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Soundproofing an apartment workshop
Old 3 weeks ago
  #1
Here for the gear
 

Soundproofing an apartment workshop

Hello,

like many of you have bedroom studios, I have a bedroom workshop. Actually, it all comes down to my own designed and built CNC router. Being on hobby level, I cannot afford to rent a space. Building a machine enclosure is not an option neither. But now I have possibility to move the machine from bedroom to a dedicated room in my apartment.

I have been reading about soundproofing and acoustic treatment for couple of weeks to get a basic idea. As this won't be recording or listening room, I do not care about acoustic treatment at all. On the other hand, I like to sing during my routing sessions, but because of the high rpm spindle and ear protectors on my head I don't hear anything of my lovely voice. So, my plan is to make the room dead. Treatment done.

My goal is to soundproof this room as much as possible. Thing is, this is an apartment in reinforced concrete building with neighbours below, above and next to me so I must handle floor, ceiling and walls. Lets ignore one window and one door to make it bit easier. More simplification - no ventilation as well as there are no long routing sessions. It looks to me that room within a room concept is suitable for my scenario. The room itself is 4 x 3 x 2,65 m (13 x 9 x 8.7 ft). The biggest problem is the floor load.

Yes, yes, I have talked to structural engineer. He told me three things:

#1 It is no problem to hang additional weight on concrete walls as this weight is transfered directly to building foundation and building will not even notice it.

#2 The code says 150 kg/m2 (30 lb/ft2) usefull load for floor. This omits a safety factor of 1.5 to 2 at least.

#3 Considering weight of my machine (300 kg or 650 lb) and it's footprint (1.3 m2 or 14 ft2), he recommended to place steel RHS (rectangular hollow section) beams (joists) under the machine to distribute the load, towards floor edges i.e. to the vertical structure.


With these rules kept in mind, I came to following idea.

1) Starting with rule #3 - if placing floor joists under the machine, why not to place them on remaining floor area as well? I want to create a joist grid as big as possible but leaving a small gap between concrete walls and grid for decoupling. Grid would be placed on rubber pads. Grid cavities filled with fiberglass insulation. More rubber pads on the top of the grid. MDF or plywood or OSB placed on top. Laminate floor on top (this is a must for easy cleaning sawdust, shavings and occasionaly cutting fluids). This step increases the floor load.

2) Applying rule #1 , adding mass to concrete walls. Attach resilient clips on concrete walls, fill air cavity with fiberglass insulation, attach channels to clips and put two layers of drywall. This mass would just hang, not touching new floor, no floor load increase.

3) Adding mass to concrete ceiling. Similiar to previous but horizontal orientation. This mass increases floor load of the apartment above but this is a small increment, no issue here.

4) Finally, my wish, the room within a room, placed on new floor, decoupled from surrounding walls, with fiberglass insulation between studs and one layer of drywall on studs, ideally two layers of drywall, ideally green glued(?). New ceiling placed on RWAR walls. RWAR weight is the major increment to floor load. Considering the floor distribution grid and distance between RWAR walls and existing concrete walls, this should not be a problem as most of the load will transfer to vertical structure.


I did not mention the noise produced by machine. I am not able to qualify it. What I think, most of it is a air borne noise. Machine in operation produces small vibrations that can be considered as impact noise, right? When I touch machine frame with my finger, I can feel gentle vibration. I definitely cannot see it, machine does not move, objects placed on working table do not jump, glass of water is still. Machine is on four rubber feets and when I touch floor with my finger, that gentle vibration in frame is almost gone or hardly to notice.

I have recorded machine sound with Zoom H4n recorder in one hand and measured dB level with SPL meter in other hand about 60 cm (2 ft) from machine. Ambient noise of 38 dB, machine turned on but idle 55 dB, machine turned on and routing wood 90 - 92 dB. I ran FFT on recorded audio to get idea on frequencies, but again, I am not able to fully interpret the results. What I think I see is that most of the noise is above 200 Hz. I generated 50, 100 and 150 Hz sine waves to verify H4n recording capabilities in low frequency range and they were all captured. This is the link to recorded audio (7 MB).

With approach described above, is it possible to get 30 dB transmission loss? There is no triple leaf situation; can the construction be done more efficient?

I am very not happy about hanging mass on concrete walls as this added mass is not fully decoupled, but it is the only option to add serious mass to a room. But if I am right with the air borne noise characteristics, that mass might do its job. Do I need RWAR at all? Other thing - the floor - mass is fine, but the weight limit...

Please, I would love to read any comments, criticism or advices from you, what would you do different, what wouldn't you do at all...

Thank you.

Boris
Old 3 weeks ago
  #2
Lives for gear
About vibration : it's not because you don't feel them that they are not going through structures.

To be safe, chose a vibration isolation solution.
300kg, you can use spring + sylomer or other damping materials.

Chose some springs with stiff springs so your machine won't move and won't affect the cutting.
Old 3 weeks ago
  #3
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Jason Foi's Avatar
 

If i understood your plan correctly you are using clips/hat channel on existing concrete wall (decoupling/ creating a new leaf), and then constructing another internal wall/ceiling on top of your new "floating" floor?

That is a 3 leaf system. Dont do that.

Read the following pdf, learn it, and understand it. When you do, you will understand what it takes to design the system.
https://www.google.com/url?q=http://...IF7IihWVh_YP-W

I do not understand why building a machine enclosure is not an option. It seems like a better idea
Old 3 weeks ago
  #4
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Quote:
Originally Posted by JayPee View Post
About vibration : it's not because you don't feel them that they are not going through structures.

To be safe, chose a vibration isolation solution.
300kg, you can use spring + sylomer or other damping materials.

Chose some springs with stiff springs so your machine won't move and won't affect the cutting.
I would try this first. If the rest of the walls are solid concrete, and the machine can be mechanically isolated from the floor that might be all that's needed. A concrete wall should have pretty decent isolation 200hz above without a 2nd leaf.

@ qwertysimo -

these are the types of products-

https://www.isotechinc.com/product-c...ion-isolators/

They need to be loaded correctly, meaning that you want to load them towards the maximum deflection (spring compression), but obviously not overload. The more deflection, the more isolation from flanking sounds.
Old 3 weeks ago
  #5
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Why not isolating the CNC machine rather than the whole room?

Isolation reacquires mass and space...in apartment you have mass AND space constraints.

Plus it will be cheaper to isolate a machine rather than a room.
Old 3 weeks ago
  #6
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Many thanks for all comments.

Quote:
Originally Posted by JayPee

About vibration : it's not because you don't feel them that they are not going through structures.
Please, can you rephrase your comment? I do not understand it. Do you mean, I don't feel vibrations when touching floor because vibrations did not go through rubber feets?


@ JayPee
@ RyanC
I will have a look at those spring based isolators. Machine itself weights 150 kg (325 lb). Another 150 kg (325 lb) is the sturdy steel base from large RHS tubes. If located in a regular workshop, I'd fill tubes with sand to get another mass. I think I have never seen CNC machines on spring loaded feets. Point is to have as rigid base and machine as possible. Is it possible that springs start to resonate in very specific conditions?


@ Jason Foi
I have already found and read that document. You are right! Now I have realised. I have designed two separated air chambers, thus a 3 leaf system. Shame on me.


Machine enclosure has been on my to-do list for very long time. Having the machine for almost four years I realised that I need access to a workpiece during machining. I do not have an industrial grade vacuum for workholding, 10" dust collection, chip blower, lubrication system etc. I do these tasks manualy. The enclosure would be open most of the time.

Another reason for room soundproofing - I use another hand power tools (drill, saw, sander etc.) for example to divide stock material to smaller pieces before cnc machining or to finish a machined piece. Having the room soundproofed, I would be happier.


Anyway, considering machine area load violating rule #2 , I must use floor joists to distribute the load. I can use spring loaded feets afterwards on new "floating" floor.

I need to remove one leaf. I can remove remove mass resiliently attached to concrete walls/ceiling, or I can remove decoupled walls/ceiling thus removing the entire RWAR. What to remove? Which option would provide higher TL?
Two drywall layers on clip/hat channel on concrete walls/ceiling versus two drywall layer RWAR?


Have you listened to that audio and analysed it? I am right saying the <200 Hz range is not my concern?


Btw, someone interested to see one of my works related to music world?
Old 3 weeks ago
  #7
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Quote:
Originally Posted by qwertysimo View Post
I will have a look at those spring based isolators. Machine itself weights 150 kg (325 lb). Another 150 kg (325 lb) is the sturdy steel base from large RHS tubes. If located in a regular workshop, I'd fill tubes with sand to get another mass. I think I have never seen CNC machines on spring loaded feets. Point is to have as rigid base and machine as possible. Is it possible that springs start to resonate in very specific conditions?
Yeah that's a good point, if the CNC movement is a little jerky, the isolated stand etc will rebound a bit when it changes directions...My understanding is that when you isolate something like this, the heavier the isolated object/deck/machine is, the less bouncy it will be- assuming that all the isolators are loaded to near their max deflection (eg tuned to the same infrasonic frequency).

The problem then that you have, is that in order to achieve mechanical isolation from the floor and have as rigid as possible of a stand/deck, the floated part will then need to be extremely heavy. Like slab of concrete on isolators heavy. At this point the slab becomes the primary driver of weight and the weight of the actual machine is fairly insignificant.

That said the heaviest things I've used the isolators for is only a couple hundred pounds- in this range, it will be bouncy enough to push it around with one finger finger...

It would be cool if one of the pros could chime in on that. My read of the situation is that the main thing you need here is mechanical isolation, more-so than room in a room. That's a somewhat educated guess though.
Old 3 weeks ago
  #8
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With greater mass supported on stiffer springs forces that act directly on the isolated mass produce smaller static and vibratory displacements of that mass.

You could use something like this.

Problem is coupling of vertical motion and rocking. What are dimensions of the machine? What is the RPM?
Attached Thumbnails
Soundproofing an apartment workshop-steel-structure.png  
Old 3 weeks ago
  #9
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Might be useful as well

https://www.mecanocaucho.com/en-BE/APPLICATIONS/
Old 3 weeks ago
  #10
Here for the gear
 

Concrete slab on spring isolators is not an option because of its weight. It would be best as it is a single block of mass with minimum bending.

Machine legs are spaced 120 cm (4 ft) x 90 cm (3 ft). I am achieving 0.03 mm (0.001") accuracy. With heavy gantry moving around table, if the machine is placed on 4 separate spring isolators, I suspect some undesired deflection/warpage of frame might occur, consequently transfered to machine itself. Even more, with rapid acceleration/deacceleration especially in repetitive short movements, machine is prone to resonate. I wish I could add more mass to frame. All I can do is to cut less agresive as a workaround.

@ JayPee , I have tried the app. Attaching picture to this post.
Graph on the left - machine in idle state, phone placed on working surface.
Graph in the center - machine cutting aluminum, phone placed on working surface.
Grap on the right - machine cutting aluminum, phone placed on floor next to one of the legs.

No idea on reading accuracy, but the vibrations are definitely present. Comparing two graphs to the right, rubber feets do some decent dampening.

Would adding more rubber pads, maybe with different hardness, help?

If I build floor joist grid and place it on many rubber pads (I have seen U-boat pads in this forum), would be vibrations distributed over the grid and dampen to higher degree by those pads underneath?

Thanks.
Attached Thumbnails
Soundproofing an apartment workshop-vibrations.jpg  
Old 3 weeks ago
  #11
Lives for gear
Quote:
Originally Posted by qwertysimo View Post
If I build floor joist grid and place it on many rubber pads (I have seen U-boat pads in this forum), would be vibrations distributed over the grid and dampen to higher degree by those pads underneath?

Thanks.
It's my understanding that we don't know a lot about the U-boats because the manufactures don't seem to want to share much about them or what they are capable of. Sortof a case where the silence there seems to speak volumes- If they work, why not share?
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