There are reasons that people build expensive systems for their Sennheiser "HD6X0" headphones (HD580, HD600, HD650, HD6XX). They have great timbre, smooth character, natural-sounding dynamic drivers, and are generally considered references for neutral and dynamic headphones.
As good as they are out of the box, some passionate audiophiles have tried to improve them through modifications. Jupiter Lee of JUPITER AUDIO RESEARCH (JAR) was one of those people, but he went further than most, spending years designing and testing various 3D-printed parts, foams, and damping materials- experimenting at the extremes of what is possible. After much experimentation, he’d invented a set of modifications that are widely regarded in the community as producing the best results.
I was eager to hear them for myself and got in touch with Jupiter to commission a rebuild.
CEE TEE: Okay! It is so nice to e-meet you...I have heard great things. I'm finally getting around to shopping for myself and want to check out your "JAR600" and "JAR650".
JUPITER: Oh that's nice, but I just stopped doing those.
Womp-womp. Jupiter had basically “retired” from working on HD600 and HD650 because the process of re-building the headphones is so time consuming and difficult. Instead, he was moving on to develop parts and to rebuild the HD800. I know the HD800 well and own a heavily-modded pair, but lately had been listening to HD600/650/6XX a LOT more...
I had to act fast. After pleading my case and asking very nicely, Jupiter kindly agreed to rebuild my HD650 and my “marble paint job” silver screen HD600. Jupiter worked on them, shipped them back to me, and when they arrived…holy cow! They did not disappoint. Improved clarity, better resolution, better bass, fixed a little bit of upper midrange "shout". Not a completely different headphone, but clearer and with an optimized frequency response.
From an engineering point of view, Jupiter’s mods work by improving the airflow and settling of the driver and baffle with bracing and damping. In layman’s terms- they keep the headphones’ existing strengths, improve a couple of areas, and make the most of them for die-hard Sennheiser fans. A good forum thread for impressions is here.
After hearing the results for myself and becoming a definite “JAR-head”, I had to try and convince Jupiter to keep rebuilding HD6X0. This is despite the difficulty of the process, which involves multiple rounds of applying, drying, cutting, and cleaning to get the material in the cups and baffles just right. So far, I have convinced Jupiter to keep re-building HD6X0 for others when he has the time.
And like Jupiter, I went further…
In an effort to make more available to the community, I convinced him to train me to perform the modifications and headphone rebuild. NITSCH is now purchasing new production HD600 directly from Sennheiser and modifying them here in the U.S.
It takes a lot of tools, parts, disposable blades, damping materials, and it makes quite a mess to squeeze that last bit of performance out of the HD600. In the end, the sound is worth it.