That has been covered too. Myself and ohters are using o-rings not for the sound dampening so much, but for the softer landing; to avoid the jarring impact to the bones and tendons. Again, 40A o-rings from WASD are top notch, they soften the landing but still provide tactile feedback telling you that you bottomed out. They also have a minimal impact on key travel (some people like short key travel and use thicker o-rings but I don't think that's ergonomically beneficial). Also, some other alternatives like the soft landing pads, are too soft, and as a result you cannot easily tell if you bottomed out or not while typing, even though some people find them very comfortable. But to me they are equivalent to pillow-top plush mattresses which aren't very good for your back.