Almost every industrial equipment business has used acoustic barriers in some way. The primary purpose of these barriers is to block airborne noise from traveling through a surface to the environment on the other side of the surface.
A prime example of a barrier is the floor mats found in the cabs of large trucks. These mats don’t eliminate all of the sounds that come from the surrounding vehicle, but they help reduce the amplitude of those sounds in the cabin of the truck or vehicle by minimizing the sound traveling up through the floor.
If there are a variety of barriers, then how do we know which ones are ideal to use for our specific equipment?
Understanding Barriers Vs. Damping
First and foremost, it is important to understand the types of barriers and how they differ from other products, such as vibration-damping products.
Polymer Technologies offers many options for your acoustic barrier needs, including custom options, should your project need something more than our standard options provide.
Barriers and damping can be helpful to minimize the noise transmitted through an enclosure wall to the outside environment or minimize the noise created by the vibration of the enclosure walls. Depending on frequency and amplitude, the vibration of the enclosure walls can create noise affecting the sound transmitted to the outside and the noise level within the enclosure.
Barrier Definition
An acoustic barrier uses a high-density mass, such as barium sulfate, held together by a vinyl or polyurethane polymer to produce a flexible material with high mass that will reduce the sound reflecting off or transmitted across hard surfaces – such as the metal body of a truck cab or the floor of a truck cab. Typically, barriers and damping materials are used with absorbers to complete an insulation package to reduce the overall noise within the cab or enclosure.
The mass of a barrier dictates its performance which varies depending on frequency. Low-frequency sound has long waves with significant energy, and higher-frequency waves are shorter and have less energy. Barriers block more energy in the higher frequency but are associated with low-frequency sound attenuation because low-frequency is difficult to absorb and control. Barriers generally have a soft, flexible decoupler that goes against the wall to eliminate the barrier being compromised by the vibrations within the wall.
Damping Definition
Damping is different from barriers and is technically more complex and difficult to understand. There are two types of damping, extensional and constrained layer. The most common is extensional damping, where a relatively thin damping layer uses a pressure-sensitive adhesive to bond the damping material directly on a vibrating surface. Dampers utilize viscoelastic technology to convert the bending energy traveling through a damped panel and converts the energy to heat. The heat generated is not significant enough to be an issue.
In some cases, a barrier can act as a “Mass Damper” by eliminating the decoupler and bonding the barrier directly to a vibrating surface. Often, it takes trial and error to determine if a mass damper can be as effective or more effective than a traditional damper. Mass dampers are usually less expensive than a traditional viscoelastic damping pad.
When to Use a Barrier vs. Damping
A better understanding of barriers and dampers will allow you to determine what product best suits your needs. Consulting with an expert is usually the best approach for analysis and an initial perspective on material choices to solve a problem.
It all comes down to what you need to accomplish, the details of the structure, and the acoustical spectrum you are dealing with. Knowing information regarding the frequency and amplitude of resonant vibration within a structure allows a more direct assessment of the utility of using damping. It is common not to have details on the vibration profile within a panel or surface. Sometimes it takes a qualitative assessment from an expert familiar with acoustic materials and solutions.
Barrier Applications
Typically, barriers are supplied with a decoupler, which is made out of either foam or fiber. The decoupler decouples the barrier from the surface. Using a decoupler with a barrier allows the barrier to work somewhat independently. More importantly, the barrier is not taking on vibration from the surface, and it helps to block noise effectively through the entire acoustical spectrum.
It’s important to note that doubling the mass of a barrier won’t double its performance. At best, it adds 5 to 6 dB per octave. Also, separating two one-pound barriers with a small air space or decoupling foam layer works better than a single two-pound barrier. By separating the barriers, they each work independently and yield a higher level of performance.
In many cases, a 1-pound/sft barrier may be used to block noise transmitted through a 2 to 4-pound/sft structure. This adds incrementally more noise blocking to the panel or compensates for the acoustical weak spots within a structure due to vibration. If the vibration is significant, a viscoelastic damping material minimizes these vibrations and allows the entire mass of the surface or structure to be used to block airborne noise. In this instance, a damper will outperform a barrier.
In all cases, low-frequency sound, which has longer waves, is more difficult to absorb, block, or damp than higher-frequency sound, which has shorter waves with less energy and, therefore, easier to block, damp and absorb. You always need to design to the lowest frequency within the spectrum that represents a problem.
Open areas dramatically affect the performance of a barrier wall. In very close proximity to the structure, away from the open area, a reasonable reduction in sound can be realized. However, In a free field or some distance from the structure, an open area of just 10% can eliminate any benefit from using a barrier to increase transmission loss.
Damper Applications
Dampers are applied directly on the panel surface using a pressure-sensitive adhesive. To gain effective damping, it is only necessary to cover about 60% of the area of the panel. Typically, the panel edges are constrained and effectively “edge damped”. This can help make damping more cost-effective. A barrier treatment can sometimes be applied directly over the damper to provide additional transmission loss or noise-blocking ability.
As you can see, utilizing a barrier with a decoupler, a barrier itself as a mass damper, or a traditional damping material is not necessarily straightforward. In most cases, limited data is available for analysis, so that options may be prioritized, and direct testing is required to identify the best option.
Finding the Best Option For You
There is a time when it is best to use a barrier and a time when it’s better to utilize vibration damping instead.
Figuring out the best option for your equipment is best handled with help from the experts at Polymer. We can provide you with our industry knowledge, test a variety of products on your equipment, and determine the best course of action and material selection to meet your project goals.