Music studio in a basement with a party wall

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matcaz
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Location: Nancy, France

Music studio in a basement with a party wall

#1

Postby matcaz » Mon, 2020-Nov-23, 08:52

Hi everybody,

First, thank you Stuart and all of the great contributors of this forum. There's a massive amount of great and useful information!! I started being interesting in soundproofing music studio for a while now looking at forums and reading books ( Rod Gervais, Marshall Long,...). Continuing to learn about it, I'd like to introduce you my project.

I am planning to build (and make build with an architect) a « soundproof » music room in the basement of my house (built in1910) that has a limestone common wall with my neighbours house.
I have an appointment with the architect in January to plan the design of the project, the way to construct it and the budget for this. So, I need to be the more accurate as possible in my requirements and objectives for this room within a room.
I post my project here and share it to you because I have a lot of questions regarding studio designs and soundproofing processes. I'd like to discuss with you about this project and the realistic requirements and objectives that I can come with for the pre-project with the architect. And to resolve some of my misunderstanding of “soundproofing” concepts.

Objectives and environment

This studio room will be used to rehearse and recording/mixing (for preprod uses) live bands (drums, bass, guitars, voices, average level of noise : 110 – 120 db). The budget I can have for this project is 15k€.
The house is located in a houses neighboorhood with two streets (level of noise outside in daytime : 50db). The basement walls are underground/below grade with the fourth wall (at right)being common with my neighbours' basement. The environment sound level in my basement without noise (washing machine, etc,...) is around 30-35db (measured by iphone app...). With the washing machine on, it rises to 55db. The sound level in the neighbour's house is approximative because I won't be able to do measurements in... because of bad relationship with my neighbours...

Assuming I don't want to annoy my neighbours in their house (especially their living room), can we say the sound level in their basement should not rise over 35db ?

Here's some views (the red area labelled 110 db is where I plan to build the studio in the basement) :
cross section view2.jpg


Here's the existing top view of the basement:
existing basement top view.jpg


The red line is the delimited space for the studio (room in a room).
The space is limited by:
_ the well. It will stay in place. It's a 4,5m concrete hole where there's 3m of water. It is used to drain the foundation. I've never noticed any water coming in the basement floor and it is safe. Architect and mason confirmed it.
_ the ducting and the pipes that go to the ground floor through the basement's ceiling. The gas pipe and the heating water pipe paths are quite weird and need to be moved away. They go through the middle wall by 2 holes. This should be useful for the HVAC system and the electrical installation.
The basement window (in the bottom wall) will be closed and could be used for the HVAC system design.

So the global idea to keep the area free for this “room in a room” little studio is:
_ move the ductings. Use the remaining holes in the wall for HVAC/electrical paths ?
_ knock down the 10 cm concrete block wall partition.
_ break a part of the 8 cm concrete slab.
_ remove interlocking concrete pavers.
_ dig 30-40 cm off the ground to have height from 2,1m to 2,4-2,5m. Regarding the height, the mason and architect tell me I could dig 40-50 cm high off of the soil without any risks to damage the building structures of the house.

Here's a more detailed picture for the foundation and new ground level:
fondation details.jpg


And here's the project global view:
basement project global top view.jpg

basement project cross section view.jpg


Dimensions are (LxWxH in cm) 480x380x(250-260).

I'm currently trying to figure out what is the best design and how to define some requirements. So, let's do the calculations using some math from Rod Gervais and/or Marshall Long. (Please let me know if I'm wrong).

First, I want to now the sound transmission loss in the 55 cm limestone common wall:
_resonant fundamental frequency for a single panel: fr = 0,45*vl*h*((1/L)² + (1/H)²)
where, h is the thickness of the panel (m),
L its length (m),
H its height (m),
vl (m/s), the longitudinal velocity of sound in the partition
vl = (E/pm*(1-s²))^(1/2)
E is Young's Modulus in (N/m²) or Gpa or Mpa
pm is the density in (kg/m3)
s is Poisson's ratio (0,2-0,3) in construction material
In my case,
_ h = 0,55m, L= 7,4m, H = 2,1m,
_ vl = [2553 – 2054] m/s where
pm for limestone is between [1800-2780] kg/m3
E = 11.10^9
s = 0,3
_ fr = [154 – 124] Hz

_ the critical frequency about bending waves and coincidence effect (from Rod Gervais);
fcr = c0^2/(1,8*h*vl)

where, c0, speed of sound = 344m/s
So, fcr = [46 – 58] Hz

Why fr is much higher than fcr since fr is the fundamental frequency ? Shouldn't it be the opposite way ?

If I refer to the mass law formula,
_ at fr, TL = 20*log(fr*m) – 47 (db), where m is the surface mass density in kg/m²
TL = [46 – 51] db, for limestone where density is between [1800 – 2780] kg/m3
_ at fcr, I read the formula in Marshall Long book but it's too far for my math skills...

About the minimum amount of insulation requirements:
_ if L0 is the level of sound in the red room, L0 = 115db
_ L1 the level of sound in my basement
_ L2 the level of sound in my neighbours basement (max 35 db)
_ T1, the transmission loss between the red room and the basement
_ T2, the transmission loss between my basement and the neighbours basement.
_ L1 = L0 – T1 and L2 = L1 – T2 (and T2 = TL)
→ L2 = L0 – T1 – T2, so T1 = L0 – L2 – T2:
T1 = 115 – 35 – [46 – 51] = [34 – 29] db.

Is it right ? And is it correct to say that I need to achieve a minimum of insulation with a transmission loss of [29 – 34] db for the red room ? (IMO, it's too low for the goal I want to achieve)

I consider 3 options for the main design of this room in a room and asking myself a lot of questions to know which one to choose (with the correct calculated data to make decisions and compromises with my budget):
(the door will be installed in front of the common wall. I'm aware this part of the room with the door will be the weaker part and where I need to put all the effort in designing and building).
design options.jpg

After reading a lot of thread and just to be sure, can you confirm me that:
_ option 3 is a kind of triple leaf MSMSM system and this can be worse for my sound insulation. Moreover the building of this can be very complex (inside out ceiling,...).
_ option 2 looks like the best option but, is the new partition wall, the inner leaf and the common wall would act as a triple leaf wall?
_ option 1 is the less expensive one and allowing the more space but... Since I'm not sure at all about my calculations, I don't know how to mae the right decision...

For example with option 1:
_ for the 3 existing walls and the wood studs facing them:

The resonant frequency for double panels for MSM systems:
fr = 84*((1/d)(1/m1+1/m2))^0,5
where d the distance between panels, m1 the surface mass density of 1st panel, m2,...
d = 0,25 m because of the 10 cm of foundation wall, a gap of +/- 5 cm to the concrete (or wood) floor and 10 cm long wood stud):
m1 = [1800 – 2780]*0,55 = [990 – 1529] kg/m²
m2 = 24 kg/m² (2 layers of gypsumboard)

→ fr = 34 Hz
f < fr, TL = 20log (f*M) – 47, where M is the mass surface density of the entire construction: TL(f=fr) = 47,4 db
f > fr, TL = TL1 + TL2 + 20log(f*d) – 29
TL (f=63 Hz) = 158 db !!!!

_ for the remaining partition
d = 2,3m then
→ fr = 2,3 Hz !!!
f < fr, TL (f=fr) = 24 db
f > fr, TL = TL1 + TL2 + 20log(f*d) – 29
TL (f=63 Hz) = 177 db !!!!

These results sounds really weird and I should miss something... And that's where I'm stucked...

I don't think yet about HVAC because I'd like to know first which design of the room in a room I need.

I compile here my questions and others thoughts about my project to summarize it a bit:
Global:
Assuming I don't want to annoy my neighbours in their house (especially their living room), can we say the sound level in their basement should not rise over 35db ? So, does it mean I can have an acceptable sound level in my basement between 55 – 60 db?

About MSM systems and calculations formulas:
Why fr is much higher than fcr since fr is the fundamental frequency ? Shouldn't it be the opposite way ?

Is it right ? And is it correct to say that I need to achieve a minimum of insulation with a transmission loss of [29 – 34] db for the red room ? (IMO, it's too low for the goal I want to achieve)

Option 2 looks like the best option but, is the new partition wall, the inner leaf and the common wall would act as a triple leaf wall?


About construction:
_ For the new floor, I hesitate to ask the architect for a new concrete slab. She said to me that we could think about the solution of having prefab concrete little slabs using them as foundation for a wood floor. I'm not sure if we talk about putting the wood frame on it or not and this floor subject was just an informative talking, no decisions were made about it now.

_ I will have to put a new coating on the walls because the coating was made with concrete and the masonry stones in the basement require a “breathable” coating. I read that having a coating make transmission loss higher than without it. Should I put insulation on it (and how to not damage the walls or the insulation for the future) or to the wood studs' side? The kind of stones the basement is made of, need to “breathe” and act as the opposite of concrete regzarding water paths.

_ What would be the minimum recommended space between foundation wall and new floor to hope having a good decoupling between the new room and the existing structure?

Supplementary notes:
_ The main goal is to be able to make a compromise with budget/reachable objectives/design/building to bring with me accurate requirements for the architect preproject appointment.
_ First is to determine the sound transmission loss in the common wall and in the basement (resonant frequency and critical frequency as well). This will conduct me to choose for a particular type of design: the room in a room (and even more questions about the MSM system).
_ According to the acoustics math formulas, I'm trying to determine what would be the best option to reach the objective of the required sound transmission loss level. This is where I'm a bit confused. For my calculations in Option 3, I don't know if I need to use the triple leaf theory with the stone wall or use the double leaf theory first for the double wall studs and then use it again with double wall system and the stone wall. The same for options 2 with the double wall facing the common wall.
_ In my case, I think the weaker part of this MSM system will be the part of the room that will face the common wall and that have the door. The building of this will have a particular attention.

I hope I don't miss anything and that you would be able to give me some help and advices about my project. Please let me now if I miss details. I'm facing some confusion about the calculations in acoustics domain and I think I misunderstood some general concept. Especially for the MSM system and the triple leaf effect...
And I apologize if I made some mistakes in English. It's not my native language and it's quite difficult to try to explain a technical context without knowing all the vocabulary of construction.
Best regards



matcaz
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Posts: 3
Joined: Fri, 2020-Nov-20, 08:47
Location: Nancy, France

Music studio in a basement with a party wall

#2

Postby matcaz » Tue, 2020-Dec-08, 06:17

Hello,

Please let me know what additionnal information you would need to give me some help and advices.



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Starlight
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Music studio in a basement with a party wall

#3

Postby Starlight » Mon, 2020-Dec-14, 06:24

Hello matcaz.

In many countries there are laws, often local laws, which dictate whether you can build a studio in a house and what levels of noise are lawful at different times of the day.

Sound going through a shared wall is not only the volume of sound that treavels through the air but also sound that travels through the building, such as when you bang on a wall the sound travels not only through the wall but along it to rooms or houses further way than just the room next to the wall.

With your bad relationship with your neighbour it could be possible that one call to the police or local authority could lead to your studio being shut down.

Taking these into consideration I would not dare to offer any advice. I would suggest that such a project needs the professional help of a studio designer, although that will use up a large enough portion of your budget - although maybe less than you think, ask one or two for a quote.



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Soundman2020
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Music studio in a basement with a party wall

#4

Postby Soundman2020 » Fri, 2021-Jun-25, 21:44

Hi matcaz, and Welcome to the forum! :thu: :) Sorry that it took so long for me to reply, but I've been out of action for a while.... And Starlight has been giving you good advice too!

I would only add the following:

The basement walls are underground/below grade with the fourth wall (at right)being common with my neighbours' basement. ... that has a limestone common wall with my neighbours house.
That's good, assuming it is fairly thick, but as Starlight mentioned sound can also potentially travel through the building structure itself, such as the floor, foundations, other walls, and ceiling, if those are shared with your neighbor. If you need high isolation, that might be a problem.

average level of noise : 110 – 120 db).
That's quite loud, but is typical for a rehearsal room with acoustic drums and the other instruments you mentioned. So you know "how loud you are": What you need to know next, is "how quiet do you need to be" on the other side of that party wall....

Assuming I don't want to annoy my neighbours in their house (especially their living room), can we say the sound level in their basement should not rise over 35db ?
That is what most people would consider "silent" or "very quiet", so it is a reasonable goal to aim for. But now comes the problem: You have a level of 115 dB inside, and you need a level of 35 dB outside. That implies that you would need about 80 dB of isolation. 80 dB is a LOT! That is very hard to achieve. Most home studios and project studios get around 50 dB isolation, maybe 60 at best. 70 dB is about as much as you can hope for in a home studio, and that is already very hard to achieve. It would also cost much more than your budget. That leaves you with three options:
1) Reduce your expectations (aim for less isolation). Eg, decide that you can only afford/achieve 50 dB of isolation, and design for that, knowing that you might still annoy your unfriendly neighbor.
2) Increase your budget a lot.
3) Play more quietly. For example, use electronic drums, play bass on headphones only (no amp), keep the electric guitar levels low, play keyboards on headphones, etc. If you could get your levels down to maybe 85 - 90 dB like that, and aim for a level of 40 - 45 in your neighbor's house (still sort-of quiet), then you would only need about 40-50 dB of isolation, which is much more realistic.

matcaz wrote:Source of the post First, I want to now the sound transmission loss in the 55 cm limestone common wall:
There's an easier way of estimating that, using what is known as the "empirical mass law" equation. It goes like this

TL = 14.5 log (M * 0.205) + 23 dB

Where: M = Surface density in kg/m2

The density of limestone is around 2,700 kg/m3, so for a thickness of 55cm the surface density would be about 2,700 * 0.55 =1,485 kg/m3. Plug that into the equation, and you get:

TL = 14.5 log (304) + 23 dB
= 14.5 * 2.482 + 23
= 59 dB

Which is great! However, that equation considers ONLY the wall itself: it does not take into account the flanking paths that I mentioned above; transmission through the building structure. That could reduce the total isolation considerably. Also, it does not take into account frequency: it only tells you about overall isolation. Low frequency isolation (drums, bass) is always lower than high frequency isolation (cymbals, female vocals).
knock down the 10 cm concrete block wall partition.
Have you checked if that is structural possible? Legally permitted? You should never knock down anything unless you first get a structural engineer to look at it, and confirm that it can be removed safely. And also that it can be removed legally: as Starlight pointed out, there might be local building code restrictions on what you can and cannot do.

break a part of the 8 cm concrete slab.
Probably not a good idea! If you do that, then the slab will not be supported on a proper foundation. You would have to dig back under the edges of that slab, and pour a new foundation. That might be possible, but is not easy, and is not cheap.

[quotet Regarding the height, the mason and architect tell me I could dig 40-50 cm high off of the soil without any risks to damage the building structures of the house.[/quote]They might think it is safe, but they are not really the right people to ask. Once again, you need a structural engineer to look at the existing building, look at what you plan to do, and tell you if it is safe or not. A structural engineer is the only person qualified to do that: masons and architects don't have the training to be able to do that, and in most places around the world, they would not be allowed to sign off on structural modifications to a building.

T1 = 115 – 35 – [46 – 51] = [34 – 29] db.

Is it right ? And is it correct to say that I need to achieve a minimum of insulation with a transmission loss of [29 – 34] db for the red room ? (IMO, it's too low for the goal I want to achieve)

Unfortunately, you can't really add and subtract isolation values like that. We are talking about decibels, which are log values, not linear, and there here are many other things going on too, such as resonance and flanking. I would expect that you will need a lot more than 34 dB isolation for your room.

matcaz wrote:Source of the post I consider 3 options for the main design of this room in a room
I would go with option #2.!! :)

These results sounds really weird and I should miss something...
Yup! Very weird! I didn't check your math, but the results are not valid. something went wrong somewhere....

Option 2 looks like the best option but, is the new partition wall, the inner leaf and the common wall would act as a triple leaf wall?
Not really: The distance between those two walls is plenty large enough that there would not be a 3-leaf problem here.

And I apologize if I made some mistakes in English. It's not my native language and it's quite difficult to try to explain a technical context without knowing all the vocabulary of construction.
Not a problem at all! You explained VERY well, and you have clearly put a lot of thought into this. I would suggest firstly getting a structural engineer to come inspect the building, then explain to him what you want to do, and find out which options are feasible, and which are not, considering your budget. Then, based on that you can decide which path is best. Once you have decided on that, then you could maybe post an update here, and we can help you further with the design.

- Stuart -




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