The legendary Sennheiser series of headphones have been loved for generations, often praised for their unmatched mid-range, timbre, and musicality. However, they are not without criticism. Those who have tried these headphones driven by a tube amp understand the improvements that can be had to the soundstage size, shape, and depth, along with improvements to midrange evenness and treble smoothness. Experiments in listening to the HD 580 with the outer grilles removed showed further improvements in similar areas as driving them off a tube amp. The 3kHz forwardness is slightly reduced, but more importantly, the dip that follows at around 4kHz is noticeably more filled in. This difference is measurable, as seen in the following frequency response graphs. The effect should apply to the other headphones in the series as well, although to a lesser degree due to the more open metal mesh design. Try it on your own pair of Sennheisers. No tools required for removing the rear grilles on these headphones.
Compensated Stock vs HD 600 Metal Mesh Grille vs No Grille
The goal of this project is to maintain the experience of an open-baffle Sennheiser, while providing a bit of protection for the rear of the drivers. While designing the replacement grilles, there were several earlier (thicker) prototypes that exhibited a noticeable improvement over the stock HD 580 grilles in terms of punch and slam, but did not compare to a fully open experience. While thicker walls may be more durable and do not drastically affect the total surface area from which the back waves from the drivers can escape, the soundstage depth was not as impressive as the later revisions. Perhaps it's because of the thicker grille shaping and guiding the sound more orthogonally to the driver. The final iteration was thinned until rigidity is maintained while keeping the sound as close to open-baffle as possible. Finally, the grille was rounded to reduce sharpness to the touch, and 3D printed using a proprietary blend of engineering resins to achieve a balance between hardness and flexibility. The grilles are then spray painted black to match the headphone baffles. The result is improved bass punch and slam, larger and more even soundstage, smoother upper-midrange tuning, and less grainy treble. These are not as drop resistant as the stock plastic or metal grille. The grilles are not designed to protect your headphones from a drop; they aim to give you an open-baffle experience while preventing you from touching the back of the drivers accidentally. Please do not drop test your headphones or these grilles.