I'm not sure if I documented it, but it's considered easy mod,
You will need :
1. medium density foam (I bought in Aliexpress in bulk, keyword is tuning foam / tuning cotton. The medium one actually is the "high density" in local store, while the real high density one, is actually marked as "Sony foam" or "imported foam". Just buy medium and high density ones, can be useful for mods in the future.
non affiliate links, just an example you can search in search bar too :
medium density one :
https://www.aliexpress.com/item/1005005992801441.html?spm=a2g0o.productlist.main.27.55a4FISVFISVsR&algo_pvid=702efba4-916e-4422-9aff-54dcb9fefacc&algo_exp_id=702efba4-916e-4422-9aff-54dcb9fefacc-13&pdp_npi=4@dis!USD!9.90!9.90!!!9.90!9.90!@2140e03217103899398414555e5eee!12000035214007649!sea!SG!0!AB&curPageLogUid=Mbx2z1IBFxya&utparam-url=scene:search|query_from:
high density one :
https://www.aliexpress.com/item/1005004772007350.html?spm=a2g0o.detail.pcDetailTopMoreOtherSeller.1.476aBCA0BCA0hf&gps-id=pcDetailTopMoreOtherSeller&scm=1007.40000.327270.0&scm_id=1007.40000.327270.0&scm-url=1007.40000.327270.0&pvid=9eb19592-067d-47c2-9c9d-c6792921abb5&_t=gps-id
cDetailTopMoreOtherSeller,scm-url:1007.40000.327270.0,pvid:9eb19592-067d-47c2-9c9d-c6792921abb5,tpp_buckets:668#2846#8114#1999&pdp_npi=4@dis!USD!4.06!2.80!!!4.06!2.80!@21010c9c17103899599883751e55c9!12000030417693703!rec!SG!!AB&utparam-url=scenecDetailTopMoreOtherSeller|query_from:
*edit : sorry the links aren't working, just search them with keyword
Don't bother to buy low density one, they are useless and the effects are negligible.
2. mesh nylon filters, or tanchjim tanya filter, just buy density level 250 and 500, mostly you will need
mesh500 in 4.8mm and 5mm size (you can buy 4.2mm size also just in case you will need it in the future, but PR2 use 4.8mm size)
search in Ali with "earphones tuning paper" and they will appear
examples :
https://www.aliexpress.com/item/1005004046291728.html?spm=a2g0o.productlist.main.3.243a2QmX2QmXZy&algo_pvid=1c6646f3-4660-4b44-a336-239fe227ef2b&algo_exp_id=1c6646f3-4660-4b44-a336-239fe227ef2b-1&pdp_npi=4@dis!USD!1.38!1.38!!!1.38!1.38!@210307c317103904837243223e085d!12000027848054756!sea!SG!0!AB&curPageLogUid=gxi0GUfjm234&utparam-url=scene:search|query_from:
If you already have those :
basically just :
1. take off the orginal nylon filter, you can use needle, and uplift the nylon filter gently from the side, don't do it from the middle (it will break your original filter, in case you want to put them back on original state), the residue is aound the side of the filter to just uplift it slowly until you can pinch it.
(yeah I didn't take photo of the PR2 mods, but here the photo from Castor, and basically, it's same concept)
2. Put in the medium density foam, side ways, not following the round shape of the nozzle, so it will still have airflow for the bass
3. Pinch a hole on mesh500 / tanchjim tanya filter, with the tip of the needle, just the tip remember, we just need tiny micro hole for airflow, if you pinch too deep until the body of the needle, the hole will be too big and high mids will be too harsh (best if you have measurement rig)
pinch a hole with paper as base and put the filter on top of the paper, do this before attaching the filter to the nozzle, not after attached on the nozzle.
4. Attach the mesh500 filter with the hole on the nozzle, and thats it! actually I double stacked my Tanya filter in my mods, but I feel the high mids a bit too dampened, since I already like lower pinna gain and feel that too dampened, other people maybe find the high mids too recessed, so try 1 filter first.
Goodluck! Feel free to ask me if there are anything you don't understand.
Btw, I did mod with my AS24 switch and have incredible results, and I like them so much. And I have KZ PR3 coming (this one have crazy uncontrolled trebles, I will use different mod techniques with rolled cotton instead)
. Oops 
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