Sennheiser HD 660S2

The HD 660S2 delivers deeper, more impactful bass than its predecessor, with an 8Hz low end and a warm sound that owners rave about. Build quality sits in the top 4% of all headphones we've tested, and a 4.7/5 user rating confirms it's a crowd-pleaser. But the 499g weight tanks the comfort score to the 10th percentile, and you absolutely need a headphone amp to get the most out of these.

Even though the HD 660S2 only lands at the 78th percentile for overall sound, that number undersells the tuning magic here. The frequency response stretches down to 8 Hz, which is deeper than most dynamic drivers manage, and the 38mm transducers deliver a bass presence that multiple owners describe as a genuine step up from the original HD 660S. You don't need to reach for EQ, the warm, open presentation handles everything from timpani rolls to synth bass with a natural feel that makes you forget you're wearing headphones. The 300-ohm impedance means these scale wonderfully with a dedicated amp; plug them straight into a phone and they'll sound thin and lifeless. Give them proper power, and the midrange clarity and instrument separation are downright addictive. The open-back design also creates a spacious stage, though it won't challenge the widest flagships for sheer width. Build quality is where these really shine. That 96th percentile rank puts them in the conversation with headphones costing much more, and the removable cable system with both 6.3mm and 4.4mm connectors is a practical touch. Just be ready for a break-in period. The clamp force out of the box can be punishing, and at nearly half a kilogram, these are among the heaviest over-ears we've tested, which explains the brutal 10th percentile comfort score. After the pads soften up, many find them fine for all-day sessions, but your mileage will vary.

Pitting the HD 660S2 against the Sony WH-1000XM6, Bowers & Wilkins Px8 S2, Bose QuietComfort Ultra, and other closed-back ANC cans is almost unfair because they serve opposite masters. The Sennheiser is a wired, open-back specialist delivering a warm, fatigue-free sound that owners call "jaw-dropping"; the Sony and Bose are marvels of modern noise cancelling and wireless connectivity. For pure music enjoyment at a desk, the HD 660S2's 8Hz bass extension and effortless mids embarrass the competition. But the moment you need to take a call, block out an airplane engine, or listen without a cable, the Sennheiser completely falls apart (its mic and ANC sit at 16th and 31st percentile). Even among open-back rivals, the HD 660S2 trades blows with pricier siblings like the HD 800S, with some owners actually preferring the S2's extra bass punch for everyday fun listening. It is a very specific tool for a very specific listener.

Price is a moving target. Listings we pulled range from a tempting $349 all the way up to a very optimistic $88,000, but the realistic sweet spot sits around the $400-$500 mark. At $349, you are getting a huge slice of audiophile performance for a fraction of what some competitors charge. When you compare it to wireless ANC flagships like the Sony WH-1000XM6 or Bose QuietComfort Ultra that often cost similar money, you are trading all the convenience features for a level of clarity, bass control, and build that those models cannot match. If you already own a decent amp, the HD 660S2 on sale is a no-brainer. Without an amp, though, you'll need to budget another $100-$200 for a basic desktop DAC/amp combo to even hear what these are capable of.

With social proof and user sentiment both hovering in the top 3-4% of all headphones we track, the Sennheiser HD 660S2 enters the scene with a very loud fan club. Owners rate it 4.7 out of 5 across 209 reviews, and our own analysis puts its build quality in the 96th percentile. This is a headphone that feels meticulously crafted, and most people find the sound to be something special, especially the newly deepened bass. But those gushing reviews don't tell the whole story. Comfort sits all the way down at the 10th percentile, and the 499g weight is a big part of why. You'll need an amp to wake these up, and there is no noise cancelling, no Bluetooth, and a pretty sad mic score if you ever tried to use it for calls. It is a wired, open-back specialist through and through.

If you need headphones that pull double duty for calls, travel, or noisy offices, look elsewhere. The 10th percentile comfort score and 499g weight mean they can feel like a head vise during break-in, and the total lack of ANC (31st percentile) plus a terrible mic (16th percentile) make them a non-starter for anyone needing an all-in-one solution. Wireless fanatics and people who listen mostly on the couch without an amp will be better served by the Sony WH-1000XM6 or Bose QuietComfort Ultra, which sacrifice audio purity for daily practicality.

The Sennheiser HD 660S2 earns its 4.7-star reputation by fixating on sound quality and build and ignoring nearly everything else. If you've got a dedicated listening space and a solid amplifier, this is one of the most satisfying open-back experiences you can get without spending four figures, especially when the sub-bass hits. The comfort struggles and total lack of features mean it is a terrible all-rounder, but as a specialist at $349 on sale, it is genuinely hard to beat. Our data and owner feedback both point to the same conclusion: it is a love letter to audiophiles who value substance over convenience.