I have just recently travelled to Seoul, Korea. I have found many goodies and wonderful shops. If you are an audiophile or just looking for a shop that sells headphones and in-ear monitors (IEM) in Seoul, this is the place you have to go.
Earphone shop sells not just earphones but headphones too. Note the website is only in korean.
Earphone shop is located at 서울시 종로구 동숭동 1-63, Dongsung-dong, Jongno-gu, Seoul. I don’t think I can provide a print screen of the map I took of Google map but just copy and paste the english or korean address to get directions. Try this Google map link, it might help.
The nearest train station is Hyehwa train station on Line 4. Exit the station using exit 1. There is a nearer exit but it isn’t labelled on google map but I assume it should be exit 2 (use that information at your own risk). Follow the direction on Google map.
The shop has rows of headphones and IEMs all set up for anyone to just walk in and try them to their hearts’ content. The staff don’t speak much english when I was there (May 2013), but things might have changed since then. Do note any purchase made there is not available for tax rebate.