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It is important to note that masonry walls will transmit impulse noise through their structure more easily than gypsum board so isolating the wall from outside sources or other parts of your structure is important.
Adding mortar or compacted sand inside concrete blocks will increase isolation. Creating a double wall system with glass fiber in the air gap will also increase isolation.
Summary Of STC Walls
In the chart below from Master Handbook Of Acoustics by F. Alton Everest and Ken C. Pohlman, we can see that the best isolation is from double concrete block walls spaced 6" apart. This system will work really well, but uses a ton of square footage in your studio. A double wall with drywall and wood framing can achieve an STC of 63, so single masonry walls for studios are not as good as a double wall system. However, single masonry walls are much better than single drywall and wood framing. A single wall in a typical home only has an STC of 36.
Comparing Concrete Walls
If we look at another diagram from the Master Handbook of Acoustics we find that a single 12" concrete wall has an STC of 51 and two concrete walls spaced 6" apart has an STC of 59. The double wall system is clearly better than a single concrete wall. Remember adding insulation in the air gap will increase the STC as would adding more mass to the outsides of both or either wall. Also remember that although the STC is not comparable to our wood framed double wall the low frequency transmission loss is going to be greater in a concrete wall than a wood framed wall.
Brick Walls
If we look at a third diagram from the Master Handbook of Acoustics we can see how different brick wall designs perform. Notice that a single brick wall is not ideal. Adding wood, furring channels or gypsum board to a brick wall will increase transmission loss. The two brick walls with glass fiber in the middle will give the best transmission loss across the frequency spectrum.
Using Masonry Walls and Wood Framing Together
I believe the best option when soundproofing is to use a masonry wall as your outside wall to the world or the rest of your house and then frame an inside wall with at least a 1" airgap using wood framing and two layers of drywall with green glue in the middle. This will give you an STC in the 65 or higher range and will also increase your low frequency isolation. I also believe this system will save you in materials cost and floor space in your studio design.
Master Handbook of Acoustics - www.amazon.com/Master-Handboo...
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0:00 - Intro
1:11 - Summary of using masonry walls
3:06 - Different Wall STC Ratings
4:57 - Two concrete block designs
5:31 - Comparing brick wall designs