Things have almost come full-circle for me and my audio experience over the last 12+ years, having started with and now come back to Sennheiser. I was very close to purchasing an HD 650 on top of the HD 600 and HD 598 I already owned at the time, and I was most certainly destined for mid-fi hell had I continued down that path. Thankfully, my budget did not allow it at the time, although there was no denying that the HD 650 was and still is one of the best set of headphones under $500. It was the price point that single-handedly stopped me then, and the HD 6XX coming in at under $200 quite often makes it a no-brainer if you are looking for a highly detailed set of open-back headphones with accuracy over anything else.

There's a reason Drop has sold nearly 140,000 of these in the ~4.5 years since they first started shipping. In fact, knowing my sample's serial number came in handy since it showed me first hand that Drop had sold ~3000 in the few weeks since I had received it. The HD 6XX is Drop's biggest success story, one that has prompted the company to work with Sennheiser and others for other such offerings. Things have certainly changed from the HD 650, but surprisingly mostly in ways I agree with, some of which are just better in 2021. I don't really see any reason to buy the HD 650 unless it costs more to buy and ship the HD 6XX to your country, in which case I feel bad for you because you might be deprived of one of the best bargains in the headphones market even today. I can't say how competitive the HD 6XX will remain for the years to come, but the longevity of the HD 650 certainly helps. Brand name and recognition play a big role in mitigating competition from smaller, yet-unknown brands from Asia without any history of reliability, and customer support plays a big role, too.

There are very few real issues I have with the HD 6XX, especially for its intended purpose and thus associated tuning. If you have done your research—and hopefully read the entire review—you will by now have a better idea of whether the HD 6XX is for you. If the tuning is to your liking, the only real concerns are the compacted soundstage and relatively warm mids compared to general expectations in the lows. The HD 600 is a more accurate set in my opinion, but costs $80–100 more, which pushes it into the territory of the likes of the HIFIMAN Sundara instead. Competition from the likes of beyerdynamic and Audio-Technica is also more relevant in the $100 range, where something such as the DT990 Pro offers more value for monitoring, but the directly comparable DT1770/1990 Pro also cost more. There's a reason the HD 6XX sells so well, and I am thus happy to recommend it wholeheartedly as a great value offering.