Ghosthack - 12 Free Buildups WAV [free]
Wav sample pack - 41 mb
Door number 13 features 12 free Buildup and Riser Sounds, perfect for placing right before your drops. They start very slowly and deep and get faster and faster, the cutoff automation is continuously rising.
All sounds are of course royalty free and could be used in private as well as commercial projects. All files together have an unpacked size of 43,5MB.