Thin but effective soundproofing

[Glowlamp]

I live in a Victorian semi detached house and there are 2 rooms that adjoin the neighbours that I would like to soundproof the adjoining wall (if that makes sense?!). One is a boxroom that I use as as office and the other is a single guest room. As both of these rooms are small I don’t want to reduce the size too much if I can help it. The other side is a rental so can’t do something together. There isn’t a huge amount of use of these rooms but it is annoying as the wall is thin. Only brick and old plaster. Has anyone done this?

Bump

I've used Soundstop before. It works really well, but you have to be fussy about how it's installed. Sound is like water and finds a way through...
Are they 'quiet' rooms already - i.e. carpeted, soft furnishings, curtains etc? This helps deaden your sound outwards, and the incoming noise from next door.

floor to ceiling wardrobes, cupboards or bookshelves, with the doors closed. Clothes or books inside will muffle sound. The doors frames fixed to the floor and ceiling, not the wall.

also look for any holes or gaps in the walls. These are likely to be in the loft and under the floor and in the fireplaces where the brickwork is shoddy and unplastered. The floor joists may be built into the brickwork and have gaps round them.

After cleaning out grit and dust, you can fill the gaps with mortar or with expanding foam (preferably the pink fire blocking grade)

Sealing the gaps will make a big difference.

If you have any bare floorboards, carpet with underfelt will help.

Thanks for these tips! They are small carpeted rooms, not enough room for cupboards and no real areas where sound escapes. It’s just a brick course between houses and very old plaster that’s the problem. Injecting foam or soundstop boards might be the only options. Thank you.