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Acoustic Floor
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Discussion
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Two masses separated by a low frequency response isolator create the environment
for noise and impact reduction many times greater than a single mass of equal weight.
The isolator seeks to emulate the stiffness properties of the air, but as this space
increases the frequency of the isolator governs the frequency of the floor system.
If noise reduction is the primary goal then enveloping walls usually rest on the
isolated floor. Ceilings with their own isolators cap the construction. If the frequency
range is above 20 hz, neoprene is generally the best choice. If vibration or impact
reduction is required, springs supporting the isolated floor by itself will normally
suffice. The professional acoustician is the best person to make these evaluations.
Thirty years ago several manufacturers working with Riverbank Acoustical Laboratories
tested an isolated room under ideal conditions. Much of what was learned for attenuating
high frequency noise (above 20 hz) and is been practiced by ABSOL.
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The Riverbank tests showed that:
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- Only an acoustically separated "room within a room" construction could attain STC's
(Sound Transmission Class) at or near 80.
- Air Gaps heavily influence the performance of isolated floors and 1" should only
be considered
for impact.
- Isolation of impact noise does not require "room within a room" construction, only
isolated floors.
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MOST IMPORTANTLY, ONCE THE ABOVE CRITERIA IS ESTABLISHED, IT IS THE ISOLATOR'S NATURAL
FREQUENCY WITH DYNAMIC STIFFNESS RESPONSE AND ITS CONTINUING LONGEVITY THAT WILL
EFFECT THE STC & IIC (IMPACT INSULATION CLASS) OF A PROTECTED SPACE!
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Product
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Natural Frequency establishes the response from one slab to the other. For the control
of high frequency noise, 10 hz is the established criteria including dynamic stiffness
correction. The elastomer must remain elastic, therefore the compounds and production
procedures are critical as is ongoing verification of quality control. Long test
histories have shown that 2" of air space should not be diminished. Neoprene floor
isolators all perform below 8.5 hz. (report ESI, 10/15/97). Compounding is to AASHO
specifications for highway materials, and molding occurs in the United Arab Emirates
under the supervision of the ABSOL International LLc which operates under the quality
guidelines set forth in Quality Standard MIL- I - 45208. The NF mounts combines
the versatility and assurance of positive adjustable air gaps with the proven isolation
of properly formulated neoprene. It eliminates the possibilities of rot, vermin,
and biologically unsafe conditions that could occur in older form work type systems.
This brochure highlights installations, specifications and typical details. Your
application may be different. Any thoughts or specific questions you have we would
be most pleased to address.
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Floor System Construction Procedure:
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1. The setting of all isolation materials shall be performed
by or under the supervision of the isolation manufacturer. 2. Set
and waterproof any drains and lower pipe seals in keeping with waterproofing specifications.
3. Cement perimeter isolation board around all walls, columns,
curbs, etc. 4. In seismic zones intersperse the perimeter
isolation board with bridge bearing quality neoprene pads the thickness of the isolation
board. 5. Place individual neoprene isolators on the sub-floor
at a maximum spacing of 48"(1200mm) in strict accordance with the approved drawings
prepared by the isolation manufacturer.
Additional reinforcement 6. Must be detailed on isolation
manufacturer's drawings when required. If sound barrier isolation walls are used,
add the following: Perimeter isolators shall be selected to support the wall weight
in 7. Addition to the perimeter of the floating floor. 8. In
seismic zones provide anchorage for the double acting resilient vertical snubbers
to the structural slab. Snubber anchor bolts must be in close proximity to the mechanical
snubbers restraining any high center of gravity equipment to withstand the overturning
moments generated by the machinery snubbers and prevent failure of the floating
floor. 9. Cover isolators with 1/2 "(12mm) AC plywood. Isolators
shall be located under joints and joints staggered. Connect plywood at abutting
edges and corners with 16 gauge steel junction plates. 10. Cover the
plywood with 6 mil (0.15mm) plastic sheeting and carry it up the walls past the
perimeter isolation. 11. Place seismic snubber housings on the anchor
bolts that protrude from the structural floor and through the plywood. 12. Place
reinforcing as shown on the drawings and pour floor monolithically. 13. After
the concrete has hardened, caulk all perimeter isolation board. 14. In
seismic zones adjust the double acting snubbers after machinery is in place to provide
a maximum up and down clearance of 0.125"(3mm).
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Quality Assurance
Floating floor system components shall be designed and fabricated by a manufacturer
with at least five years experience in fifty similar installations. The floating
floor isolation materials and panel board forms shall be installed under the supervision
of the isolator manufacturer.
Site Conditions
If site conditions are unsatisfactory or raise questions about the installation
of the floating floor, the work will not proceed until the condition has been corrected
in a manner acceptable to the isolation manufacturer.
Sequencing and Scheduling
Coordinate work with other trades and coordinate scheduling with the construction
supervisor to minimize delays.
Plywood
Type AC exterior grade 1 (12mm) thick.
EXECUTION
Installation
Install the floating floor systems according to the installation and adjustment
procedures and drawings submitted by the isolator manufacturer and approved by the
architect.
Neoprene supported floating floor system is to be constructed utilizing cast in
place isolation mountings. Housings are to be designed to sequentially lift the
floating slab to desired finished elevation after concrete has cured. Neoprene isolation
element is to be molded to AASHO standards in accordance with table 1 as shown below.
Deflections shall be between .20" to .30". Isolator natural frequency shall not
exceed 10 hz including dynamic stiffness correction. Verification of natural frequency
shall be at a nationally recognized test facility that is ISO 9000 certified. Casting
heights including extensions shall accommodate a floor thickness of " 150 "and accommodate
an air space of " 2". Castings will have provisions for chairing woven wire mesh
reinforcing or two 1/2" diameter reinforcing bars. Actual rebar size and spacing
shall be as determined by the project's structural engineer. An accessory neoprene
locator plug will seal the threaded portion of the housing from concrete during
the pour. The floating floor shall be kept clear of the perimeter walls or rectangular
penetrations utilizing perimeter isolation board manufactured from either 3/4" thick
10 lb. coated fiberglass or 1/2" thick neoprene sponge rubber. All cylindrical penetrations
shall use neoprene cylindrical covers. Six mil plastic sheeting with seams overlapped
a minimum of 24" turned up and over all perimeter isolation shall act as a bond
breaker during pour. Type FFD floor drains shall be used where slab drainage is
required. A non-hardening pour grade caulking shall be used to seal the perimeter
board and floor after final height adjustments if waterproofing is required. Submittals
shall include casting details and neoprene load versus deflection information. ISO
9000 natural frequency test data as outlined above shall be part of this submittal.
Manufacturers shall have a minimum of 5 years experience in this field. All components
shall be manufactured in the U.A.E., not just assembled. Products shall be type
NF as manufactured by ABSOL International LLC.
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Data Sheet
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