I have heard of the legendary HD 600 series headphones for years. They have existed for over 2 decades, but I wasn’t a fan of open back headphones. Until I finally got a chance to review the newest HD 660 S. That changed my perception and led me to a new revelation that completely altered the way I listen to music at home.

Sennheiser HD650 HD660S HD6XX headphones review

Benefits of Open Back Headphones

The Fidelio X2 I owned is an semi-open back headphones, meaning it offers some isolation but the audio leaks from the earcups. The headphones offer bright treble and strong bass which I loved 2 years ago, giving it very high ratings on my review. But my appreciation for audio balance has changed. The X2 treble is bright, but not as resolving (i.e. detailed, amount of audio information). The X2 bass is pumping but lacks extension upwards and warmth.

Sennheiser HD 660 S review

My experience with Sennheiser HD 660 S changes my perception for open back headphones. Once shunned by me due to sound leakage, I found out an excellent advantage: I can hear what’s happening around me. And why is that a good thing? Well, it keeps me connected to my family when I am listening to music at home, which is a big deal. The reason why I do not listen to headphones at home is I do not want to isolate myself.

Sennheiser HD 660 S review by Chester Tan

With Sennheiser HD660S (or HD600, HD650, HD 6XX for that matter), I can still hear my family, so at least I can acknowledge them when needed. These legendary Sennheiser headphones have such huge ear cushions that covers more than your ears that they feel absolutely comfortable to wear. After a while, I almost forgot I am wearing them.

Sennheiser HD 660 S review by Chester Tan

The very nature of open back headphones is that they do not isolate from the surrounding noise, and you cannot get that kind of musical details into the ears compared to closed back or ANC headphones. But come to think of it, this is no different from playing music over loudspeakers. Then why not listen with speakers? Because open back headphones are way less noisy than loudspeakers, so it is a fantastic compromise.

Sennheiser HD 650: Benchmark

The HD650 is the oldest model among the 3, so I shall use this as the benchmark to describe the rest. I bought the HD 650 after auditioning the HD660S loan unit, and reluctantly sold off the MrSpeakers Aeon. While I enjoy the latter, I find the HD650 a fantastic value and lower maintenance cost (cheap replacement ear cushion and cables). The glossy titan-grey colour plastic sets it apart from the other 2.

Sennheiser HD650 HD660S HD6XX headphones review

The HD650 appeals to me with its generous ear cushion size that do not press on my ears and my specs. I also love the open-room sound staging, the comfortable audio tuning that is neither harsh nor fatiguing. The bass lacks the pumping intensity but therein lies the musicality without overpowering. The midrange is well portrayed with the right amount of warmth yet the energy dissipates to avoid lingering too long to cause any hazing. The treble is expressively natural, devoid of the excessive sizzle, which many get too used to, resulting in the perception that the HD650 is “flat”. What the headphones need is a capable amplifier to drive the 300 ohm so that the musical reproduction can be better presented. What I experience is a more open, room-like acoustics. I do admit that there are headphones out that that delivers excellent high treble fidelity yet not fatiguing, and the HD650 is not one of them.

MrSpeakers Aeon delivers a more impactful and clinically detailed sound thanks to the closed back isolation, but my ears get hot after a while, and the headphones are even more picky to drive.

Official retail price is S$699, visit the website here for more info.

Sennheiser HD 6XX: Massdrop Version

I was undecided whether to get the HD650 or the HD6XX Massdrop edition, but I managed to find a friend who ordered it, so I borrowed from him. From what I hear, the HD6XX sounds identical at the lower frequencies, but at the upper range, I felt there is a slight veil, which is only noticeable if you do a comparison. If you prefer your treble to be a little bit more comfortable, the HD6XX might be a better option. Given that they are technically identical, the differences may be attributed to batch differences, age, cable, earpads.

Sennheiser HD650 HD6XX headphones review

The other difference is the finishing, which is matt midnight blue, and the shorter cable with a terminating 3.5mm connector, which is mobile-friendly.

This headphone is officially not available for Singapore, but Massdrop sells it at US$199.99 during limited periods, and you can get it through a forwarder or from Carousell.

Sennheiser HD 6XX review by Chester Tan

Sennheiser HD 660 S: New Generation

The HD660S has a matt black finishing with the logo imprinted in white at the left instead of centre. Besides the standard 3-metre 6.3mm connector, it comes with 4.4mm balanced cable.

Sennheiser HD 660 S with Sony WM1Z

The transducer is different from the other 2, resulting in a brighter sound signature that might please the younger generation of listeners that are more inclined towards a higher fidelity sound, while the lower frequencies remain somewhat similar. With an impedance of 150 ohms, these headphones are much easier to drive than the other 2. I like the HD660S sound thanks to its heightened treble tuning. If you doubts on the “flat treble” of the HD650, then the HD660S will appeal. But people familiar with the old HD650 signature might need adjusting to the new headphones.

Official retail price is S$829, visit the website here for more info.

Sennheiser HD650 HD660S HD6XX audio rating by musicphotolife.com

And in case you are wondering, these 3 headphones have identical mould, so accessories are compatible. What sets them apart are the colours, and the HD660S has a Sennheiser logo on the metal mesh.


The HD660S sounds the best given its clearer treble profile, but at S$829, it might not be as appealing given there are so many competitive headphones that gives excellent audio quality for less, though I agree the comfort is hard to beat. The HD650 is readily available in the preowned market for around S$350 to S$450 depending on age, making it a great value. As for the HD6XX, the cost to ship to Singapore is a little prohibitive, but if you have contacts who can bring it in, then it is definitely the best value option to own a brand new Sennheiser HD600 series.

What is Sennheiser’s best headphones ever? Read this!

Review Date
Reviewed Item
Sennheiser HD 660 S, HD 650 and HD 6XX
Author Rating


  1. I think the difference sonically that you found with the 650 vs 6xx is likely just variation in the units themself.
    The 650 and 6xx have been confirmed to be sonically identical with various reliable sources including Sennheiser who have confirmed this.

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