What is the best way to soundproof a single pane window without replacing it?

Answer 1

I don't think you can soundPROOF it, but you can reduce the noise transmitted through it. You can try an "inside storm window" using a kit of tape and heat-shrink clear plastic, or a pane of plexiglass. If you don't mind blocking the view you can place insulating material against it and cover that with some type of finishing material.

Answer 2

The best and cheapest way is to wear ear plugs or ear cuffs with music piping in.

Answer 3

put cork over it,
no way to sound proof it with out blocking the view,