Hi - i've built a frame using 70mm x 16mm pine, approx 2m wide x 1m high. It's divided down the middle, so i have two holes, approx 1m x 1m to fill. I was going to use acoustic foam, but the price worked out well over £100, so i wondered if there was anything as effective but a lot cheaper. I'm actually trying to keep noise out, rather than in, but i assume the principle's the same. Any suggestions? Thanks.