The following are common laws and rules of thumb for noise mitigation that we use (and so can you) to understand and measure sound and noise levels.
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Many customer come to us wanting to reduce the noise in a space and often confuse decibels for loudness. The reality is that for every 10db reduction you halve the noise. So when someone with a noise source of 80dB says they want to halve the noise to 40db, the correct statement would be reducing the 80db source to 70db to halve the noise.
It makes sense that a denser barrier would prevent more sound transmission. In fact, it&#;s a law that for every doubling of the mass that there is a 5dB increase in the STC. As discussed previously, a 10db reduction equates to 50% less noise, so 5db is halfway and clearly noticeable.
When looking to reduce the transmission of noise with a barrier it is a rule of thumb that the barrier should be as close to the noise source as possible and be double the height and length of the noise source. This is particular relevant in exterior applications such as construction and outdoor sport facilities. If you can see a loud noise source, chances are you can hear it. If your barrier is the same height and width of a noise source, that noise will work its way around and you&#;ll still be able to hear it.
When a customer approaches us with noise issues coming from another space, one of the first things we look for are gaps and airways leading into the area of concern. Gaps can be present in doorways, ceilings, ductwork, etc. By sealing these gaps we can cut down on sound transmitting into a space.
According to the Inverse Square Law of Sound, it states that in an open field test (an area with no reflective surfaces or reverberation) that for every doubling of distance away from a noise source equates to &#; 6dB reduction. This is a way of understanding something we are already aware of on a basic level: that sound gets quieter as we travel away from the source.
Whenever you have two or more noise sources in an area, you might assume that 45dB + 45dB = 90dB. In fact, decibels is logarithmic rather than additive. In the previous example the sound would be 250% louder!
The rule of thumb is that you only add two noise sources at a time and then continue down the line. The addition of noise sources is as follows:
Those are some of the basic rules of thumb for noise mitigation. If you have any questions or need help solving your noise problem, contact us!
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There are two ways that sound walls are considered by KYTC:
&#;&#;&#;&#;1. Federally funded roadway project that adds through lanes (capacity) to the roadway.
Per the KYTC Noise Analysis and Abatement Policy, measurements are taken to identify a feasible and reasonable noise abatement measure for impacted receptors that approach or exceed the Noise Abatement Criteria specified in 23 CFR Part 772. &#;
A noise barrier must meet both the feasibility and reasonableness criteria specified by KYTC to be proposed. This type of project requires an in-depth environmental review process.
A noise barrier is considered feasible if it would provide a substantial noise reduction (5 dBA or more) for three or more impacted receptors and would not pose safety or maintenance problems. The determination of reasonableness is based upon the noise reduction design goal (7 dBA or more for at least 50% of front row benefited receptors), cost-effectiveness (a cost per benefited receptor of $35,000 or less), and the desires of the benefitted receptors (via a public involvement process to be conducted during final design).
NOTE: If no federally funded highway project is being planned or designed in your area, then KYTC cannot conduct a noise analysis. &#;
2. State-funded stand-alone projects that are identified by the General Assembly/Legislature.
These sound walls are commonly referred to as a retro-fit project. It is for stand-alone noise walls where major reconstruction is not planned in the near future. KYTC project funding is appropriated through the legislatively enacted Highway Plan in a two-year budget cycle. The Highway Plan is how the Kentucky General Assembly authorizes major highway improvement projects. Sound wall/barrier pr&#;ojects can be identified and funded by the General Assembly as part of the biennial highway plan and do not require any reasonable or feasible analysis. Historically, more projects are listed in the Highway Plan than funds available. We suggest you contact your state representative and senator about this issue.&#;
NOTE: If no federally funded highway project is being planned or designed in your area, then KYTC cannot conduct a noise analysis.
For more Noise Barrier Manufacturerinformation, please contact us. We will provide professional answers.