Sennheiser HD660 S Review

A high-quality pair of open-back headphones has always been on my list of things to purchase because of the natural, spacious sound they’re known for. Now that I’m doing a lot of work at my home office, I wanted to have a pair of headphones that I could slip on for hours to immerse myself in music that sounds great.

After much contemplation, I saved up for a pair of Sennheiser’s HD660 S and was lucky enough to find them when they popped up on sale on the company’s online store. Taking that as a sure-fire sign that I had to have them, I ordered a pair and anxiously waited for their arrival.

The shipping was fast and the product arrived early with no damage. Though the headphones came in a discreet Sennheiser-branded box, it was worth monitoring the tracking so I could bring them inside before unwanted eyes could notice them as an easy target on the front step.

Though a tad plain, the product box offers a safe place to store the headphones when I’m not jamming out to tunes, and that’s convenient. The overall construction of these headphones impressed me right out of the box. Yes, they’re made mostly of plastic, but they feel sturdy and like they could last a long time. 

Trying these headphones on, I found the clamping pressure to be a touch noticeable, a feeling that went away fairly quickly once they were broken in. The thick-padded earmuffs fit comfortably around my ear, feeling open and cool to the touch, even after extended listening. I found these headphones to be extremely light, which also added to their comfort level when listening for long periods of time.

The HD660S phones have an unobtrusive, subtly classic look, a design some people may find to be uninspiring. I, on the other hand, am drawn to the clean lines of these headphones and dig their matt-black look, especially compared to the overly “space-age” design seen on numerous headphones these days. 

At this point, I bet you’re wondering how these headphones sound. Well, as I excitedly hit the Play button on the first track, I had high hopes and was ready to be blown away. Yet I wasn’t immediately blown away, and interestingly, that’s part of the magic of the 660S phones. You see, the music that pours through them is beautifully flat and clear. On initial first use, when I first hit that Play button, I was expecting the sounds to truly stick out. Instead, what I heard was an even, natural sound, sort of an anomaly in music these days. So once I relaxed and really listened to the track, I discovered how the vocals took over the soundscape without being belligerent; how every instrument had its own space in the mix, which allowed them to breathe dynamically; how the effects on the vocals had more depth and clarity than I’ve ever noticed before; and how tracks that I’ve listened to for years suddenly felt remastered and fresh. 

Yes … now I was blown away.

What you’re getting with these headphones are all of the hidden details in the tone and timber of the music that have been hiding just under the surface of your favorite songs. They’re so subtle, in fact, that it took me a few minutes to fully appreciate them and what a pair of “reference” headphones are supposed to do. 

I found that the 660S phones stood out most when listening to a musically busy track with a lot going on. Songs that have many layers of instruments and effects can sometimes sound mushy and undefined, especially during high-energy parts. But the 660S phones don’t flinch during these portions of the musical composition; rather; they offer the same clean, open sound one might hear on a soft, uncomplicated song.

The only area in the sound spectrum of these headphones that I found to be somewhat underwhelming was the low end, which I would describe as “undramatic.” Sure, there was still some punch as well as strong definition here—a definition, I might add, that is often lost on most headphones and speakers—but it felt like the low-end sound was lacking power within the sub bass. Nonetheless, this flat low-end sound gels well with the rest of the sounds heard on the headphones, and I appreciate the consistency of that naturalness, which, as mentioned, the 600-series phones are known for.

One reason I choose the 660S over their older siblings (the 600 and 650) is because of their nominal impedance of 150 ohms. This allowed me to plug them directly into my laptop without a headphone amp. While I can do this and the level is comfortable, I’m excited to explore what they’ll sound like with a proper headphone amp. I listened to a few of my favorite vinyl albums while plugged directly into my stereo headphone output and noticed a dynamic improvement.

As you might imagine, I was nervous when I made this purchase because paying hundreds of dollars for headphones is a lot of money. But after trying them out in a few different ways these past two or three months, I’m more than happy with my decision. The 660S phones have allowed me to appreciate music in a whole new way and have paved the way for a new standard of quality.

Now, time to slip on my 660S headphones, push play, and get back to work.