When I first read our prompt my immediate reaction was Sound Waves. I usually go with the first thought and as I love pattern and repetition I did an image search on them.
Image searches are a wonderful way to get an instant library of images to get your mind in the zone.
Even though you can’t use them due to copyright issues they certainly take your creative mind into areas you might never have thought of.
Here are some of ones that took my fancy
So this is the direction I am working on and I have already started