As noise has gained prominence in quality of life data, demand for engineered noise control has increased, particularly in low frequency. Initially used in the industrial manufacturing sector, engineered noise control has expanded to include modes of transportation, the military, construction sites, offices, housing and schools. A greater intensity in demand has been realized in the transportation sector, as modes of transporting goods and people have increased in speed, noise and the cost of fuel. Coincidentally, the manufacturers and suppliers of noise control materials have consolidated over the past decade into the passive vs. active methods and flexible vs. metal fabricators/manufacturers. Both of the above factors have lead to markets that have placed more demands on the traditional acoustic materials, often requiring more rapid delivery of finished parts as well as guaranteed results for the engineered systems. Market segments are often divided into military, architectural, industrial, commercial and original equipment manufacturers (OEMs).
The majority of acoustic systems in the industrial and commercial arenas have relied upon mass to reduce the low and mid frequency sound. As the noise level increases, the weight of the system grows. However, when the industry doubles the weight per square foot to reduce specific low frequency noise, the enhanced noise abatement is not significant, often exhibiting only a 2-3 dB reduction with the additional weight. Moreover, as the weight increases, the support system upon which the materials are installed also must be enhanced to accommodate both the acoustic panels and environmental factors such as wind or snow loads.
We now have a viable alternative that solves many of the issues noted above. DuPont LoWave is a new acoustic material that incorporates a patented passive technology. The actual material required for the technology to reduce low and mid frequency sounds (60 to 400Hz) is 1″ thick which allows the designer to add other materials to meet specific application requirements such as thermal, acoustic absorption, UV protection, etc. Moreover, the technology can easily be incorporated into existing passive systems, both flexible and rigid. As LoWave adds insignificant weight or thickness, fuel savings in the transportation sector is considerable. Moreover, LoWave can be inserted into existing acoustical systems without redesigning or reconfiguring parts. And LoWave is installed using typical methods for other acoustic materials. HVAC, yachts, aircraft, air compressors, generators, motors, fans grinders – the list of LoWave applications seems endless. Low frequency, LoWave.
Sound is energy and the amount of energy determines the quality of the sound as well as the ability of the sound to travel through air, walls, water or other mediums. Low frequency sound waves have tremendous energy and, therefore, can be heard miles from the noise source. If you have lived in an apartment, you know the music you hear from the adjacent apartment is the bass, the low frequency sounds. High frequency sound contains small amounts of energy and can be diminished by standard sheetrock or other types of mass barrier.
To reduce noise transmission from one area to another, three methods are commonly used: treat the noise source, treat the noise path or isolate the receiver (the person who is hearing the noise). Treatment of the noise source is typically the most effective and economical. As an illustration, picture a light bulb (noise source) in the center of the room. Your goal is to keep the room dark (quiet). If you encapsulate the bulb, the room is dark. However, once the room is lit, reducing the light by adding materials to the room is not very effective (treating the noise path). If you use sunglasses on the eyes of the receiver (the person who desires darkness or quiet), you will have to provide sunglasses (ear plugs) for anyone who enters the room. The above clearly demonstrates the economy of treating the noise source or light bulb instead of the path or receiver.
The effects of noise? We often think of our ears when discussing effects of noise. Research validates the effects of noise impact our entire bodies. From Handbook of Environmental Acoustics by James P. Cowan:
- Physiological: hearing loss, hypertension, cardiac disease, ulcers, endocrine and biomedical disorders, nausea, headache, dizziness.
- Psychological: Insomnia, annoyance, fear, stress, learning disability.
- Others: compromising safety, speech interference, sleep interference, compromising privacy, lack of concentration, compromising enjoyment of leisure activities.
Let’s reduce the noise in our world.
The wooden box story has been told for many years to illustrate the problems faced when attempting to reduce noise. The story begins with a noise source, let’s pretend it’s a generator in your backyard. Neighbors are complaining about the noise so you buy some plywood to build a box around the compressor so it will be quieter. Before the box is in place, the noise level is 90 dB(A). After you have constructed 4 sides and a top from the plywood and placed it around the generator, the noise level is 94 dB(A). “Hey”, you ask, “What happened here? How can the noise be louder when the generator is inside the box?”
There are two basic types of materials used to reduce noise: an absorber and a barrier. The absorber is soft, flexible material such as fiberglass or foam. The barrier can be flexible or rigid and incorporates mass, typically at least 1 pound per square foot. We can use these materials separately but often use them in a composite to achieve best results. The absorber reduces reverberation (echo). A common absorber is the acoustic ceiling tile in your office. It reduces the echo in your office but allows the person on the other side of the wall to hear everything you say. (You didn’t know that?) The barrier reduces noise transmission (energy traveling from one area to another). If you place the proper barrier on top of the acoustic ceiling tiles, sound transmission will be reduced. Your office mate will no longer be able to hear your conversations. The reason we use these two materials in a composite is that used separately, unintended consequences sometimes happen. It you put a barrier without an absorber around a noise source, the reverberation increases as the sound hits the reflective barrier and the noise level increases. If you use the absorber without a barrier, your office is quieter but adjacent offices can hear your voice.
There is a happy ending to the wooden box story. You have lined the box with a well chosen acoustic absorber and reduced the noise level to 70 dB(A). The ending could have been happier if you had chosen a flexible barrier/absorber composite but that’s a lesson for another day.