Wireless headphones are great for sports and outdoor uses, since they don’t require you to connect to a music player using wires. Instead, wireless technology connects the headphones to your music player, giving you freer movement and fewer tangles.

Most wireless headphones use Bluetooth, a technology that digitally encodes audio and transmits sound wirelessly over short distances. Bluetooth is a popular format because it’s highly reliable, and most new smartphones and laptops have built-in Bluetooth functionality — syncing with Bluetooth-enabled headphones is quick and easy. Of course, there are other types of wireless technologies as well.

There are a few critical specs you should be aware of when comparing models:

Stereo vs. Mono: Stereo sound consists of two separate channels: a left channel and a right channel. With stereo headphones, you are hearing a different audio channel in each ear to give a sense of dimension to whatever you are listening to. For example, a guitar in a song you enjoy might sound like it’s slightly to the left of you instead of directly in front of you because it is a little bit louder in the left channel than the right one.
Alternatively, mono sound is a single audio channel, so in mono headphones you are hearing the identical sound in both ears. Some headsets that include a boom mic only have one earcup, and there are several single-ear Bluetooth headsets as well. In cases like these, the audio is mono, since you’re only hearing it in one ear.

Frequency response: Expressed in hertz (Hz), frequency response represents the range of frequencies a pair of headphones can accurately reproduce. The range of human hearing is generally estimated at 20Hz–20kHz, but claimed frequency response often exceeds that range. Bear in mind that two sets of phones with identical frequency response specs will absolutely not sound the same; each design has its own “signature” sound, influenced by many other factors.

Sensitivity: Expressed in decibels per milliwatt (db/mW), a headphone’s sensitivity measures the relative amount of volume it can produce from a given amount of input power. Headphones with higher sensitivity (about 100db or higher) are recommended for use with portable listening devices, which typically have less powerful amplifiers than home audio components.

Impedance: Expressed in ohms, impedance is a measure of electrical resistance, and is related to the sensitivity spec. Some studio reference headphones have as much as 600 ohms of impedance, requiring powerful and clean amplification to reach desirable listening levels. Most consumer-level phones for casual listening fall between 16 and 64 ohms of impedance, and are designed to work with low-powered portable audio devices.