Impedance: Generally speaking, the lower the headphones' electrical impedance (aka resistance), the easier it is to get higher volume. But here again, the low impedance is no guarantee of high volume capability; other factors can still limit loudness potential. Since many MP3 players have feeble power output -- the iPod is a notable exception -- smart shoppers should check the loudness before purchasing any pair of headphones. To be sure, listen with your player.
If you’re choosing earbuds over full-sized headphones, you’re already probably going to make some concessions when it comes to sound quality. Most often, earbuds tend to be thin in range, forfeiting snappy mids and piercing highs in favor of an overly bassy, monotoned low-frequency response. That’s where dual drivers come in. With a pair of RHA T20i earbuds, you'll get double the power of a standard bud, and because each driver is typically tuned to a different part of the spectrum, you tend to get better performance altogether.
Although their control scheme provides all the essential functions, the buttons are very stiff, which makes them difficult to use. They’re also rather bulky: the earbuds themselves protrude quite a bit of out the ears and their charging case doesn't fit in your pockets as nicely as that Anker SoundCore Liberty Air Truly Wireless. That said, they're the best Bluetooth earbuds for sound and are a very good choice for those who want something durable without compromising on sound quality.
This varies with headphones, but in general the larger over-ears are better at achieving this than smaller in-ears because the sound has a chance to bounce around your ear before reaching your eardrum. Earbuds pump sound directly into your ear, so there isn’t much room for sound to move around and create the illusion of space. This kind of leads into the next topic.
Earphones might not be as eye-catching as headphones, but they can be much more convenient. Besides their size and weight, earphones are often more resilient than headphones when dealing with moisture. This is important if you want to listen to music at the gym. Earpads can get soaked and worn with a solid sweat, and they aren't built to withstand the regular, constant friction that comes with working out. Earphones can be built to be water- and sweat-resistant, and hold up much better to activity.