Since I began working out, thirty years ago, I've seen a cavalcade of playback devices and earphones used in my gym-of-choice. In the beginning it was iPods and earbuds, but that soon gave way to smartphones, Bluetooth connections, and all manner of personal transducers from the ubiquitous Apple earbud to more exotic fare from Beats, Bose, Sol Republic, as well as more traditional earphones from older, more audio-oriented firms.
But I don't want to focus at any particular brand of earphones today, I want to look at what an earphone needs to do right to be a good workout earphone. First, in my humble opinion, big full-sized over-ear headphones look goofy in a gym. There's also the issue that over-ear "pro" headphones often come with a non-detachable coiled cord, which is almost as big and bulky as the cans themselves and it can easily get snagged on your typical lat pull-down machine.
My ideal workout earphone is an in-ear monitor. And it needs to be lightweight and it must have a fit that, once inserted, does not need to be periodically readjusted. And that is not easy to find.
Locating an in-ear monitor of any kind that, once installed, stays in place has been a challenge. Even some of the custom-fitted in-ears I've had made lose their seal when I do sideways plank for a minute and a half. I often wonder how rocker's keep their custom in-ear monitors in place as they crowd-surf...
For a number of years I used a pair of Etymotic 6iE with their standard triple-flange tips as my go-to workout in-ear, but I found that after a couple of years my costs for replacement filters (the 6iE has a filter to prevent debris and moisture from affecting the driver) had far exceeded my initial investment in the earphones. Also after several years of gym use the 6iE, although they still worked perfectly (with a fresh filter) was beginning to turn yellow/green.
After the Etymotic 6iE I went through a cavalcade of in-ears, most of which used compressible foam Comply-type tips. With some in-ears the foam tip solution worked reasonably well - keeping the in-ears in place without fiddling. But with the majority of foam-tips the isolation wasn't quite as good as I would have liked, especially when the background was full of loud, bad, workout music.
Recently I reviewed the new versions of Etymotic's ER4, the ER4 SR and ER4 XR. After going back and forth between the triple-flange and Comply tips I settled on the triple-flange because they delivered a better seal, more isolation, and a less finicky fit. Taking the ER4 XR to the gym reminded me of why I had happily used the 6iE in the gym for so many years - once inserted the Etymotic triple-flange "deep insertion" fit will not slide out no matter how much I sweat or move. And while it's been a while since I managed to snag my headphone cable on a bike or weight apparatus, having a removable/replaceable cable is still a gym essential.
Now, for some folks the Etymotic deep insertion triple flange is not comfortable, and I will admit that if I use deep insertion fit earphones too often or for too long my ear canals do get a might bit tender, but for me the deep insertion fit has proven over time to be the best solution when I need maximum isolation and don't want to have to stop in the middle of a series of reps to readjust my earphone's fit...