I have a whole wall that I need to block off with some sort of door. I'm thinking that a bi-fold door would be awesome. However, my husband kind of wants a sliding door. I just think how cool it'd be to have a whole wall made up of a door that could easily be tucked away when needed. This would make outdoor barbecues a lot easier. It would sure save me from having to open the door every time. http://www.superiorwindows.com.au/content/Products/BifoldDoors.aspx 

A sliding door is just a big window, and if correctly built in (check if the glass is the correct sized for the door if a bit old) with the correct sized lintels this should not be a big problem as the loads would be transferred to the sides, allowing the door to slide easily. Silicon spray (being a Yachtie were we use this stuff everywhere), we now use silicone spray on all our windows in our 1930 home and the windows glide across with one finger before they used to tilt when trying to open them. I would place the door head up to line up with the others and one thing you might consider is placing a window seat, (rebate the bottom channels into the window seat) and have the window seat in and out, place a cushion over the entire seat, should be fantastic and if the deck is built, than no balustrade is required. If it is a stacker slider, i would do the seat for the entire length. So instead of looking a bit funny they will think it was supposed to be like that. We should all think outside the square more often. RAM

Is the door solid core? If not, a solid door would help somewhat, but would have to check the track can withstand extra weight. We have a couple of very heavy solid hardwood doors in steel frames which run on steel tracks. The bignheavy doors do dampen noise but certainly doesn't eliminate it entirely. Heavy drapery, rugs, soft furnishings, tapestries and large textile wall hangings will help to absorb sound from within the room, but still won't entirely eliminate it. If you don't already have carpet runners or rugs in your kitchen, adding some will also will help. Same goes for any other rooms which adjoin the music room/library. I knew a couple who soundproofed their small music room when they built their house. Their son played drums. As I recall, they used a special acoustic plasterboard for the walls, and the floor was carpeted. I think it helped considerably. there are also acoustic panels/tiles that can be installed on the ceiling, but this may be more trouble than it's worth. I'm not sure but the installation might be something like a suspended ceiling.

Corrie Z, everybody has their own taste. Your wish to remove the 1960's doors as you say they are incredibly dated and ugly is exactly opposite to many of my clients who purchase 1960's houses that still have these original features. I have even had clients who have wanted to re-instate glazed sliding doors that have been removed as they like the flexibility and ability to partially close a room off. So while they may be original not everybody agrees with you that they are ugly. Hopefully somebody who does appreciate them will be able to buy them if you put them on ebay or gumtree rather than go to landfill. Best of luck, Dr Retro of Dr Retro House Calls