We compare products from their published specs and features; the verdicts below are our independent editorial opinions.
Updated: 2026-10-06 · 6 min read · Independent comparison
If you want a longer-lasting, more private open-ear setup for audiophiles who hate sound leakage, choose QCY Crossky C50; if you need the lightest possible ear-hook fit with punchier drivers and a rotating case you can clip to a bag, choose Monster Open Ear AC390. Both carry an IPX5 waterproof rating, so the real decision comes down to battery strategy, driver size, and how each one handles calls.
• QCY Crossky C50 — biggest strength: 35 hours of total playtime with a 4-mic AI call system (up to 45dB noise cancellation) and reverse soundwave tech that cuts leakage by 90%.
• QCY Crossky C50 — biggest trade-off: The clip-style earpiece and 10.8mm dynamic driver won't deliver the same raw punch as a larger diaphragm, and the sharper feature set takes a little more setup (app, firmware notes).
• Monster Open Ear AC390 — biggest strength: Featherweight 5g-per-bud ear-hook fit, an 18mm dynamic driver, and a rotating charging case with a lanyard for grab-and-go carry.
• Monster Open Ear AC390 — biggest trade-off: Total playtime tops out at 24 hours (8 per charge plus 16 from the case), and the open-ear hook design leans more toward all-day comfort than isolation.
• Who each pick is for: QCY Crossky C50 for commuters, call-heavy users and long-session listeners who want the most hours and the most private sound; Monster Open Ear AC390 for gym-goers and commuters who prioritize a barely-there feel and a bigger driver.
The Crossky C50 is the "more headroom" pick of the two. On a single charge you get 7.5 hours, and the charging case adds three more recharges for up to 35 hours total — a genuinely long runway for people who forget to plug things in. If you're chasing a fast-charging, long-endurance rhythm, that 380mAh case is the spec that matters most. For an in-ear-style listener used to small earbuds, the open-ear clip gives you the ambient awareness while still pushing audio inward.
Where it earns its keep for audiophiles is the directionality. Reverse soundwave technology is rated to cut sound leakage by 90% versus standard open-ear earbuds, which is the difference between "everyone on the train hears my podcast" and "this actually sounds private." Pair that with a 10.8mm dynamic driver, 40-ohm impedance and a 20kHz frequency response, and you get a controlled, bass-forward tuning rather than a thin, tinny open-ear sound. The leather-textured shell and silicone-plus-titanium memory alloy hooks also read as more premium than typical plastic clip-ons.
The trade-offs: it's a clip-style open ear, so it won't seal or isolate — noise control is passive. And the richer feature set (QCY app, dual-device connection, auto L/R correction, firmware updates) means there's a small learning curve. If you want a no-fuss, plug-and-play pair with zero app involvement, this is more than you asked for. If you want maximum hours, private audio and a call system that fights wind and background chatter, this is the one I'd point you toward.
The AC390 is the comfort-and-carry pick. At just 5g per earbud — lighter than a sheet of paper, as the brand puts it — the soft silicone ear hook is designed to sit on the ear without pressure, and that low weight is the whole pitch. If your problem with earbuds has always been the "something is jammed in my ear" feeling, an open-ear hook at 5g solves it. It's aimed squarely at workouts, commuting and extended wear.
The headline audio spec is the 18mm dynamic driver with a PU titanium diaphragm. A driver that size in an open-ear bud is the reason this one leans bass-heavy and lively. It won't have the sealed thump of in-ear earbuds, but for an open design it should carry more low-end weight than a smaller-diaphragm rival. Calls rely on Dynamic Noise Cancellation and the control set covers touch, voice and Siri, which is handy if you live hands-free.
The honest limits: 8 hours per charge plus 16 from the case equals 24 hours total, which is a full tier below the QCY. The rotating charging case with a lanyard is a nice touch for hiking or clipping to a backpack, and the open-ear fit means zero isolation — you'll hear traffic, gym clatter and office noise. The AC390 fits people who want the lightest possible feel and a bigger driver, and who don't need the longest battery in the category.
• Best for total battery life → QCY Crossky C50: up to 35 hours versus 24 hours on the Monster.
• Best for lightest fit → Monster Open Ear AC390: 5g per bud versus the QCY's 45.6g total kit weight.
• Best for private listening → QCY Crossky C50: 90% less sound leakage via reverse soundwave tech.
• Best for bigger-driver bass punch → Monster Open Ear AC390: 18mm dynamic driver versus 10.8mm on the QCY.
• Best for call clarity in windy or busy places → QCY Crossky C50: 4 mics, wind-noise reduction and up to 45dB call noise cancellation.
• Best for carry convenience → Monster Open Ear AC390: rotating case with a lanyard that's easy to clip on.
• Best for multi-device switching → QCY Crossky C50: dual connection lets you take a call while watching on a TV.
• Best for a no-app, hands-free-control experience → Monster Open Ear AC390: touch, voice and Siri controls without needing an app.
If I'm buying for myself as an audiophile who wants the most hours, the most private sound and the strongest call handling, I'd go with the QCY Crossky C50. The 35-hour total playtime, 90%-reduced leakage and 4-mic noise cancellation are the specs that actually change how you use open-ear buds day to day. The Monster AC390 is the better pick only if comfort and low weight are your absolute top priority, or if you specifically want that 18mm driver and rotating lanyard case. For a fast-charging, long-session open-ear companion, QCY gets my vote.
are headphones waterproof
Most headphones are not fully waterproof — they're water resistant to a set rating. The QCY Crossky C50 and Monster Open Ear AC390 both carry IPX5, which means they handle sweat, splashes and light rain, but not swimming or full submersion.
are headphones water resistant
Many modern wireless earbuds are, and both of these are IPX5 water resistant. That rating covers workouts, outdoor runs and daily commutes in light rain, but it doesn't mean you can wash them or take them into a pool.
IPX5 is rated for water jets and splashes, not prolonged heavy rain or immersion. For intense workouts and light rain both are fine, but if you're caught in a downpour, it's safer to pocket them.
The QCY Crossky C50 lasts longer overall: 7.5 hours per charge with up to 35 hours total via the case. The Monster AC390 gives 8 hours per charge but only 24 hours total with its case.
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