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We compare products from their published specs and features; the verdicts below are our independent editorial opinions.
Updated: 2026-09-30 · 7 min read · Independent comparison
If you want a lightweight, noise-isolating in-ear pair you can pocket and wear all day, choose Sennheiser CX 300S; if you need big, comfortable over-ear headphones for long listening and studio-style setups, choose Superlux HD660PRO.
• Sennheiser CX 300S — biggest strength: a compact in-ear design with four sizes of ear adapters (XS, S, M, L), so you can get a snug, individualized fit that naturally blocks ambient noise.
• Sennheiser CX 300S — biggest trade-off: it's a wired in-ear with a single-button remote, so there's no volume control on the cable and no over-ear comfort for marathon sessions.
• Superlux HD660PRO — biggest strength: 40mm neodymium drivers in a closed-back over-ear shell, with a wide 10Hz–30KHz range and an upgraded leather headband plus velvet ear pads built for long wear.
• Superlux HD660PRO — biggest trade-off: it's bulkier, heavier and clearly a sit-down headphone, and it has no inline controls or noise isolation at all.
• Who each is for: the CX 300S suits commuters, phone listeners and anyone who wants sound isolation in a tiny package; the HD660PRO suits home listeners, creators and anyone who wants an over-ear fit for hours.
The CX 300S is the small, simple option. It's a wired in-ear headphone with 3.5mm connectivity, an 18-ohm impedance and a 17Hz–21,000Hz frequency range driven by a dynamic driver. That low impedance number is the interesting spec here: 18 ohms means it doesn't demand much power to get loud, which is exactly what you want from a phone, tablet or laptop headphone jack. Sennheiser's own description talks about detailed, dynamic sound with extended bass response, and the in-ear, rounded-tip silicone design is the reason it can sound fuller than you'd expect from something this small.
The fit story is where it earns its keep. You get four sets of ear adapters in XS, S, M and L, and Sennheiser is explicit that the seal matters — if the tips don't match your ear canals, you lose both sound quality and call performance. Get the right size and the in-ear design gives you real reduction of ambient noise, which is the closest thing to "noise cancelling" you'll get without electronics. There's also a one-button inline remote for play, pause and taking calls, so you're not digging your phone out every time someone rings.
Superlux HD660PRO: Who It's For
The HD660PRO is the opposite philosophy: a closed-back over-ear headphone with 40mm neodymium drivers, 32-ohm impedance, 92dB sensitivity and a 10Hz–30KHz frequency range. The 32-ohm rating is the headline for everyday buyers — Superlux designed it to sit between studio gear and casual devices, so it will run from a smartphone, laptop or tablet while still handling a mixer, interface or guitar amp. The closed-back cup design keeps your sound in and some room noise out, which is why it's marketed toward recording and monitoring as much as music.
Comfort is clearly a priority in the design. You get an upgraded leather headband and ultra-soft velvet ear pads, plus an adjustable headband and swiveling ear cups so you can dial in the fit. That combination is what makes long sessions tolerable — the over-ear fit spreads pressure across the side of your head instead of pressing into your ear canal. It's noticeably heavier than the Sennheiser at 11.4 ounces, so this is a headphone you wear at a desk, not one you forget you're wearing.
Connectivity is flexible: a 3.5mm plug plus a 6.3mm adapter, and a long 8.2-foot straight cable. That reach matters if you're plugged into a mixer across the room or moving around a desk setup. The package includes the conversion plug and a storage pouch, and there's a one-year manufacturer warranty.
Who should buy it: home listeners who want an over-ear fit for hours, podcasters, bedroom producers, anyone plugging into a mixer or interface, and people who prefer velvet pads over silicone tips. Who should skip it: if you need portability, cable controls, or any form of noise isolation, this is the wrong shape and the wrong feature set. As with any purchase, check the current price on Amazon.
Side-by-Side: Which Should You Choose?
• Best for portable listening → Sennheiser CX 300S. 10.8g, in-ear, fits in a pocket.
• Best for long listening sessions → Superlux HD660PRO. Velvet pads, leather headband, over-ear fit built for marathons.
• Best for plugging into studio gear → Superlux HD660PRO. 3.5mm plug plus 6.3mm adapter and an 8.2-foot cable.
• Best for low-power devices → tie, with a lean to the CX 300S. 18 ohms is easier to drive than 32 ohms, though 92dB sensitivity keeps the Superlux friendly too.
• Best for extended frequency range → Superlux HD660PRO. 10Hz–30KHz versus 17Hz–21,000Hz.
• Best for cable controls → Sennheiser CX 300S. One-button smart remote for play, pause and calls; the HD660PRO has none.
• Best for a desktop or studio desk → Superlux HD660PRO. Swiveling cups and an adjustable headband suit a fixed setup.
In my opinion, most people shopping for music headphones should buy the Superlux HD660PRO. The over-ear comfort, the 40mm drivers, the wider frequency range and the flexible 3.5mm-plus-6.3mm connection make it the more versatile headphone for real listening at home or at a desk — and the velvet pads mean you'll actually keep them on.
I'd only steer you to the Sennheiser CX 300S if portability and noise isolation are non-negotiable. If you listen on a commute, in a shared space, or straight from a phone in your pocket, the in-ear seal and 10.8g weight win. Otherwise, the HD660PRO is the one I'd pick.
how to make headphones music louder
First, check the fit. Sennheiser specifically notes that if the ear tips don't match your ear canals or the headset isn't worn properly, you won't get the correct sound quality — so try the XS, S, M or L adapters until the seal is snug. Beyond fit, raise the volume at the source device, since both headphones are wired and neither has its own amplifier or inline volume control.
how to test stereo headphones
Play a track you know well and listen for whether sound is balanced between the left and right sides. Because both of these are wired headphones with a 3.5mm jack, a quick check is to swap the plug between devices and confirm both channels still output. On the CX 300S, also confirm the one-button remote plays and pauses as expected; on the HD660PRO, test with the 6.3mm adapter if you're plugging into larger gear.
how to fix stereo headphones
Start with the simple things: reseat the 3.5mm plug, try a different device, and check that the cable isn't strained. If one side is silent, the usual culprits are a damaged cable or a poor connection at the jack. The CX 300S includes a spare set of ear adapters and a two-year manufacturer warranty; the HD660PRO carries a one-year manufacturer warranty, so if a fault appears early, that's the route to take.
how to make stereo headphones
You can't build these from scratch, but you can get the most out of them. Match the ear tips to your ears on the CX 300S so the seal is correct, and on the HD660PRO adjust the headband and swivel the cups so the drivers sit centered over your ears. Correct positioning is the single biggest factor in getting the intended stereo image from either pair.
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