For older models of telephones, the headset microphone impedance is different from that of the original handset, requiring a telephone amplifier for the telephone headset. A telephone amplifier provides basic pin-alignment similar to a telephone headset adaptor, but it also offers sound amplification for the microphone as well as the loudspeakers. Most models of telephone amplifiers offer volume control for loudspeaker as well as microphone, mute function and switching between headset and handset. Telephone amplifiers are powered by batteries or AC adaptors.
Using headphones at a sufficiently high volume level may cause temporary or permanent hearing impairment or deafness. The headphone volume often has to compete with the background noise, especially in loud places such as subway stations, aircraft, and large crowds. Extended periods of exposure to high sound pressure levels created by headphones at high volume settings may be damaging to hearing; Nearly 50% of teenagers and young adults (12 to 35 years old) in middle and high income countries listen to unsafe levels of sound on their personal audio devices and smartphones. however, one hearing expert found in 2012 (before the worldwide adoption of smartphones as the main personal listening devices) that "fewer than 5% of users select volume levels and listen frequently enough to risk hearing loss." The International Telecommunication Union recently published "Guidelines for safe listening devices/systems" recommended that sound exposure not exceed 80 decibels, A-weighted dB(A) for a maximum of 40 hours per week. The European Union have also set a similar limit for users of personal listening devices (80 dB(A) for no more than 40 hours per week) and for each additional increase of 3-dB in sound exposure, the duration should be cut in half (83 dB(A) for no more than 20 hours, 86 dB(A) for 10 hours per week, 89 dB(A) for 5 hours per week and so on. Most major manufactures of smartphones now include some safety or volume limiting features and warning messaging in their devices. though such practices have received mixed response from some segments of the buying who favor the personal choice of setting their own volume levels.
Communication headsets are used for two-way communication and typically consist of a headphone and attached microphone. Such headsets are used in a variety of professions as aviation, military, sports, music, and many service-oriented sectors. They come in all shapes and sizes, depending on use, required noise attenuation, and fidelity of communication needed.
The Bose QuietComfort 25 were released in 2015 and you can still buy them today. They are kind of like a wired version of the Bose QuietComfort 35. They have a slightly dated look, and boast almost as good levels of active noise-cancellation and sound quality as Bose’s QuietComfort 35. The important thing to remember is that even though these are wired headphones, they still need to be charged so you can turn on the active noise cancellation. Otherwise, they just work as normal over-ear headphones.
Generally, headphones are able to reproduce richer low-end audio, since they have larger drivers than earphones and they don't rely on an in-ear seal to deliver sound. Some listeners also find headphones more comfortable to wear, and easier to put on and take off, than they do earphones. This naturally means that headphones are bulkier, and less suited to the gym.
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.
Binaural recordings use a different microphone technique to encode direction directly as phase, with very little amplitude difference below 2 kHz, often using a dummy head. They can produce a surprisingly lifelike spatial impression through headphones. Commercial recordings almost always use stereo recording, rather than binaural, because loudspeaker listening is more common than headphone listening.
There’s a lot of debate in the headphone world about wireless audio. Wireless standards like Bluetooth are capable of making music sound great, but because Bluetooth relies on data compression, it will never sound quite as good as a wired connection. The big question is, with the improvements in Bluetooth, can anyone tell the difference anymore between Bluetooth audio and wired audio? We’re skeptical that the difference is meaningful, so here’s our best advice: if you’re an audiophile who cares about hearing music in high fidelity, you’ll probably be better off with a set of wired headphones; if you need everything to sound great but prefer the convenience of wireless connections, go for a pair of Bluetooth headphones.