Knightfly! Floating floor questions

[dymaxian]

Greetings! Couple questions about floating floors. I read thru the sticky about floated floors, and paid special attention to the waterproofing thing, so while I may have missed something (I spent 2 weeks worth of lunchbreaks reading this stuff) I think I have the basics down. Didn't want to add this stuff to a 20-post thread, but I can re-type the answers to this thread over there to add to it... Just a couple things still pop up in my mind.

First- I don't mean to be questioning your knowledge of physics, but what you say about a "spring not acting as a spring near the ends of it's travel" don't apply to a compressive load, at least not in my mind. I understand the effect of over-compressing the load and having sound transmit straight into the structure if the rubber is overloaded, but on the other end of the spectrum, having the rubber far over-designed doesn't seem like it'd hurt the effectiveness of the floated floor. If the rubber is close to the TOP end of it's travel (impossible for it to be exactly at it with any sort of load) how would it lose it's springiness? Looked at in slo-motion, the floor's vibration would translate to vertical motion; as the floor moved downward, the rubber would compress to absorb this motion (presuming it didn't over-compress), and as the floor moved upward, it may or may not lose contact with the rubber and bounce, but the resulting downward impact that followed would again be absorbed by the rubber.

The only thing I can think of that would be a bad side-effect is that your entire room has the potential of vibrating across the concrete floor beneath. There would need to be some kind of bumpers to keep it from wandering off on you, and perhaps having the inner walls contact the outer walls, making a structural bridge for the sound that way.

Like I said, I don't want to sound argumentative: I just don't see the physics behind the floated floor being ineffective from over-designing the rubber.

The second question builds off of the first one. Working as an architect, I know a dozen roofing companies off the top of my head that use EPDM rubber for flat roof systems, and throw away scraps all the time. Getting that stuff would be as close to free as I could get. EPDM has much greater compressive strength than Neoprene, so overdesigning wouldn't be all that hard.

Thanks in advance for all the help- our offer to purchase a new house was accepted, and the new basement has about 3 times the space that I currently have... you all have been a big help in my study of studio construction, so I'm sure the new rooms will do the place justice!

Kase
www.minemusic.net

[AVare]

If the rubber is close to the TOP end of it's travel (impossible for it to be exactly at it with any sort of load) how would it lose it's springiness? Looked at in slo-motion, the floor's vibration would translate to vertical motion; as the floor moved downward, the rubber would compress to absorb this motion (presuming it didn't over-compress), and as the floor moved upward, it may or may not lose contact with the rubber and bounce, but the resulting downward impact that followed would again be absorbed by the rubber.

Easy one. The frequency of the floor spring(rubber/EPDM) system is inversely proportional to the square root of the steady state deflection of the spring. At lower deflections, the floor will bounce exactly as you described in the last part of the quote above.

Remember, at the resonant frequency the floor spring system actually AMPLIFIES the sound.

Hope this helps.

Resilient Andre

[Paul Woodlock]

Greetings! Couple questions about floating floors. I read thru the sticky about floated floors, and paid special attention to the waterproofing thing, so while I may have missed something (I spent 2 weeks worth of lunchbreaks reading this stuff) I think I have the basics down. Didn't want to add this stuff to a 20-post thread, but I can re-type the answers to this thread over there to add to it... Just a couple things still pop up in my mind.

First- I don't mean to be questioning your knowledge of physics, but what you say about a "spring not acting as a spring near the ends of it's travel" don't apply to a compressive load, at least not in my mind. I understand the effect of over-compressing the load and having sound transmit straight into the structure if the rubber is overloaded, but on the other end of the spectrum, having the rubber far over-designed doesn't seem like it'd hurt the effectiveness of the floated floor. If the rubber is close to the TOP end of it's travel (impossible for it to be exactly at it with any sort of load) how would it lose it's springiness? Looked at in slo-motion, the floor's vibration would translate to vertical motion; as the floor moved downward, the rubber would compress to absorb this motion (presuming it didn't over-compress), and as the floor moved upward, it may or may not lose contact with the rubber and bounce, but the resulting downward impact that followed would again be absorbed by the rubber.

Greetings dymaxian

A floated floor is a mass-spring-mass system. And therefore has a resonant freqeuncy.

As Avare correctly states, at the resonant freqeuncy you will get AMPLIFICATION. And not just at the resonant freqeuncy, but upto about 1.4 times the resonant freqeuncy. In fact it's actually 2^0.5 ( sq rt of 2 ) abvoe the resonant freqeuncy. At this point you get neither amplification nor isolation, and only above this freqeuncy you start to get into the Isoaltion zone.

The amplification around the resonant freqeuncy is determined by the damping factor of the mass-spring-mass system. To se the effect of removing the damping of such a system, remove the shock absorbers from your car and enjoy the ride!!!


Avare says

Easy one. The frequency of the floor spring(rubber/EPDM) system is inversely proportional to the square root of the steady state deflection of the spring. At lower deflections, the floor will bounce exactly as you described in the last part of the quote above.

That is a simplification, and there are other factors invloved if you want to do it properly.

The resonant freqeuncy of a mass spring mass floated floor is determined by these factors....

1] Load/area on the elastomer blocks

2] Modulus of elasticity of Elastomer, which is can change with variations of these parameters

a] Time

b] temprature

c] Load

d] Shape of the blocks themselves


The aim is to get the resonant frequency of the system as low as possible and at least 2, and preferably 4 octaves below the lowest frequency your monitors can reproduce. 8 to 10Hz is practically achievable with Elastomers, but below that your really looking at special 'air' or steel coiled springs and are extremely expensive.

Increasing the load on the elastomer will lower the resonant freqeuncy UP TO A POINT.

A ridiculous amount of load will, as you already understand, cause the elastomer to 'bottom out' and not be a spring anymore.

However even before this 'bottom out' point you can run the risk of the Elastomer having a very short service life if you place too much dead load upon it. And that's serious when you build a studio on a floated floor, as the only means of replacing the elastomer is to dismantle the WHOLE studio.

A properly designed floating floor where special regard to loads has been applied can have a service life of 20 to 30 years. Overloading the elastomer can reduce the service life to months, and in extreme cases..days.

The only thing I can think of that would be a bad side-effect is that your entire room has the potential of vibrating across the concrete floor beneath. There would need to be some kind of bumpers to keep it from wandering off on you, and perhaps having the inner walls contact the outer walls, making a structural bridge for the sound that way.

This is almost impossible in a properly designed system.

The Elastomer blocks are glued to both masses in any case.

The sort of situation where vibration can cuase the mounts to come unstuck is in the case of isolating heavy manufacturing machinary where the start up or stopping vibrations equal the resonant freqeuncy of the mass-spring-mas system.

In fact this can have catastrophic effects. Ever see the old black and white film of the bridge that evetually collapses due to wind exciting the bridge at it's rsonant frequency?

In the situation of studio floating floors the amount of vibration is minute compared to the actual deflection of the Elastomer, and sideways bumpers are not required.

Like I said, I don't want to sound argumentative: I just don't see the physics behind the floated floor being ineffective from over-designing the rubber.

The second question builds off of the first one. Working as an architect, I know a dozen roofing companies off the top of my head that use EPDM rubber for flat roof systems, and throw away scraps all the time. Getting that stuff would be as close to free as I could get. EPDM has much greater compressive strength than Neoprene, so overdesigning wouldn't be all that hard.

......

Kase
www.minemusic.net

If you can get free Elastomer then great. I wish I had

However it's not a case of over designing or under designing. It's about getting it right.

If you don't do proper calculations, which is more involved than JUST the deflection, you run a high risk of either a] having a resonant frequency in your audio band and having the floor amplify instead of isolate and/or b] considerab;y reducing the service life of the floor.

This Webpage is an excellent tutor for vibration isolation, and provided you have the detailed specifications ( Importantly the nomographs for Modulus of elasticity v. time temprature and load ) for the Elastomer you have chosen to use, it will serve to help you calculate your floor.

hope that helps

Paul

[dymaxian]

Ok, it's starting to make sense. And from what I gather from the link Paul provided and other discussions about Neoprene, EPDM's greater resilience will mean that it's resonant frequency would be higher than that of a similar neoprene system.

Gotcha.

Good thing I have a calculator handy- my wife is reading this thread over my shoulder and it's making her brain melt.

[Paul Woodlock]

Ok, it's starting to make sense. And from what I gather from the link Paul provided and other discussions about Neoprene, EPDM's greater resilience will mean that it's resonant frequency would be higher than that of a similar neoprene system.

Gotcha.

Good thing I have a calculator handy- my wife is reading this thread over my shoulder and it's making her brain melt.

greetings

I'd advise setting up a spreadsheet if you wanna calculate it yourself

There's lots of variables interacting with each other. it would take a more than bearable number hours to get an optimum design using a calculator alone.

Elastomers come in different grades of hardness, and the trick is find the grade that will work with what's practical in the size, shape and spacing of the blocks.

I set up a complex spreadsheet that would automatically calculate the resonant frequency from simply entering the loads, size and spacing of the blocks, and the grade of elastomer AND the price. The price increases with hardness, and changing grades and using a different amount of elastomer can save you hundreds.

The spreadsheet also calculated the Shape factor from the block dimensions to correct the Modulus of Elasticity.

The other benefit of the spreadsheet, was I was able to split the floor up into zones epending on how much load there was. For example the area that held up the walls had the most load, while the general flor area had the least. There was also the area where the heavy soffit/speaker assemblies would be. The density of the blocks ( or the size of the blocks ) has to change in these high load areas, to keep the load across the floor even.

Becuase I was floating a concrete floor, I also had to consider the maximum spacing of the blocks to prevent the wet concrete sagging the plywood form holding it up.

Forget the calculator!!


Have fun! My brain melted a few times even WITH the spreadsheet

Paul

[cadesignr]

If you don't do proper calculations, which is more involved than JUST the deflection, you run a high risk of either a] having a resonant frequency in your audio band and having the floor amplify instead of isolate and/or b] considerab;y reducing the service life of the floor.

Hmmmm, I knew I heard that frequency in a Beatles tune The BBC should have known better.

Are you really suggesting someone could hear this on a recording or what? I think this is getting REALLY preposterous. 50 years of recordings and it's come to this. No wonder I'm loosing interest.

[AVare]

Are you really suggesting someone could hear this on a recording or what? I think this is getting REALLY preposterous. 50 years of recordings and it's come to this

Nothing new here. There are recordings made by the BBC of classical music in a studio built over the tube and the rumbling of the passing trains is quite audible. Yes, the studio was rebuilt at great expense to correct this acoustical problem. Sound familiar?

Quietly;
Andre

[edit] After thinking about it, what I recall is that what actually happened was that the subway was built AFTER the studio, and the problem then started. This was in the sixties.

[dymaxian]

cadesignr, I guess it depends on how far you're willing to go.

I'm not floating a concrete floor here- it'll probably be either 2 layers of 3/4" osb or a combination of osb and 1/2" drywall. I'm floating the floor more for moisture protection in an existing basement than anything else. My new home's basement doesn't have any serious water problems, but I know there's going to be at least a little moisture down there and since I'm building the walls up from the floor I want to make sure I dont even give mold a chance. I'm floating the plywood deck on top of pressure-treated 2x4s laid flat, and the primary reason for the EPDM will be to lift the wood off the concrete 1/8" so that little bits of water don't just wick right up into the floor. The structural isolation is a secondary point; I just don't want to make my isolation worse instead of better by doing all this.

If the resonant frequency of the floor is within the audible range, I'll have a problem somewhere- not just from my monitor speakers, but my 1000-watt bass amp.

The isolation of my room is going to depend mostly on my doors- I know this for a fact. Structural vibration coming down thru the floor will be a little concern, obviously, but my wife and daughter usually enjoy being able to hear what I'm working on, so it's not too big of a deal. And I'm not going to get mad if I can't play full-volume at 2:00am. If I knew precisely how heavy everything in my tracking and control rooms are going to be, I could run the numbers on the compression of rubber pucks to float my room, but I'm not yet sure what I'll be using for wall paneling yet, and I'm still designing my mixing desk.

Here's a good question for the floating floor gurus... given this situation, would it be better for me to bolt the pressure-treated lumber right thru the rubber, tightly tying it down to the concrete? It'd lose the structural isolation, but the water protection is the primary reason for the rubber. Would it be better to do this than risk having an audible floor resonation?

This is an opinion question more than anything. How much risk is there?

[Paul Woodlock]

If you don't do proper calculations, which is more involved than JUST the deflection, you run a high risk of either a] having a resonant frequency in your audio band and having the floor amplify instead of isolate and/or b] considerab;y reducing the service life of the floor.

Hmmmm, I knew I heard that frequency in a Beatles tune The BBC should have known better.

Are you really suggesting someone could hear this on a recording or what? I think this is getting REALLY preposterous. 50 years of recordings and it's come to this. No wonder I'm loosing interest.

Physics doesn't care whether you think it's preposterous or not.

[Paul Woodlock]

cadesignr, I guess it depends on how far you're willing to go.

I'm not floating a concrete floor here- it'll probably be either 2 layers of 3/4" osb or a combination of osb and 1/2" drywall. I'm floating the floor more for moisture protection in an existing basement than anything else. My new home's basement doesn't have any serious water problems, but I know there's going to be at least a little moisture down there and since I'm building the walls up from the floor I want to make sure I dont even give mold a chance. I'm floating the plywood deck on top of pressure-treated 2x4s laid flat, and the primary reason for the EPDM will be to lift the wood off the concrete 1/8" so that little bits of water don't just wick right up into the floor. The structural isolation is a secondary point; I just don't want to make my isolation worse instead of better by doing all this.

If the resonant frequency of the floor is within the audible range, I'll have a problem somewhere- not just from my monitor speakers, but my 1000-watt bass amp.

The isolation of my room is going to depend mostly on my doors- I know this for a fact. Structural vibration coming down thru the floor will be a little concern, obviously, but my wife and daughter usually enjoy being able to hear what I'm working on, so it's not too big of a deal. And I'm not going to get mad if I can't play full-volume at 2:00am. If I knew precisely how heavy everything in my tracking and control rooms are going to be, I could run the numbers on the compression of rubber pucks to float my room, but I'm not yet sure what I'll be using for wall paneling yet, and I'm still designing my mixing desk.

Here's a good question for the floating floor gurus... given this situation, would it be better for me to bolt the pressure-treated lumber right thru the rubber, tightly tying it down to the concrete? It'd lose the structural isolation, but the water protection is the primary reason for the rubber. Would it be better to do this than risk having an audible floor resonation?

This is an opinion question more than anything. How much risk is there?

There's a high risk. And I know that from running lots of combinations of numbers in these calcs.

A basement should be properly 'tanked' to keep out water and moisture in the first place.

Personally If you are going to skip the floating floor from an isolation point of view, and given your situation this would make sense, I wouldn't bother with the expense of rubber to prevent water ingress.

I'm not a structural expert, but I do know that concrete and wood ( and drywall! ) are porous. Your basement walls and floor SHOULD have some sort of DPM ( Damp Proof Membrane ) laid underneath and behind them already.

If you've got moisture under your floating floor, the rubber won't help things, as the moisture in the AIR under the floor will get into the wood in any case. Ventilation is normally used to prevent the build up of this moisture.

I would consider laying a DPM ( essentially a plastic sheet ) on the floor before laying your 4 x 2's down. but do NOT pierce the DPM with screws, nails or fixings.

But like I say, I'm no expert on structural things like water/moisture prevention. I would talk to someone who is.

I can say though, that a couple of layers of board on wooden strips on your floor WILL affect the acoustics of the room. It will 'boom'

Stamp your foot on hard concrete, and then stamp your foot on a wooden floor upstairs will easily demonstrate the difference.

Moisture and Floating aside I'd much rather have a hard concrete floor


Paul

[dymaxian]

I'm moving into a 30-year old house. I work as an architect, and I happen to know the contractor who built the house (he's good, but he's also a cutter of corners). This means I know the place is built fairly well (or I wouldn't be buying it!) but it also means I know he didn't go out of his way to water-proof the basement.

So what I plan to do is this: run pressure-treated 2x4s at 24" on center, but NOT block between them. This will allow some (not much, but some) ventilation for a dehumidifier to keep moisture from seriously building up under the floor. If I put down a plastic sheet, I'll trap moisture underneath it (even if it's just a little bit, it'll be unable to escape and eventually build up) so I'd rather lay the 2x4s on rubber pucks, even 1/8" thin, just to get the off the floor. This will keep most of the moisture from even getting into the pressure-treated lumber. The extra paranoia on my part is more about mold than vibration isolation, so if it'd work better I'd rather use the rubber only as moisture spacers and thru-bolt the 2x4s to the floor.

On top of that it's looking like 3/4" osb - 1/2" drywall - 1/2" osb, but not sure yet. We'll see. Something heavy.

But just in case I get experimental, can you post that excel chart for us to use? Or is it floating around the board somewhere already?

Thanks for all the help guys. This may have prevented a serious problem.

[cadesignr]

Physics doesn't care whether you think it's preposterous or not.

This isn't about physics anymore. IF you need this much isolation in your HOME, you have more than a physics problem.

Nothing new here. There are recordings made by the BBC of classical music in a studio built over the tube and the rumbling of the passing trains is quite audible. Yes, the studio was rebuilt at great expense to correct this acoustical problem. Sound familiar?

Nothing new? If your HOUSE is over the tube, I'd suggest MOVING. BTW, I don't know anyone who records symphonies in thier home. Of course, I don't know anyone who could afford that large of a studio in the first place.
Let alone in thier home.

[Paul Woodlock]

Physics doesn't care whether you think it's preposterous or not.

This isn't about physics anymore. IF you need this much isolation in your HOME, you have more than a physics problem.

Greetings

Why all the negativity? Is there something I'm missing?

The principles of floating floors has been explained already.

It's quite simple. For those that need LOTS of Isolation ( Like me for example ) a floating floor done properly is something that should be seriously considered.

For those that don't, then it's unlikely a floating floor is needed. Which should be good news, considering the cost of such a thing.

Paul