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Sounding Board

The Science of Sound

Picture yourself standing under the stillness of a sunrise in a national park. Although the sun warms your skin and the light dances on the landscape, what really captures you is the natural quiet that hangs over the setting. A soft wind is heard drifting across the ground and through the plants. Perhaps there is a stream trickling nearby as the songs of birds greet the morning. Here, you are free from the noise of cars, planes, technology - and even other people. Here, you feel renewed, healthful, and contemplative. This is the power of sound.

The unimpaired sounds of our national parks are valued and protected resources. This website, called Sounding Board, provides information related to the science and management of sounds in parks and protected areas. As you browse through the pages, you’ll learn about emerging research from a multitude of disciplines that details the profound impacts that sounds have on ecological and human well-being.

This website provides background knowledge on the science of sound and its value in parks and protected areas. Read along to learn more about this work as well as the efforts of the PARC Listening Lab at Penn State University who are working to better understand and protect soundscapes of national parks.

Physics Of Sound

What is sound? Sound is created by pressure variations that move in waves through a medium such as air or water. It is measured in terms of frequency and amplitude.

Frequency

Measured in hertz (Hz)
The number of times per second that a
sound pressure wave repeats itself.
A drum beat has a lower frequency than a whistle
A cricket has a higher frequency than a bullfrog call

AMPLITUDE

Measured in decibels (dB)
The relative strength of sound waves,
which we perceive as loudness or volume.
Threshold of human hearing
Volcano
crater (Haleakala National Park)
Leaves
rustling (Canyonlands National Park)
Crickets
at 5m (Zion National Park)
Casual speech
at 5m (Whitman Mission National Historic Park)
Motorcycle
at 30m (Yellowstone National Park)
Thunder (Arches National Park)
Military jet
at 100m AGL (Yukon-Charley Rivers National Park)
Cannon fire
at 150m (Vicksburg National Military Park)

Click on the icons above to hear the sounds live

Sounds above 85dB are considered harmful if exposed for long periods of time. Exercise caution when listening to sound clips with the caution icon.

Decibels

A small change in decibels means a big change in loudness.

That’s because decibels work on a logarithmic scale. An increase of 10dB represents
a ten-fold increase in sound level, which causes perceived loudness to double.

Decibel Level Sound Level/Intensity Perceived Loudness
20 dB
× 100 (102)
× 2
30 dB
× 1000 (103)
× 4
40 dB
× 10000 (104)
× 8

If 1 vacuum cleaner measures 70dB than 80dB equals 10 vacuum cleaners.

70 dB
=
80 dB
=
How Sounds Travel

Propagation

How a sound wave travels outward from the
source, through a medium, like air or water.
Noise levels in park transportation corridors today are at 1000 times the natural level.
*For illustrated purposes only and not an accurate representation of scale.
Road noise impacts on wildlife have been shown to extend over a mile into the forest (Brumm 2004).
*For illustrated purposes only and not an accurate representation of scale.

Key Words

ACOUSTIC RESOURCES
Physical sound sources including natural sounds (wind, water, wildlife, vegetation) and cultural and historic sounds (battle reenactments, tribal ceremonies, etc).
SOUNDSCAPE
The human, or animal, perception of all combined acoustic resources.
ACOUSTIC ZONES
Areas with similar vegetation, terrain, animals, and weather likely have similar acoustic characteristics, including sound sources and sound characteristics. Acoustic zones may be based on existing management zones.
Zion National Park has different 7 unique Acoustic Zones
NOISE FREE INTERVAL
The period of time between noise events, during which no human-cause sounds are audible.
In a transportation
corridor, the noise free
interval can be as small as
seconds 30 during high traffic times!
Close
flying-bird
Listen carefully to see if you can hear the eagle crying.
Close
lizard
Did you hear the lizard? If you missed it, listen to the clip below and see if you can hear it again.

Listen
Close
coyote
Can you still hear the coyote howling when one of the noises are clicked?

Spectrogram

A spectrogram is a graphical representation of acoustic measurements. Acoustic spectrograms have three axes: time, frequency, and intensity.

Natural Ambient

Composed of the natural sound conditions in a park that exist in the absence of any human-made noise (e.g. mechanical, electrical, and other non-natural sounds).

Choose an environment

Forest
Desert
Lake
Flute

Noise

Noise is defined as any non-natural, human-made sound.

Choose a human-made noise

Boat
Car
Airplane
Thunder
Visitors

Masking

The process by which the ability to hear a sound is reduced by the presence of another sound. Just as smog limits the ability to see a landscape, noise masks our ability to hear sound.

Choose an environment

Forest
Desert
Lake

Then choose a noise to experience masking

Boat
Car
Airplane
Thunder
Visitors
360 3600 Experience

Functional Effects

THE BEHAVIORAL, PHYSIOLOGICAL, AND ECOLOGICAL CONSEQUENCES OF NOISE

When these effects are combined with other stressors such as winter weather, disease, and food shortages, functional effects of noise can have a big impact on the health and vitality of wildlife populations within a park.

Frogs

Female frogs exposed to traffic noise have more difficulty locating the male’s signal. (Brumm 2004)

Affected Animal Behavior:

  • Mating
  • Habitat Patterns
  • Hunting
  • Predator Avoidance

Bats

Gleaning bats avoid hunting in areas with road noise. (Brumm 2004)

Affected Animal Behavior:

  • Mating
  • Habitat Patterns
  • Hunting
  • Predator Avoidance

Squirrels

Tree squirrels in noisy areas spend less time foraging for food, and more time on the look out for predators —resulting in reduced food intake. (Francis et al., 2009)

Affected Animal Behavior:

  • Mating
  • Habitat Patterns
  • Hunting
  • Predator Avoidance

Songbirds

Songbirds show greater nest desertion and abandonment within 100 m of off-road vehicle trails. (Barton & Holmes, 2007)

Affected Animal Behavior:

  • Mating
  • Habitat Patterns
  • Hunting
  • Predator Avoidance

Pronghorn

The endangered Sonoran pronghorn avoids noisy areas created by military jets. (Brumm 2004)

Affected Animal Behavior:

  • Mating
  • Habitat Patterns
  • Hunting
  • Predator Avoidance

Facilitate Recovery

Nature sounds can help facilitate recovery from psychological stress. (Alvarsson et al., 2010)

  • Benefit
  • Negative Effect

Physical Effects

Exposure to aircraft or road traffic noise can result have physiological impacts including high blood pressure, increased heart rate, and increased stress hormones. (Babisch 2011)

  • Benefit
  • Negative Effect

Appreciation

One study found that helicopter noise interferes with the quality of the visitor experience and even affects the perceived aesthetic quality of landscapes. (Weinzimmer et al., 2014)

  • Benefit
  • Negative Effect

Experience Peace

95% of Americans say one of the most important reasons for preserving national parks is to provide opportunities to experience natural peace and the sounds of nature.(McDonald et al., 1995)

  • Benefit
  • Negative Effect

Annoyance

Park visitors reported that air tours, maintenance equipment, noisy visitors, loud talking, and other related sounds substantially detract from the quality of the visitor experience. (Pilcher et al., 2009)

  • Benefit
  • Negative Effect

Disturbance

Noise has been shown to be more disturbing to visitors if it is loud, occurs in bursts (Bell et al., 2010), is unpredictable, or if it interferes with quiet activities such as bird watching. (Miller et al., 2014)

  • Benefit
  • Negative Effect

LISTENING AREA

The listening area is the region that an organism can gain information about its environment from the soundscape.
(Francis et al. 2017)

Mate
Our subject’s listening area decreases further as the airplane gets closer. Now she is unable to hear her mate who may be calling for her.
Prey
The airplane is now directly above our subject reducing her listening area even further. The sound from the airplane masks the noise of her prey who was hiding near the bushes.
Red Fox
The red fox’s listening area spans a 100-foot radius. Currently, she can hear her prey, her mate, and a predator. Move the slider to see how her listening area is affected by background noise.
Predator
An airplane has entered our environment from the left. Our subject’s listening area has decreased and she can no longer hear the mountain lion lurking around.
100 ft
60 ft
20 ft
20 ft
60 ft
100 ft
Move the slider to start the experience
360 3600 Experience

Tips

FOR MANAGING SOUNDSCAPES

Learn from park employees and scientists about soundscape management tips that can reduce noise emissions and increase visitor engagement and enjoyment of acoustic resources.

christina

USE QUIET TECHNOLOGY

Transportation, including vehicles, aircraft, watercraft, and recreational vehicles can contribute large amounts of human-caused noise in park settings. Implementing quiet technology can help reduce noise emissions from transportation. This can include new types of motors, new tires/treads, or a variety of other technologies.

Christina White from Yellowstone National Park, tells us how she is implementing techniques like this to reduce over-snow vehicle noise:

“We lowered noise emission standards for snowmobiles in Yellowstone, and we created an additional policy incentive to encourage manufacturers to build quieter snowmobiles in the future. I also worked with snowcoach operators to implement the use of low pressure tires instead of tracks, making snowcoaches 4–5 times quieter.”
design

CONSIDER SITE DESIGN

Sometimes the structure of a site can contribute to poor soundscape quality. If this is the case, site design can go a long way in helping to reduce noise emissions in park settings. This can include noise-reducing pavements, quieter boardwalks for visitor use, and reducing the speed limit of vehicles.

For example, [personnel from Death Valley NP] describes how rethinking pavement helped to reduce vehicle noise in the park:

“Lorem ipsum dolor sit amet, consectetur adipiscing elit. Mauris fermentum egestas diam. Nulla fringilla tellus neque, at porttitor dolor gravida nec. Donec fermentum rutrum odio in cursus. In id leo pretium, egestas purus at, sodales enim. Proin ac velit finibus, accumsan odio vel, dignissim augue. Nullam ullamcorper tortor vel tristique.”
maintenance

WORK WITH MAINTENANCE CREWS

Maintenance equipment, such as a leaf blower, lawn mowers, chain saws, and other types of equipment can generate noise in park settings. Maintenance and facilities crews can consider sheduling louder activities during more appropriate times of the day or week. Similar to transportation, quiet technology can also be used to reduce noise emissions.

Douglas Law from Salem Maritime/Saugus Iron Works National Historic Sites explains how minor changes to maintenance schedules and equipment can improve soundscape conditions:

“We implement grounds work using “Future Leaders” in the youth program on weekends to give the visitors and neighbors a break from the noise. We have found a little planning allows us to get the “noisy” work completed during the weekdays. We have also replaced mowers, weed-wackers, leaf blowers, and chain saws with battery powered equipment. This has really helped with not only noise polution, but reducing our carbon footprint as well.”
zoning

USE ZONING

Parks are often not homogenous places. Instead, they provide a variety of different recreation opportunities for visitors. Zoning can help managers focus on placing limited resource in strategic areas for reducing noise emissions. Zoning is not only spatial, but also temporal.

Take for example Muir Woods National Monument. In this park, managers implemented both “quiet zones” and “quiet days” which reflect the spatial and temporal aspects of zoning. (Stack et al., 2011)

framework

FOLLOW MANAGEMENT-BY-OBJECTIVES FRAMEWORK

Frameworks, like the Visitor Experience and Resource Protection and Visitor Use Management frameworks, can help establish successfully manage soundscape resources by using a five-step process. Here is how:

  1. Establish management objectives
    These broad narrative statements describe the desired conditions of park resources and experiences.
  2. Identify indicators and thresholds
    Indicators are measurable and manageable variables that relate to your management objectives. Thresholds are the range of acceptable conditions for an indicator and allow managers to understand how observed conditions related to management objectives.
  3. Monitor the indicators
    Gathering data from the indicators helps you describe current conditions and understand what needs to be done to achieve your managment objectives.
  4. Implement management actions
    Armed with an understanding of current conditions and thresholds regarding the indicators, management can be enacted in an adaptive process to help achieve management goals.
  5. Repeat steps 4 and 5
    Periodic monitoring will allow you to understand the effect of your management actions, and whether new or additional actions need to be implemented.

Dr. Peter Newman has conducted research in parks using management-by-objectives frameworks for over XX years. According to Dr. Newman:

“Management-by-objective” frameworks institutionalize science based decision making where managers set desired conditions, create indicators and standards of quality and use science based approaches to measure change and efficacy of management actions. This process allows agencies to learn and adapt to rapidly changing and complex human-ecological systems.”
engage

ENGAGE VISITORS

Kurt Fristrup, the Science and Technology Branch Chief of the Natural Sounds and Night Skies Division of the NPS, believes that encouraging visitors to attentively engage soundscapes in parks can enrich their experiences (Selleck & KellerLynn, 2010). Some studies show that over 90% of visitors find the opportunity to experience natural quiet and the sounds of nature to be compelling reasons to visit parks (McDonals et al., 1995)

In Glacier National Park, interpretive signs help encourage visitors on the Trail of the Cedars to enjoy the natural sounds of the trail.

education

USE EDUCATION AND INTERPRETATION

Education and interpretation can be used in parks for both reducing noise emissions and mitigating impacts related to noise. This can include not only reducing things like visitor-caused sounds, but can also help visitors cope with noises that are present but hard to manage. (Taff et al., 2014)

[Lorem ipsum name] talks about how education is in Muir Woods National Monument:

Dr. Derrick Taff explains the role of education in Sequoia National Park:

“Military overflights in Sequoia National Park have a negative impact on visitor experience, but are likely to continue. We found that implementing an education program about the overflights helped increase the acceptability of military aircraft sounds to visitors by up to 15%”
SUMMARY OF TIPS
SUMMARY: TIPS AT A GLANCE
1Use quiet technology
2Work with maintenance crews
3Follow management-by-objectives frameworks for more effective soundscape management
4Use education and interpretation for reducing noise emissions and mitigating impacts
5Engage visitors to experience and learn about sounds and highlight the importance of soundscape management
6Use zoning to focus limited resources on key areas
7Consider site design

Soundboard Quiz

Start Quiz»
"The relative strength of soundwaves which we perceive as loudness or volume” is the definition of:
Next Question
If a sound goes from 20 decibels to 40 decibels, how many times greater would be the perceived change in loudness to people?
Next Question
The impacts of road noise can extend of one mile into a forest.
Next Question
A soundscape is defined as:
Next Question
A spectrogram is a visual representation of acoustic measurements. Which of the following is not an axis of a spectrogram?
Next Question
Masking is defined as:
Next Question
Which of the following animal behaviors are affected by human-caused noise?
Next Question
Research shows that human-caused noise affects ground-squirrels by:
Next Question
True or false: Bats spend more time foraging near roads because insects have a harder time detecting them.
Next Question
Airplane and traffic noise have which of the following physiological effects on people?
Next Question
True or false: Human-caused noise may impact visitors perceptions of the aesthetic quality of a landscape.
Next Question
Fill in the blank: ____ % of Americans say that one of the most important reasons for preserving the national parks is to provide opportunities to experience natural peace and the sounds of nature.
Next Question
Fill in the blank. Human-caused noise reduces a person or animals _______. This can impact animals’ ability to communicate with others of their own species, find prey, and detect predators.
Next Question
Education and interpretation can be used to:
Next Question
Which one of the following is NOT a tip for managing soundscapes
Next Question
"A science-based decision making process where managers set desired conditions, create indicators and standards of quality, and use science-based approaches to measure change and efficacy of management actions/” is the definition of:
Finish

CONGRATULATIONS!

You have completed the quiz. Review your results.

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Please select an answer

PARC LISTENING LAB

The Protected Areas Research Collaborative (PARC) Listening Lab at Penn State University was established in 2023 in collaboration with the Natural Sounds and Night Skies Division of the National Park Service (NPS). The primary goal of this lab is to inventory sounds recorded in National Parks to better understand base level natural soundscapes of ecosystems and the influence of humans in those ecosystems. To accomplish this, undergraduate researchers analyze thousands of hours of acoustic data collected each year within park units. Results provide the NPS with a better understanding of base-levels of natural soundscapes, and over time monitoring changes allowing NPS staff to better understand global changes from climate, population change, human dynamics, changing technology and shifts in wildlife dynamics.

This lab is a collaborative effort between the Department of Recreation, Park, and Tourism Management in the College of Human Health and Development and the Graduate Program in Acoustics in the College of Engineering. Data from the lab can then be used to understand sound sources that naturally exist within units and those that may be intrusive. To accomplish this, PIs of this project are be equipped with “big-data” methods that go beyond traditional methods of “listening.” This team utilizes traditional acoustic data processing techniques and also pushes the concept of the “listening lab” to the next level using Artificial Intelligence” (AI) and Machine Learning through the development of algorithms that help in sound detection and identification.

Our work is funded by the National Park Service and the National Science Foundation Graduate Research Fellowship Program, among others.

HOW WE DO IT?

Scientists at national parks across the country have set up microphones to record sounds throughout the NPS system. The systematic recording and analysis of sounds help us to understand and mitigate the impact of human activities have on park auditory environments. By deploying sensitive microphones and recording equipment in various parks, the Natural Sounds and Night Skies Division captures a wide range of sounds, from the subtle rustle of leaves to the calls of wildlife. The collected data helps inform management practices aimed at reducing noise pollution, enhancing visitor experiences, and safeguarding the natural acoustic environment for future generations. This initiative underscores the importance of natural sounds as a critical component of ecological integrity and visitor enjoyment in national parks.

The recordings are then transferred to the PARC Listening Lab here at Penn State, where our students listen to, analyze and inventory the sounds heard. Using National Park Service software, The Listening catalogs both natural and anthropogenic sounds. Software is used to analyze sound frequency, duration, and intensity, allowing us to discern patterns and assess the health of the soundscape. This analysis helps pinpoint sources of noise pollution, such as aircraft, vehicles, and human activities, and evaluate their impact on wildlife and visitor experiences. Additionally, these data are used to train machine learning algorithms to increase productivity and strengthen our understanding of park soundscapes.

The insights gained from these data are crucial for developing strategies to minimize noise pollution, such as implementing quiet zones, altering traffic patterns, or creating buffer zones. By leveraging comprehensive data sets, the National Park Service can make informed decisions to preserve the natural acoustic environment, ensuring that the serene sounds of nature remain a vital part of the national park experience. Once sounds are analyzed, the findings are sent back to officials at respective parks and used to inform management decisions about how best to protect natural quiet.

PUBLICATIONS

Abbott, L., Newman, P., & Benfield, J. (2015).

The influence of natural sounds on attention restoration (Doctoral dissertation, Pennsylvania State University).

Alvarsson, J. J., Wiens, S., & Nilsson, M. E. (2010).

Stress recovery during exposure to nature sound and environmental noise. International Journal of Environmental Research and Public Health, 7(3), 1036–1046.

https://doi.org/10.3390/ijerph7031036

Babisch, W. (2011).

Cardiovascular effects of noise. Noise and Health, 13(52), 201–204.

https://doi.org/10.4103/1463-1741.80148

Barber, J. R., Levenhagen, M. J., Francis, C. D., Newman, P., Taff, D., Abbott, L. C., … & Petrelli, A. R. (2016).

Barber, J. R., Levenhagen, M. J., Francis, C. D., Newman, P., Taff, D., Abbott, L. C., … & Petrelli, A. R. (2016). Ecosystem services provided by soundscapes link people and wildlife: Evidence from mitigation studies in a protected natural area. UW-National Park Service Research Station Annual Reports, 39, 81-89.

Barton, D. C., & Holmes, A. L. (2007).

Off-Highway Vehicle Trail Impacts on Breeding Songbirds in Northeastern California. Journal of Wildlife Management, 71(5), 1617–1620.

https://doi.org/10.2193/2006-026

Bell, P.A., Mace, B.L, & Benfield, J.A. (2010).

Aircraft overflights at national parks, Conflict and its potential resolution. Special Issue: From landscapes to soundscapes: Park Science, 26(3).

Benfield, J., Taff, B. D., Weinzimmer, D., & Newman, P. (2018).

Motorized recreation sounds influence nature scene evaluations: The role of attitude moderators. Frontiers in Psychology, 9, 495.

Brumm, H. (2004).

The impact of environmental noise on song amplitude in a territorial bird. Journal of Animal Ecology, 73(3), 434–440.

https://doi.org/10.1111/j.0021-8790.2004.00814.x

Dumyahn, S. L., & Pijanowski, B. C. (2011).

Soundscape conservation. Landscape Ecology, 26, 1327–1344.

https://doi.org/10.1007/s10980-011-9635-x

Ferguson, L. A., Newman, P., McKenna, M. F., Betchkal, D. H., Miller, Z. D., Keller, R., … & Taff, B. D. (2023).

How much noise is too much? Methods for identifying thresholds for soundscape quality and ecosystem services. Applied Acoustics, 209, 109388.

Ferraro, D. M., Miller, Z. D., Ferguson, L. A., Taff, B. D., Barber, J. R., Newman, P., & Francis, C. D. (2020).

The phantom chorus: birdsong boosts human well-being in protected areas. Proceedings of the Royal Society B, 287(1941), 20201811.

Francis, C. D., Newman, P., Taff, B. D., White, C., Monz, C. A., Levenhagen, M., … Barber, J. R. (2017).

Acoustic environments matter: Synergistic benefits to humans and ecological communities. Journal of Environmental Management, 203, 245–254.

https://doi.org/10.1016/j.jenvman.2017.07.041

Francis, C. D., Ortega, C. P., & Cruz, A. (2009).

Noise Pollution Changes Avian Communities and Species Interactions. Current Biology, 19(16), 1415–1419.

https://doi.org/10.1016/j.cub.2009.06.052

Freimund, W., Sacklin, J., Patterson, M., Bosak, K., & Saxen, S. (2011).

Soundscapes and the Winter Visitor Experience. Yellowstone Science, 19(2), 6–13.

Levenhagen, M. J., McClure, C. J., & Barber, J. R. (2021).

Does experimentally quieting traffic noise benefit people and birds?. Ecology and Society.

Levenhagen, M. J., Miller, Z. D., Petrelli, A. R., Ferguson, L. A., Shr, Y. H., Gomes, D. G., … & Barber, J. R. (2020).

Ecosystem services enhanced through soundscape management link people and wildlife. People Nat, 3(1), 176-189.

Levenhagen, M. J., Petrelli, A. R., Miller, Z. D., Ferguson, L. A., Shr, Y., Gomes, D. G., … & Barber, J. R. (2020).

Quieting soundscapes increases birds, heightens human experience and amplifies support for conservation. People and Nature, (PaN-65).

Manning, R., Newman, P., Barber, J., Monz, C., Hallo, J., & Lawson, S. (2018, January).

Principles for studying and managing natural quiet and natural darkness in national parks and other protected areas. In The George Wright Forum (Vol. 35, No. 3, pp. 350-362). George Wright Society.

McDonald, C.D., Baumgartner, R.M., Iachan, R. (1995).

Aircraft management studies. USDI Report 94-2 Denver, CO.

Miller, Z. D., Hallo, J. C., Sharp, J. L., Powell, R. B., & Lanham, J. D. (2014).

Birding by Ear: A Study of Recreational Specialization and Soundscape Preference. Human Dimensions of Wildlife, 19(6), 498–511.

https://doi.org/10.1080/10871209.2014.921845

Miller, N. P. (2008).

US National Parks and management of park soundscapes: A review. Applied Acoustics, 69(2), 77–92.

https://doi.org/10.1016/j.apacoust.2007.04.008

Miller, Z. D., Rice, W. L., Newman, P., Taff, B. D., Gottschalk, J., Meyer, C., & Beeco, J. A. (2021).

Pavement treatment type influences visitor experiences related to vehicular road sound in Death Valley National Park. Journal of Ecotourism, 20(3), 211-223.

Rice, W. L., Newman, P., Miller, Z. D., & Taff, B. D. (2020).

Protected areas and noise abatement: A spatial approach. Landscape and Urban Planning, 194, 103701.

Rice, W. L., Newman, P., Zipp, K. Y., Taff, B. D., Pipkin, A. R., Miller, Z. D., & Pan, B. (2022).

Balancing quietness and freedom: Support for reducing road noise among park visitors. Journal of Outdoor Recreation and Tourism, 37, 100474.

Pilcher, E. J., Newman, P., & Manning, R. E. (2009).

Understanding and managing experiential aspects of soundscapes at Muir Woods National Monument. Environmental Management, 43, 425–35.

https://doi.org/10.1007/s00267-008-9224-1

Selleck, J., & KellerLynn, K. (2010).

Integrating Research and Resource Management in the National Parks. Special Issue: From landscapes to soundscapes: Park Science, 26(3).

Stack, D. W., Newman, P., Manning, R. E., & Fristrup, K. M. (2011).

Reducing visitor noise levels at Muir Woods National Monument using experimental management. The Journal of the Acoustical Society of America, 129(3), 1375–1380.

https://doi.org/10.1121/1.3531803

Taff, D., Newman, P., Lawson, S. R., Bright, A., Marin, L., Gibson, A., & Archie, T. (2014).

The role of messaging on acceptability of military aircraft sounds in Sequoia National Park. Applied Acoustics, 84, 122–128.

https://doi.org/10.1016/j.apacoust.2013.09.012

Weinzimmer, D., Newman, P., Taff, D., Benfield, J., Lynch, E., & Bell, P. (2014).

Responses to Simulated Motorized Noise in National Parks. Leisure Sciences, 36(3), 251–267.

https://doi.org/10.1080/01490400.2014.888022

For a complete list of resources, download the bibliography from the link below:

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