Sennheiser HD 660S2 300 Ohm Open-Back Audiophile Headphones

Nominal impedance

Acoustic design

Driver system

Published frequency response

Detail with low-end depth

A revised 300-ohm driver and lightweight aluminium voice coil support precise reproduction, while extended sub-bass brings added weight to your music. Use familiar recordings and a consistent listening level when assessing sound with your usual audio equipment.

Comfort for your listening space

Soft velour earpads and a padded headband complement the 260 g design. The open earcups suit a quiet room where you can settle into an album.

Two ways to connect

Choose the supplied 6.35 mm cable or 4.4 mm balanced cable, each 1.8 m long. A 3.5 mm adapter and carry pouch are also included.

The Driver System in This Model

The listed driver arrangement is Dynamic, open-back, 38 mm. The manufacturer’s stated frequency response is 8–41,500 Hz (–10 dB). Listen with familiar speech, instruments and transient-rich recordings while keeping the playback source and listening level consistent. Driver size describes the construction; the full listening result also depends on fit and your audio chain.

Match the Source to the Actual Load

This configuration has a listed impedance of 300 Ohm. Source output capability and headphone sensitivity both affect the available listening level. Choose an appropriate headphone output, start at a low setting and adjust around your recordings. A plug adapter changes the connector size; it does not add amplifier power.

Which headphone configuration is this?

Sennheiser HD 660S2 300 Ohm Open-Back Audiophile Headphones. 300 Ohm is the listed impedance; choose the exact model rather than transferring specifications from another version.

Is the acoustic design suitable for my room?

Open-back headphones allow sound into and out of the earcups. A quiet environment helps, and nearby microphones or people may hear the playback.

Do I need a headphone amplifier?

300 Ohm is the impedance, but sensitivity, source capability and your desired level also matter. Use a suitable headphone output; higher-impedance models can need more voltage than a phone or controller provides.

What cable or plug is specified?

Detachable OFC cable, 1.8 m. Use the connection and any adapter specified for this exact model.

Does it include a voice microphone?

These are dedicated listening headphones. Add a separate microphone and the appropriate recording input if your setup needs voice chat or recording.

How should I interpret the recommended audio equipment?

The recommendations offer alternative audio chains. A standalone amplifier needs a suitable analogue source; a standalone DAC needs an amplifier. Keep the normal stereo cable with the matching headphone output.

Which K11 R2R output matches the supplied balanced cable?

HD 660S2 includes a genuine 4.4 mm balanced cable. Use that cable with K11 R2R’s 4.4 mm balanced output, whose recommended load is 8–350 Ohm. The 300-ohm headphone is above the stated 8–150 Ohm recommendation for K11 R2R’s 6.35 mm single-ended output. A plug adapter does not convert a single-ended cable to balanced.