Impedance
Impedance refers to the headphone's nominal resistance to AC current, such as an audio signal.
Other things being equal, a higher impedance reduces distortion, but requires a more powerful amplifier — otherwise the headphones simply will not be able to produce sufficient volume. Thus, the choice of resistance depends primarily on which signal source you plan to connect the "ears". So, for a portable gadget (smartphone, pocket player), an indicator of
16 ohms or less is considered optimal,
17 – 32 ohms is not bad. Higher values —
33 – 64 ohms and
65 – 96 ohms — will require quite powerful amplifiers, like those used in computers and televisions. And models with a resistance of
96 – 250 ohms and
above are designed mainly for Hi-End audio equipment and professional use; for such cases, detailed recommendations for selection can be found in special sources.
Card reader
The presence of a card reader in the headphones — a device for reading removable memory cards, usually microSD format.
Like built-in memory (see above), such cards are used to store various information — most often music files (accordingly, most models with card readers also have a built-in player and can play music without connecting to external devices at all). In this case, a memory card can be either an addition to the built-in drive, or the only supported media type. The second option is much more common: "removable" memory in terms of gigabytes of volume is much cheaper than the built-in one. In addition, if one card is not enough, the music can be kept on several, "recharging" the card reader as needed.
Note that even cards of the same type are usually produced in different standards — for example, in addition to the "regular" microSD, more capacious and advanced microSDHC, and more recently microSDXC have gained popularity. These formats are not 100% compatible, so before using a card reader, be sure to check which card types it supports.
FM receiver
A built-in tuner that allows you to receive FM
radio broadcasts using headphones — it is in this range that most modern music stations broadcast (because it allows you to broadcast sound in stereo). In other words, "ears" with this function allow you to listen to the radio without the use of additional equipment — except that you may need to connect a wire, which in this case plays the role of an antenna.
Weight
The total weight of the headphones; for true wireless models (see "Cable Type"), the weight of each individual earbud is listed.
This parameter is directly related to the design (see above) and some features of the functionality. Thus, the mentioned true wireless devices are very light, their weight
does not exceed 25 g. More traditional in-ears and in-ears can be noticeably heavier,
up to 50g for in-ears and up
to 100g for most in-ears. Overhead models, for the most part, are quite massive: among them there are many models weighing
200 – 250 g,
250 – 300 g and even
more than 300 g. It should be noted that a significant weight for false ears is often not a disadvantage, but an advantage: it allows them to stay on the head more securely, creates an impression of solidity and reliability, and most often does not create significant inconvenience.
