Sennheiser HD 660S2 Wired Audiophile Stereo Headphones with Deep Sub Bass Review: The Legend Reborn with a Thunderous Heart

In the world of high-fidelity audio, there’s a pursuit that borders on obsession: the search for perfect sound reproduction. For years, I, like many fellow audiophiles, have navigated a landscape of compromise. We seek headphones that can render the delicate pluck of a classical guitar string with breathtaking realism, yet also deliver the gut-punching impact of a sub-bass drop in a modern electronic track. Too often, these two desires are mutually exclusive. Analytical headphones can sound thin and sterile, while bass-heavy cans often present a muddy, bloated mess that tramples over the crucial mid-range frequencies. This was the precise dilemma with the otherwise brilliant predecessor, the HD 660S. It was a master of detail and clarity, but for many genres, it left us yearning for that foundational low-end weight. The fear of investing in a premium pair of headphones only to find them lacking in a key area of the frequency spectrum is a real and frustrating hurdle. The Sennheiser HD 660S2 Wired Audiophile Stereo Headphones with Deep Sub Bass enters the arena with a bold promise: to end this compromise and deliver a sound that is both exquisitely detailed and profoundly powerful.

An Audiophile’s Primer: What to Consider Before Buying High-Impedance Studio Headphones

A set of audiophile headphones is more than just a device for listening to music; it’s a precision instrument designed for critical listening and pure enjoyment. It’s a key solution for those who want to hear their favorite albums exactly as the artist and sound engineer intended, revealing layers of detail and nuance lost on consumer-grade equipment. The primary benefit is unparalleled sound quality—clarity, separation, and a frequency response that brings music to life. It’s about creating an intimate, immersive experience where the hardware disappears, leaving only you and the sound.

The ideal customer for this type of product is the dedicated music lover, the home studio producer, or the critical listener who has a quiet space to enjoy their craft. They understand that achieving the best sound requires a complete audio chain, including a quality source and amplification. Conversely, these headphones might not be suitable for those who prioritize portability, wireless convenience, or noise cancellation for commuting. Someone who needs to listen in a noisy office or on public transport would be better served by a closed-back or active noise-cancelling model, as the open-back design of the HD 660S2 is meant to be porous, leaking sound in and out by design.

Before investing, consider these crucial points in detail:

• Comfort & Ergonomics: You’ll likely be wearing these for hours. We found the Sennheiser HD 660S2 Wired Audiophile Stereo Headphones with Deep Sub Bass, at a mere 260 grams, to be exceptionally light. The plush velour earpads and well-distributed clamping force are critical for long-term comfort, preventing pressure points and overheating.
• Performance & Amplification: This is paramount. With a high impedance of 300 Ohms, these headphones require more power to drive than a standard smartphone or laptop can provide. To unlock their true potential—the dynamics, the detail, and especially the bass—a dedicated headphone amplifier or a powerful digital audio player (DAP) is not just recommended; it’s essential. As one user aptly noted, “Without a headphone amplifier, you don’t get out of this headphone what it’s actually capable of.”
• Materials & Durability: Sennheiser has a storied reputation for build quality. While primarily constructed from high-quality plastics, the headphones feel robust and well-engineered. Designed in Germany and manufactured in Ireland, they are built to last. The inclusion of detachable cables is a huge plus for longevity, as the cable is often the first point of failure.
• Open-Back vs. Closed-Back Design: Understanding this is non-negotiable. The HD 660S2 is an open-back design, meaning the back of the earcups is grilled and open to the air. This creates a wider, more natural, and speaker-like soundstage. However, it provides virtually no sound isolation, meaning you will hear your environment, and others will hear your music. This makes them suitable for quiet, private listening sessions only.

Making an informed choice ensures you get an instrument that will bring you joy for years, rather than a frustrating mismatch for your listening habits. If the open-back design gives you pause, exploring other options is a wise move.

While the Sennheiser HD 660S2 Wired Audiophile Stereo Headphones with Deep Sub Bass is an excellent choice for its intended purpose, it’s always wise to see how it stacks up against the competition, especially if sound isolation is a priority. For a broader look at top models designed for studio environments where isolation is key, we highly recommend checking out our complete, in-depth guide:

First Contact: Unboxing a Modern Classic

The unboxing experience of the Sennheiser HD 660S2 Wired Audiophile Stereo Headphones with Deep Sub Bass is a statement of intent. There’s no excessive flair, just purposeful, premium packaging that protects its valuable contents. Sliding the sleeve off reveals a sturdy, branded storage pouch, and nestled within are the headphones themselves. The immediate impression is one of surprising lightness. At 260 grams, they feel almost ethereal compared to many of their planar magnetic competitors. The classic, no-nonsense Sennheiser aesthetic is present, with a matte black finish and bronze logo accents that add a touch of modern elegance. Also in the box are two high-quality, 1.8-meter detachable cables—one terminating in a standard 6.35mm jack and the other in a 4.4mm Pentaconn balanced connector for use with high-end amplifiers and DAPs. A 6.35mm to 3.5mm adapter is thoughtfully included, expanding compatibility. The plush velour earpads and headband padding feel luxurious to the touch, promising the long-session comfort for which the 600 series is famous. It’s an unboxing that feels less like opening a gadget and more like being handed a precision musical instrument.

Performance Deep Dive: An Autopsy of an Audiophile Masterpiece

This is where we move beyond specs and into the soul of the sound. After weeks of intensive listening across multiple genres, amplifiers, and sources, we can confidently say that Sennheiser has not just tweaked a formula; they’ve perfected it. The Sennheiser HD 660S2 Wired Audiophile Stereo Headphones with Deep Sub Bass is a triumph of audio engineering, addressing the singular major critique of its predecessor while enhancing its legendary strengths.

The Bass Reimagined: Power Without Corruption

Let’s address the headline feature first: the bass. Sennheiser claims double the sound pressure at the lowest octaves, and our ears confirm this is no marketing hyperbole. The transformation is staggering. Listening to tracks like “Angel” by Massive Attack, the subterranean bass line isn’t just a suggestion; it’s a physical presence that you feel as much as you hear. On electronic tracks from artists like Daft Punk or Aphex Twin, the kick drums are tight, fast, and hit with genuine authority. What’s truly magical, and what separates the HD 660S2 from lesser bass-focused headphones, is the control. Sennheiser achieved this through a new vented magnet system and an ultra-light aluminum voice coil. This technology allows the 42mm transducer to move air with greater force at low frequencies while maintaining incredible speed and agility. The result is a deep, textured, and articulate bass that never, ever sounds bloated or slow. As one user listening to “drum n bass” and other genres confirmed, “everything sounds amazing.” Another noted the “impresionantes bajos sin contaminar los medios” (impressive bass without contaminating the mids). This is the holy grail: powerful low-end that serves as a solid foundation for the music, rather than a muddy blanket smothering it.

The Legendary Sennheiser Mid-Range: More Intimate Than Ever

For decades, the Sennheiser 600-series has been the benchmark for natural, realistic mid-range reproduction, and the HD 660S2 proudly carries that torch. This is where the music truly lives—the emotive strains of a cello, the raw texture of an electric guitar, and most importantly, the human voice. Listening to acoustic sets from artists like Tracy Chapman or Chris Cornell, the presentation is so intimate and lifelike it feels like a private performance. Every subtle vocal inflection, breath, and nuance is laid bare with astonishing clarity. The enhanced bass response actually benefits the mids, giving male vocals more body and authority, and anchoring instruments like pianos and acoustic guitars with a more realistic sense of weight and scale. The sound is often described as being somewhere between neutral and warm, a characterization we wholeheartedly agree with. It’s an inviting, non-fatiguing sound that encourages you to get lost in the music for hours on end. A user from Japan praised the sound for being fatigue-free, with a gentle character in the highs and a rich, pleasant low-end, making them a joy to listen to for extended periods.

Soundstage and Imaging: A Coherent and Precise Performance

As open-back headphones, the Sennheiser HD 660S2 Wired Audiophile Stereo Headphones with Deep Sub Bass naturally provides a more spacious and “out-of-head” listening experience than its closed-back counterparts. While it may not have the vast, concert-hall-like soundstage of its much more expensive sibling, the HD 800S, what it offers is perhaps more practical and engaging for most music. The soundstage is wide enough to feel expansive but intimate enough to remain coherent and focused. The real star of the show is the imaging. On well-recorded jazz or classical pieces, you can pinpoint the exact location of every instrument in the orchestral space with surgical precision. This exceptional instrument separation means that even in the most complex musical passages, nothing gets lost or smeared together. This quality also makes them surprisingly potent for gaming. One reviewer highlighted this, noting that they could now hear “extremely small sounds that were completely inaudible before,” allowing them to react faster in games. This is a testament to the headphone’s incredible detail retrieval and spatial accuracy.

The Amplifier Imperative: Unlocking the Beast

We cannot stress this enough: to experience everything we’ve just described, you must use a headphone amplifier. The 300-ohm impedance is a deliberate engineering choice that contributes to the driver’s control and low distortion, but it presents a significant hurdle for low-power sources. Plugging these directly into a smartphone or a standard laptop headphone jack will result in a sound that is quiet, thin, and lifeless. The bass will be absent, and the dynamics will be crushed. Multiple users echoed this sentiment, with one German reviewer stating they initially thought their AirPods Max were peak audio until they paired the HD 660S2 with a proper amplifier, at which point it was “Tschüss Airpods Max” (Goodbye AirPods Max). We tested the headphones with several DAPs and desktop amps, including a FiiO K9 Pro ESS and a Chord Mojo 2. In every case, providing adequate power was like flipping a switch. The sound opened up, the bass slammed into place, and the full dynamic range of the music was unleashed. Investing in the Sennheiser HD 660S2 Wired Audiophile Stereo Headphones with Deep Sub Bass means committing to the full audio chain; to do otherwise would be a disservice to both the headphones and your music library.

What Other Users Are Saying

The consensus among users is overwhelmingly positive, with many calling the sound quality “incredible” and “amazing.” A common thread is the sheer level of detail and the quality of the bass, which many describe as a perfect evolution of the Sennheiser sound. One user was so impressed they said, “I wish I could give 6 stars.” The mandatory nature of an amplifier is the most frequently cited caveat, serving as a critical piece of advice for potential buyers. Users who pair it with quality gear, like a FiiO M23 or a HiBy R6 III, report a sound that is “as close to analog as possible.”

However, the experience isn’t universal. One reviewer found them to be only “okay at best,” feeling their wireless Bang & Olufsen headphones offered comparable performance and opted to return them in favor of a much more expensive Focal Clear MG. This highlights an important point in high-end audio: personal preference and synergy with existing gear play a massive role. The Sennheiser sound signature, while refined, may not appeal to everyone, especially those accustomed to a different style of presentation. Nonetheless, for the vast majority, the HD 660S2 seems to hit a musical sweet spot that is hard to beat.

How Does It Compare? The Sennheiser HD 660S2 vs. The Alternatives

While the Sennheiser HD 660S2 Wired Audiophile Stereo Headphones with Deep Sub Bass excels in its niche, it’s important to understand how it fits into the broader market. Here, we compare it to three distinct alternatives to help clarify who each product is best for.

1. Skullcandy Smokin’ Buds 2 In-Ear Headphones

This is a comparison of two entirely different worlds. The Skullcandy Smokin’ Buds 2 are ultra-portable, budget-friendly in-ear headphones designed for on-the-go listening and hands-free calls. Their primary benefits are convenience, portability, and a low price point. In contrast, the HD 660S2 is a premium, specialized piece of home audio equipment. Someone would prefer the Skullcandy buds if their primary needs are listening to podcasts during a commute, taking calls at the gym, and having something they can easily throw in a pocket. Audio fidelity is secondary to convenience and function, making them a polar opposite to the Sennheiser’s purpose-built design for critical listening in a quiet room.

2. RØDE NTH-100 Professional Over-ear Headphones

The RØDE NTH-100 offers a much more direct comparison, but with a critical difference in philosophy and design. These are closed-back studio monitor headphones built for content creators, producers, and audio engineers. Their goal is to provide a neutral, uncolored sound signature for mixing and editing, coupled with excellent sound isolation to block out external noise. A user might prefer the NTH-100 if they are recording a podcast, tracking vocals, or mixing music and need to hear every flaw in the audio without being disturbed. While the Sennheiser HD 660S2 can also be used for professional work, its open-back design and slightly warmer, more engaging tuning make it lean more towards the audiophile’s chair for pure listening enjoyment rather than the producer’s desk for strict analytical work.

3. Audio-Technica M50xGM Monitor Headphones

The Audio-Technica M50x is a legendary workhorse in the audio world, beloved by DJs and studio professionals for its robust build, good isolation, and energetic, V-shaped sound signature (emphasized bass and treble). Compared to the HD 660S2, the M50x offers a more “fun” and less nuanced presentation. Its bass is punchy but less detailed, and its mids are less forward and natural. A musician tracking in a studio or a DJ wanting a durable, isolating headphone with an exciting sound would likely prefer the M50x, especially given its significantly lower price point. The HD 660S2, however, is a substantial upgrade in every technical aspect: detail, soundstage, realism, and overall refinement. It’s the choice for the discerning listener who has moved beyond monitoring and into pure appreciation.

The Final Verdict: Is the Sennheiser HD 660S2 Worth It?

After extensive testing, we can say with certainty that the Sennheiser HD 660S2 Wired Audiophile Stereo Headphones with Deep Sub Bass is not just an incremental update; it’s a phenomenal success and a worthy successor to a legendary lineage. It masterfully solves the bass deficiency of its predecessor, delivering a low-end that is both deeply satisfying and technically brilliant, all without compromising the sublime mid-range that is the hallmark of the Sennheiser brand. They are supremely comfortable, well-built, and offer a level of musical insight that is truly captivating.

This is not a headphone for everyone. It demands a quiet room, a proper amplifier, and an appreciation for nuanced, high-fidelity sound. But for the dedicated audiophile, the home listener who wants to fall in love with their music all over again, the HD 660S2 is a resounding triumph. It represents one of the most complete and musically engaging packages available at its price point. If you are ready to make a serious investment in your listening pleasure and have the necessary equipment to power them, we give them our highest recommendation. To hear your music with newfound depth, clarity, and emotion, we encourage you to explore the full specifications and check the latest availability today.