Architectural Isolators - Tech Notes
DESIGN & APPLICATIONS
To effectively reduce objectionable noise and vibration, we need to examine the characteristics of sounds generated by mechanical equipment, the transmission path and the sound receivers. Sound receivers are generally the people occupying a building that can become annoyed by noise and unwanted sound. The sound source is typically HVAC equipment, which has inherently high noise levels. The sound source can also be traffic, subway trains, bowling alleys, fitness areas or any other low- to mid-frequency range energy. Unfortunately, the sound source or receiver characteristics are often unalterable. Thus, the noise control expert is usually restricted to modifying the sound transmission path to achieve desired sound levels in the occupied areas of a building. Structure-borne noise can be transmitted through walls, ceilings and floors of buildings. Airborne noise, while easier to attenuate, can excite and travel through these paths as well. VMC Group has developed a series of products designed to increase the Sound Transmission Loss (STL) characteristics of standard building materials through the separation of floors, walls and ceilings from the base building construction.
ISOLATED WALLS
STL through a single cavity two-wall system is significantly increased by resiliently separating one wall from the other. VMC Group’s Isolated Wall System, WIB Series (Wall Isolation Brace), WAB Series (Wall Angle Brace), MWIP Series (Masonry Wall Isolation Pad) and the TMRB Series isolators (Track Mounted Ring and Bushing) are cost effective, high performance products that involve simple installation.
ISOLATED CONCRETE FLOORS
The origins of isolated floors are mostly credited to the Korfund brand, about seventy years ago, when we recognized that when two masses are separated by an isolation medium in an air space, the STL through the spatial mass was significantly better than a single mass of equal weight with no separation.
Practical floor thicknesses of 3 to 6 inches and air spaces of 2 to 4 inches can rival the performance of many feet of solid concrete. VMC Group’s lift-slab design allows the acoustician to vary the air space, decrease stiffness, and improve performance without increasing cost. Our interchangeable spring casting design provides the ability to change the use of a space as the need arises.
Neoprene or fiberglass can be used as the basis of isolated construction when high levels of mid-band frequency ranges need to be attenuated. Springs are typically used when incoming frequencies are low or impact is the problem.
The next generation of spring floating floors uses new wire rope springs with high damping and low natural frequencies. Proprietary simulated design programs with supporting test data to model a structure for a particular use are being used, giving us the ability to remove any questions from isolated construction design.
ADJUSTABLE SPRING FLOATING FLOOR
By applying known isolation formulas for mechanical equipment and similar formulas for shock, it became apparent that springs should be the medium of support for floors that have to attenuate either positive or negative isolation with frequencies below 20 Hz. Typical building construction of lightweight structural floors on 30 foot or greater column spacing often requires springs having deflections ranging from 1.5 to 3 inches.
Spring floors are more dynamic than other less resilient isolation materials. Therefore, the space of the entrapped air between the floors should be a minimum of 2 inches, quite often more. However, this is strictly a guide. We recommend consulting a professional acoustician for specific design concerns.
Designing an easy-to-use and adaptable product that lifts, supports, and isolates the floor had become our goal. The Adjustable Spring Floating Floor (ASFF) Series combines simplicity with performance and a wide range of adaptations coupled with a user-friendly installation:
? Isolator deflections up to 3 inches for a greater low-frequency attenuation range
? Larger outer diameter springs for increased lateral stability
? Precision concentric threads for easier lifting
? Interchange capability for spring, neoprene, and seismic applications
? Access after installation for change of use spaces
ADJUSTABLE NEOPRENE FLOATING FLOOR
Neoprene is generally the best choice if the input disturbing frequency range is above 20 Hz. If noise reduction is the primary goal, then interior walls will rest on the isolated floor. If vibration or impact reduction is required, springs supporting the isolated floor by itself will normally suffice. A 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. The Riverbank tests showed that:
? Only an acoustically separated “room within a room” construction could attain an STC (Sound Transmission Class) at or near 80
? Air gaps heavily influence the performance of isolated floors and one inch should only be considered for impact
? Isolation of impact noise does not require “room within a room” construction, only isolated floors
Most importantly, it is the isolator natural frequency with dynamic stiffness response and its continuing longevity that will affect the STC and IIC (Impact Insulation Class) of a protected space. 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 neoprene must remain elastic. Therefore, the compounds and production procedures are critical as is ongoing verification of quality control.
The Adjustable Neoprene Floating Floor (ANFF) Series floor isolators all perform below 8.5 Hz. Neoprene compounding is to AASHO specifications for highway materials, and molding occurs in the U.S. under the supervision of our quality control laboratories that operate within the quality guidelines set forth in Quality Standard MIL-I-45208 & ISO-9001:2015.
ISOLATED CEILINGS
Sound barrier ceilings have proven to be a capable tool for the control of noise occurring above or in a treated room. Until now, space requirements for that ceiling or the penetrating of barrier construction to support mechanical services has often been a nightmare both to the designer searching for height and the consultant seeking effectiveness.
The introduction of our Low Profile ceiling hanger systems addresses these two primary design requirements. This system allows for:
? Minimal ceiling space above framing members
? Code approved support of services and/or a secondary ceiling without a myriad of penetrations
? Installations with as little as 1/4 inch above the cold-rolled suspension members
? Combination of the sound barrier, finished ceiling, and mechanical/electrical services, all suspended from the same isolation hanger without multiple penetrations
? Isolator deflections from 0.35 to 2.35 inches
LOW PROFILE CEILING ISOLATION HANGERS
The basic mass laws that apply to isolated floor construction for sound transmission loss act similarly, though not as well, for isolated ceiling systems. While improvement numbers are varied, 10 to 15 db is typical.
The modern ceiling isolation hanger uses isolation elements of neoprene, springs or a combination of both. Neoprene by itself attenuates high frequency energy while springs attenuate low frequencies. Together these materials effectively handle all ranges.
The housing or hanger that surrounds the isolator is installed in series with vertical attachments to the structure above and ceiling below. The hanger occupies 4 to 10 inches of space above the framing members of the ceiling.
When mechanical services or an additional ceiling needs to be installed, new isolators are traditionally used. The supports penetrate the first ceiling, referred to as the barrier. The myriad of wires or rods supporting the secondary ceiling or mechanical services must also be isolated from the barrier ceiling. Isolation bushings that ensure that the isolated barrier will not have its resiliency compromised must be used at each penetration. An effective installation is both expensive and difficult to carry out.
VMC Group takes great pride in offering the most space saving, efficient, cost effective design for the isolation of a suspended ceiling. For the first time, isolated ceilings take no additional space above or below standard drywall construction without isolators. In fact, this system takes up less space. The unique housing construction of the LP Series hangers allow for standard 1 ? inches cold rolled channel suspension members to be installed tight to the deck overhead, occupying as little as 3 ? inches total of valuable space for the entire system including furring channels, two layers of ? inch sheetrock and isolator deflection.
Unlike conventional isolation hanger assemblies that rob space from limited roof heights, the LP Series is installed without the use of clips, eyelets and pencil rods below and either tight with inserts or wire/pencil-rodded above. Without clips, there are no failure points. This system utilizes two cold-rolled channels that add stiffness to the ceiling — positively affecting performance. It also allows for an increase in center distances between isolators as well as the cantilevered distance from the last isolator to the ceiling edge. The slight added cost of the channel material is offset by a reduction in labor and materials.
Compared to this product, there is no application we can think of where conventional ceiling isolation hangers are better suited. Once the initial concept of the Low Profile Series was executed, the approach was broadened to include:
? Neoprene, higher capacity isolation hangers capable of supporting accessory ceilings and mechanical services
? Spring and neoprene designed for low-frequency attenuation
? Spring and neoprene higher capacity hangers for the support of accessory ceilings and mechanical services
If the suspended ceiling is lightweight, its value is to reduce reverberation time within a space or the time it takes for a sound to die out. For reducing the passage of sound from one vertical area to another, the more mass the better. Two layers of suspended sheetrock are good, three is better.
VMC Group offers a full line of architectural isolators.
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