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.
Sensitivity
Rated headphone sensitivity. Technically, this is the volume at which they sound when a certain standard signal from the amplifier is connected to them. Thus, sensitivity is one of the parameters that determine the overall volume of the headphones: the higher it is, the louder the sound will be with the same input signal level and other things being equal. However, we must not forget that the volume level also depends on the resistance (impedance, see above); moreover, it is worth choosing “ears” for a specific device first by impedance, and only then by sensitivity. In this case, one parameter can be compensated for by another: for example, a model with high resistance and high sensitivity can work even on a relatively weak amplifier.
As for specific figures, headphones with indicators of 100 dB or less are designed mainly for use in a quiet environment (in some similar models, the sensitivity
does not exceed 90 dB). For use on the street, in transport and other similar conditions, it is desirable to have more sensitive headphones — about
101 – 105 dB, or even
110 dB. And in some models, this figure can reach
116 – 120 dB. and even
more.
It is also worth noting that this parameter is relevant only for a wired connection according to the analogue standard — for example, via a 3.5 mm mini-
...jack. When using digital interfaces like USB and wireless channels like Bluetooth, the sound is processed in the built-in headphone converter, and if you plan to mainly use this kind of application, you can not pay much attention to sensitivity.Case battery capacity
The capacity of the battery installed in the case (case) for headphones.
This parameter is relevant only for true wireless models (see "Cable type"). Recall that these headphones are charged from a case, which is usually equipped with its own battery and actually works in standalone power bank mode. Knowing the capacity of the battery in the case and in the headphones, you can estimate how many charges of the “ears” will last for one charge of the case. However, it should be taken into account that in the process of charging the headphones, part of the energy is inevitably spent on third-party losses, and the effective capacity of the case turns out to be somewhere 1.6 times less than the claimed one. This is the starting point for calculations: for example, a 300 mAh case will actually be able to transfer 300 / 1.6 = 187 mAh of energy to the headphones, and 30 mAh “ears” from such a battery can be fully charged about 6 times (187 / 30 ≈ 6).
Operating time (with case)
The maximum operating time of TWS headphones, taking into account recharging with a native case. But this time is not continuous use, it takes into account breaks for "refueling". Anyway, this parameter allows you to understand for how long you can leave the network (for example, how many nights to spend in a tent to the accompaniment of your favorite artist).
