The Sennheiser HD 660S2 Open-Back Headphones is a headphone designed for focused home listening. Its core specification combines Open-back over-ear, 8 Hz to 41.5 kHz and 300 ohms. That feature set makes it a practical choice when you want stationary listening where an open acoustic design and wired connection make sense. The emphasis stays on stated hardware and connection details, making it easy to see where this model fits in a real listening or home-entertainment setup.

For day-to-day ownership, balanced connection is 4.4 mm cable, while unbalanced connection is 6.35 mm cable. Adapter is specified as 6.35 mm to 3.5 mm adapter. Those details shape how the product connects, how it is used and what you need from the rest of your system. It is best suited to hi-fi and desktop systems and long-form music sessions, with the exact Sennheiser model features kept front and centre so you can choose it for the capabilities that actually matter.

Ideal For

Key Features

Designed Around the Right Use Case

Stationary listening where an open acoustic design and wired connection make sense. The specification focuses on acoustic design, frequency response and impedance.

Connections and Everyday Ownership

Balanced Connection: 4.4 mm cable. Unbalanced Connection: 6.35 mm cable. These are the details that determine how the product works with the rest of a setup.

Control and Practical Detail

Adapter: 6.35 mm to 3.5 mm adapter. This keeps the ownership experience grounded in the functions built into this exact model.

How It Compares

Compared with closed-back headphones, this open-back design does not target acoustic isolation. It is intended for stationary listening where its wired connection and open acoustic structure are appropriate.

The Verdict