how can I make the back wall transparent?

LR57 - RE:

"I was also wondering if I could use vinyl as a type of crown moulding behind me."

Do you mean the hard vinyl crown moulding?

I think Hard vinyl will probably scatter sound waves - a type of dispersion - but that could also be beneficial. Wood may be better though.

I also wondered if crown moulding could be effective - if you try it let us all know please

I have seen polystyrene crown moulding, which may react similar to vinyl given it's elastic properties? After all, polystyrene is used for soundproofing also.

I also looked up some acoustic specialist sites and one recommend "treating"  the ceiling corners of the room first, then move down the vertical corners of the room and lastly, if there was still an issue, look at wall panels - but they were using acoustic foam to treat  a home recording studio.

They did caution about using too much treatment, which can deaden the entire room and make the presentation quite dull.

I guess the profile of the crown moulding (concave vs convex) also plays a role ?

• concave - would that cause the sound to be focussed close to the ceiling?  So that may not be desirable - standing waves?
• Convex - that would probably disperse the sound - but I do not know if that would cause any issues somewhere else in the room
  

Another material - I just remembered a wall treatment my father used (in the UK) primarily for heating/insulation purposes - Polystyrene wall insulation (similar to wall paper). You use a paste to bond it to the wall just like wall paper - it's available on the web - e.g.

http://www.homebase.co.uk/en/homebaseuk/warmaline-wall-veneer---914-x-500mm-072492

You could then paper over it with a textured wall paper - like...

https://www.grahambrown.com/uk/product/18500/brush

And then paint to match the rest of the room - practically invisible!

And you've treated the entire wall, but it's more work than one piece of crown moulding.

A little crazy I know, but then - what about this hobby is NOT crazy :-)

Regards...

OK - the roller blind is now installed!

There are two kinds of vinyl that can be selected for the blind I purchased...

1. Single colour - which is just a single sheet of very thin vinyl
2. Dual colour - This type of vinyl is made from two different coloured layers of vinyl welded onto a cotton middle layer.
   

I purchased the dual colour and the size was 92" x 78".

The original sheet I tried was 72" x 24 and was at least twice the thickness of the vinyl on the roller blind I purchased.

Both were mounted about 1" from the ceiling.

1. as far as I could remember, the sound was pretty much identical
2. I then dropped the blind to around 4 feet and noticed a slight change - improved imaging.
3. Finally I dropped the blind to cover the window completely, at which point I really noticed significantly more depth to the image and a little more width with improved clarity and a more even bass reproduction
   

Perhaps the extra width of the roller blind provided some additional benefits, but it appeared that when both blinds were set to 24" the thickness of the first piece of vinyl I tried did not appear to offer any additional benefits over the thinner vinyl on the roller blind - i.e. in my room at least.

It would appear the vinyl is a pretty good material when it comes to absorbing sound waves.

The roller blind works very well  my room, since it covers the window behind my listening chair (framed with drapes on both sides) and looks very tidy when rolled up - very high on the WAF !

So that's it! - no plans for a remote controlled motorized option ;-)

Hope you find it useful

Regards...