the outside noise, so does this type of headphones employ passive noise canceling. This type of headphones are typically used for both professional mixing and monitoring, like in broadcast and recording studios, and such other applications. Passive headphones are basically designed to playback music/audio true to the actual original recording, with minimal, compression, EQ, and such other sound enhancements.
On the other hand, Active headphones use batteries in order to power the built in Digital Signal Processing (also abbreviated as DSP) technology which processes play back for a particular reason, for example, to enhance the bass and the high end. Due to the enhancement of playbacks with sharper high ends and more bass, active headphones are more popular for general listening and listening to music for pleasure. Active noise cancelling headphones are also made of materials which help in blocking out outside noise, however, they take things a step further by making their very own sound waves; the sound waves created mimic the outside noises, but are a mirror image of each other, thus cancels each other out.
Wired Headphones Vs Wireless Headphones
When choosing a pair of headphones, deciding between wireless vs. wired is among one of the most overlooked factors. Wireless headphones might be a more popular choice, however, the wired headphones also have their own set of benefits. Well, that being said, as a general rule of thumb, between wireless headphones and wired headphones, assuming a similar price between the models; the wired headphones usually offer a much better quality. Also, the audio quality may get compromised over Bluetooth.
You can opt for the wireless headphones if you are not much of an audiophile, and you tend to travel a lot. If you really don't like getting the cables of your headphones getting tangled, or caught while listening to music/audio, then the choice should be rather simple; go for wireless headphones.
You can opt for the wired headphones if you are an audiophile, and you do not necessarily bother with the wireless options unless absolutely essential like using them when traveling, or keeping the headphones as a backup. As aforementioned, the wired headphones are way ahead in terms of output quality as compared to the wireless headphones. You will never have to worry about running out of batteries, unless you happen to opt for wired headphones which cancel noise. In addition, you will never suffer from interference from the other commonly used wireless electronic devices. However, you will need to take good care of the wired headphone cables, or they will eventually break.