How We Research
We compare products from their published specs and features; the verdicts below are our independent editorial opinions.
Updated: 2026-09-26 · 6 min read · Independent comparison
• Sennheiser Pro Audio Professional — biggest strength: closed-back on-ear design with high sensitivity (120 dB) and 70-ohm impedance, a detachable single-sided cable and a screw-on 3.5 mm to 6.3 mm jack adapter. Built for DJing, studio monitoring and sound reinforcement.
• Sennheiser Pro Audio Professional — biggest trade-off: it's wired only (3.5 mm jack, no Bluetooth), so you're tethered to your gear and there's no microphone or voice-assistant control.
• Koss KSC35 — biggest strength: Bluetooth 5.2 wireless freedom with an integrated microphone and audio remote, up to 18+ hours of play/talk time per USB-C charge, and a unique ear-clip fit that stays put during movement.
• Koss KSC35 — biggest trade-off: no wired jack at all, so if the battery is flat you're not listening; noise control is listed as none, and the 6-hour charge time is slow.
• Who each pick is for: Sennheiser for DJs, engineers and anyone who wants a tough corded monitoring headphone; Koss for runners, gym-goers and commuters who want cable-free on-ear listening and hands-free calls.
The Sennheiser Pro Audio Professional HD 25 is a closed-back, supra-aural on-ear headphone — the rounded earcups sit on your ears rather than around them, which is exactly what you want when you need isolation from stage bleed without a bulky over-ear shell. The spec sheet tells a clear story: 70-ohm impedance, 120 dB sensitivity, a 16 Hz to 22,000 Hz frequency range and dynamic drivers using lightweight aluminium voice coils. High sensitivity plus a closed-back cup is a deliberate combination — it means the headphone can reach serious volume from ordinary gear, and the sealed cup keeps that sound in (and stage noise out).
Who should buy it: DJs, studio engineers, live sound techs and anyone doing sound reinforcement. The details that matter here are durability-oriented. The cable is detachable and single-sided, so a snagged cable doesn't mean a dead headphone — you swap the cable, not the can. A screw-on 3.5 mm to 6.3 mm jack adapter is included, which is the difference between plugging into a laptop and plugging into a mixer or interface without hunting for an adapter. At 140 g it's light enough for long sessions, and the earcups are designed to stay comfortable over extended use. A carrying case and a 2-year warranty round it out.
Who should skip it: anyone who wants wireless. There's no Bluetooth, no microphone and no voice-assistant control — just a 3.5 mm wired connection and a touch-based volume control. If you listen from your phone on a run, this isn't your headphone. If you monitor from a desk or a booth and want something that takes abuse, it is.
The Koss KSC35 is a different animal entirely. This is a wireless Bluetooth 5.2 ear-clip headphone with a 15 Hz to 25 kHz frequency range, a 60-ohm impedance and dynamic drivers. The ear-clip design hooks around your ear instead of clamping over it, which is the whole point: it stays put during movement. Koss positions it for active listeners — running, working out, traveling — and the spec sheet backs that up with a 10-metre Bluetooth range and a lightweight build (3.8 ounces including accessories).
The headline feature is battery and convenience. Koss lists up to 18+ hours of play/talk time from a single USB-C charge, plus an integrated microphone and audio remote so you can answer and end calls, adjust volume, and pause, play or skip tracks without touching your phone. There's also voice-assistant activation. A protective carrying case and cable management clips are included, and Koss notes that the cushions are customizable with standard and oversized options in a variety of colours — a nice touch if fit or looks matter to you.
Who should buy it: runners, gym-goers, commuters and anyone who wants on-ear listening without a cable. The microphone and remote make it a genuinely usable headset for calls, not just music.
Who should skip it: anyone who needs a wired connection, low-latency monitoring, or isolation. There's no jack at all, noise control is listed as none, and the charge time is 6 hours — so you'll want to plan around topping it up. If you're in a loud environment and need to block it out, this isn't the tool.
• Best for wired, low-latency monitoring → Sennheiser Pro Audio Professional. No Bluetooth pairing, no lag, just a 3.5 mm jack and an included 6.3 mm screw-on adapter.
• Best for wireless freedom and movement → Koss KSC35. Bluetooth 5.2, a 10-metre range and an ear-clip fit designed to stay on during runs and workouts.
• Best for battery life → Koss KSC35. Up to 18+ hours of play/talk time per USB-C charge; the Sennheiser is wired, so battery isn't a factor.
• Best for taking calls → Koss KSC35. Integrated microphone, audio remote and voice-assistant activation. The Sennheiser has no microphone.
• Best for loud environments and sound isolation → Sennheiser Pro Audio Professional. Closed-back, supra-aural cups with sound isolation control and 120 dB sensitivity.
• Best for travel and portability → Koss KSC35. A protective carrying case and cable management clips are included in the box.
• Best for durability and serviceability → Sennheiser Pro Audio Professional. The detachable single-sided cable means a damaged cable is replaceable, and a 2-year warranty is listed.
• Best for fit customization → Koss KSC35. Koss offers standard and oversized cushions in a variety of colours.
If I had to pick one, I'd pick the Sennheiser Pro Audio Professional HD 25 — but only because of what I'd be using it for. In my opinion, if your listening happens at a desk, a mixer or a booth, the closed-back isolation, the 120 dB sensitivity, the detachable cable and the included jack adapter make it the more capable and more repairable tool. If your listening happens on the move — running, lifting, commuting, taking calls — I'd recommend the Koss KSC35 instead, because no amount of sound quality beats a headphone that's actually with you and wire-free. Decide where you listen first, then the choice makes itself.
FAQ
how to fit on ear headphones
how to clean on ear headphones
Focus on the parts that touch your skin. The Koss KSC35 uses foam cushions, which are the simplest to look after and are also replaceable in standard and oversized sizes. The Sennheiser HD 25 uses soft earpads and ships with a carrying case, so storing it in the case between sessions keeps dust and grime off the cups.
how to open ear headphones
Most on-ear headphones don't "open" — the cups are fixed to the headband. What you can open up is the cable side: the Sennheiser HD 25 uses a detachable, single-sided cable, so you can unplug and replace it rather than opening the housing. The Koss KSC35 has no jack, so there's nothing to unplug.
how to ear headphones
If you mean how to wear them, the rule is simple: on-ear cups sit on your ears, over-ear cups surround them. The Sennheiser HD 25 is on-ear and closed-back for isolation; the Koss KSC35 lists a wireless ear-clip design that hangs on the ear for an open, movement-friendly fit.
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