Calculating transmission loss of walls

Hi Guys I hope you can help me with some knowldge on the theoretical transmission loss of my new studio walls. I 'm in the early stages of planning a new studio which will be built as a standalone structure at the bottom of a garden in the UK. Full background and details can be found in my construction thread http://www.johnlsayers.com/phpBB2/viewtopic.php?f=1&t=13258 but to summarise: This will be a home studio that may be used for more commercial purposes in the future. It will be a completely new build from the foundations up. The building is 20m away from the nearest residential neighbours and is not connected to any other buildings. My plans at the moment are to build the external walls with hollow core concrete blocks (100mm at the moment but could change) with a concrete roof of similar thickness (block & beam). The floor will be a reinforced slab isolated from the external concrete walls which will be built on strip foundations. I'm proposing a room in a room design with internal walls of the "inside out" design to squeeze the most out of the space available. The internal rooms will be sealed to ensure they are airtight. I am trying to calculate the expected transmission loss of the walls to make sure I'm making the right decisions on the construction (and to try and learn a bit along the way). I come from an engineering background so I'm reasonably comfotable with the maths (if a bit rusty !) I've been doing a lot of reading on the forum and have Rods book, but I still seem to have a few gaps in my knowledge. I probably know enough to be dangerous at the moment :-) To summarise what I think I know: Tranmission Loss is Frequency dependant. When a wall is constructed as a MAM structure there will be resonant frequency which will exhibit a much lower Transmission loss. By adding insluation in the airgap (MSM) the resonant frequency will decrease. I should be aiming to get the resonant freq as low as possible which means adding mass and using as wide a gap as practical. Please fell free to correct anything that is innaccurate Question 1 How do I calculate the total TL of a wall constructed as follows: From outside working in: 100mm thick hollow core concrete block sealed on both sides with a waterproof sealant 50mm air gap filled with standard house insulation 2 Layers of 18mm plasterboard with green glue in the middle, supported on an "inside out" timber frame using 4" *2" studs at 24" oc I've seen lots of values quoted for timber / plasterboard walls and for single concrete walls but nothing for a combination of the two. Any help greatly appreciated. Question 2 I understand that the formula for calculating the resonant frequency of a wall filled with insulation is F = 43 / sqrt(md) Where m= kg/m2 of the wall and d = width of gap in metres Is "m" the value for the combined kg/m2 of the plasterboard AND the concrete wall or just the plasterboard ? I'm assuming it's the sum of both but not sure ? Question 3 The loudest level I plan to record is acoustic drums which I assume will peak at around 115dB's As the nearest neighbours are 20m away I want to mke sure that they are not disturbed when sitting inside with a window open, so I'm guessing I should aim to target the average background noise level that they would normally experience. I guess that this is about 45 - 50dB's. I can't check actual levels yet but will do as soon as we move into the house. I know the answer to this will be "it depends" but I'll ask anyway..... Does that feel like a resonable target level assuming the neighbours are not hypersensitive and have the hearing ability of a bat ? So, the house is 20m away from the studio. Can anyone help understand how I calculate what the target level should be directly outside the studio ? I'm guessing for bass frequencies the air between the studio and the neighbours doesn't reduce the sound levels by much and depends on the humidity. Maybe I'm getting ahead of myself here but I'm keen to understand some of this theory. Thanks for any help / advice you can give. I'll keep the forum updated on the build as I progress. Cheers

Lemon, I admire the thought process. I might suggest you perhaps stick to the basic tenets you've outlined and build the best room you can, rather than going through the calculations. You can't simply sum the various STC (Rw) ratings of each component since they are logarithmic. Also, you introduce inumerable variables in a real-life setting. Your ideas are right on track. Do what you can to lower that LF resonance point. You have that already. Decoupled framing, absorption, mass and cavity depth each march that LF resonance point down further.

Hi Ted Thanks for the reply - It's encouraging to know I'm on the right track. Will take your advice and build the best I can. Cheers

Certainly you are on the right track. Those are the factors to manipulate