Sound affects people in both positive and negative ways. Besides sound being the primary communication channel for most people, our reactions to sound provide a key trigger for protecting ourselves from harm. This protective reaction is usually accompanied by an increase in stress hormones, which can cause physical damage to our bodies over time. Sound level limits in noise regulations and guidelines used for environmental impact evaluations are meant to protect people from this harm.
Quantifying the effects of project-associated noise on humans is important; however, misinformation about human noise impacts can derail your project. Dudek Lead Acoustician Jim Cowan debunks three human noise impact myths, so you can craft noise analyses that address noise effects responsibly and defensibly.
Myth 1: Low-Frequency Sound and Infrasound are Especially Damaging.
The Facts: Sound level and length of exposure, not frequency, are the most significant factors in determining the effect of sound on humans. Certain sound frequencies can be annoying, but annoyance does not pose the types of health risks that regulations and guidelines are intended to limit.
Low-frequency sound refers to sounds with frequencies between 20 Hz and 200 Hz and infrasound refers to sounds with frequencies below 20 Hz (generally considered to be the lower limit of audibility). Examples of natural low-frequency sound and infrasound sources include thunder, ocean waves, avalanches, earthquakes, and sounds made by large animals such as whales and elephants.
Many articles espouse the health hazards associated with low-frequency sound and infrasound, with no regard for the sound’s magnitude or level. The most severe illnesses linked with noise exposure have been cited in articles that either wrongly extrapolate data of very high magnitudes or provide anecdotal information without a scientific basis. To strengthen their arguments, individuals often include complex jargon and impressive author credentials when presenting their case to individuals who may have limited knowledge of acoustics and cannot offer a sufficient counterargument.
Myth 2: The dBA Scale Models Human Hearing Sensitivity for All Sound Levels
The Facts: Hearing sensitivity varies depending on the level of sound. The dBA scale is based only on human hearing frequency sensitivity trends for sound levels in the moderate sound level range of 40 to 70 dBA.
Most federal, state, and local agencies use the dBA (A-weighted decibel) scale to rate the acceptability of sound-level exposures. The dBA scale models loudness in a way that corresponds to the sensitivity of the human ear for sound levels in the moderate sound level range of 40 to 70 dBA. Our hearing frequency sensitivities are different for sound levels outside that range, so even though it’s convenient to use the dBA scale for all sound levels, such use won’t provide an accurate representation of what we hear below 40 dBA and above 70 dBA.
Most environmental studies don’t consider this point, but it should be acknowledged, especially when dealing with sound levels exceeding 70 dBA. When analyzing complex aural environments, this aspect must be considered to ensure the analysis provides an accurate perspective on associated human effects even when modeled sound levels adhere to regulatory requirements.
Myth 3: Noise Exposures of 85 dBA Can Cause Immediate Permanent Hearing Damage
The Facts: The Occupational Safety and Health Administration’s (OSHA) 85-dBA limit for occupational noise is based on time-weighted average exposures of 40 hours per week over 20 years. Isolated exposure to 85dBA environments does not meet that threshold.
Although it’s uncomfortable to be in an area where noise levels exceed the 85 dBA OSHA limit, exposure to sound levels in the 85 to 95 dBA range for short periods will not cause immediate, permanent hearing loss. The speech test is an easy way to determine whether sound levels exceed 85 dBA. If you need to shout to be heard by someone standing next to you, the levels are in the 85 to 95 dBA range.
If you can’t be heard even when shouting, the levels are over 95 dBA. It’s not wise to stay in spaces with noise levels above 95 dBA for very long because noise at those levels can at least do temporary damage to your hearing. These levels are routine in nightclubs and urban subway terminals, but permanent effects are typically felt after extended, not short-term, exposure to levels in the 95 dBA range.
Immediate, permanent hearing damage can occur when exposures exceed 115 dBA, which is the threshold of pain for sound exposures. This sound level would be physically unbearable, and you’d either reach for hearing protection, cover your ears, or leave the area. One exception to this is quick, high-level impulsive sounds, such as those you’d experience by using a firearm. At firing ranges, sound levels can exceed 160 dBA at the shooter’s ear, so, without hearing protection, you won’t have enough time to react and protect your ears. Sound levels at some live concerts can exceed 130 dBA, so attending a single concert under the right conditions could also cause a permanent effect.
Trusted Experts to Solve Your Noise Challenges
Dudek’s acoustics experts have been at the forefront of research into the effects of sound on people for more than 30 years. With this knowledge, we can distinguish credible sound-impact claims from unfounded ones. Additionally, our credentials and collection of peer-reviewed, published research provide robust support for our assessments of project-associated noise impacts.
Contact us for more information on our acoustics services or for support collecting and interpreting defensible acoustics data.