The Science of Sound as it Pertains to the Design of Optimal Experiences
Abstract
This paper discusses the significance and application of the science of sound to experience design & experimental innovation. Various types of collective sounds and fields of sound study that are related to the experience of life on Earth will be explored. This paper will also investigate the relationship between sound and public health, the management of sound, and the role of physics in the process of designing a more optimal and sustainable future for life on Earth.
Introduction
Experience design & experimental innovation refers to the design of optimal experiences and innovation through experimental exploration. Sound is essential to experience design and experimental innovation because it assumes an inevitable role in the processes of this universe, for if there is movement and life then there will be vibrations, waves, and frequencies that result. As a sensual, perceptual, and physical inevitability of existence, sound is necessary to study for the sake of designing and engineering optimal experiences for organic life. The significance of the relationship between sound and experience design will be further revealed in this paper.
The Study of Sound and its Significance
Auditory cues tell us about the world. Sounds transmit information that is essential to safety, awareness, and navigation. They can indicate or suggest the size, speed, force, mass, density, shape, and material properties of the objects and our environment. They can also warn us about dangerous situations and hazardous weather. They tell us about the movement and location of objects. They can be used to inform us about the mechanical quality of industrial objects. Auditory cues can also help indicate the strength, weakness, or hollowness of natural objects such as trees and rocks. These cues are also used for human and industrial alarm systems. Some auditory cues help indicate the emotional state of a fellow human or animal. There are many different ways in which sound can be described and classified.
Soundscape refers to the audible result of sound(s) that is produced within an environment. One example of a soundscape is the collective sounds a listener may hear amidst a tropical forest that is bustling with the sounds of animals, insects, and waterfalls. Another example of a soundscape is the collective sounds of being on a busy metropolitan street, amidst pedestrian and automotive traffic. Soundscape is a term that is used to describe the set of combined sounds witnessed in an environment. It is important to consider soundscape in the design process because of the immediacy with which it affects the experiencer's perception and well-being, and also because of how strongly it characterises experiences. Soundscape encompasses anthrophony, biophony, geophony, and technophony when any are present (see below). According to the pioneer of soundscape, soundscape consists of the three elements: keynote sounds (background sounds), soundmark (sound that is landscape-specific), and sound signals (foreground sounds). John Cage contributed to bringing soundscape to the foreground of widespread attention with his 1952 composition titled 4'33".
Anthophony, biophony, geophony, and technophony are the main domains of soundscape. Anthrophony refers to the anthropogenic noise and sounds that are created by human activity. The study of anthrophony is used in soundscape ecology and in the study of anthropogenic/human impact upon natural environments and resources. Biophony refers to the sounds that are manifested by the Earth's living organisms. These include amphibians, insects, animals, birds, and even human vocalisations. Biophony is characterised by more spectral and temporal variation than found in geophony. Biophony is affected by speech interference caused by noise pollution. Biophony overlaps slightly with bioacoustics, which refers to the scientific study of sound reception, production, and dispersion in animals and humans. Also related is the Lombard effect, or Lombard vocal response, which refers to the increased loudness that results from a speaker's involuntary inclination to speak more loudly or with more effort when in loud or noisy environments such that their voice is more audible or intelligible. This results in an increased signal-to-noise ratio of the speaker's voice. Animals have been found to demonstrate the Lombard effect when transmitting vocal sounds through an environment characterised by anthropogenic noise pollution. Geophony refers to the collective sounds created by inorganic geophysical activity and includes earthquakes, water flow, rainfall, thunder, hail, and volcanoes. Technophony is a branch of biophony (and arguably anthrophony) that refers to the sounds created by humans' use of extrasomatic material and energy to manifest their lives through technological innovations. Since the advent of technology, machinery and devices have been increasing in manufacture and use along with the noise they bring. Technophony can be used to describe the environmental noise that has resulted from industrial human life.
Soundscape ecology is a new scientific field being pioneered that focuses on discovering information about an area by studying landscape-specific soundscapes. It yields potential significance for early indicators of changes in the natural environment. Such signals can include changes in weather patterns, climate, or landscape formation. Soundscape ecology has allowed us to discover that bird choruses can indicate changes in the ecosystem. The information we uncover about a landscape's ecological characteristics informs us by measuring the changes, patterns, and health of an ecosystem. An example would be the discovery of birds having lower reproductive success (fewer offspring) in areas characterised by noisy machinery than the amount of offspring compared in a similar though quiet habitat. The findings from soundscape ecology have allowed us to compare how natural and informative soundscapes produced by wildlife or geophysical processes have been replaced by urban noise resulting from consequential (versus intentional) sounds. The findings also allow us to examine more concretely the negative effects of industrial human life on the natural processes of wildlife.
Noise commonly refers to unwanted sound. In physics and engineering, however, it refers to the addition of insignificant sounds (such as random environmental byproducts) to a sound (referred to as "signal") that is established as the desired auditory data. Noise in high levels can interfere with meaningful signal communication by preventing or distorting signal transmission. Noise is different than soundscape in that soundscape does not carry the negative connotation of being unwanted or undesirable as it refers to simply the collective sounds that are evident. A soundscape, however, can consist of noise. One type of noise is industrial noise, which is also known as occupational noise. Occupational noise refers to typically technophonic noise experienced in a workplace situation. Another type of noise is background noise, which is also sometimes called ambient noise. It refers to any and all sounds that occur in addition to (but are not) the sound being primarily observed, which tend to consist of environmental noises. This term is used for A/V engineering and creating noise regulations. Background noise can originate internally or externally; an example of an internal source of background noise would be an air-conditioning system. Other examples of background noise can include mechanical waves, human conversations, animal conversations, mechanical devices, and traffic. Environmental noise usually refers to background noise or the soundscape of a particular area. The excess of noise is commonly referred to as noise pollution. Noise pollution describes the excess of undesirable audible stimuli from an environment that negatively impacts human or animal life. It is usually characterised by anthropogenic environmental noise such as technophony and biophony.
Environmental acoustics is a term used in acoustical engineering to refer to the control and evaluation of vibrations and sounds in a staged outdoor environment typically involving technophony or industrial noise with the goal of determining acceptable noise levels. Environmental noise control refers to the implementation of noise barriers and buffer zones to control outdoor noise. Cities are designed such that walls are built around highways and residential zones are further away from industrially loud zones such as airports. This is a form of environmental noise control using buffer zones.
When sound travels inside an architectural space, the space itself and the objects within it affect the ways in which the sound propagates. Architectural acoustics is a term used in acoustical engineering to refer to the science of controlling sound and vibrations within buildings and the application of indoor sound propagation. This field began with buildings designed specifically for musical performances and later extended to include all interior environments and room acoustics. Architectural acoustics considers important aspects of indoor experiences. Hypothetical examples of the implementation of architectural acoustics include the suppression of noise or noise-cancelling technology for privacy in a shared structure or speech intelligibility in rooms. HVAC and plumbing systems are a significant source of vibration and noise in buildings. The American National Standards Institute (ANSI) decided the maximum acceptable noise level of classroom HVAC systems. Certain architectural designs can imply negative health effects (see noise health effects below). Architectural acoustics takes into consideration that indoor sound propagation can be affected by sound absorption, reverberation time/noise, diffraction, refraction, and overall sound pressure.
Sound and Health
Various disciplines have been created to investigate, explore, and study how sounds affects the health of humans and living organisms. These disciplines allow us to examine the social costs for a society when it comes to sound playing a destructive role. Soundscape ecology suggests that if human life and wellness depends upon the wellness of all other ecosystems on this planet, then it is important to assess how all organic life is affected by sound. As previously reviewed, the field contributes to our understanding of the health of animals and natural ecosystems to which human-induced anthrophony and technophony pose as a problem. The field of psychoacoustics also allows us to understand how sound affects human health, however it is more anthropocentric. Psychoacoustics is the study of the perception of sound and its associated physiological and psychological responses in humans.
There are a plethora of public health effects or noise health effects that are important to consider when evaluating industrial and post-industrial human experiences. Noise health effects refer to any negative health consequences of sound levels considered to be hazardous or unsafe. Research from the past three decades collectively reflects these health effects. These effects vary and can involve birth defects, immune system changes, cardiovascular disease, hypertension, and vasoconstriction. The various consequences that result from elevated sound levels that can present psychological and physiological issues in communities and individuals will be explored.
Hearing Impairment is a major issue that is often caused by sustained exposure to industrial/occupational or recreational noise. Hearing impairment can take the form of temporary or permanent hearing loss or impairment. This can occur from acute exposure to a loud sound or chronic exposure to loud sound levels. These distinctions are referred to as a noise-induced temporary threshold shift (NITTS/TTS) or a noise-induced permanent threshold shift (NIPTS). Tinnitus is a ringing sensation that develops after acute exposure to excessive sound levels. It is perceived as a sound inside the ear when no corresponding sound exists externally. Especially at frequencies of about 4,000 Hz, the ear often becomes desensitised. The threshold returns to normal if the sound overload is removed, while continued exposure or frequent exposure can result in a permanent shift. The human ear is most resilient when it comes to acute sound overload. Long-term exposure to unhealthy sound levels can play a destructive role to the inner ear's sensitive structures. The impairment to hearing is often associated with the damaging of cilia or stereocilia, which are fine hair cells that lie on the basilar membrane of the inner ear. These cilia are what convert oscillatory data into neural data. Once they are damaged or expire, they cannot naturally regrow or restore. NIHL or "noise-induced hearing loss” is a commonly occurring occupational illness. Presbycusis, also known as "age-related hearing loss", is the progression of impairment to human hearing that is known to take place as humans age. Experiences that may produce hazardous noise levels are commonly occupational or recreational. These can involve everyday industrial sounds exposed to humans in a workplace environment, or less frequent recreational sounds exposed to humans at musical performance or sport events. Tools such as sound level meters (discussed later) aid in the prevention of sound-induced deafness.
The National Institute for Occupational Safety and Health (NIOSH) have established guidelines for the maximum duration of time that a human can be exposed daily sound pressure levels (from varying time-weighted averages) over forty years. Exceeding the threshold of sound pressure level or exposure can be hazardous.
Maximum Decibel Levels Maximum Exposure
85 dB 8 hours
88 dB 4 hours
91 dB 2 hours
94 dB 1 hour
97 dB 30 minutes
100 dB 15 minutes
103 dB 7-1/2 minutes
106 dB 3-3/4 minutes
There are many psychological concerns that impact society as a consequence of sound. Studies are indicating that sound can lead to issues such as aggression, fear, stress, anti-social behaviour, sleep disturbance, annoyance, and communication interference. Sound can be a hazardous environmental stressor for living things, particularly in the form regarded as noise. Recent animal experiments have demonstrated negative effects of noise stress. Studies have shown an increase in human stress hormones such as cortisol when exposed to noise from aircraft or traffic while asleep (Spreng, 2000). Such daily industrial sounds can cause chronic stress for dwellers of dense urban environments. Stress is particularly negative because of how it weakens the immune system, atrophies neurons, and shortens telomeres (Blackburn et al., 2004). This presents a large social cost for a society's performance and wellness. The noise/stress hypothesis suggests that noise activates the body's stress hormones. Experiments for acute and chronic noise have frequently discovered changes in the stress hormones cortisol, epinephrine, and norepinephrine, which may lead to cardiovascular disorders and other negative health outcomes (Babisch, 2002). A study published later indicated that chronic exposure to environmental noise led to an increased risk of ischaemic heart diseases. (Kruppa, 2004). Similar research also indicated that humans are subject to increased cardiovascular risk if their daytime intake of sound emission exceeds 65 dB(A) (Ising & Kruppa, 2004).
Learning in academic environments can be inhibited due to noise or poor acoustic design. It is important that the execution of sound experiences be rigourously designed for context, for the quality and performance of a society depend upon it. Learning hindered by the reverberation noise experienced in a classroom presents an educational issue that can be avoided by utilising architectural acoustics to calculate the reverberation noise of the inside of the classroom (and even simulate it prior to build).
There are also studies on the effect of noise on task performance. While it might not reduce quantity of work, it can reduce quality and accuracy (Miller, 1974). Steady noise levels are less detrimental to performance than intermittent noises. Sudden noises considered to be startling stimulate muscular reflexes that allow for the body to be ready to defend itself against the source of noise. Also observed in response to noise are vasoconstriction, reduced skin resistance, breathing rate changes, heart rate changes, pupil dilation, and saliva secretion (Davis, Buchwald, and Frankmann, 1955). Pathological effects in animals have also been observed in studies involving intense noise. Such abnormalities included brain damage, abnormal fetal development, sexual dysfunction, and hypertrophied adrenal glands (Miller, 1974).
Sleep interference is caused by noise from unusual or unfamiliar sounds, however research in this subject remains scant. There are also other factors to consider, such as the sleeper's physical and emotional state, the stage of sleep when interference takes place, the age and sex of the sleeper, and the nature of the noise stimulus (Rossing, 2002). A sleeper is least likely to be awakened in the REM stage of sleep, and is most likely to be awakened during stages three and four. Noise stimuli of 50 dB(A) tend to cause an awakening or change in sleep stage, while stimuli of 70 dB tends to cause an awakened response. Sleepers tend to have trouble falling asleep at 40-50 dB(A) noise levels. Noise levels above 35 dB(A) should not be present in order for most sleepers to be protected from sleep disturbance (Rossing, 2002).
Animals and wildlife have also been impacted by noise, as soundscape ecologists are currently exploring. Both marine and terrestrial ecosystems have witnessed the effects of noise. One way that noise can impact animal life is by reducing the amount of usable habitat and replacing it with areas that become polluted with noise. This type of activity has seen the reduction of bird offspring (discussed earlier) and can even lead species to extinction. Further research on this topic is currently being investigated. This is especially important to consider for the design of a more sustainable future.
While sound can play an alarmingly harmful role in human life, there are also studies that have investigated the positive health benefits to a society when it comes to employing sound in a restorative manner. Sound in the form of music can have a positive impact upon emotional affect and can also have the effect of reducing human stress levels.
The implementation of sound for human learning can yield positive effects for the purpose of human advancement. Studies have shown that listening to music (especially if it is enjoyed by the listener) results in positively impacting childrens' cognitive abilities (Schellenberg & Hallam, 2006). Another study has indicated that exposure to music in childhood is positively associated with academic ability and that such intellectual functioning can be later reflected in adulthood (Schellenberg, 2006).
Music therapy is a medical practice established in the 1950s to improve cognitive functioning, psychological functioning, behaviour, motor skills, and overall health of individuals. These experiences may involve listening to live/recorded music, singing, moving to music, discussing music, and playing musical instruments. It has been implemented in venues such as hospitals, schools, and even correctional facilities. There are many therapeutic effects of music, such as the regulation of blood pressure when it is too high or too low, such that it adjusts to an ideal level for recovering or healing. Positive effects upon health-related outcomes of ill and rehabilitating individuals have been studied. In a study that examined the effect of music upon visitors in a hospital intensive care unit for which the presence/absence of music was controlled, results demonstrated a reduction in stress levels in individuals (Routhieaux & Tansik, 1997). Studies have also shown that music promotes heart health. Positive cardiovascular health effects can result from listening to music that arouses evokes positive affect in the listener (Seiler & Levitt, 2005). Such positive cardiovascular effects include the dilation of tissue in response to music such that blood flow is increased (which is similar to findings from a study on laughter conducted in 2005). Scientific findings such as these suggest that music should be used in medical intervention.
The Management of Sound
While the regulation of acoustic noise has posed as a problem in industrial and post-industrial societies, the execution of solutions have remained controversial and subpar. Noise regulation refers to the laws and guidelines established by different levels of government to regulate the transmission of sound. In the 1960s, national noise-regulation laws were enacted in the UK and Japan, however there were issues with the design and execution of those laws. They were not comprehensive enough to address ambient noise levels that would witness a gradual rise over time. They also were not easy to enforce given the lack of clear enforcement procedures for government personnel and difficulty when making distinctions between single versus collective sound sources. The U.S. Noise Pollution and Abatement Act of 1972 was an attempt at nationwide noise-regulation. This federal program was launched to minimise noise pollution in order to preserve public health on a national scale. The program established noise emission regulations and standards for HVAC systems, motor vehicles, aircraft, and other industrial equipment. In 1981, the act ceased to receive federal funding under President Ronald Reagan, after which the problem was then left to state and local governments. The Environmental Protection Agency (EPA) is currently responsible for assisting state and local governments with the regulation of noise, and is working to revive national noise regulations that have been abandoned. The Federal Transit Administration has published procedures for conducting noise and vibration impact assessments to apply to buses and trains. While there exist regulations at all for the management of sound in society, these regulations are unfortunately not enough to address the problem of the public health costs of noise.
Measuring sound pressure allows for the design of healthier acoustic experiences. There are different ways to measure sound pressure, vibration, and noise levels, along with many different instruments with which to measure these. A sound level meter is an instrument that measures sound pressure levels. The most popular instrument for measuring sound level is by using a sound level meter that uses A-weighting. Fletcher and Munson's contributions in the 1930s allowed for the development of A-weighting, which involves each frequency being assigned its own weight such that it corresponds to the sensitivity of human ears. The application of A-weighting is evidenced by sound pressure levels expressed as dB(A). Ambient noise level is a measure of the location-specific sound pressure level of background noise. Ambient noise level is often measured in decibels using a sound level meter, such as an A-weighting scale that has a reference pressure level of .00002 Pa.
Noise floor in signal theory refers to the measure of the signal that results from a combination of noise and undesirable signals in a system. Noise here refers to all signals outside of the desired signal, such as cosmic noise, thermal noise, atmospheric noise, industrial signals, or incidental noise. Noise floor can be measured by a seismograph or spectrum analyser. Noise floor can tell us about the soundscape that is unique to a particular environment. Noise floor is significant in that it is employed as the reference point with which to measure a signal-to-noise ratio.
When designing roadways and planning for urban environments, noise analysis is conducted to gather noise data to analyse. Architects also have the ability to simulate noise analyses for buildings they design prior to construction. This is used mostly for products, buildings, or services to comply with environmental regulations.
Modal Analysis is used by noise and vibrations engineers to reduce the level of noise produced by products by identifying sources of vibrations and analysing the data acquired. It studies the structural and dynamic character of a mechanical structure while being subject to vibrational excitation. We can use modal analysis to understand how structure vibrates and any issues it may have with vibrations. This involves being sensitive to a structure's resonant frequency, as well as the application of sound damping. Modal analysis also lends knowledge about the speed at which vibrational energy dissipates from a structure and returns to rest once an excitation force is withdrawn. An example of where modal analysis was either needed or failed is the Tacoma Bridge. Modal Analysis involves the use of input forces that vary sinusoidally, an accelerometer, and means to measure amplitude. These tests help reduce the negative effects caused by the vibrations of structures that near the structure's resonant frequency, which reduces the likelihood of internal or overall structural failures. Modal Analysis is significant because it is what allows us to design progressively quieter industrial and technological products for everyday use. We use it to test cars, machinery, buildings, and products. It allows designers and engineers to build with vibration reduction in mind. It can also be used experimentally to increase the melodic qualities of consequential sound experiences (e.g. HVAC systems).
Sound absorption is a method used to control noise levels in an acoustic environment, which are most often rooms. Sound absorption by porous materials (e.g. carpet, drapery, upholstery, acoustical tile, glass fibre) takes place when the vibrating air particles resulting from acoustic energy interact with the material's fibres and become converted to heat energy. Engineering sound absorption depends mainly on a) the volume of the space and b) the properties and surface area of all surfaces within the space (walls, ceiling, objects). To calculate reverberation time, it is important to know the ratio of volume to surface in the room. A small room with a small ratio would result in rapid sound decay (Rossing, 2002). Moving the place of objects, adjusting the material properties of objects, and adding/removing objects would result in the manipulation of this ratio and the experience of sound in a room.
Soundproofing refers to the reduction of sound pressure levels for any reason and may involve the use of sound generators that counteract noise, noise barriers, damping, or distancing efforts. Acoustic damping refers to reducing mechanical or acoustic resonance within a structure through reflection or diffusion. An example of acoustic damping would be soundproofing through the application of acoustic devices, such as sound absorption tiles that allow for the reduction of oscillations. Damping is a component of acoustic quieting, which involves the damping of vibrations in a process to make machines quieter such that they are less likely to be observed. Acoustic quieting was primarily developed to make submarines less likely to be detected. Like many other advancements that emerged from military goals, this technology became adapted for the use of consumer industries (e.g. automobiles and computers).
Damping and acoustic quieting are forms of active noise control, in that they aim to prevent or reduce background noise or unwanted sound(s). It can also be referred to as noise cancellation or active noise reduction. Noise-cancelling headphones are an example of a consumer product that uses active noise control. Other examples of active noise control include anti-noise generators or sound damping devices.
Scientific Applications to Improve Organic Coexistence with Sound
The application of the physics of sound can aid the design of optimal experiences with rigour and precision. We can use physics to calculate the propagation of sound, understand and manipulate sources of vibratory excitation, and analyse existing situations that need improvement.
Signal-to-noise ratio (SNR) tells us about desired or meaningful sound information measured in contrast to unwelcome and extraneous sound information. It refers to the ratio of power between the amplitude of background noise to the amplitude of a signal. "Signal" refers to meaningful or desirable information, whereas "(background) noise" refers to meaningless or undesirable information. These subjective terms are commonly used by scientists and engineers to measure and compare (and usually average) signal power to noise power.
P(x+∆x)=P(x) e^(-α(ω)∆x),α(ω)=α_0 ω^η
P = average power
SNR=P_signal/P_Noise =〖(A_signal/A_Noise )〗^2
Where A is root mean square amplitude.
SNRs are commonly expressed using decibels because of the high dynamic range of many signals. Dynamic range refers to the ratio of measurement between the strongest and least distorted signal through a medium and the least perceptible signal (which is often the noise level). To calculate SNR is decibels:
SNR=10*〖log〗_10 P_Signal/P_Noise =P_(Signal,dB)-P_(Noise,dB)
SNR=10*〖log〗_10 (〖A_Signal/A_Noise )〗^2=20* 〖log〗_10 (A_Signal/A_Noise )
Measuring SNR requires a reference signal. An example would be a 1 kHz sine wave at a standardised nominal such as +4 dBu. Any ratio above 1:1 reveals that the signal level is more powerful than that of the noise. The relationship between SNR and soundscape is such that SNR can be applied in the acoustical design process of urban soundscapes where many human experiences are shared and observed.
Acoustic Attenuation measures the loss of energy loss when sound propagates through different media. The following power law describes acoustic waves:
P(x+∆x)=P(x) e^(-α(ω)∆x),α(ω)=α_0 ω^η
Where α(ω) is the attenuation coefficient, ∆x is the wave propagation distance , ω is the angular frequency, α_0 and η are real material parameters acquired by experimental data, and P is pressure.
Acoustic quieting can be further understood by the following equation, which expresses how sound intensity level changes as the distance between the source of a signal and the receiver of that signal changes:
∆dB=20*〖log〗_10 (d_2/d_1 )
Conclusion
There are many opportunities for designers, engineers, urban planners, politicians, and architects to reform the future of human experiences by regulating, designing, engineering, and constructing safer and healthier sound environments for humans. There are also many opportunities for experiments to take place that will allow for innovation in the implementation and design of better sound experiences. The dynamic relationship between human life and wildlife ecosystems can also be improved such that wildlife and biodiversity are preserved. Now that we know that noise increases stress, and that music reduces stress, a challenging task for designers might be to explore how urban soundscapes can be designed to result in the reduction of stress levels versus an increase in stress levels. Another topic for exploration is understanding how healthier experiences can be designed that don't induce hearing loss, or how more silent experiences can be created such that people can take asylum from noise stress. Psychoacoustics reveal that sound, which greatly impacts the mental health of communities and society as a whole, should be carefully considered when designing for more optimal human experiences. It is fundamentally important to understand the social costs for a society, such as poorer health and performance. The positive effects of music on cognitive abilities and emotional affect reviewed in this paper suggest that sound can be strategically implemented to advance the human race while complementing the human experience.
While there are still many unknowns about noise and sound, and the complex relationship between the functioning of organic life is still not yet well understood, however, as of the past ten to fifteen years we have begun witnessing a steady progression in the challenge of this insufficient body of knowledge by many researchers. As our knowledge about the complex relationship between life and sound continues to improve, we can begin experimental applications based upon data gathered so far in order to begin investigating a healthier relationship between industrial life, human life, and wildlife.
References
Routhieaux, R., & Tansik, D. (1997). The benefits of music in hospital waiting rooms. The Health Care Supervisor, 16(2), 31-40. PMID:10174442
Schifferstein, H. N. J., & Hekkert, P. (2008). Product experience. Oxford: Elsevier.
Davis, R. C., Buchwald, A. M., & Frankmann, R. W. (1955). Automatic and muscular responses and their relation to simple stimuli. Psychol. Monogr., 69(20), 1.
Miller, J. D. (1974). Effects of noise on people. Acoustic Society of America, 56, 729.
Rossing, T. D., Wheeler, P. A., & Moore, F. R. (2002). The science of sound. (Third Edition ed.). San Francisco Boston New York Cape Town Hong Kong: Addison-Wesley.
Schellenberg, E. G., & Hallam, S. (2005). Music listening and cognitive abilities in 10- and 11-year-olds: the blur effect. Ann N Y Acad Sci., 1060, 202-9. PMID: 16597767
Schellenberg, E. G. (2006). Long-term positive associations between music lessons and IQ. Journal of Educational Psychology, 98(2), 457-468.
Rauscher, F. H., Shaw, G. L., & Ky, C. N. (1993). Music and spatial task performance. Nature, 365(6447), 611. doi: 10.1038/365611a0
Ising, H., & Kruppa, B. (2004). Health effects caused by noise: Evidence in the literature from the past 25 years. Noise & Health, 6(22), 5-13.
Noise Control Act of 1972. 42 U.S.C. § 4901-4918 (1972)
Spreng, M. (2000). Possible health effects of noise induced cortisol increase. Noise & Health, 2(7), 59-63.
WHO/europe | Health effects of noise. (2012). Retrieved from http://www.euro.who.int/en/what-we-do/health-topics/environment-and-health/noise/facts-and-figures/health-effects-of-noise
Age-related hearing loss - pubmed health. (2010, December 13). Retrieved from http://www.ncbi.nlm.nih.gov/pubmedhealth/PMH0002040/
Rabinowitz, P. M. (2000). Noise-induced hearing loss. Am Fam
Physician., 61(9), 2749-2756.
Irvine, K., Devine-Wright, P., Payne, S., Fuller, R., Painter, B., & Gaston, K. (2009). Green space, soundscape and urban sustainability: an interdisciplinary, empirical study. Local Environment, 14(2), 155-172.
Modal Analysis. (2012). Retrieved from http://en.wikipedia.org/wiki/Modal_analysis
Moussavi-Najarkola, S., Khavanin, A., Mirzaei, R., Salehnia, M., Muhammadnejad, A., & Akbari, M. (2012). Temporary and permanent level shifts in distortion product otoacoustic emissions following noise exposure in an animal model. The International Journal of Occupational and Environmental Medicine, 3(3), 145-52.
Pijanowski, B.C., L. Villanueva-Rivera, S. Dumyahn, A. Farina, B. Krause, B. Napoletano, S. Gage and N. Pieretti. 2011. Soundscape ecology: the science of sound in landscapes. BioScience 61(3): 203-216.
Pijanowski, B.C., A. Farina, S Dumyahn, B. Krause, and S. Gage. 2011. What is soundscape ecology? Landscape Ecology.
Richards, T., Johnson, J., Sparks, A., & Emerson, H. (2007). The effect of music therapy on patients’ perception and manifestation of pain, anxiety, and patient satisfaction. MEDSURG Nursing, 16(1), 7-14. Retrieved from http://www.mhtp.org/data/web/med surg rn doc.pdf
Noise Analysis (Seismic) (2011) Retrieved from http://wiki.seg.org/index.php/Dictionary:Noise_analysis_(seismic)
Wallheimer, B. (2011, March 1). Purdue newsroom - new scientific field will study ecological importance of sounds. Retrieved from http://www.purdue.edu/newsroom/research/2011/110301PijanowskiSoundscap.html
Mandel, S., Hanser, S., Secic, M., & Davis, B. (2007). Effects of music therapy on health-related outcomes in cardiac rehabilitation: a randomized controlled trial. J Music Ther., 44(3), 176-97. PMID: 17645384
Seiler, B., & Levitt, E. (2008, November 11). Joyful music may promote heart health, according to university of maryland school of medicine study http://www.umm.edu/news/releases/music-cardiovascular.htm
Sherwood, C. (2011, March 3). What the science of sound tells us about the world. Retrieved from http://www.smartplanet.com/blog/pure-genius/what-the-science-of-sound-tells-us-about-the-world/5660
noise pollution. (2012). In Encyclopædia Britannica. Retrieved from
http://www.britannica.com/EBchecked/topic/417205/noise-pollution
Hema lab - purdue university. (2011, March 6). Retrieved from http://ltm.agriculture.purdue.edu/soundscapes_theme.htm
Hema lab - purdue university. (2011, March 6). Retrieved from http://ltm.agriculture.purdue.edu/footprints.htm
Human Impact on the environment. (2012). Retrieved from http://en.wikipedia.org/wiki/Human_impact_on_the_environment
Purdue Soundscape Ecology Project (2012) Retrieved from http://1159sequoia05.fnr.purdue.edu/bioscience/
Krause, B., Gage, S. H., Trubit, R., & Hines, J. (2008). Real: Project - snp. Retrieved from http://real.msu.edu/projects/one_proj.php?proj=snp
Scientists Tune In To The 'Voices Of The Landscape'. (2011, March 26). Retrieved from http://www.npr.org/2011/03/26/134425597/scientists-tune-in-to-the-voices-of-the-landscape
Psychoacoustics. (2012). Retrieved from http://en.wikipedia.org/wiki/Psychoacoustics
Blackburn, E.H., Epel S. E., Lin, J., Dhabhar, F. S., Adler, N. E., Morrow, J. D., Cawthon, R. M. (2004). Accelerated telomere shortening in response to life stress. The National Academy of Sciences, 101(49), 17312-17315.
Abstract
This paper discusses the significance and application of the science of sound to experience design & experimental innovation. Various types of collective sounds and fields of sound study that are related to the experience of life on Earth will be explored. This paper will also investigate the relationship between sound and public health, the management of sound, and the role of physics in the process of designing a more optimal and sustainable future for life on Earth.
Introduction
Experience design & experimental innovation refers to the design of optimal experiences and innovation through experimental exploration. Sound is essential to experience design and experimental innovation because it assumes an inevitable role in the processes of this universe, for if there is movement and life then there will be vibrations, waves, and frequencies that result. As a sensual, perceptual, and physical inevitability of existence, sound is necessary to study for the sake of designing and engineering optimal experiences for organic life. The significance of the relationship between sound and experience design will be further revealed in this paper.
The Study of Sound and its Significance
Auditory cues tell us about the world. Sounds transmit information that is essential to safety, awareness, and navigation. They can indicate or suggest the size, speed, force, mass, density, shape, and material properties of the objects and our environment. They can also warn us about dangerous situations and hazardous weather. They tell us about the movement and location of objects. They can be used to inform us about the mechanical quality of industrial objects. Auditory cues can also help indicate the strength, weakness, or hollowness of natural objects such as trees and rocks. These cues are also used for human and industrial alarm systems. Some auditory cues help indicate the emotional state of a fellow human or animal. There are many different ways in which sound can be described and classified.
Soundscape refers to the audible result of sound(s) that is produced within an environment. One example of a soundscape is the collective sounds a listener may hear amidst a tropical forest that is bustling with the sounds of animals, insects, and waterfalls. Another example of a soundscape is the collective sounds of being on a busy metropolitan street, amidst pedestrian and automotive traffic. Soundscape is a term that is used to describe the set of combined sounds witnessed in an environment. It is important to consider soundscape in the design process because of the immediacy with which it affects the experiencer's perception and well-being, and also because of how strongly it characterises experiences. Soundscape encompasses anthrophony, biophony, geophony, and technophony when any are present (see below). According to the pioneer of soundscape, soundscape consists of the three elements: keynote sounds (background sounds), soundmark (sound that is landscape-specific), and sound signals (foreground sounds). John Cage contributed to bringing soundscape to the foreground of widespread attention with his 1952 composition titled 4'33".
Anthophony, biophony, geophony, and technophony are the main domains of soundscape. Anthrophony refers to the anthropogenic noise and sounds that are created by human activity. The study of anthrophony is used in soundscape ecology and in the study of anthropogenic/human impact upon natural environments and resources. Biophony refers to the sounds that are manifested by the Earth's living organisms. These include amphibians, insects, animals, birds, and even human vocalisations. Biophony is characterised by more spectral and temporal variation than found in geophony. Biophony is affected by speech interference caused by noise pollution. Biophony overlaps slightly with bioacoustics, which refers to the scientific study of sound reception, production, and dispersion in animals and humans. Also related is the Lombard effect, or Lombard vocal response, which refers to the increased loudness that results from a speaker's involuntary inclination to speak more loudly or with more effort when in loud or noisy environments such that their voice is more audible or intelligible. This results in an increased signal-to-noise ratio of the speaker's voice. Animals have been found to demonstrate the Lombard effect when transmitting vocal sounds through an environment characterised by anthropogenic noise pollution. Geophony refers to the collective sounds created by inorganic geophysical activity and includes earthquakes, water flow, rainfall, thunder, hail, and volcanoes. Technophony is a branch of biophony (and arguably anthrophony) that refers to the sounds created by humans' use of extrasomatic material and energy to manifest their lives through technological innovations. Since the advent of technology, machinery and devices have been increasing in manufacture and use along with the noise they bring. Technophony can be used to describe the environmental noise that has resulted from industrial human life.
Soundscape ecology is a new scientific field being pioneered that focuses on discovering information about an area by studying landscape-specific soundscapes. It yields potential significance for early indicators of changes in the natural environment. Such signals can include changes in weather patterns, climate, or landscape formation. Soundscape ecology has allowed us to discover that bird choruses can indicate changes in the ecosystem. The information we uncover about a landscape's ecological characteristics informs us by measuring the changes, patterns, and health of an ecosystem. An example would be the discovery of birds having lower reproductive success (fewer offspring) in areas characterised by noisy machinery than the amount of offspring compared in a similar though quiet habitat. The findings from soundscape ecology have allowed us to compare how natural and informative soundscapes produced by wildlife or geophysical processes have been replaced by urban noise resulting from consequential (versus intentional) sounds. The findings also allow us to examine more concretely the negative effects of industrial human life on the natural processes of wildlife.
Noise commonly refers to unwanted sound. In physics and engineering, however, it refers to the addition of insignificant sounds (such as random environmental byproducts) to a sound (referred to as "signal") that is established as the desired auditory data. Noise in high levels can interfere with meaningful signal communication by preventing or distorting signal transmission. Noise is different than soundscape in that soundscape does not carry the negative connotation of being unwanted or undesirable as it refers to simply the collective sounds that are evident. A soundscape, however, can consist of noise. One type of noise is industrial noise, which is also known as occupational noise. Occupational noise refers to typically technophonic noise experienced in a workplace situation. Another type of noise is background noise, which is also sometimes called ambient noise. It refers to any and all sounds that occur in addition to (but are not) the sound being primarily observed, which tend to consist of environmental noises. This term is used for A/V engineering and creating noise regulations. Background noise can originate internally or externally; an example of an internal source of background noise would be an air-conditioning system. Other examples of background noise can include mechanical waves, human conversations, animal conversations, mechanical devices, and traffic. Environmental noise usually refers to background noise or the soundscape of a particular area. The excess of noise is commonly referred to as noise pollution. Noise pollution describes the excess of undesirable audible stimuli from an environment that negatively impacts human or animal life. It is usually characterised by anthropogenic environmental noise such as technophony and biophony.
Environmental acoustics is a term used in acoustical engineering to refer to the control and evaluation of vibrations and sounds in a staged outdoor environment typically involving technophony or industrial noise with the goal of determining acceptable noise levels. Environmental noise control refers to the implementation of noise barriers and buffer zones to control outdoor noise. Cities are designed such that walls are built around highways and residential zones are further away from industrially loud zones such as airports. This is a form of environmental noise control using buffer zones.
When sound travels inside an architectural space, the space itself and the objects within it affect the ways in which the sound propagates. Architectural acoustics is a term used in acoustical engineering to refer to the science of controlling sound and vibrations within buildings and the application of indoor sound propagation. This field began with buildings designed specifically for musical performances and later extended to include all interior environments and room acoustics. Architectural acoustics considers important aspects of indoor experiences. Hypothetical examples of the implementation of architectural acoustics include the suppression of noise or noise-cancelling technology for privacy in a shared structure or speech intelligibility in rooms. HVAC and plumbing systems are a significant source of vibration and noise in buildings. The American National Standards Institute (ANSI) decided the maximum acceptable noise level of classroom HVAC systems. Certain architectural designs can imply negative health effects (see noise health effects below). Architectural acoustics takes into consideration that indoor sound propagation can be affected by sound absorption, reverberation time/noise, diffraction, refraction, and overall sound pressure.
Sound and Health
Various disciplines have been created to investigate, explore, and study how sounds affects the health of humans and living organisms. These disciplines allow us to examine the social costs for a society when it comes to sound playing a destructive role. Soundscape ecology suggests that if human life and wellness depends upon the wellness of all other ecosystems on this planet, then it is important to assess how all organic life is affected by sound. As previously reviewed, the field contributes to our understanding of the health of animals and natural ecosystems to which human-induced anthrophony and technophony pose as a problem. The field of psychoacoustics also allows us to understand how sound affects human health, however it is more anthropocentric. Psychoacoustics is the study of the perception of sound and its associated physiological and psychological responses in humans.
There are a plethora of public health effects or noise health effects that are important to consider when evaluating industrial and post-industrial human experiences. Noise health effects refer to any negative health consequences of sound levels considered to be hazardous or unsafe. Research from the past three decades collectively reflects these health effects. These effects vary and can involve birth defects, immune system changes, cardiovascular disease, hypertension, and vasoconstriction. The various consequences that result from elevated sound levels that can present psychological and physiological issues in communities and individuals will be explored.
Hearing Impairment is a major issue that is often caused by sustained exposure to industrial/occupational or recreational noise. Hearing impairment can take the form of temporary or permanent hearing loss or impairment. This can occur from acute exposure to a loud sound or chronic exposure to loud sound levels. These distinctions are referred to as a noise-induced temporary threshold shift (NITTS/TTS) or a noise-induced permanent threshold shift (NIPTS). Tinnitus is a ringing sensation that develops after acute exposure to excessive sound levels. It is perceived as a sound inside the ear when no corresponding sound exists externally. Especially at frequencies of about 4,000 Hz, the ear often becomes desensitised. The threshold returns to normal if the sound overload is removed, while continued exposure or frequent exposure can result in a permanent shift. The human ear is most resilient when it comes to acute sound overload. Long-term exposure to unhealthy sound levels can play a destructive role to the inner ear's sensitive structures. The impairment to hearing is often associated with the damaging of cilia or stereocilia, which are fine hair cells that lie on the basilar membrane of the inner ear. These cilia are what convert oscillatory data into neural data. Once they are damaged or expire, they cannot naturally regrow or restore. NIHL or "noise-induced hearing loss” is a commonly occurring occupational illness. Presbycusis, also known as "age-related hearing loss", is the progression of impairment to human hearing that is known to take place as humans age. Experiences that may produce hazardous noise levels are commonly occupational or recreational. These can involve everyday industrial sounds exposed to humans in a workplace environment, or less frequent recreational sounds exposed to humans at musical performance or sport events. Tools such as sound level meters (discussed later) aid in the prevention of sound-induced deafness.
The National Institute for Occupational Safety and Health (NIOSH) have established guidelines for the maximum duration of time that a human can be exposed daily sound pressure levels (from varying time-weighted averages) over forty years. Exceeding the threshold of sound pressure level or exposure can be hazardous.
Maximum Decibel Levels Maximum Exposure
85 dB 8 hours
88 dB 4 hours
91 dB 2 hours
94 dB 1 hour
97 dB 30 minutes
100 dB 15 minutes
103 dB 7-1/2 minutes
106 dB 3-3/4 minutes
There are many psychological concerns that impact society as a consequence of sound. Studies are indicating that sound can lead to issues such as aggression, fear, stress, anti-social behaviour, sleep disturbance, annoyance, and communication interference. Sound can be a hazardous environmental stressor for living things, particularly in the form regarded as noise. Recent animal experiments have demonstrated negative effects of noise stress. Studies have shown an increase in human stress hormones such as cortisol when exposed to noise from aircraft or traffic while asleep (Spreng, 2000). Such daily industrial sounds can cause chronic stress for dwellers of dense urban environments. Stress is particularly negative because of how it weakens the immune system, atrophies neurons, and shortens telomeres (Blackburn et al., 2004). This presents a large social cost for a society's performance and wellness. The noise/stress hypothesis suggests that noise activates the body's stress hormones. Experiments for acute and chronic noise have frequently discovered changes in the stress hormones cortisol, epinephrine, and norepinephrine, which may lead to cardiovascular disorders and other negative health outcomes (Babisch, 2002). A study published later indicated that chronic exposure to environmental noise led to an increased risk of ischaemic heart diseases. (Kruppa, 2004). Similar research also indicated that humans are subject to increased cardiovascular risk if their daytime intake of sound emission exceeds 65 dB(A) (Ising & Kruppa, 2004).
Learning in academic environments can be inhibited due to noise or poor acoustic design. It is important that the execution of sound experiences be rigourously designed for context, for the quality and performance of a society depend upon it. Learning hindered by the reverberation noise experienced in a classroom presents an educational issue that can be avoided by utilising architectural acoustics to calculate the reverberation noise of the inside of the classroom (and even simulate it prior to build).
There are also studies on the effect of noise on task performance. While it might not reduce quantity of work, it can reduce quality and accuracy (Miller, 1974). Steady noise levels are less detrimental to performance than intermittent noises. Sudden noises considered to be startling stimulate muscular reflexes that allow for the body to be ready to defend itself against the source of noise. Also observed in response to noise are vasoconstriction, reduced skin resistance, breathing rate changes, heart rate changes, pupil dilation, and saliva secretion (Davis, Buchwald, and Frankmann, 1955). Pathological effects in animals have also been observed in studies involving intense noise. Such abnormalities included brain damage, abnormal fetal development, sexual dysfunction, and hypertrophied adrenal glands (Miller, 1974).
Sleep interference is caused by noise from unusual or unfamiliar sounds, however research in this subject remains scant. There are also other factors to consider, such as the sleeper's physical and emotional state, the stage of sleep when interference takes place, the age and sex of the sleeper, and the nature of the noise stimulus (Rossing, 2002). A sleeper is least likely to be awakened in the REM stage of sleep, and is most likely to be awakened during stages three and four. Noise stimuli of 50 dB(A) tend to cause an awakening or change in sleep stage, while stimuli of 70 dB tends to cause an awakened response. Sleepers tend to have trouble falling asleep at 40-50 dB(A) noise levels. Noise levels above 35 dB(A) should not be present in order for most sleepers to be protected from sleep disturbance (Rossing, 2002).
Animals and wildlife have also been impacted by noise, as soundscape ecologists are currently exploring. Both marine and terrestrial ecosystems have witnessed the effects of noise. One way that noise can impact animal life is by reducing the amount of usable habitat and replacing it with areas that become polluted with noise. This type of activity has seen the reduction of bird offspring (discussed earlier) and can even lead species to extinction. Further research on this topic is currently being investigated. This is especially important to consider for the design of a more sustainable future.
While sound can play an alarmingly harmful role in human life, there are also studies that have investigated the positive health benefits to a society when it comes to employing sound in a restorative manner. Sound in the form of music can have a positive impact upon emotional affect and can also have the effect of reducing human stress levels.
The implementation of sound for human learning can yield positive effects for the purpose of human advancement. Studies have shown that listening to music (especially if it is enjoyed by the listener) results in positively impacting childrens' cognitive abilities (Schellenberg & Hallam, 2006). Another study has indicated that exposure to music in childhood is positively associated with academic ability and that such intellectual functioning can be later reflected in adulthood (Schellenberg, 2006).
Music therapy is a medical practice established in the 1950s to improve cognitive functioning, psychological functioning, behaviour, motor skills, and overall health of individuals. These experiences may involve listening to live/recorded music, singing, moving to music, discussing music, and playing musical instruments. It has been implemented in venues such as hospitals, schools, and even correctional facilities. There are many therapeutic effects of music, such as the regulation of blood pressure when it is too high or too low, such that it adjusts to an ideal level for recovering or healing. Positive effects upon health-related outcomes of ill and rehabilitating individuals have been studied. In a study that examined the effect of music upon visitors in a hospital intensive care unit for which the presence/absence of music was controlled, results demonstrated a reduction in stress levels in individuals (Routhieaux & Tansik, 1997). Studies have also shown that music promotes heart health. Positive cardiovascular health effects can result from listening to music that arouses evokes positive affect in the listener (Seiler & Levitt, 2005). Such positive cardiovascular effects include the dilation of tissue in response to music such that blood flow is increased (which is similar to findings from a study on laughter conducted in 2005). Scientific findings such as these suggest that music should be used in medical intervention.
The Management of Sound
While the regulation of acoustic noise has posed as a problem in industrial and post-industrial societies, the execution of solutions have remained controversial and subpar. Noise regulation refers to the laws and guidelines established by different levels of government to regulate the transmission of sound. In the 1960s, national noise-regulation laws were enacted in the UK and Japan, however there were issues with the design and execution of those laws. They were not comprehensive enough to address ambient noise levels that would witness a gradual rise over time. They also were not easy to enforce given the lack of clear enforcement procedures for government personnel and difficulty when making distinctions between single versus collective sound sources. The U.S. Noise Pollution and Abatement Act of 1972 was an attempt at nationwide noise-regulation. This federal program was launched to minimise noise pollution in order to preserve public health on a national scale. The program established noise emission regulations and standards for HVAC systems, motor vehicles, aircraft, and other industrial equipment. In 1981, the act ceased to receive federal funding under President Ronald Reagan, after which the problem was then left to state and local governments. The Environmental Protection Agency (EPA) is currently responsible for assisting state and local governments with the regulation of noise, and is working to revive national noise regulations that have been abandoned. The Federal Transit Administration has published procedures for conducting noise and vibration impact assessments to apply to buses and trains. While there exist regulations at all for the management of sound in society, these regulations are unfortunately not enough to address the problem of the public health costs of noise.
Measuring sound pressure allows for the design of healthier acoustic experiences. There are different ways to measure sound pressure, vibration, and noise levels, along with many different instruments with which to measure these. A sound level meter is an instrument that measures sound pressure levels. The most popular instrument for measuring sound level is by using a sound level meter that uses A-weighting. Fletcher and Munson's contributions in the 1930s allowed for the development of A-weighting, which involves each frequency being assigned its own weight such that it corresponds to the sensitivity of human ears. The application of A-weighting is evidenced by sound pressure levels expressed as dB(A). Ambient noise level is a measure of the location-specific sound pressure level of background noise. Ambient noise level is often measured in decibels using a sound level meter, such as an A-weighting scale that has a reference pressure level of .00002 Pa.
Noise floor in signal theory refers to the measure of the signal that results from a combination of noise and undesirable signals in a system. Noise here refers to all signals outside of the desired signal, such as cosmic noise, thermal noise, atmospheric noise, industrial signals, or incidental noise. Noise floor can be measured by a seismograph or spectrum analyser. Noise floor can tell us about the soundscape that is unique to a particular environment. Noise floor is significant in that it is employed as the reference point with which to measure a signal-to-noise ratio.
When designing roadways and planning for urban environments, noise analysis is conducted to gather noise data to analyse. Architects also have the ability to simulate noise analyses for buildings they design prior to construction. This is used mostly for products, buildings, or services to comply with environmental regulations.
Modal Analysis is used by noise and vibrations engineers to reduce the level of noise produced by products by identifying sources of vibrations and analysing the data acquired. It studies the structural and dynamic character of a mechanical structure while being subject to vibrational excitation. We can use modal analysis to understand how structure vibrates and any issues it may have with vibrations. This involves being sensitive to a structure's resonant frequency, as well as the application of sound damping. Modal analysis also lends knowledge about the speed at which vibrational energy dissipates from a structure and returns to rest once an excitation force is withdrawn. An example of where modal analysis was either needed or failed is the Tacoma Bridge. Modal Analysis involves the use of input forces that vary sinusoidally, an accelerometer, and means to measure amplitude. These tests help reduce the negative effects caused by the vibrations of structures that near the structure's resonant frequency, which reduces the likelihood of internal or overall structural failures. Modal Analysis is significant because it is what allows us to design progressively quieter industrial and technological products for everyday use. We use it to test cars, machinery, buildings, and products. It allows designers and engineers to build with vibration reduction in mind. It can also be used experimentally to increase the melodic qualities of consequential sound experiences (e.g. HVAC systems).
Sound absorption is a method used to control noise levels in an acoustic environment, which are most often rooms. Sound absorption by porous materials (e.g. carpet, drapery, upholstery, acoustical tile, glass fibre) takes place when the vibrating air particles resulting from acoustic energy interact with the material's fibres and become converted to heat energy. Engineering sound absorption depends mainly on a) the volume of the space and b) the properties and surface area of all surfaces within the space (walls, ceiling, objects). To calculate reverberation time, it is important to know the ratio of volume to surface in the room. A small room with a small ratio would result in rapid sound decay (Rossing, 2002). Moving the place of objects, adjusting the material properties of objects, and adding/removing objects would result in the manipulation of this ratio and the experience of sound in a room.
Soundproofing refers to the reduction of sound pressure levels for any reason and may involve the use of sound generators that counteract noise, noise barriers, damping, or distancing efforts. Acoustic damping refers to reducing mechanical or acoustic resonance within a structure through reflection or diffusion. An example of acoustic damping would be soundproofing through the application of acoustic devices, such as sound absorption tiles that allow for the reduction of oscillations. Damping is a component of acoustic quieting, which involves the damping of vibrations in a process to make machines quieter such that they are less likely to be observed. Acoustic quieting was primarily developed to make submarines less likely to be detected. Like many other advancements that emerged from military goals, this technology became adapted for the use of consumer industries (e.g. automobiles and computers).
Damping and acoustic quieting are forms of active noise control, in that they aim to prevent or reduce background noise or unwanted sound(s). It can also be referred to as noise cancellation or active noise reduction. Noise-cancelling headphones are an example of a consumer product that uses active noise control. Other examples of active noise control include anti-noise generators or sound damping devices.
Scientific Applications to Improve Organic Coexistence with Sound
The application of the physics of sound can aid the design of optimal experiences with rigour and precision. We can use physics to calculate the propagation of sound, understand and manipulate sources of vibratory excitation, and analyse existing situations that need improvement.
Signal-to-noise ratio (SNR) tells us about desired or meaningful sound information measured in contrast to unwelcome and extraneous sound information. It refers to the ratio of power between the amplitude of background noise to the amplitude of a signal. "Signal" refers to meaningful or desirable information, whereas "(background) noise" refers to meaningless or undesirable information. These subjective terms are commonly used by scientists and engineers to measure and compare (and usually average) signal power to noise power.
P(x+∆x)=P(x) e^(-α(ω)∆x),α(ω)=α_0 ω^η
P = average power
SNR=P_signal/P_Noise =〖(A_signal/A_Noise )〗^2
Where A is root mean square amplitude.
SNRs are commonly expressed using decibels because of the high dynamic range of many signals. Dynamic range refers to the ratio of measurement between the strongest and least distorted signal through a medium and the least perceptible signal (which is often the noise level). To calculate SNR is decibels:
SNR=10*〖log〗_10 P_Signal/P_Noise =P_(Signal,dB)-P_(Noise,dB)
SNR=10*〖log〗_10 (〖A_Signal/A_Noise )〗^2=20* 〖log〗_10 (A_Signal/A_Noise )
Measuring SNR requires a reference signal. An example would be a 1 kHz sine wave at a standardised nominal such as +4 dBu. Any ratio above 1:1 reveals that the signal level is more powerful than that of the noise. The relationship between SNR and soundscape is such that SNR can be applied in the acoustical design process of urban soundscapes where many human experiences are shared and observed.
Acoustic Attenuation measures the loss of energy loss when sound propagates through different media. The following power law describes acoustic waves:
P(x+∆x)=P(x) e^(-α(ω)∆x),α(ω)=α_0 ω^η
Where α(ω) is the attenuation coefficient, ∆x is the wave propagation distance , ω is the angular frequency, α_0 and η are real material parameters acquired by experimental data, and P is pressure.
Acoustic quieting can be further understood by the following equation, which expresses how sound intensity level changes as the distance between the source of a signal and the receiver of that signal changes:
∆dB=20*〖log〗_10 (d_2/d_1 )
Conclusion
There are many opportunities for designers, engineers, urban planners, politicians, and architects to reform the future of human experiences by regulating, designing, engineering, and constructing safer and healthier sound environments for humans. There are also many opportunities for experiments to take place that will allow for innovation in the implementation and design of better sound experiences. The dynamic relationship between human life and wildlife ecosystems can also be improved such that wildlife and biodiversity are preserved. Now that we know that noise increases stress, and that music reduces stress, a challenging task for designers might be to explore how urban soundscapes can be designed to result in the reduction of stress levels versus an increase in stress levels. Another topic for exploration is understanding how healthier experiences can be designed that don't induce hearing loss, or how more silent experiences can be created such that people can take asylum from noise stress. Psychoacoustics reveal that sound, which greatly impacts the mental health of communities and society as a whole, should be carefully considered when designing for more optimal human experiences. It is fundamentally important to understand the social costs for a society, such as poorer health and performance. The positive effects of music on cognitive abilities and emotional affect reviewed in this paper suggest that sound can be strategically implemented to advance the human race while complementing the human experience.
While there are still many unknowns about noise and sound, and the complex relationship between the functioning of organic life is still not yet well understood, however, as of the past ten to fifteen years we have begun witnessing a steady progression in the challenge of this insufficient body of knowledge by many researchers. As our knowledge about the complex relationship between life and sound continues to improve, we can begin experimental applications based upon data gathered so far in order to begin investigating a healthier relationship between industrial life, human life, and wildlife.
References
Routhieaux, R., & Tansik, D. (1997). The benefits of music in hospital waiting rooms. The Health Care Supervisor, 16(2), 31-40. PMID:10174442
Schifferstein, H. N. J., & Hekkert, P. (2008). Product experience. Oxford: Elsevier.
Davis, R. C., Buchwald, A. M., & Frankmann, R. W. (1955). Automatic and muscular responses and their relation to simple stimuli. Psychol. Monogr., 69(20), 1.
Miller, J. D. (1974). Effects of noise on people. Acoustic Society of America, 56, 729.
Rossing, T. D., Wheeler, P. A., & Moore, F. R. (2002). The science of sound. (Third Edition ed.). San Francisco Boston New York Cape Town Hong Kong: Addison-Wesley.
Schellenberg, E. G., & Hallam, S. (2005). Music listening and cognitive abilities in 10- and 11-year-olds: the blur effect. Ann N Y Acad Sci., 1060, 202-9. PMID: 16597767
Schellenberg, E. G. (2006). Long-term positive associations between music lessons and IQ. Journal of Educational Psychology, 98(2), 457-468.
Rauscher, F. H., Shaw, G. L., & Ky, C. N. (1993). Music and spatial task performance. Nature, 365(6447), 611. doi: 10.1038/365611a0
Ising, H., & Kruppa, B. (2004). Health effects caused by noise: Evidence in the literature from the past 25 years. Noise & Health, 6(22), 5-13.
Noise Control Act of 1972. 42 U.S.C. § 4901-4918 (1972)
Spreng, M. (2000). Possible health effects of noise induced cortisol increase. Noise & Health, 2(7), 59-63.
WHO/europe | Health effects of noise. (2012). Retrieved from http://www.euro.who.int/en/what-we-do/health-topics/environment-and-health/noise/facts-and-figures/health-effects-of-noise
Age-related hearing loss - pubmed health. (2010, December 13). Retrieved from http://www.ncbi.nlm.nih.gov/pubmedhealth/PMH0002040/
Rabinowitz, P. M. (2000). Noise-induced hearing loss. Am Fam
Physician., 61(9), 2749-2756.
Irvine, K., Devine-Wright, P., Payne, S., Fuller, R., Painter, B., & Gaston, K. (2009). Green space, soundscape and urban sustainability: an interdisciplinary, empirical study. Local Environment, 14(2), 155-172.
Modal Analysis. (2012). Retrieved from http://en.wikipedia.org/wiki/Modal_analysis
Moussavi-Najarkola, S., Khavanin, A., Mirzaei, R., Salehnia, M., Muhammadnejad, A., & Akbari, M. (2012). Temporary and permanent level shifts in distortion product otoacoustic emissions following noise exposure in an animal model. The International Journal of Occupational and Environmental Medicine, 3(3), 145-52.
Pijanowski, B.C., L. Villanueva-Rivera, S. Dumyahn, A. Farina, B. Krause, B. Napoletano, S. Gage and N. Pieretti. 2011. Soundscape ecology: the science of sound in landscapes. BioScience 61(3): 203-216.
Pijanowski, B.C., A. Farina, S Dumyahn, B. Krause, and S. Gage. 2011. What is soundscape ecology? Landscape Ecology.
Richards, T., Johnson, J., Sparks, A., & Emerson, H. (2007). The effect of music therapy on patients’ perception and manifestation of pain, anxiety, and patient satisfaction. MEDSURG Nursing, 16(1), 7-14. Retrieved from http://www.mhtp.org/data/web/med surg rn doc.pdf
Noise Analysis (Seismic) (2011) Retrieved from http://wiki.seg.org/index.php/Dictionary:Noise_analysis_(seismic)
Wallheimer, B. (2011, March 1). Purdue newsroom - new scientific field will study ecological importance of sounds. Retrieved from http://www.purdue.edu/newsroom/research/2011/110301PijanowskiSoundscap.html
Mandel, S., Hanser, S., Secic, M., & Davis, B. (2007). Effects of music therapy on health-related outcomes in cardiac rehabilitation: a randomized controlled trial. J Music Ther., 44(3), 176-97. PMID: 17645384
Seiler, B., & Levitt, E. (2008, November 11). Joyful music may promote heart health, according to university of maryland school of medicine study http://www.umm.edu/news/releases/music-cardiovascular.htm
Sherwood, C. (2011, March 3). What the science of sound tells us about the world. Retrieved from http://www.smartplanet.com/blog/pure-genius/what-the-science-of-sound-tells-us-about-the-world/5660
noise pollution. (2012). In Encyclopædia Britannica. Retrieved from
http://www.britannica.com/EBchecked/topic/417205/noise-pollution
Hema lab - purdue university. (2011, March 6). Retrieved from http://ltm.agriculture.purdue.edu/soundscapes_theme.htm
Hema lab - purdue university. (2011, March 6). Retrieved from http://ltm.agriculture.purdue.edu/footprints.htm
Human Impact on the environment. (2012). Retrieved from http://en.wikipedia.org/wiki/Human_impact_on_the_environment
Purdue Soundscape Ecology Project (2012) Retrieved from http://1159sequoia05.fnr.purdue.edu/bioscience/
Krause, B., Gage, S. H., Trubit, R., & Hines, J. (2008). Real: Project - snp. Retrieved from http://real.msu.edu/projects/one_proj.php?proj=snp
Scientists Tune In To The 'Voices Of The Landscape'. (2011, March 26). Retrieved from http://www.npr.org/2011/03/26/134425597/scientists-tune-in-to-the-voices-of-the-landscape
Psychoacoustics. (2012). Retrieved from http://en.wikipedia.org/wiki/Psychoacoustics
Blackburn, E.H., Epel S. E., Lin, J., Dhabhar, F. S., Adler, N. E., Morrow, J. D., Cawthon, R. M. (2004). Accelerated telomere shortening in response to life stress. The National Academy of Sciences, 101(49), 17312-17315.
