BoingBoing pointed me to this German company selling groovy reproductions of 1970s-era wallpaper. My brain works quite visually and told me that I had seen something similar before. In Helsinki, Finland… At an art exibition… Hmm…
So I flipped through my pictures in Adobe Photoshop Album. And actually found the picture I was looking for. An equally groovy installation of psycedelic patterns and loudspeakers and microphones. Everything connected so the patterns got a very strange accompanying sound made entirely by feedback from the microphones and amplifiers.

Maybe they bought the wallpaper in Germany?