Floating floor question

[The Niz]

Howdie to you all,

Currently I'm soundtreating my attic for turning it into a small homestudio (for personal usage only).

I've read a lot about soundproofing basics on the web (SAE, John Sayers site, this forum, etc) and I've read some books on the topic, but I've still got a question about the next step to tackle: the floating floor.

The attached jpg shows what I'm planning to do. I've got all the material ready to do it, my question is the following:

As you can see on the jpg (hopefully, if I succeed to attach it ;-), the actual floor will be 2 layers of 18mm x 2 = 36mm MDF right on top of each other. As I still have plenty of this "car seat fabric" left, I was thinking what would be the best thing to do in order to have the best sound proofing results:

option1: leave it like in the drawing (2 layers MDF on top of each other)

option2: put an extra layer of car seat fabric inbetween the 2 MDF-boards.

Would this be worth the extra effort? Or wouldn't it make a lot of difference?

Are there other suggestions or tips on the design of the floor or simple things I can do differently to have the maximum degree of soundproofing possible with the materials as shown?

I'm very curious about your comments. Thanks in advance!

Greetings,
The Niz

 

[John Sayers]

Niz - the rubber/carpet will do the isolation - I'd use the car seat stuff - which I assume is dacron - for other wall treatment.

cheers
john

 

[sjoko2]

I don't know what you think about this John, but personally I believe putting carpet underneath a floating floor might create problems.

Potential problems can be the (inevitable) compacting of the carpet underneath the pressure points, which can mean the whole floor "sliding" against a wall, causing vibration. In the worse possible scenario the carpet can become a membrane which amplifies vibration.

 

[The Niz]

Thanks John and Sjoko2 for the replies and advice!

I will stick to my first design and leave out the "car seat fabric" (which is actually a thin layer of foam with some textile glued to it - I've got about 400m² of this stuff...) between the MDF.

Sjoko2,
The floor ends will not touch the wall, I'll leave minimum 20 mm buffer from every wall.
I'm planning on filling these gaps up with 40mm sound insulation foam (called Aglofoam - it's confetti coloured) which I'll squeeze into the gap. On this floor and next to the walls, I'll construct a wooden frame (with rubbers all around) which will hold the same foam (but 60mm thick), and this will be finished off with the infamous "car seat fabric" and/or "anechoic pyramid foam" (sorry for these lousy definitions of materials...

Do you think that with the weight of the frames the floor will tend to slide towards the walls (worst case)?

All input is welcome.

Greetings,
The Niz

 

[sjoko2]

I'm still worried about the carpet - waiting for John's response.

Second thing is that I would NOT use any kind of foam - even if it says "for acoustic purposes". For your purpose you need a barrier product, so you'd be much better of with a 25 plus year guarantee caulk.

 

[knightfly]

Personally, I don't think the carpet would be a problem. If (when)it gets compressed, it will effectively just "go away", from an acoustic standpoint - you'll still have the rubber for isolation.

As to sliding sideways, I would think that the rubber would have a high enough coefficient of friction to keep that interface from sliding, and the weight of the floated floor would do the same for the interface between carpet and main floor.

As to the "surround" material, I agree with Sjoko 110% - (in best authoritarian police voice) "Step aWAY from the FOAM! Do NOT attempt to embrace the FOAM. Keep your HANDS where we can SEE them, and nowhere NEAR the foam...

Seriously, check out these guys - they don't push foam, so I like them even if they are expensive. I bookmarked their site mostly for ideas/reference. I've attached one of their pix to show their use of "soundboard" type of material as surround, thoroughly caulked with the best non-hardening caulk you can find. If you're lucky enough to find a source for REAL ACOUSTIC-rated caulk, even better.

http://www.kineticsnoise.com/floatsyst.html

Here's a link to more info, check out the STC ratings-

http://www.kineticsnoise.com/fcfmrim.html

I'm not sure how well their "puck on a roll" system would work with the lesser mass of a WOOD floor, you'd need to ask them about proper compression. It might be fine if you built your inner walls on TOP of the floor, instead of beside it... Steve

 

[sjoko2]

The reason I would worry about the carpet is that, on 2 occasions, I have encountered situations where a floating floor had to be removed (demolished would be a better word) because the cotton and bastik carpet backing had been pressured into a 'new' membrane which caused something I can best describe as a 'rubber truncheon' effect. In other words, any vibrations were captured and amplified to the floor below. I would therefore say that if you use, especially double carpet, you stand a good chance of having a floor that will function that way in time.

If you do want something under the floor, there are better and cheap ways to improve efficiency. One system I have used successfully in the past is a couple of layers of the thickest asphalt paper you can get. Very effective.

Regarding what you call the "puck on a roll" floor These floors are exellent but ONLY for well calculated concrete floors, or to support entire "building within a building" studios. I was working in a studio near here constructed entirely like that when we had a small quake. We didn't notice a single thing.

 

[knightfly]

Sjoko, did those two floors ALSO have the rubber in addition to the carpet, as the diagram in Niz' post shows, or was the carpet the ONLY compressible? I can't see where compressed carpet would hurt if the rubber was still there to isolate...

And, yeah, I figured you'd have to "stick to the program" for kinetics' stuff to work right, hence my comments to that effect. But, that would also be true of any DIY floor for the same reasons. At least the pro's have already done the research and come up with loading values that work... Steve

 

[kristian]

what exactly is the point of carpet? it has no acoustic value, you aren't walking on it, and it just sounds like an extra vacuum of money. I think the rubber and floating on their own do the work. carpet won't isolate any sound, so ir is useless unless it is really thick and you are trying to keep your feet warm on a cement floor. otherwise, sounds like an ill thought out idea.

 

[knightfly]

In this case, I think the idea of the carpet is that it's already there. There certainly isn't a good reason to ADD it, and if possible (for whatever reason) there's a good reason to REMOVE it - While I was at it, I'd consider replacing it with another layer of mass, although that probably won't be necessary with the concrete that's already there... Steve

 

[The Niz]

To answer to kristian and knightfly about the carpet:
it's was already in there when I bought the house, one is removable, the lower one is glued. I'll keep those 2 in, I think they won't have negative impact on the isolation results plus keeping them there saves me some work

The reason for the extra layer of fabric/foam: it's lying around and I just thought to stick it there, under the floor. If it's there and doesn't degrade the isolation results, at least I don't have to move it again to my garage. No really, it's optional, I can also use it for wall treatment, or something else. If it has zero isolation result, I might as well save me the work.

Knightfly: the inner walls will be build ON the floating floor, not beside them.

Sjoko2, I'm not sure what you mean with "asphalt paper". Does someone has a pic or link to it?

Thanks already for your feedback guys!
The Niz

 

[knightfly]

Not sure if it's the same thing, but in the US we can get two different thicknesses of what is called Roofing Felt - it's available in 15 lb per square (100 sq ft) and in 30 lb per square.

There is also a product called 90 lb roll roofing, which is heavier (duh) and has grit embedded in one side for wear, so that it can be used as an outer roofing material.

They all come in rolls that are 36" wide, and all are heavily impregnated with a substance similar to roofing tar. The two lighter weight ones are used under final roofing materials, the heaviest can be used alone if laid perpendicular to the roof slope and properly overlapped (like shingles)

The downside is that they all are pretty flammable, which is a BIG NO-NO in my book.

There is another good reason for removing the infamous carpet before you float your floor - if you use a sound-board surround to isolate the floor from the outer walls, then install the floated floor and caulk properly all around, then the carpet compresses more, you may end up with broken seals where the carpet compresses. It could make a negative difference in your sound proofing efforts... Steve

 

[The Niz]

You're right, using the carfabric is not worth the effort and can even have negative impact on soundproofing. So I decided not to put it in.

I've started to put a part of the floor for the drum area (see pic). Note that I'm only building a small homestudio.

Thanks for the advice guys!

Greetings,
The Niz