Sennheiser HD 660S2

Overview

The Sennheiser HD 660S2 are open-back, circumaural headphones developed for audio enthusiasts and professionals who require high-fidelity sound reproduction. Positioned as an evolution of the HD 660S, this iteration focuses on refined bass response and improved treble clarity, aiming to deliver a more engaging and detailed listening experience across various genres and media types. The HD 660S2 is suitable for critical music listening, studio monitoring, and audiophile-grade gaming setups where soundstage and positional audio are prioritized. Its open-back design naturally extends the soundstage, providing a sense of spaciousness often preferred for immersive audio experiences.

These headphones are characterized by their relatively high impedance of 300 ohms, which indicates they benefit from a dedicated headphone amplifier or a high-output audio interface to achieve optimal performance. This design choice is common in audiophile-grade headphones, as it allows for greater control over the driver and reduced distortion when paired with appropriate amplification. The HD 660S2 comes with two detachable cables: one terminated with a 6.3mm TRS connector and another with a 4.4mm Pentaconn balanced connector, catering to different amplifier types and balanced audio setups. A 3.5mm adapter is also included for broader compatibility with consumer devices.

The HD 660S2 excels in scenarios where audio accuracy and detail retrieval are paramount. For music listeners, this translates to hearing subtle nuances in recordings and a faithful representation of the original mix. In gaming, the open-back nature contributes to a wide and accurate soundstage, which can enhance spatial awareness in titles that leverage advanced audio engines. The comfortable velour ear pads and lightweight construction are designed for extended listening sessions, a critical factor for both professional use and prolonged gaming. While the open-back design provides sonic benefits, it also means these headphones offer minimal passive noise isolation, making them less suitable for noisy environments but ideal for quiet listening spaces.

Compared to closed-back alternatives, the HD 660S2's open design mitigates pressure build-up within the earcups and reduces reflections, which can lead to a more natural and less fatiguing sound. This characteristic is a key selling point for users who prioritize sonic transparency and comfort over isolation. The headphones are constructed with durable materials, ensuring longevity for regular use. Sennheiser, founded in 1945, has a history of producing audio equipment for both consumer and professional markets, and the HD 660S2 continues this legacy by targeting users who demand high performance from their audio peripherals.

Key features

• Open-Back Acoustic Design: Provides a wide, natural soundstage and reduced ear fatigue by allowing air to pass through the earcups, creating a more spacious listening experience.
• Refined Transducer System: Features a redesigned voice coil and diaphragm optimized for improved bass extension and enhanced treble detail, aiming for a more balanced and engaging frequency response compared to its predecessors, as noted in professional reviews of the HD 660S2's sound profile by RTINGS.com.
• 300 Ohm Impedance: Engineered to pair with dedicated headphone amplifiers or high-output audio interfaces for optimal performance, ensuring precise driver control and minimal distortion.
• Detachable Cables: Includes two 1.8-meter cables with different terminations: a 6.3mm stereo jack for standard audio equipment and a 4.4mm Pentaconn balanced connector for compatible balanced amplifiers, along with a 3.5mm adapter.
• Comfort-Oriented Design: Equipped with large, elliptical earcups and soft velour pads designed for extended wear during long listening sessions or gaming, reducing pressure points.
• Robust Construction: Built with durable components to withstand regular use, reflecting Sennheiser's engineering standards for longevity in their audiophile headphone line.
• High-Resolution Audio Capability: Designed to reproduce high-resolution audio files with clarity and detail, making them suitable for lossless music formats and advanced audio codecs.

Pricing

The Sennheiser HD 660S2 is positioned in the premium segment of the audiophile headphone market. Pricing information is current as of May 7, 2026.

Common integrations

As a hardware audio peripheral, the Sennheiser HD 660S2 primarily integrates with audio playback and amplification systems. It does not feature software APIs or SDKs as it is not a programmable device. Effective integration focuses on pairing it with appropriate audio sources and amplification for optimal sound quality.

• Headphone Amplifiers: Due to its 300-ohm impedance, the HD 660S2 benefits significantly from a dedicated headphone amplifier to drive the transducers effectively and provide sufficient power for dynamic range.
• Digital-to-Analog Converters (DACs): Pairing with a high-quality DAC can improve the digital audio signal conversion, reducing noise and distortion before amplification, particularly for high-resolution audio files.
• Audio Interfaces: For recording artists, streamers, or gamers using professional audio setups, integrating the HD 660S2 with an audio interface that features a strong headphone output is common.
• Balanced Audio Systems: Utilizing the included 4.4mm Pentaconn balanced cable with a compatible balanced amplifier can reduce noise and crosstalk, potentially enhancing stereo separation and overall clarity.

Alternatives

Several other open-back headphones cater to a similar audience seeking high-fidelity audio for critical listening and gaming:

• Beyerdynamic DT 900 PRO X: A professional open-back studio headphone with a lower impedance, often praised for its analytical sound and robust build quality, suitable for studio monitoring and detailed listening.
• HIFIMAN Sundara: A planar magnetic open-back headphone known for its expansive soundstage and detailed, airy presentation, offering a different driver technology compared to the HD 660S2's dynamic drivers.
• Audio-Technica ATH-R70x: An open-back reference headphone with a lightweight design and high impedance, often chosen for its neutral sound profile and comfort in professional audio environments.

Getting started

The Sennheiser HD 660S2 is a plug-and-play hardware device. There is no software or code required for its basic operation. The primary setup involves physical connections to an audio source and, ideally, an amplifier. The following steps outline a typical setup for optimal performance:

1.  Unbox and Inspect: Remove the HD 660S2 headphones, both detachable cables (6.3mm and 4.4mm Pentaconn), and the 6.3mm to 3.5mm adapter from the packaging.
2.  Choose Cable: Select the appropriate cable for your audio source. If connecting to a standard headphone jack (e.g., on a computer, phone with adapter, or basic audio interface), use the 6.3mm cable and the 3.5mm adapter if needed. If connecting to a balanced headphone amplifier, use the 4.4mm Pentaconn cable.
3.  Connect Cable to Headphones: Insert the two-pin connectors of the chosen cable firmly into the corresponding jacks on the bottom of each earcup. Ensure they click into place.
4.  Connect to Audio Source/Amplifier:
    *   For direct connection to a device with a 3.5mm jack: Attach the 3.5mm adapter to the 6.3mm cable, then plug into the device.
    *   For devices with a 6.3mm jack: Plug the 6.3mm cable directly into the device.
    *   For balanced amplifiers: Plug the 4.4mm Pentaconn cable directly into the amplifier's balanced output.
5.  Power On Amplifier (if applicable): If using a dedicated headphone amplifier, ensure it is powered on and configured correctly.
6.  Adjust Volume: Start with a low volume level on your audio source or amplifier and gradually increase it to a comfortable listening level.
7.  Break-in Period: Some audiophiles suggest a "break-in" period for new headphones, typically involving 50-100 hours of playback, though the sonic impact of this is debated. The headphones are ready for use out of the box.

For optimal sound quality, especially for critical listening or high-resolution audio, pairing the HD 660S2 with a dedicated DAC and headphone amplifier is recommended to fully realize its potential, given its 300-ohm impedance. Information on suitable amplification can often be found in reviews of the HD 660S2, such as those detailing performance characteristics on Tom's Hardware.