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post #1 of 17 Old 12-04-2018, 04:08 PM - Thread Starter
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Floating Floor Resonant Frequency

I'm in the early stages of designing the Gearhead Garage Theater which will be an addition over an existing 2-car garage. I'm considering using the Kinetics Noise Control RIM Isolation pads for a floating floor, and I was wondering what the optimum resonant frequency should be to minimize bass transmission through the floor joists into the rest of the house. From the attached spec sheet, you can see that there are a number possible resonant frequencies obtainable from ~10Hz on up.

I'm guessing lower is better, but I'd like to hear from some of the acoustics Illuminati with regards to spec'ing a floor system.

Also, what happens if you play sustained bass notes close to resonant frequency? Will my floor self-destruct like the Tacoma Narrows bridge and collapse into the garage below?!?

Looking forward to the discussion.
Mike
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File Type: pdf Kinetics Isolation Pads - Natural Frequency - 2 inch.pdf (248.7 KB, 24 views)
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post #2 of 17 Old 12-06-2018, 12:12 PM - Thread Starter
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@SierraMikeBravo , @Nyall Mellor , @sdurani , @Dennis Erskine , @Tedd

Do any of you guys have any experience with this product or something similar?

Given your knowledge and experience, what resonant frequency should I target?

Thanks in advance,
Mike
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post #3 of 17 Old 12-06-2018, 01:55 PM
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Having built theaters designed by three of those guys I can tell you that two designers use 3/8 - 1/2 inch rubber mat with a floated subfloor over top. If you float a single layer of OSB/Plywood it needs to be glued, If you use two layers of 1/2 inch material and overlap the seams you can skip the adhesive, just screw the two layers to each other, but you may want to add Green Glue between the layers of OSB. No mechanical fasteners through the floated layer into the original subfoor. See https://www.soundproofingcompany.com...dproof-floors/


To save money you can use recycled rubber tire "horse stall mats" from Tractor supply for the rubber mat component.

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post #4 of 17 Old 12-06-2018, 02:28 PM
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Quote:
Originally Posted by BIGmouthinDC View Post
Having built theaters designed by three of those guys I can tell you that two designers use 3/8 - 1/2 inch rubber mat with a floated subfloor over top. If you float a single layer of OSB/Plywood it needs to be glued, If you use two layers of 1/2 inch material and overlap the seams you can skip the adhesive, just screw the two layers to each other, but you may want to add Green Glue between the layers of OSB. No mechanical fasteners through the floated layer into the original subfoor. See https://www.soundproofingcompany.com...dproof-floors/


To save money you can use recycled rubber tire "horse stall mats" from Tractor supply for the rubber mat component.

Any thoughts about using MDF (or higher density stuff, call it HDF) in lieu of OSB or plywood?


And separately, isn't plywood a bit more prone to warping than OSB (and fiberboard)?

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post #5 of 17 Old 12-06-2018, 02:55 PM
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MDF should work,

Warping? Maybe, depends on the quality of the plywood and the environment where it is being installed. I've used 3/4 tongue and grove without issue.
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post #6 of 17 Old 12-06-2018, 09:32 PM - Thread Starter
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Quote:
Originally Posted by BIGmouthinDC View Post
Having built theaters designed by three of those guys I can tell you that two designers use 3/8 - 1/2 inch rubber mat with a floated subfloor over top. If you float a single layer of OSB/Plywood it needs to be glued, If you use two layers of 1/2 inch material and overlap the seams you can skip the adhesive, just screw the two layers to each other, but you may want to add Green Glue between the layers of OSB. No mechanical fasteners through the floated layer into the original subfoor. See https://www.soundproofingcompany.com...dproof-floors/

To save money you can use recycled rubber tire "horse stall mats" from Tractor supply for the rubber mat component.
Thanks @BIGmouthinDC . The Tractor Supply mats are my fallback position. I'm just worried that the durometer of that product is too high and will thus transmit substantial bass energy into the floor joists/trusses and from there into the rest of the house. I'm planning a 2nd floor theater over our garage with a room-in-room for sound isolation so all of the interior walls, which will also support the ceiling, are resting on the floating floor. All that bass will have a direct flanking path into the house unless I can substantially isolate the floor from the structure beneath. I am really worried about bass down to ~15Hz, as that is the tune for my ported subwoofers. Granted, the TS mats are 1/3 (maybe 1/4) the cost of the KIP pads, but if they can cut the 15-100Hz energy from flanking into the house, it would be worth it in the long run.

Mike
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post #7 of 17 Old 09-25-2019, 06:02 AM
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I got most of my understanding about floor isolation from a discussion on another site entitled: Is a Floating Floor Right For You? Answer: Probably NOT. It seems to me that the "gold standard", if there is one, is a concrete slab raised up off the base floor. The raising up part is one thing but the mass of the floor is just as crucial, and both are required for it to be effective. There's a company called Farrat that has floor isolation products specifically for (commercial) cinemas called Cinefloor and they have data sheets to go with them. It certainly looks like a job for the professionals.

In a post from another thread you alluded to the fact that you would be poring a 3" concrete floor so I guess you've decided to go with the gold standard. How are the plans working out for that? I'm interested because I'm planning a build too and although it's on the ground floor I was still concerned about vibrations from the sub(s) and whether a floating floor might still be something to consider. I have a concrete slab sitting on the earth below and I plan to do a box-in-box construction on top of the slab. I feel like I have 5 sides of the box covered but the floor is a potential weak point. I would not want to get it wrong as rectifying later would probably be a nightmare. I don't believe I need to do anything special but I wondered if you (or anyone else) had any thoughts given route you've decided to go down.
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post #8 of 17 Old 09-25-2019, 08:42 PM
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If concerned about a too high spring rate per unit area of horse stall mats, simply reduce the coverage percentage to something less than 100%, and you will I'm turn reduce the effective spring rate.

How much? Who knows. A total guessing game. One I'm contemplating guessing about.
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post #9 of 17 Old 09-25-2019, 09:11 PM - Thread Starter
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Hey OH,

I reread most of the threads you linked to above, and the decision tree is very dependent upon the location of the planned space. Most of their discussion covered the value of a floating floor on top of an existing slab-on-grade. My use case is driven by a 2nd floor location, a spouse that is very intolerant of added noise in the household, very different sleep-wake schedules (I am a night owl), and my desire to watch action adventure/bass heavy movies late at night. All these factors pointed to a maximum isolation design is crucial for my enjoyment of the theater and it all starts with the floor!

As I mentioned, we are still in the engineering phase. Low frequency isolation performance is the main driver for our designs at this point. Typically, anything you do to contain <100Hz will also do a great job at all the freqs > 100Hz. The goal is to match the STC performance of the floor, walls and doors. Over-engineering any one area just adds cost without adding to overall STC performance. Nyal modeled both a 1.5" and a 3" Gypcrete floor and the heavier floor had nearly 10dB better isolation in the 50Hz region.

We originally considered a 4" tall Kinetics Noise Control KIP pad, but these would need to be custom manufactured, and our guess was that this would be prohibitively expensive eg >$5k just for the KIP pads. The KIP pads are the active component of the KNC RIM system. After additional modeling by Nyal, we settled on a 2" KIP + 2x4 stringers to support the Gypcrete. This actually gave a slightly larger airspace beneath the floor once the pads are compressed, and this seems to be an important aspect for bass isolation. The change from the 4" KIPs to the 2" KIPS increased the natural frequency somewhat, but Nyal reports there should not be a significant loss of isolation in the lower octaves since we kept nearly the same airspace. The heavier Gypcrete floor also requires a a stiffer KIP, which also increases the natural frequency slightly, but this is more than offset by the additional mass and improved isolation.

Preliminary ball park quotes suggest the cost of the floor alone will be ~$6K for just the KIPs and the Gypcrete. This does not included the cost of the subfloor underlayment, adhesives, perimeter foam isolation, acoustic caulking, additional cost of stronger floor joists, structural engineer, etc....


Mike
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post #10 of 17 Old 09-25-2019, 11:07 PM
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Expensive stuff but it sounds like you're going about it the proper way i.e. get professional engineering advice. Bigus sorry but when it comes to soundproofing, and in particular soundproofing of your foundation, "guessing" is by all accounts the very last thing you want to do. I also tend to agree with advice that any product without an accompanying datasheet stating the laboratory tested benefits also falls under the category of guesswork. Correct me if I'm wrong, but Serena Mat® Underlay falls into that category therefore.

I can't find the resource now but I'm sure I read that it's possible to install a floating floor after you've completed all the walls and ceiling. Ideally you have the walls of the inner box resting on the floating floor itself (more engineering calculations needed for this) but there's still benefit to be had even if the floor floats in isolation of the walls. Given my case and the expense you've alluded to I think I'm going to be relying on installing a floating floor after I see that flanking noise/vibrations are a problem - though hopefully they won't be.

Last edited by The OH; 09-25-2019 at 11:29 PM. Reason: Add mention about Serena Mat
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post #11 of 17 Old 09-26-2019, 11:45 AM
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walls should never rest on a floating floor if the floor is below grade (basement). There are just too many chances for a minor water event that while not a knee depth flood are deep enough that most cleanup companies that your insurance company recommends would expect to remove any built up subfloor as a precaution to prevent mold. Something as simple as a blocked drain line for your air-conditioner condensate can result in a thoroughly soaked carpet.
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post #12 of 17 Old 09-26-2019, 03:18 PM - Thread Starter
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Wow BIG,

What a nightmare scenario that would be if you had mold beneath the floating floor of your room-in-room theater. It would require a complete demolition of the entire theater.....It makes me shudder just thinking about it!

Mike

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post #13 of 17 Old 09-26-2019, 03:24 PM
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float the floor inside the wall framing, usually the walls are salvageable.
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post #14 of 17 Old 09-27-2019, 08:45 AM
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What a nightmare scenario that would be if you had mold beneath the floating floor of your room-in-room theater. It would require a complete demolition of the entire theater.....It makes me shudder just thinking about it!
In your situation, what with your theater being on the second floor, it seems to me that you could address the problem from the room below and leave the theater in tact... theoretically.
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post #15 of 17 Old 09-27-2019, 09:18 AM
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Originally Posted by BIGmouthinDC View Post
walls should never rest on a floating floor if the floor is below grade (basement). There are just too many chances for a minor water event that while not a knee depth flood are deep enough that most cleanup companies that your insurance company recommends would expect to remove any built up subfloor as a precaution to prevent mold. Something as simple as a blocked drain line for your air-conditioner condensate can result in a thoroughly soaked carpet.
I would have never considered that scenario. Who's the poor soul you witnessed with this problem!?

Disasters aside, the walls on floating floor is according to the Farrat cinema guide the "generally accepted" method of creating a box-in-box room. This was the resource I couldn't find earlier in fact. They say the following about the alternative, whereby walls are built "off" (i.e. not on top of) the floating floor:

"Such a method has been successfully used in a number of scenarios with very high levels of acoustic performance. It also has the advantage that the floating floors can be installed at the end of the build programme when the acoustic ceiling, overhead services, walls and seating structures have been erected. The acoustic floors can then be installed just before fit out works meaning no concern needs to be given to the potential for overloading floating floors or damaging their finishes, especially if they have been powerfloated."

See the second diagram of the attached image.

If I ever finish a home theater and find the floor is an issue, I'm relying on this as a get-out-of-jail card!
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post #16 of 17 Old 09-27-2019, 01:11 PM
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You can easily cut 3/4 inch thick rubber strips and put under the bottom plate of standard wall framing. https://www.tractorsupply.com/tsc/pr...t?cm_vc=-10005
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post #17 of 17 Old 09-27-2019, 05:42 PM - Thread Starter
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In your situation, what with your theater being on the second floor, it seems to me that you could address the problem from the room below and leave the theater in tact... theoretically.

Yah, I'm not worried about a wet basement ruining my theater. It was just such a nightmare scenario...
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