- Members: Krystal (0:53), Amber (1:04), Luna (1:37), Victoria (2:54)
- The teaser for this album was a physical exhibit in Itaewaon, South Korea, open between October 21 and 27. A room was projected with pictures and videos from the album’s promotional photoshoot [^1].
- When the title “4 Walls” was released, fans thought this was a play on SM’s notorious use of box sets when filming music videos. Funnily enough, this is the first f(x) music video to not be shot on a box set.
- In 2014, a few weeks after releasing “Red Light”, fifth member Sulli decided to stop performing with f(x), thus prematurely ending promotions. Rumors spread that she selfishly departed from the group to be with her boyfriend, but her sudden leave was never clearly explained. She officially left the group in August 2015 to focus on her acting career.
- Sulli is good friends with IU, supposedly giving IU inspiration for a song on her last album CHAT-SHIRE from this drawn image of them: https://instagram.com/p/9MGSJLxEfL/
