Sennheiser is probably the most famous headphone brand all over the world. Same goes for their HD series. It has fans all over the world. Widely known ones including HD600, HD650, HD800 and HD800S. There are tons of discussions made about HD series. Good and bad. We’ll try our best to evaulate HD650’s reborn brother, HD6XX. Massdrop and Sennheiser collaborated and created this particular model. They named it “HD6XX.” “X” is Massdrop’s signature, we’ve seen it over and over again before, in Ei.X, K7XX etc. Its tuning is exactly the same as HD650, except they painted it over and decreased its price which made it irresistible to buy. Yes, tens of thousands of people tried to buy it from Massdrop’s site when the drop opened. The site was immediately down, Blood has been shed. Fingers lost. It was a mess. In that battlefield we gloriously managed to prevail.


Specifications & Highlights

  • Massdrop x Sennheiser Collaboration
  • Color: Midnight blue
  • Transducer principle: Open, dynamic
  • Frequency response: 10 Hz – 41 kHz
  • THD: < 0.05%
  • Nominal impedance: 300 ohm
  • Cable length: 6 ft (1.8 m)
  • Connector: ⅛ in (0.3 cm)
  • Weight without cable: 9.2 oz (260 g)
  • Made in Ireland by leprechauns. (source may vary)

Testing Equipment

  • iFi Micro iDSD
  • Chord Hugo
  • Hand-built DoubleHelix Silver Headphone Cable


Accessories | Box

HD6XX comes with an ordinary Sennheiser box. The box itself has a great quality for the price. Joints are metal. The box is hardened, you don’t need to worry about any damage when you’re carrying the headphone with its box.

HD6XX doesn’t come with any accesories except the manual, 3.5mm to 6.3mm connector and warranty book. I find this lack of accessories fair, considering the price.

Design | Build

The design of HD6XX is the same as HD600 and HD650. I always find Sennheiser’s ellipse shape of cups comfortable but I must admit, I’m not a very big fan of the headband. After trying Hifiman’s wide, leather headbands Sennheiser seems and feels a little uncomfortable BUT in overall, the headphone itself isn’t heavy and the cups are comfortable, I could say the comfort is a go. I can wear them 18 hours straight without discomfort.


Sound Signature

HD6XX has a very warm, full bodied and a little darkish sound. I wouldn’t call it “very” dark since it has a good treble extension. It also features a dip on 6kHz. Some people call it “The Sennheiser Veil”, but no, it is not a veil, it is just a unique signature that makes vocals and cymbals smoother, non-sibilant and I think that is what makes this headphone an emotional rollercoaster. Upper-mid sensitive audiophiles, hear my warcry, attack the Sennheiser, request the drop and make HD650 great again! Anyway, back to topic.

We have an upcoming FitEar review, just like TG334, HD6XX has a thing with women vocals. In forums they’ve given it a name “magical mids” I must admit, I’ve never listened 12 hours of Diana Krall, ever. I literally lost the track of time. Good stuff.


For gearheads, I measured HD6XX in some ways, including frequency response as you can see it below.


HD6XX has a rounded not-so-agile low end. Its tightness may be a concern but if you don’t listen to high PRaT tracks with twin pedal frenzies, you will be fine. I mentioned mids being like FitEar TG334, bass response also reminds me of TG334’s. Not perfect, not bad, just good enough.

Sub-bass extension is another matter. It doesn’t have the best extension but it doesn’t feel artificial. If you plan to use this headphone with a tube power amp and a flagship desktop dac, please do me a favor and completely ignore this section because HD6XX scale and respond quite remarkably to high-end equipment.



Mids on the other hand, is HD6XX’s secret weapon. It just might have the smoothest, most enjoyable and relaxed mids I’ve ever heard. Because of its upper mid dip, it doesn’t cause any crispness or harshness. Women vocal performance is outstanding. Diana Krall, Melody Gardot, Zaz, Joan Baez.. Just let the music take you away.

Tonality wise it is not -accurate- it focuses on other aspects. It is warm, smooth, musical..



Everyone keeps saying HD6XX has recessed highs. I’m not going to object but I’m going to fix this sentence. HD6XX has SLIGHTLY recessed highs. It is a bit dark, that’s all.

The high frequency extension is very good. There is no fading or discolouration. Its treble is better than most of the TOTL IEMs as quality and extension and probably more realistic than any sub-$400 headphones up to this date.


Soundstage, Imaging & Instrument Separation

Its soundstage is medium sized compared to other open-back headphones. There are enough space for everything. Instrument placement is accurate. Warmness of the headphones generally cripples the soundstage and the imaging. With HD6XX, they are not crippled at all. Instrument separation is also quite well. As I mentioned before, HD6XX isn’t the fastest, tightest headphone in the market. Most enjoyable? Perhaps.

You can see my impulse response and group delay measurements below.

Quick Comparisons

vs. Beyerdynamic Amiron Home (600€)

The main difference between HD6XX and Amiron is the sound signature. Amiron is flatter, has more prominent treble response and tighter bass. It’s mids are somewhat dry compared to 6XX. Amiron’s soundstage is wider and it is generally airier than 6XX.

Detail-wise, Amiron is better and more revealing. For me however, 6XX is a joy to listen to, while Amiron can get quite harsh with badly mastered tracks.


vs. Hifiman HE-400S ($300)

400S is tighter, faster, brighter, a little easier to drive and it can be sibilant sometimes. HD6XX is warmer, has a better sub-bass extension, better imaging and a darker sound. They similarly have smooth mids but 6XX is more bodied.


vs. Beyerdynamic DT770 250Ohm ($200)

DT770 is brighter, can be sibilant sometimes and has a similar sub-bass extension. HD6XX is darker, smoother, has a better soundstage. HD6XX is hot cocoa, DT770 is mint lemonade.


vs. Hifiman HE-500 ($899)

Technicality-wise, HE500 is superior. HD650 becomes a viable choice when you put the “enjoyment” card into play. HE500 offers a more balanced frequency spectrum. HD650’s vocals are warmer, arguably more enjoyable because of its bold tonality. Bass-wise HE500 completely destroys 6XX. Tighter, punchier, faster bass response. *Hence the price difference* One more thing to say is, HE500 is much harder to sate. People often use desktop sized amplifiers to satisfy the giant. Without proper amplification, HE500 is a lifeless contender. So amp up!



HD6XX is not for critical listening, it is not for mixing or mastering. It is for grabbing your favourite drink and listening to your favourite tunes in complete tranquility. After all, it is one of the most satisfying headphones I’ve ever auditioned. HD6XX is a piece every audiophile should be adding to their collection, especially with this ridiculous price tag.