For passive noise cancellation you would need to add material that absorbs/dampens sound, or you would create a baffle/muffler of some sort. The only alternativ

For passive noise cancellation you would need to add material that absorbs/dampens sound, or you would create a baffle/muffler of some sort. The only alternative I know of is ANC. This PC case fan (https://noctua.at/en/noctua_anc_project https://noctua.at/en/noctua_anc_project) is designed for ANC. It generates the inverted signal inside the fan.