Strengthen weak part in existing wall - need help

Hello everybody! I`m almost finished with planning our new basement studio, part of construction has already begun. Thanks to all of you for this huge amount of information on this board! 8) One thing I didn`t concern too much is a weak part in the existing wall. It`s been a door or kind of entrance and is now closed with bricks, normal modern kind. The rest of the wall is much older and much thicker. The basement consists of several rooms. Our neighbour behind this weak spot in the wall is a musical teacher (percussion!), who shows his students how to annoy studio-builders... :wink: We never thought of treating this part in the wall differently, but a few days ago he had a session and we now definitely know that we have to do something! The former entrance has quite poor STL in comparison to the rest... It`s obvious that a huge amount of sound comes directly from this thinner brickwall. Although we didn`t measure anything, it seems that the mids/low mids of the drums are the most problematic issue - no bass problem... The weak part will be behind our inner wall (plasterboard 1/2" (1.25cm) on wooden studs, air gap filled with rockwool) in the control room. Now my question. I thought about it a lot, but I don`t find an answer... How should we strengthen this weak spot??? a.) Make the weak spot as strong as the rest of the wall with a small gap filled with rockwool and then multiple layers of plasterboard?? The whole construction with our inner wall would be a 3-leaves-wall.... (FIRST PICTURE) b.) Strengthen the thinner brickwall by attaching multiple layers of plasterboard directly to the wall (add some mass to one layer). The whole construction would have 2 leaves with just a tiny bit more airspace between the leaves... ;-) (SECOND PICTURE) c.) Don`t attach any plasterboard to the weak spot and just leave the airgap as big as possible and add the additional layers to the inner wall of the control room. (no picture) d.) any combination of this three versions.... What do you guys think?? Any ideas?

something I forgot: The mortar/cement of the weaker wall doesn`t seem to be very soundproof. In addition to the weak bricks there`s noticeable lack of sound from the gaps between the bricks - probably the reason for also much mids/high mids travelling through the whole wall. Could be an argument for first of all dealing with getting it as strong as the rest of the wall??? One big M-A-M isn`t a great improvement when it has such a weak spot, what do you think? regards, Schroeder

In addition to the weak bricks there`s noticeable lack of sound from the gaps between the bricks - probably the reason for also much mids/high mids travelling through the whole wall.

In my opinion the first thing to do is to plaster the wall (if possible on both sides) with gypsum or cement. at least 1,5 - 2cm thick. If it's still 2 weak I would put 2-3 layers of plasterboard directly on the wall (without airgaps!) and then build the inner room so avoiding 3leaf. Btw, what kind of brick did you use for the wall? solid or the hollow type? This is a little problem in my room. on one side there is hollow brick with vertical holes in it and plaster on both sides. It's already a multible leaf system without the inner wall:? Florian

Good idea!! Plastering the wall is indeed a simple way to start solving our problem! The additional layers of plasterboard will do the rest! I don`t know what kind of bricks were used. The wall was already there. They`re probably the hollow-core ones. Standard. A wall with hollow bricks (with or without plasterboard-layer) is definitely already a two-leaves system. I think they are more effective as single brick depth wall without holes... don`t they? After all the posts I read (many....) I still don`t understand the fear of building multiple-leaves walls... They perform better in the mids/highs and worse under 150Hz. "Better or worse performance compared to ... " means: with the SAME amount of material and space. Am I right? In those cases, where you have existing walls/constructions, you can often only improve the STLs by doing the best you can. So strengthen 3 leaves with additional mass can`t be wrong. In my case it`s supposably best (as you`ve proposed) to NOT create 3 leaves because the additional mass could be used more effectively. hmm... regards, Schroeder

After all the posts I read (many....) I still don`t understand the fear of building multiple-leaves walls... They perform better in the mids/highs and worse under 150Hz.

Have you ever had a car drive by you with the sound so loud that the BASS shakes everything around the car? Lows are the limitng factor for music islation. Andre [edit] put the sentence into english.

I must admit you`re absolutely right... Sure, I also had a car with killer-bass.... ;-)