Extract to:

C:\Program Files (x86)\Steam\steamapps\common\left 4 dead 2\left4dead2\sound\music\flu\concert

Note: Location may differ depending on where you have steam installed

*IMPORTANT: Make sure you type "snd_updateaudiocache" (Without quotation marks) in console after installation,

The sounds will not play back correctly without this step!

Enjoy!

Part 1: http://www.fpsbanana.com/sounds/12391

Part 2: http://www.fpsbanana.com/sounds/12402