etymotic er2/4 knowles filters

[magicalmouse]

hi i understand it is possible to tune these by changing the green filter for another - does anyone have knowledge of where these can be sourced (UK) and what effect the different ones have?

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[FastAndClean]

https://www.aliexpress.com/item/32580267018.html?spm=a2g0s.9042311.0.0.6ba04c4dOzwVSA