WC Freeze HD6XX - Cooling Gel Earpads for Sennheiser HD6XX, HD58X, HD600, HD650, HD660S, HD660S2, HD580, HD565 & more, Made by Wicked Cushions | Extra Comfortable and Cool | Black

These pads, more precisely the attached inner foam sheets that sit between your ears and the headphone speakers, completely ruin the sound of your expensive audiophile headphones. I bought these despite the warnings in other reviews, thinking, how bad can it be? Those reviews gave 5 stars. But it's bad. Unlistenable. The foam sheet is a lot thicker and denser than the one found in the original HD600, as you can tell by holding them both up to a light. The engineers at Sennheiser knew that you need AIR to correctly transmit sound, especially high frequencies. The foam inside these pads feels like acoustic foam made to absorb sound. I'm over 50 years old and can't hear anything above 13kHz, so these must be rolling off everything starting around 5kHz. Ugh.Two stars instead of one, because they were easy to install, and the pads themselves feel reasonably comfortable enough at first use, although warmer and cheaper feeling than the originals.I'll be cutting out the foam sheet until I find a better solution. For £26 I'm pretty disappointed.

These look great,, they are very comfortable and the cooling gel works very nicely and I appreciate the patterned designs. However, unfortunately they change the sound signature of the headphones (HD650 in my case) quite significantly, not by a massive amount but enough to likely be a deal breaker for audiophiles. The integrated foam speaker covers are noticeably thicker than the loose original Sennheiser ones, and as such, sound is a bit more muffled with trebles taking a bit of a hit. If you don't mind that, then these are a great, well made alternative to the Sennheiser originals. Also worth noting is that these will make headphones quite a bit heavier.