Press embargo until 6/25/2018 sometime today. Someone move this over if I forget or can't. HD58X Review and Measurements Executive Summary: BUY THIS INSTEAD OF THE HD660S. The HD660S, a new headphone that Sennheiser released a while back, wasn't well received on SBAF because it seemed like yet another variant of the already well regarded HD6xx headphones, but with less resolution (less windings on voice coil), greater efficiency, sharper sounding edges, but at much higher cost ($500). We now have the HD58X - again? I do not know if the original batch of HD58X headphones were delivered, but I do know that Massdrop spent some time tweaking the original HD58X measured here: https://www.superbestaudiofriends.o...-x-sennheiser-hd58x-jubilee.5564/#post-181759 UPDATE: The original HD58X never shipped. Massdrop took your money and improved the product while you weren't not looking before delivering. This revision 2 corrects minor issues with the original pre-production HD58X such as the lack of bass extension and a small peak at 5.5kHz. The issues were minor, and given Massdrop's price, easily forgiveable. Now that these issues have been corrected, what we have now is a headphone with an amazing performance-to-price ratio. The lows now extend as well as the HD6XX headphones, and actually sound clearer. There is actually more clarity in the bass than the HD6XX! Not quite as good as the HD600, but somewhere in between, closer to HD600. The distortion measurements below actually show better performance than the HD660S! The only thing I am not sure of about the HD58X r2 is its efficiency compared to the HD660S. I will investigate later tonight. Now the question of course is why should I get the HD58X r2 over the HD6xx, HD650, HD600? The latter headphones with their 300ohm voice coils are more resolving with better gear. Also, I think the channel matching isn't quite as exact with the HD58X. However, he HD58X r2 remains an amazing budget choice - the budget choice with those for more modest gear. And even then, many may prefer the flavor of the frequency response, transients, and decay characteristics of the HD58X r2 over the others. HD58X (revision 2) Frequency Response. FR is much better than the original. We have much better bass extension and the 5kHz bump is less. Here it is compared to the initial HD58X measurement in YELLOW. And here is a comparison to the HD6XX in YELLOW. Just as much bass extension, but more laid back in upper mids. And here it is compared to HD660S in YELLOW. FR is very similar!