Sound Absorber performance is expressed as a decimal value. A perfect sound absorber is rated at 1.00. The higher the decimal value the more effective the absorber will be. Effectiveness is expressed as NRC (Noise Reduction Coefficient) .NRC: Percentage of acoustical energy absorbed calculated as an average of laboratory test data at several frequencies.
PRODUCTS QUIET A ROOMFUL OF BUZZ SAWS!
If you've ever used a power saw in the basement, your family was probably more irritated with the noise than excited about your creation. Imagine what a saw mill sounds like!
The operators of this saw mill didn't have to imagine anything; this compact, efficient sawmill cuts and planes hardwood from raw logs for the furniture industry.
After a building renovation the building, it was determined that the new walls and ceilings contributed to a significant increase in noise levels. It was a problem that their insurance company wanted resolved for the comfort and safety of the employees.
The noisiest part of the operation, the actual sawing, could not be isolated because every piece of equipment had to remain accessible to perform that function. Acoustic enclosures were considered impractical. Instead of isolating the noise at the source, they decided to treat the environment.
Noise-Control Materials
In order to control noise, designers must first determine where the noise source or sources are how much each is contributing to the overall level, and their frequency signatures. This can be done with a combination of instruments: a Type I 1/3-octave band sound-level meter, a sound intensity analyzer, and if there may be significant structural-borne noise, by model analysis of various components.
Once the sources have been identified and quantified, they can be ranked by how each contributes to the overall noise level. This is most important because if lower-level noise contributors are silenced first, this will not reduce the overall level. For example, when the exhaust is louder than the air intake on a gas or diesel engine, reducing the air intake noise gains little noise reduction until a properly sized muffler is installed.
When trying to control noise in any type machinery, designers generally end up employing some, if not all, four elements of noise control. These are absorption, barrier, dampers, and gasketing materials.
Absorption material: A good candidate will "soak up" airborne sound-energy waves by changing the wave energy into heat as it passes through the absorption medium. Absorption materials are generally either fibrous or cellular. Common fibrous material are fiberglass, mineral wool, and ceramic. These are applied as blanket or semirigid sheets which can be cut to shape. Generally, they are film faced or bagged to prevent the fibers from being dislodged and causing problems in air-handling systems or rotating machines when bearings or other components could prematurely wear out if they became contaminated.
Newly developed melamine and polyimide cellular materials offer significant advantages over traditional urethanes in many respects. The melamine required only 40% the weight of a comparable urethane, costs 30% more, and has no smoke or toxic by-product of combustion. The polyimide foam has similar characteristics to the melamine but costs 10 to 12 times as much, and is not as hydrolytically stable.
Film facing will reduce overall absorption at higher frequencies. This may be a problem if most of the noise energy generated is also at these frequencies.
Barriers: There are two types of barriers -- those that already exist (walls, cabinets, enclosures, etc.) and supplemental barriers. Supplemental barriers are those which you add if the existing enclosure wall is not thick enough. In this case, mass is the key to controlling noise. The mass law for homogeneous materials gives a rough approximation of the amount of noise that can be reduced given a specific materials mass.
However, the same reduction cannot be achieved at all frequencies. There is less attenuation (noise reduction) in the lower frequencies than the highs for a given mass, in this case, 9.6 oz/ft², or lead. The mass law predicts only 6-dB additional attenuation if the weight is doubled. But separating the two sheets of lead with a ¼-in. decoupling layer of open-cell urethane foam produces a significantly greater increase particularly above 500 Hz. Bonding a single layer of 10 oz/ft² to a 20-gage steel panel would result in even greater noise reduction.
These figures all assume "perfect" walls in which there are no openings. This is not very practical in most everyday applications. When openings are created for pipes, wires, air, and products to enter and exit, noise is let out. The amount of noise reduction expected from a perfect wall or enclosure diminishes drastically in the real world. As the opening size increases as a percentage of the total enclosure area, the actual noise reduction decreases.
For example, with a transmission loss potential of 20 dB or greater and 10% opening, designers can never get more than 10-dB noise reduction. However, this can be drastically increased by sealing around wires, pipes, and air ducts. In addition, noise reduction is increased by providing absorption-lined tunnels for materials that have to be fed into and out of the enclosure. These "supplemented" barriers are easy to fabricate and install either mechanically or with preapplied pressure-sensitive adhesive.
Damping: All materials have a natural frequency. When they are excited by some source at this natural frequency, they will vibrate. This causes the air surrounding the material to vibrate and produce noise. Sometimes referred to as "oil can" or "drum head" phenomenon, this type of noise can be controlled by damping. Properly applied damping materials will only work if the metal or plastic to which they are applied is vibrating at or near their resonant frequency. If a mechanically driven plate is vibrating, damping will not stop it. And it should be noted that all damping materials are temperature sensitive, so they must be selected both for their temperature range and the operating temperature of the material to which they are applied.
Damping materials work to reduce the vibration in the material to which they are applied by dissipating the vibrating energy as heat, rather than radiating it as acoustic energy or noise. Damping materials are termed "viscoelastic," having both elastic and viscous properties. Essentially, the material is stretched when it is bonded to a vibrating surface. There are two types of damping material, homogeneous or free-layer damping and constrained layer. Homogeneous/free-layer materials are generally vinyls which have platelet-type fillers in them. As the material to which they are applied vibrates, the platelets slide against one another, and this friction between platelets converts the vibration energy into heat.
Free-layer damping material, made from stable vinyl and other polymers, work over an extremely wide frequency (50 to 5,000 Hz) and are very stable over a long period of time (10 to 20 years or more).
The other type of damping is constrained layer. Here, the viscoelastic polymer is homogeneous (not filled) and is sandwiched between two plates. These are bonded together, usually with a structural epoxy adhesive. The ratio of the base thickness to the constraining plate thickness is between 1:1 and 4:1. Better damping is achieved at the 1:1 ratio.
Polymer thickness is determined by the frequencies to be attenuated. Generally, the thicker the polymer, the lower the frequency and conversely the thinner the polymer, the higher the frequency.
Polymer selection is a function of the operating temperature of the material to which it will be applied. Again, each formulation has a finite temperature range over which it will be effective. This temperature range is somewhere in the neighborhood of 80°F, for any given polymer, so that one that works are -20 to 60°F will not be suitable for the 80 to 160°F range. All manufacturers of damping materials give the specific temperature range, frequency, and thickness of the constraining layer.
Damping treatment can achieve considerable noise reduction. As much as 14 dB have been achieved by this method alone, but it must be properly designed.
Gasketing: Although this is a subject which generally receives little attention, it is essential to achieving the full potential of a cabinet enclosure. Gasketing materials are generally soft, pliable foamed vinyls, urethanes, or neoprenes, although other materials are used.
The most important characteristic they exhibit for noise control is sealability or conformability to the irregular surfaces between which they are placed. Closed-cell materials make better gaskets than open cell, but their design is more complicated because they are harder to compress due to the entrapped gas in each cell. This is overcome by extruding them with cross sections having profiles such as "H, X, and Z." Costs for gaskets are minimal compared to the noise reduction they can achieve. A good gasket material properly designed for the application will easily reduce noise by 6 dB or more, and cost about $0.25/linear ft.
ArtUSA Noise Control Products Inc. was formed by a group of highly motivated and experienced individuals with the desire to provide a vast array of noise control products and services. Products and services that today's market place is demanding. We realize that NBL is a relatively new name in the noise control market place,, along with that name comes decades of experience in the noise control industry, as well as a modern, precision fabrication methodology. Combined, our team brings more than 25 years of experience in both product development and noise control solutions.
The ArtUSA Noise Control Products Inc. family currently includes: barrier systems; absorption panels; complete enclosure systems, and; specialty products. These products will meet the highest quality standards. Better still, our manufacturing capabilities allow us to handle custom projects with the same ease as standard products.
Our goal is to be in the forefront of the market bringing innovative products and solutions, while also being flexible to create new designs and satisfy individual customer requirements. To that end, our clients will receive a very personal level of customer service.
The entire ArtUSA staff, as well as our established group of highly professional manufacturer representatives, will always be ready to assist YOU! Please contact ArtUSA Noise Control Products Inc. to help us fulfill your requirements today, and in the future.
Currently, ArtUSA Noise Control Inc. has a few openings for representation. If you are a high energy and motivated professional with an established business please email franka@noisecontrolproducts.com to check out the possibility of joining the ArtUSA Team.
Products supplied by ArtUSA Acoustics include, metal noise control enclosures, fiberglass noise control enclosures, aluminum noise control enclosures, stainless steel noise control enclosures, metal, fabric, and foam ceiling, wall, and fence absorbing and barrier panels, traditional polyurethane foams, Class 1 Melamine foams, high density fiberglass panels covered in Guilford of Maine's FR701 fabric, high NRC wall fabrics, dense mass barrier materials, diffusers of wood and metal or formed plastic, prefabricated low frequency bass traps, sculptured ceiling tiles, decoupling devices, and other specialty items. Typical brand names for these items are Sonex, FireFlex, FabTec, Soundtex, Channels, RPG, Sound Seal, SDG, TubeTrap and a variety of private labels. We offer sound solutions and the best noise control products available for: noise control, noise control materials, noise control products, industrial noise control, noise control solutions, noise control product, noise control materials, kinetics noise, kinetic noise control, active noise control, noise barriers, industrial noise, noise pollution control, industrial noise reduction, noise pollution, noise and vibration control, high noise levels, noise reduction, acoustic, acoustical, acoustical consultants, acoustical insulation, acoustical wall panels, acoustic enclosure, acoustic enclosures, acoustic material, acoustic materials, acoustical material, acoustical materials, acoustical enclosures, acoustical enclosure, acoustic products, acoustic panel, acoustic panels, acoustical panel, acoustical panels, acoustic wall panel, acoustic wall panels, acoustical wall panel, acoustical wall panels, acoustic foam, acoustic foams, acoustical foam, sound deadening, sound control, acoustical foams, acoustic sound control, acoustical sound control, sound barriers, sound barrier, sound damping, sound control products, sound absorber, sound deadener, sound absorbers, sound dampening, sound reduction, sound absorber, sound isolation, soundproofing foam, soundproof, sound proof, wall soundproofing, soundproof wall, soundproof walls, soundproofing insulation, soundproofing a room, soundproofing studio, sound proofing, sound insulation, vibration isolators, vibration isolation, vibration isolation table.
