These are the ER-20 Hi-Fi Ear Plugs that retain good sound quality while dampening the overall volume. I've read a few recommendations by devotees that these do what they say. Now I've bought them and can confirm that they work fine. You can still hear the crisp sound of the cartels – just more softly.
Now I'm happy that I don't have to run and hide when they pull out the whompers at the Sunday Feast. Our temple has marble floors and glass walls which make a deafening reverberation for the heavy artillery.
They have a kid size too so I'm thinking of ordering them for our little one. He likes kirtans and dancing but we don't want him to go deaf so we carry him out of the temple room when things get extremely loud. (most festival and Sunday feast kirtans)
Personally, I don't understand how for some folks it seems VOLUME = BHAKTI but rather than contend with them I'll just wear these. If you are in the same boat as me (like to stay for the kirtans but also like protecting your hearing so that you can hear the kirtans in old age) I recommend them.