Brompton Speaker Shelf for Stem

It's a little shelf to keep your little bluetooth speaker on while you bike so you don't break the law (or your body) wearing headphones

Secure it with a couple 8" zip ties

If you want the shelf on it, mount it before tying it on. The corners can grab a couple heavy rubber bands to hold your speaker in place. Mine has a screw on the back, thus the keyhole slot will hold it on.