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HEADPHONES

Sennheiser HD 660S2

black with bronze accents · 300 ohm · 1.8 m balanced and unbalanced cables · Sennheiser part 700240

Acoustic design
Open-back
Wearing style
Over-ear (circumaural), open-back dynamic headphones
Nominal impedance
300 ohm

The HD 660S2 is an open-back, over-ear headphone with a 38 mm dynamic driver rated 8–41,500 Hz (−10 dB) at 300 ohms. Sennheiser revised its acoustics for stronger sub-bass, and it ships with 1.8 m 6.35 mm unbalanced and 4.4 mm balanced cables plus a 3.5 mm adapter.

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Price history · US
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Item price · same listing and exact model

Latest check$365.00
Lowest shown$365.00

2 observed days · 16 Oct–17 Oct

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$365.0017 Oct, 12:05 UTC

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Exact listing · eBay US · USD
Checked (UTC)Item price
$365.00
$365.00

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THE ACTUAL PRODUCT
Sennheiser HD 660S2 open-back over-ear headphones with model badge and detachable cable visible
Official product image · Image source detailsProduct imagery does not establish a retailer’s bundle or condition.
Compare with Sennheiser HD 600
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Specifications checked 11 Sept 2026Manufacturer specifications, not a hands-on test.

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Every specification. With its source.

Full specifications

Suggest a correctionOur publishing standard

Exact configuration: 700240 · black with bronze accents · 300 ohm · 1.8 m balanced and unbalanced cables

24 specifications in 5 groups. Values are manufacturer specifications unless a row says “Measured result” or “Calculated from cited specifications”.

Design & fit

6 items
Acoustic design
Open-backSource
Wearing style
Over-ear (circumaural), open-back dynamic headphonesSource
Weight
260 g

Approximate, without the cable.

Source
Replaceable parts
Detachable cable and replaceable ear pads

Replacement procedures are in the manual; spare-part availability varies.

Source
Ear pads
Velour ear pads; replaceable

Replacement procedure shown in the manual.

2 sources
Rated contact pressure
Approximately 6.0 N ±1.0 N

Nominal clamping force; individual fit and comfort can differ.

Source

Connections & battery

5 items
Wired / wireless connections
Wired analogue stereo; 1.8 m cables with 6.35 mm unbalanced and 4.4 mm balanced plugs; included 3.5 mm adapter
2 sources
Battery life
Not listed by the manufacturer

The reviewed exact sources do not explicitly establish battery life or that no battery is required for operation. A wired/dynamic audio path, omitted charger or Battery included N is not an explicit operating-power requirement.

Source
Included cable length
1.8 m

Length of the supplied cable.

Source
Supplied plug configuration
6.35 mm unbalanced cable; 4.4 mm balanced cable; 6.35 mm-to-3.5 mm adapter

The 4.4 mm balanced cable needs a balanced headphone output; an XLR-4 cable is optional.

2 sources
Included and optional cables
Detachable 1.8 m unbalanced and 4.4 mm balanced cables included; XLR-4 cable optional

Optional cables are sold separately; balanced cables need a balanced headphone output.

2 sources

Audio specifications

9 items
Nominal impedance
300 ohm

Nominal impedance; check that your amplifier or audio source can drive this load.

Source
Rated sensitivity
104 dB SPL at 1 kHz, 1 V rms

Rated at 1 kHz with 1 V rms; not directly comparable with dB/mW ratings.

Source
Rated frequency range
8–41,500 Hz (−10 dB)Source
Driver construction
38 mm open dynamic transducer; aluminium voice coil and vented magnet system

Sennheiser lists 38 mm as the transducer size.

Source
Frequency equalisation
Diffuse-field equalisedSource
Rated total harmonic distortion
≤0.04% at 1 kHz, 100 dB SPL

Rated at 1 kHz and 100 dB SPL; other models use different test levels, so compare with care.

2 sources
Rated long-term input power
Maximum 500 mW under EN 60-268-7

Rated to EN 60-268-7; the maximum input the headphones can handle, not the amplifier power they need.

Source
Published acoustic changes
Revised 300-ohm coil, more compliant surround, 70 Hz resonance and revised transducer airflow

Sennheiser describes these changes as the S2 revision of the HD 660S.

Source
Manufacturer sub-bass claim
Double the sound pressure at the lowest frequencies

Sennheiser does not give the frequency range or comparison model for this claim.

Source

Calls & noise control

2 items
Active noise cancellation
Not listed by the manufacturer

The reviewed exact sources do not explicitly establish active noise cancellation absence. Preserve separately sourced acoustic design and passive attenuation; they cannot turn omitted ANC into a false capability.

Source
Microphone
Not listed by the manufacturer

The reviewed exact sources do not explicitly establish microphone absence. Omission from a package or technical inventory, a stereo audio connector, and a without-remote statement do not establish microphone=false.

Source

Operating limits

2 items
Static magnetic field at the surface
4.5 mT

Static magnetic field at the headphone surface.

2 sources
Operating temperature
−10 °C to +55 °CSource
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