It is quite a change Andy once you start treating the room with acoustic material and I found it took sometime for me to work out what had changed. Its a subtle but noticeable effect but so far I have found no downsides.

Without committing to any proper acoustic materials it is a good idea to try stuff you have lying around. Cushions, duvets and thick curtains are all good candidates to start with and even a blind drawn down over a window will. stop some first reflections. Furniture and carpet make a big difference and all add up!

However when you commit to making a few panels I can help point you in the right direction for very little money! See how you get on with the other stuff first. I would concentrate on first reflections first, they are the biggest bang for bucks!