Field Test · Studio Gear Review
Sennheiser HD 660S2
Technical assessment of Sennheiser’s HD 660S2 open-back headphones
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- Powerful bass in a lightweight design
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Spec Sheet
- Wired
- Circumaural
- Open design
- Dynamic
- Frequency range: 8 – 41,500 Hz
- Impedance: 300 Ohm
- Sound pressure level: 104 dB (1V)
- Driver size: 38 mm
- Distortion factor: <0.04% (1 kHz, 100 dB)
- Velour ear pads
- Two-sided cable routing
- Weight: 260 g
- Colour: Black
- Incl. 1.8 m cable (6.3 mm stereo jack), 1.8 m cable (4.4 mm balanced), 6.3 mm to 3.5 mm stereo adapter and carrying pouch
- Made in Ireland
Studio Log
| Available since | February 2023 |
|---|---|
| Item number | 557336 |
| Sales Unit | 1 piece(s) |
| Design | Over-Ear |
| System | Open |
| Impedance | 300 Ohms |
| Frequency range | 8 Hz – 41500 Hz |
| Adapter | Yes |
| Replacable Cable | Yes |
| Marrone/Argento | Black |
| Max. SPL | 104 dB |
| Sensitivity | 104 dB |
| Type Of Connector | Jack(stereo) |
| Adaptor | Yes |
| Weight | 260 g |
| Replaceable Cable | Yes |
| Colour | Black |
Demo Footage
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QC Pass — Field Test
Customer Review Summary
Introduction
The Sennheiser HD 660S2, released in February 2023, is an open-back, over-ear headphone designed to deliver high-fidelity audio with a focus on balanced sound and improved bass response. Priced at £389 and manufactured in Ireland, it targets audiophiles and studio professionals seeking accurate reproduction with some warmth. We examine its core features, performance, and usability based on technical data and user feedback.
Design and Build Quality
The HD 660S2 is a dynamic, circumaural headphone featuring velour ear pads for comfort during prolonged use. It weighs 260 grams, making it relatively lightweight for its class. The open design allows sound to breathe, which contributes to a more natural spatial experience, even if some users note the soundstage is less expansive compared to the HD 800S model.
Materials and finish are practical rather than luxurious, with a black colour scheme and utilitarian styling. The build quality is consistent with Sennheiser’s reputation: robust and functional, though it lacks premium touches typical of higher-end or boutique offerings. Cable management includes replaceable two-sided cables, enhancing longevity and flexibility.
Technical Specifications Overview
- Driver Size: 38 mm dynamic drivers
- Impedance: 300 Ohms, requiring a capable amplifier for optimal performance
- Frequency Response: 8 Hz to 41,500 Hz, covering an extremely wide audible spectrum
- Sensitivity: 104 dB, allowing for adequate volume with compatible sources
- Max SPL: 104 dB (1V)
- Distortion: Below 0.04% at 1 kHz and 100 dB, indicating clean sound reproduction
- Cables Included: 1.8 m stereo jack 6.3 mm, 1.8 m balanced 4.4 mm, plus 6.3 mm to 3.5 mm adapter
Sound Quality and Listening Experience
The HD 660S2 delivers a notably warmer sound compared to its predecessor, with improved bass extension that is described as dry, crisp and precise. This sub-bass enhancement enriches the listening experience, especially for genres demanding low-end depth, such as electronic or techno.
Midrange and treble are well defined, but some listeners report a slight lack of clarity in complex mixes. Instruments occasionally lose precise placement, producing a less spacious soundstage than premium models like the HD 800S. The sound is intimate, with the audio image feeling close rather than wide.
This headphone excels at revealing mix imbalances and brings out details that might be missed on other devices. It is especially suitable for users who prefer a more engaging and dynamic listening session rather than purely analytical neutrality.
Bass Performance
The promise of boosted low-end is fulfilled, yet the bass remains controlled and avoids muddiness. However, techno enthusiasts aiming for a pronounced deep bass may find the output less forceful without a dedicated external amplifier, as the 300 Ohm impedance demands substantial power to reveal the full potential.
Treble and Mids
Midrange frequencies retain warmth and contribute to a harmonious overall tonal balance, while the treble maintains clarity without brightness or harshness. Some wearers mention a subtle lack of resolution in the high frequencies, which might disappoint those accustomed to extremely crisp treble reproduction from competitors.
Comfort and Usability
The velour ear pads and moderate clamping force ensure the HD 660S2 is comfortable for extended listening periods. Its circumaural design effectively envelopes the ears, though the overall contact pressure is slightly higher than some comparator models like the Sennheiser HD 400 Pro, which offers marginally better comfort.
Weight and design contribute positively to wearing stability, including during head movement. The inclusion of replaceable cables and a balanced 4.4 mm option caters to audiophiles interested in maximising connection quality, though the provided 1.8 m cable length is somewhat short by professional standards.
A carrying pouch is supplied, but users note the absence of a firmer protective case, which would be preferable to safeguard the headphones during transport.
Comparison and Final Thoughts
The HD 660S2 fits well between entry-level open-back headphones and the higher-end specialist models in Sennheiser’s range. It offers improved bass and warmer sound relative to the predecessor, making it attractive for both casual listening and studio work focused on low-end detail.
However, in terms of absolute spatial clarity and resolution, it lags behind flagship models such as the HD 800S or alternatives like the Beyerdynamic DT 1990 Pro, which can deliver a more analytical soundstage and sharper detail at similar price points.
For professionals requiring extended sessions with a slightly fuller bass response, the HD 660S2 presents an excellent choice, particularly when paired with a quality amplifier to drive its 300 Ohm load effectively. Audiophiles seeking a warm, inviting sound with good overall balance will find it rewarding.
Summary
- Pros: Enhanced bass without losing clarity, wide frequency range, comfortable velour pads, replaceable cables including balanced options
- Cons: Less spacious soundstage, moderate treble resolution, short cable length, no protective hard case
- Ideal for: Listeners prioritising musical enjoyment with precise bass detail, studio mixing of low-end frequencies, users with appropriate amplification
Overall, the Sennheiser HD 660S2 is a strong performer within its price bracket, delivering a nuanced and satisfying audio experience. It rewards careful pairing and appeals to those valuing rich bass and dependable build quality balanced against detailed, if slightly intimate, sound reproduction.
