Noise mitigation is often required to comply with permits for a variety of projects. Misunderstanding the most effective noise control methods can derail your project, wasting time and money in implementing ineffective noise control methods. Dudek Lead Acoustician Jim Cowan debunks four noise control myths, so you can develop noise control measures that reduce noise effects responsibly and defensibly.
Myth 1: Noise Barriers Can Solve Any Noise Problem
The Facts: Barriers alone are only effective at reducing mid-frequency noise by 10 to 15 dBA within 100 feet of the barrier. Noise reduction potential decreases the farther the source or receptor is from the barrier.
Many noise prediction models show sound reductions in excess of 20 dBA for receptors hundreds of feet away from barriers. Though results from a model may satisfy conditions for project approval, often, once barriers are installed and project operations begin, it becomes clear that the modeled noise levels do not match project conditions. The effectiveness of outdoor noise barriers is limited by the fact that sound waves diffract over and around them. Atmospheric effects on sound travel compound this issue, making noise barriers completely ineffective beyond 500 feet. Their effectiveness is also reduced further for low frequencies (below 250 Hz).
Myth 2: Planting Trees is an Effective Noise Control Measure
The Facts: A single row of trees provides no noticeable noise reduction from any sound source. Noticeable noise reduction requires a forest at least 300 feet deep with trees so dense that people can’t see through them.
Though they’re nice to look at and may shield a noise source from vision (see Myth 4), planting anything less than a dense forest provides no noise reduction whatsoever. If the objectionable sound source is composed of mostly low frequency (below 200 Hz) energy, even the dense forest will do little to reduce the sound.
Additionally, when trees are planted on a berm or close to a solid barrier with branches visible above the top of the berm or barrier, the branches reflect and scatter sound waves, actually enhancing sound travel, and effectively reducing the already limited noise reduction effect of the berm or barrier.
Myth 3: “Acoustic” Panels Can Solve Any Noise Problem
The Facts: The purpose of acoustic panels is to reduce unwanted reflections that cause reverberation or echoes. As such, using acoustic panels alone will only solve a noise problem that is exclusively related to reverberation or echoes.
We have become accustomed to seeing “acoustic” panels mounted on ceilings or walls, or as a set of porous tiles fully covering a ceiling area. When “acoustic” is used to describe a physical object, it is implied the object has an absorptive quality or absorbs a significant amount of sound energy.
In fact, acoustically absorptive materials only control sound reflected off surfaces at a distance from a sound source or listener. They do not affect the sound traveling directly from the source to the listener, especially if the source and listener are close to each other. In order to effectively block sound traveling from one location to another, heavy and multilayered materials that fully enclose the listener are required.
Myth 4: Visual Privacy Implies Acoustic Privacy
The Facts: Ensuring acoustic privacy requires materials such as sealed, heavy or multilayered walls and penetrating wall components, rather than just a physical visual barrier.
Out of sight does not mean out of mind (or ear). It’s likely you can recall a time when, despite being separated by a solid wall, you were able to hear the conversation happening in the room next to you loud and clear. While a visual barrier between a sound source and a listener may reduce noise somewhat, that does not guarantee the unintelligibility or inaudibility of the source by the listener. Sound can leak between rooms in many ways that compromise acoustic privacy. All of these sound leak paths must be eliminated using the appropriate materials and designs to achieve true acoustic privacy.
Making Informed Noise Control Decisions
Understanding the facts of these common myths about noise control methods is crucial to avoid project setbacks, wasted resources, and ineffective noise reduction.
- Noise barriers, although they have some efficacy within a limited distance and frequency range, can only solve some noise problems.
- Planting trees, unless in a dense forest configuration, provides no noticeable noise reduction.
- Acoustic panels are designed to tackle reverberation and echoes, not block sound transmission.
- Visual privacy does not guarantee acoustic privacy, as additional materials are required to achieve sound reduction.
By understanding these realities, you can make informed decisions and develop noise control measures that address the specific challenges at hand, ensuring responsible and defensible noise reduction strategies for your project.
Our INCE Board-Certified acousticians have extensive experience running noise models, interpreting the results, and implementing proven noise control methods. For more information on our acoustics services or for support planning and implementing sound control methods on your project, contact us.