Sennheiser HD 660 S  Headphones Review

The Sennheiser HD 660S are good-looking headphones that resemble other premium Sennheiser cans, like the Sennheiser HD 650 and Sennheiser HD 600, but with a black matte finish. The grille on the outside of the large oval ear cups shows off their drivers, and the pads are covered with a microfiber-like fabric that gives the headphones a premium feel.

These headphones are decently comfortable, if a little tight. If you have a larger head or prefer a looser fit, these might not be the most comfortable for you. For reference, they have about double the clamping force of the Sennheiser HD 598. On the other hand, the microfiber-like fabric on the ear cup padding is soft and feels nice to the touch, and the cups themselves are very large and suitable for most ear sizes and shapes. Their headband design is more comfortable than the Sennheiser HD 600, as it distributes weight more effectively across the whole headband.

While not as breathable as other Sennheiser headphones with a lighter clamping force, like the Sennheiser HD 598, the open-back design of the Sennheiser HD660 S means they still have acceptable breathability. They create a good seal around your ears that does trap some heat under the ear cups, but the grille design helps with airflow.

These audiophile headphones aren't designed to be very portable. They're bulky and large, and you can't fold them into a more compact format or lay the ear cups flat. They also don't come with a dedicated case or pouch to carry the headphones in, which is slightly disappointing, but it's unlikely that you'll be on the go much with these cans.

These headphones have a good build quality. Like the Sennheiser HD 6XX, they are mostly made of plastic, with a metal headband and metal grilles covering the drivers. The headband feels durable but isn't very flexible, and the joint that connects the headband to the ear cups feels susceptible to breaking under stress. The cables are detachable and thus replaceable if broken.

These headphones maintain a very stable fit on the head when used for their intended purpose of indoor listening, but vigorous headbanging may cause them to slip off. It's also possible their wire might snag on something if used on the move.

• Sennheiser HD 660 S headphones
• 1/4" audio cable
• 0.17 inch (4.4 mm) balanced audio cable
• 1/4" to 1/8" adapter
• Manuals

These headphones are generally well-balanced with excellent accuracy in the mid-range, so mixes sound even, and vocals are present without being honky or harsh. A dip in the low-treble and a small boost in the high-bass regions gives them a slightly warm and mid-forward sound. That said, as open-backs, they lack some low bass, so fans of bass-heavy genres like EDM might be slightly disappointed by the Sennheiser HD660 S's lack of thump. Their successor, the Sennheiser HD 660S2, are better for listeners who prefer a touch more boom.

These headphones have very good frequency response consistency, with stellar performance across the mid-range in particular. Bass performance is excellent, too, with minimal deviation throughout the entire bass region. Treble consistency is another story, with peaks and dips depending on the headphone's fit and seal, so it's worth taking some time to ensure these sit well on your head.

These headphones have decent bass accuracy. Like many open-back headphones, their low bass is slightly attenuated, so they don't accurately produce the thump of a kick drum, and they're short of mid-bass, so bass sounds lack a little punch. That said, they make up for this somewhat with a small boost in the high-bass region, which helps give these cans their warm tonality and keeps basslines feeling present and full.

These cans have outstanding mid-range accuracy. With an even and flat response across the entire range, vocals, instruments, and effects sound natural and present, with little honk or harshness. When listening to songs like Dua Lipa's 'New Rules,' her vocals come across as loud and powerful without overwhelming the song's drums or synths, just as you'd expect from a pop song.

These headphones have a decent treble response. The lower end of the low treble is fairly flat, so instruments and vocals sound present and detailed. However, a dip from the higher end of this range progresses into the mid-treble, which veils higher harmonics and dulls cymbals and sibilants. The headphones' fit and seal also slightly affect the mid-treble region.

These headphones have a very good peaks and dips performance and generally follow their sound profile well. The peak in the high-bass helps keep basslines audible despite the headphone's relative lack of punch and thump from the low- and mid-bass, but it can also make already-warm content sound a touch muddy. On the other hand, the dip between the low- and mid-treble regions dulls sibilants and cymbals, and the peak in the mid-treble can make some audio sound harsh or piercing.

The imaging performance of these headphones is superb. Sennheiser's audiophile headphones are usually subject to excellent quality control, and while imaging varies between units, our Sennheiser HD 660 S lives up to the Sennheiser reputation. The group delay response is inaudible, resulting in a tight bass. Our unit's left and right drivers are closely aligned in amplitude, phase, and frequency throughout the mid and treble ranges. This means objects like voices, instruments, and effects are accurately placed within the stereo image.

The Sennheiser HD 660 S have an okay passive soundstage. They're open-back headphones and interact greatly with your environment, giving them a more natural and spacious sound than closed-back designs. On the other hand, the sound doesn't seem like it's coming from outside the listener's head, nor does the soundstage feel very large.

These headphones have a very good weighted harmonic distortion performance. While distortion rises slightly at moderate volumes between the low- and mid-bass and between the high-mid and low-treble ranges, this will not affect the purity of your audio unless you are an incredibly discerning audiophile.

These are the settings used to test these headphones, and our results are only valid in this configuration.

These headphones have very bad noise isolation. This is unsurprising, as open-backs leak audio by design to create a more immersive passive soundstage. That said, they provide no isolation in the bass range, where the rumble of a plane engine lives, nor do they block any mid-range noise, so the sounds of speech and other office sounds aren't attenuated. They block some treble out, so they'll reduce piercing sounds in your vicinity a little, but you'll still hear them.

As these headphones are designed to leak audio and interact with your environment, their terrible leakage performance is to be expected. Although bass sounds won't be especially audible to anyone around you, the broad peak between the high-mids and high-treble range means most audio content, like dialogue or music, will be heard by those around you, even at moderate volumes. These headphones are designed primarily for people listening in private, enclosed spaces.

The Sennheiser HD 660S are wired headphones that come with a 1/4" (6.35 mm) TRS audio cable and an adapter for use with 1/8" (3.5mm) input devices. They have an impedance of 150 ohms and a sensitivity of 104dB (1 V), so you may want to consider adding an amp to get the most out of them.

You can plug these headphones into any 3.5 mm jack on your computer, but they don't have a microphone, so you can only receive audio.

These headphones are compatible with your PlayStation controller's 3.5 mm jack. Since they lack a microphone, you can only use them to hear audio.

You can plug these headphones into your Xbox controller, but you can only receive audio as they don't have a built-in microphone.