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Floating Floor

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Re: Floating Floor

Postby Paul Woodlock » Tue Nov 23, 2004 6:41 pm

Greetings Folks

My first post in the V3 Forum, so HELLO :)


Some comments about floating floors...


A floating floor is a mass-spring-mass system, and as such has a resonant frequency.

At this resonant frequency, you will NOT get Isolation. In fact, on the contrary, you will get AMPLIFICATION.

At about 1.4 times the resonant frequency you will go from the Amplification zone into the Isolation zone.

This means when designing a floating floor you MUST make sure the resonant frequency is LOWER than the lowest frequency you wish to isolate. In fact it's recommended to have a resonant frequency at least 2 to 4 octaves BELOW the lowest emitted freqeuncy


The resonant frequency of the floating floor system depends upon....

1] The mass/area on the resilient material. Usually an Elastomer such as Sylomer, EPDM, Neoprene, rubber, etc

2] The air gap between the floated floor and the supporting floor ( Which should be filled with absorption ( rockwool )to dampen void resonances

3] The SHAPE of the elastomer blocks supporting the floated floor

You should aim for a natural freqeuncy af around 10Hz or lower. This is easily achieveable with Elastomers


To calculate the resonant freqeuncy, you need to know the Modulus of Elasticity of the Elastomer you want to use.

The Modulus of Elasticity isn't a static value. It is influenced by Load, Time and Temprature and as such the specifications of the Elatomer come as nomographs.

Time is a particularly important factor in designing Floating floors.

To explain....

Generally the greater the load on the Elastomer, the lower the natural frequency. However, if you place too much load on the Elastromer blocks, you may achieve a low resonant frequency, but the system won't last long. Becuase the high load causes the Modulus Of Elasticity to change quickly over time.

This is very important, specifically for floating floors. A well designed floating floor will last 20 to 30 years. Too high a load, and the floor could only last months, or even weeks in a worse case. And for room within a room designs you can't simply replace the elastomer blocks without demolishing the whole studio.


I mentioned above the SHAPE of the elastomer blocks. This is also important. You must apply the Shape Factor to calculate a corrected Modulus of Elasticity. The shape factor is the ratio of the area of the top and bottom of the block ( ara under load ) to the area of the sides of the blocks ( area not under load ). The shape factor can greatly influence your deswign, so don't over look it.


So to conclude....

Building a floating floor WITHOUT calculation, means you are just plain gambling. And you could extremely easily end up with something that is actually WORSE than having no floating floor at all.

Another factor is floating floors need to be STIFF. Simply placing joists on elastomer blocks, and covering with a couple of layers of boards without calculation can not only give you a resonant frequency within the audio band, and thus amplifying it, it can also alter the acoustics of the room, due to a kind of resonant drumskin effect.

A good solution for a wooden floating floor is to build a structure that can be filled with sand.

And lastly....

Do you actually NEED a floating floor at all.

Floating floors are only really necessary for those with extremely high Isolation requirements.

And bear in mind that ALL the Isolation elements must balance. i.e it's no good having a super isolated floating floor, if your walls, ceilings, windows, doors, etc arent upto spec.

If you want to learn more about calculating floating floors properly then see this Web Page. If you have the correct specifictions of the elastomer it will give you all the info you need to do the calcs.

http://www.earsc.com/HOME/engineering/TechnicalWhitePapers/Vibration/index.asp?SID=61


Hope that Helps :)


Paul
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Re: Floating Floor

Postby Doublehelix » Wed Nov 24, 2004 2:41 am

Thanks Paul, it does help, but it is also quite depressing! :frown:

Why does everything have to be so danged complicated???
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Re: Floating Floor

Postby Paul Woodlock » Wed Nov 24, 2004 3:33 am

Doublehelix wrote:Thanks Paul, it does help, but it is also quite depressing! :frown:

Why does everything have to be so danged complicated???

Tell me about it :)

I had to do some serious learning to design my own floating concrete floor. I lost many brain cells doing that, and lost a few more cells tweaking all the parameters in a very complicated spreadsheet to get everything right.

but that's DIY for you. Get a company who specialises in Vibration Control and they'll use specially designed ( and expensive ) software to sort it for you. And charge you a LOT of money of course.

btw- the mass-spring-mass principles and amplification at the resonant frequency apply not only to floors, they apply to ANY decoupling, including speakers on Elastomer pads, and even double leaf walls.

And take the shock absorbers off your car, and you'll soon see how nasty MSM resonant freqeuncy amplification can be. ;) Years ago, both rear shocks failed on my old banger, and I couldnt' drive more than about 2 miles an hour without bouncing all over the road :shock:

You might find this thread interesting, which shows the pitfalls of not designing the MSM resonance correctly on a double leaf wall. Thankfully it was only an experiment and not an actual build...

http://forum.studiotips.com/viewtopic.php?t=1198

:)


Paul
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Re: Floating Floor

Postby Doublehelix » Wed Nov 24, 2004 6:22 pm

Ya know Paul, your post definitely has me thinking a bit about the overall goal of my control room. My main goal is to make a control room that I can sit in comfortably while loud instruments are tracking in the live room, not total isolation. This is a "home" studio after all, and not a purpose-designed "pro" facility.

I certainly don't want to make things worse with specific resonant frequencies, but I really need to keep things in perspective with regard to my needs and the level of isolation that I really need.

Your "bomb shelter" as you call it is *way* beyond anything that I have a need or desire for in my current location. If I was going to get that serious with my building, I would not do it in my home! I need a good control room with a fair amount of isolation (certainly not a -60 dB room!!!).

So in your opinion, would it be better not to float the floor at all??? How can Auralex get by with selling the U-Boat floaters as a generic iso device? There must be *some* benefit to de-coupling the control room floor from the live room floor?
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Re: Floating Floor

Postby Paul Woodlock » Wed Nov 24, 2004 6:57 pm

Doublehelix wrote:....Your "bomb shelter" as you call it is *way* beyond anything that I have a need or desire for in my current location. If I was going to get that serious with my building, I would not do it in my home! I need a good control room with a fair amount of isolation (certainly not a -60 dB room!!!).

So in your opinion, would it be better not to float the floor at all??? How can Auralex get by with selling the U-Boat floaters as a generic iso device? There must be *some* benefit to de-coupling the control room floor from the live room floor?

Good question :)

And I would certainly think very hard before commiting to a floating floor.

I have a need for a lot of Isolation. but a floating floor was something I had to think very hard about actually doing as well.

In a DIY situation it's very hard to predict exactly how well one's isolation design acutally performs in practise. I went for the floating floor in the end ( even though it swallowed up 40% of my budget ) because I wanted to be safe rather than sorry.

IOW, the 7 layer ceiling and wall design could have been enough without the floating floor, but there was no real DIY method of ascertaining this. My studio is for life ( not just for christmas ;) ) so disppointment wasn't an option :)


And I would say I need more than -60dB of Isolation. I wish I didn't, it would have been a lot cheaper and a lot easier :)

If you don't need the HIGH TL value that I do,then I would hazard an educated guess that you probably don't need a floating floor. If your not sure, then either get a professional acosutic company in to make some predictions ( ££££ ), OR build one anyway just to be safe.

The POINT is.... If you are going for a floating floor, then you MUST do it properly and calculate the resonant frequency properly. anything else is an expensive gamble.


There are other ways to decouple the floors of two rooms. disc cutting a slot on original the concrete floor is quite effective. Soil doesn't transmit sound half as eaily as hard conrete. but to so this you just be aware of any structural implications. i.e if the floor is part of the foundations ( as in a raft foundation ), then it's unwise. but if the concrete floor is sepereate from the foundations, then it's usually OK to cut the slab.

For a medium Isolation studio, you'll probably be OK by building two iner rooms ( control room and Recoding room ), leaving a decent sized air gap ( partially filled with rockwool ),and use as many layers of plasterboard as you can afford.

I got my plasterboard from Travis Perkins for £3.45+VAT for a 2400x1200x12.5 sheet. Use square edge plasteboad, NOT tapered edge btw.

What isn't good is building a floating floor that has a resonant Frequency in he audible freqeuncy range, and also lacks enough stiffness so that it negatively effects the acoustics in the room(s)

I'm sorry I can't give you a definite answer, as every room is different. And everyone's needs are different

Paul :)
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Re: Floating Floor

Postby Doublehelix » Thu Nov 25, 2004 12:10 am

Thanks Paul...great post.

I have been struggling with this whole control room/live room issue, and have another thread where I talk about some of the issues:

How Far do I need to go thread

Certainly cost is an issue as far as materials and time, but I want to make sure that whatever money and time I do invest is well-spent. As Max says in the other thread, "do it once, and do it right" (or words to that effect).
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Re: Floating Floor

Postby Paul Woodlock » Thu Nov 25, 2004 12:25 am

Doublehelix wrote:Thanks Paul...great post.

I have been struggling with this whole control room/live room issue, and have another thread where I talk about some of the issues:

How Far do I need to go thread

Certainly cost is an issue as far as materials and time, but I want to make sure that whatever money and time I do invest is well-spent. As Max says in the other thread, "do it once, and do it right" (or words to that effect).

Thanks :)

And I couldn't agree more with Max here. Which means calcs for floating floors ;)

If you haven't seen it already, take a look at my studio build diary. I've been through a lot of the things you're intending, and you may find the practical experience useful

Link in my studio diary thread I just created in this forum :)


Paul
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Re: Floating Floor

Postby Doublehelix » Thu Nov 25, 2004 3:10 am

I have indeed seen your diary, and have followed it off and on for a while. Great reading for those that have not seen it!

I am certainly nowhere near building anything on that scale...the way you have floated the cement floor is beyond belief! My needs are much more modest, and will be in a basement, so I am not worried about outside sounds or isolating to the outside world, but I just want a comfortable environment to track and mix, and get myself separated from the live room.
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Re: Floating Floor

Postby Paul Woodlock » Fri Nov 26, 2004 4:38 am

Doublehelix wrote:I have indeed seen your diary, and have followed it off and on for a while. Great reading for those that have not seen it!

I am certainly nowhere near building anything on that scale...the way you have floated the cement floor is beyond belief!

:) I can tell ya that learning how to do it, and then designing it, caused the death of far more brain cells than actually building it.

The only hard bit was pouring the concrete. You have to be FIT to shovel 6 tons of concrete around. And I am NOT FIT :)

The worst was pouring the first supporting slab of concrete. I'd never laid a concrete slab before, and while screeding it flat I crouched down, and soaked my a55 with wet concrete for 2 hours. I later discovered the concrete ( strong alkali ) had burnt the skin of a 6" diameter area on my a55. it fvcking hurt for weeks!! I've still got a bad scar :frown: :)


My needs are much more modest, and will be in a basement, so I am not worried about outside sounds or isolating to the outside world, but I just want a comfortable environment to track and mix, and get myself separated from the live room.

Well, if you have modest Isoaltion needs, and the main gaol is isolation between the two rooms....

First investigate if the original floor can be disc cut to decouple the rooms without causing structural problems/distasters. If it doesn't, then do it. It won't cost much, but is VERY DUSTY.

Then whether you disc cut or not, you should build your inner rooms with the biggest air gaop you can afford between the rooms, and use as many layers of drywall on your walls and if possibel ceiling as you can afford.

Floating the floor will lose you room height anyway. And to do it to any degree of success will cost you a LOT of money.

:)



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