The team of researchers from the Centre for Metamaterial Research and Innovation at the University of Exeter used devices, known as thermophones, to create a fully controlled array from just a thin metal film attached to some metal wires.
The results, published in Science Advances, could pave the way for a new generation of sound technology, including home cinema systems.
Traditionally, arrays have been used in a host of every day applications, including ultrasound and sound systems. Arrays allow sounds from several sources to be ‘steered’ in a certain direction, to gain greater control and clarity of the sound produced.
Conventional speaker arrays rely on the production of sound through driven movement of some object — such as a speaker cone. The new study, however, pioneers arrays of speakers that produce sound entirely by heat: thermophones.
Although thermophones have been in existence for more than 100 years, they have, until now, had limited real-world application. However, they have a host of advantages from their mechanical counterparts — including no moving parts and the ability to be mass produced from inexpensive, sustainable materials.
Crucially, they can even be made transparent and flexible, which is desirable for the new wave of flexible technologies being produced.
For the study, the researchers found that, when combined into an array, thermophones are able to reproduce the same control over sound fields as traditional arrays.
However, they do much more than this: as they are driven by electrical currents, the sound they produce mirrors the subtle movement of the current carriers as they flow through the device and, as a result, they create a much richer sound field than traditional arrays.
The researchers suggest that the study opens a route to radically simplify array design, showing that with thermophone technology, it is possible to create a fully controlled array from nothing more than a thin metal film attached to some metal wires.
David Tatnell, lead author of the study and a PhD researchers at the EPSRC Centre for Doctoral Training in Metamaterials said: “Using heat to produce sound is a game changer as it allows us to make speaker arrays smaller than ever before. This, as well as the ability to make the speakers flexible and transparent, has a lot of exciting potential applications, such as haptic feedback systems in smartphones and other wearables.
The shape of the room defines the movement of the sound waves within the room. Placement of acoustic materials should be determined by the way the sound moves in that particular room in order to ensure optimal efficiency of the materials.
1. NARROW ROOMS
Placing the sound absorbing materials on the ceiling in a narrow room will not create the wanted acoustic effect.
Sound absorbers must be placed as close to the sound source as possible. Therefore, the absorbing materials must primarily be placed on the walls
The sound moves towards the constructive centre thereby creating echoes.
The sound diffusing elements should be placed on the curved surfaces in order for the sound to be dispersed in many directions.
3.1 LARGE ROOMS WITH LOW CEILING
In large rooms the sound spreading is experienced as the greatest challenge, since the speech sounds can be heard over long distances.
Sound absorbing and sound diffusing materials should be used, and sound barriers should be applied to the ceiling. The sound regulation from the floor is secured by furniture and the use of sound barriers.
3.2. LARGE ROOMS WITH HIGH CEILING
The acoustic environment in large rooms is sometimes experienced as the one at a railway station. This is partially connected to the fact that it is difficult to concentrate due to the relatively high noise level. Another reason for this is the fact that the conversation over short distances is impeded due to the sound being masked or drowned by the surrounding noise
It is therefore important that all the available surfaces are equipped with effective sound absorbers and sound diffusers. The furniture along with the sound barriers play a highly active role by diffusing the sound and thereby making the existing sound absorbers and diffusers even more efficient.
4. SMALL ROOM WITH PARALLEL WALLS
In small rooms, the low frequencies often seem to be predominant. Therefore, the speech appears to consist primarily of humming sounds. Sound absorbers with a low-frequency profile should be used and placed on the ceiling surface.
5. CEILING DOMES
The sound diffusing elements should be placed on the curved surfaces in order for the sound to be dispersed in many directions.
6. INCLINED CEILING
Inclined ceilings have both a sound spreading and a sound concentrating effect. In most cases, the sound is concentrated because the sound regulation of the area around the inclined ceiling has not been considered carefully.
The wall area opposite the inclined ceiling should also be equipped with sound absorbing materials. As a principal rule, all surfaces above the normal ceiling height (2.60 m) including the end walls should be equipped with sound absorbers.
Inclined walls have both a sound spreading and sound concentrating effect.
The sound spreading effect is achieved by inclining the wall in proportion to other walls and the ceiling. In general, the walls inclined by more than 6 degrees ensure an excellent sound diffusion. The most effective diffusion is obtained by applying several angles.
8. VAULTED CEILING
In rooms with vaulted ceilings, the sound is concentrated in the constructive centre making the sound appear with a stronger intensity. The sound movements also appear stronger along the curve.
9. CONNECTED ROOMS
Rooms that are linked by a large opening in between, influence each others sound environment. A room without acoustic regulation can act as an echo chamber reinforcing the sound, when connected to an acoustically regulated room.
Both rooms must be equipped with sound absorbers. If the distance between the opening and the opposite walls is short (5-6 m), the walls much be covered with sound absorbers or diffusers.
10. ROOMS WITH MEZZANINE
In rooms with mezzanine, it is possible to create different sound environments in the same room. In the large, open room, an environment with long reverberation time is created. The space above and below the mezzanine has a shorter reverberation time. The challenge posed in this type of rooms is the sound reflection and the harmonization of the different reverberation times.
The wall opposite the mezzanine should be equipped with sound absorbers or diffusers. In addition, sound absorbers should be placed on the underside and the banister of the mezzanine. In order to prevent large differences in the reverberation times between the large room and the space around the mezzanine, sound barriers can be applied.
Credit: KNAUF DANOLINE
Check out our free reverberation online calculator (for basic rooms).
2020 has been a year full of ups and downs. One big thing that affected, in fact, is still affecting the whole world is undeniably the Covid-19 pandemic. No doubt that the pandemic has caused a lot of downhills in the development of many aspects, like economy and social, but there is one thing that have shown obvious positive sign during this situation: the environmental change.
According to a Malaysian news report by Ming Teoh from The Star, the movement control order (MCO) that was carried out to tackle the Covid-19 spread in Malaysia has brought positive environmental impacts to the country (Teoh, 2020). People were amazed by the clean rivers, clear blue skies and the recovery of nature and wildlife. Of course, due to the MCO where a lot of human activities were restricted, the streets and urban roads have been very quiet as compared to the usual noise level. The improved noise quality resulted in lower noise pollution, which made the sounds of the fauna more apparent. But once everyone gets back to normal life when the MCO is lifted, how long can this positive environmental situation last? Will there be enough time for the environment to heal properly?
The Department of Environment (DOE), Ministry of Energy, Science, Technology, Environment and Climate Change (MESTECC), Malaysia
The Department of Environment (DOE) from the Ministry of Energy, Science, Technology, Environment and Climate Change (MESTECC) of Malaysia have been very concerned about this issue all the while, specifically on the noise quality of the country. They have constantly been updating the guidelines to handle noise or vibration for various applications, for example vehicle-noise, ambient noise, or outdoor noise sources in the environment. In one of the published guidelines for environmental noise limits and control (2009), the DOE have specified a table showing the permissible sound levels for different applications, shown in Table 1 as one of the examples from the guidelines (Air & Noise, 2019).
The permissible sound levels differ by the applications (i.e. use of land, human density) and the different times of the day, to ensure that the circumstances of various conditions are taken into account during the sound level measurements. For instance, the ambient noise limits are set such that it is an absolute limit based on the average level of noise (which should not be exceeded in a specified period), or in accordance with a relative limit based on the permitted increase in noise level with respect to the background level. It is mentioned that the limits should always be consistent with the environmental noise climate of the location. The rest of the noise limit schedules listed in the guidelines include those for land use, road traffic, railway/transit trains, construction, and maintenance, which are the main sources of outdoor noise in the country.
Besides that, the report also covers guidelines on planning process, noise impact assessments, quantifying of noise disturbance, and guidance in environmental noise mitigation through planning and control. These are ideally applied in new and existing projects planning, in which the projects can cover anything that involves noise, as a potential concern or needed to be measured and assessed. This is a very imperative measure from the DOE to enforce noise control in the country to work on controlling the noise impact of the relevant applications, thus overcoming the noise pollution in Malaysia. With these actions being taken and followed, the goal to maintaining a better noise quality in the country can be achieved in near future.
Khei Yinn Seow
Air & Noise, P. S. C. S., 2019. Guidelines for Environmental Noise Limits and Control (Third Edition), Putrajaya: Department of Environment Malaysia.
Teoh, M., 2020. Blue skies, less waste: Covid-19 and the MCO’s effects on the environment., s.l.: The Star.
A lot of activities and businesses have the potential to have negative effects to their environment because of the vibration that they produce. For example, construction (for example during piling), mining and and other vibration-generating activities. This vibration can disturb the comfort and health of people around it, and even can have destructive effects to nearby buildings.
In Indonesia, the vibration limit is regulated through Ministerial Decree of Ministry of Environment No. 49 Year 1996. This regulation was made to ensure healthy environment for human and other living creatures to live in. Consequently, the vibration generated from human activities need to be regulated.
In this regulation, businesses and activities are required to:
Comply to the vibration limit in the decree. This is required for businesses and activities to obtain certain relevant permits to be able to operate.
Use vibration reduction equipment
Report vibration monitoring activities at least once in 3 (three) months to the Governor, Minister, Government agencies that are responsible to control environmental impact, other technical institutions that is responsible for the activities and other organizations that might need the vibration monitoring report.
The vibration limit is separated into few parts which are:
Vibration limits for health and comfort
Mechanical vibration limits based on its destructive effects
Mechanical vibration limits based on building types
The following table and graphs is the vibration limit for health and comfort:
Acceleration = (2πf)2 x displacement
Velocity = 2πf x displacement
The graphic representation of the table above is as follows:
The table below is the vibration limits based on the destructive effects:
As seen above, the peak velocity limit from the vibration is separated into 4 categories which are:
Category A: non-destructive
Category B: Possibly destructive for plastering (crack, or in certain cases the plaster can fell off the wall)
Category C: Possibly destructive for structural components that bear loads
Category D: High risk of destruction of load bearing walls
The following graph is the vibration limit based on destructive effects in a graphical form:
Mechanical vibration limit can also be categorized into the types of buildings. The buildings are categorized into 3 which are:
Buildings for commercial, industrial, and other similar use.
Residential and other buildings with similar design and usage
Structures that are sensitive to vibration and cannot be categorized into category 1 and 2, for example preserved buildings with high cultural value
Below is the vibration limits for the building category above:
The table below is shock limit for buildings:
Maximum velocity (mm/s)
Old buildings with high historical value
Buildings with existing defects, cracks can be seen on the walls
Buildings with good condition, minor cracks on plaster is acceptable
Buildings with high structural strength (for example industrial building which is made from concrete and steel)
10 – 40
The ministerial decree also describe the measurement and analysis method for vibration as follows:
Vibration transducer (Accelerometer or seismometer)
Vibration measurement device or analysis device (Vibration meter or vibration analyzer)
1/3 octave or narrow band filter
Vibration measurement related with health and comfort:
Place transducer on the floor or other vibrating surface, and connect it to the measuring device with filtration
Set the measuring instruments to measure displacement. If the measuring instruments do not have that on display, the conversion from acceleration or velocity can be used
Reading and recording is conducted for frequency between 4-63 Hz or with signal recording device
Measurement results with at least 13 data shall be plotted on graph
Vibration measurement for structural health:
The measurement method is similar with the vibration measurement above, however the physical measure that is assessed is the peak velocity.
The 13 data which are plotted on graph shall be compared with the vibration limits. The vibration is considered above the limit if the vibration level exceeds the limit at any frequency.
The definition used in the regulation of ministry of environment No 49 Year 1996 is as follows:
Building structure is a part of building that is planned, calculated, and functioned to:
Support any kind of load (static load, dynamic load, and temporary load)
Functioned for building’s stability as a whole. For example: frame and bearing wall
Structure’s component is a part of a building structure that contributes to structure’s function. For example: beams, columns, and slab.
Bearing wall is a building structure which is a vertical plane that is functioned to support loads on top of it such as slab or roof.
Non-structure components are parts of building that is not planned or functioned to support load. For example partition walls, door and window frames, etc.
Destructive impact on structure and non-structure:
Destructive impact on structure: Destructive impacts that can endanger building stability (for example destruction of columns that potentially make a building collapses)
Destructive impact on non-structure: Not dangerous to building stability, but can be a danger for building occupants (for example: when a partition wall collapses, it will not make the building collapse, but can injure occupants)
Degree of building destruction:
Light: not dangerous for building stability and can be fixed without reducing building’s strength
Moderate: Destruction that can reduce structural strength. To fix this, added reinforcement must be used.
Severe: Degree of destruction that can endanger the building and potentially makes the building collapses.
Previously, we have discussed how the human auditory system works and recognizes the sound direction. Now, we will discuss how sound is perceived through our mind. In acoustics, the sound processing into the human auditory system is divided into 2 different mechanisms, namely hearing and listening. Hearing is the process of the mechanism of sound wave propagation into the human auditory system due to the sensitivity of the human auditory system to the vibration of sound waves with a certain frequency and intensity. While listening is a process of hearing along with the interpretation of information about the environment of a place based on the details contained in the vibration of sound waves that are heard.
Interpretation of sound information in the listening process is the vibrations of sound waves that are heard by humans. That not only represents the source of the sound but also contains information about the environment in which the sound is heard due to the physical mechanism that occurs when the sound wave propagates. Listening is considered a complex mechanism because it involves multi-level attention and higher cognitive functions. There are three levels in listening that are used to explain the complexity of listening namely listening-in-search, listening-in-readiness, and background listening.
Listening then forms us in an interpretation and perception in an environment based on its acoustic conditions. For example, if we close our eyes and we are given a stimulus in the form of the sound of water, squeaking, and the sound of wind with a certain level of sound pressure (SPL) we can interpret this as a feeling of being in a park. Then if the sound is added to the vehicle’s sound stimulus with a sufficiently audible sound pressure level, this might disturb the atmosphere of the park, and we feel uncomfortable. The action and interaction of natural factors and / or human factors acoustically in a place is called soundscape. This is because the sound in the environment does not only focus on a person, but also how one interacts with the sound and how one’s attention to the sound that arises.
Simple soundscape involves the type of sound source, location related to activities that occur in the related environment, environmental conditions and various subjective things that shape one’s perception and interpretation. This relates to the definition of soundscape in building one’s perception where it is also influenced by their socio-cultural and also the soundscape approach is seen from various disciplines.The soundscape process can be seen in the process diagram in Figure 1.
The analysis of soundscape can produce information for the basis for taking action in the form of sound management, which is to sort out what sounds should be heard and what sounds should be covered with other sounds (masking noise), by directing the attention of visitors to certain sounds that are in line with expectations they are based on the function of the related place.
1. B. Truax, Acoustic Communication. Ablex Publishi, 1984
2. A. Ozcevik and Z. Y. Can, “A Field Study on The Subjective Evaluation of Soundscape,” in Acoustics 2012, 2012, no. April, pp. 2121–2126.
3. F. Aletta and J. Kang, “Soundscape descriptors and a conceptual framework for developing predictive soundscape models,” no. October 2017, 2016.
The British Standards Institution, “BS ISO 12913-1:2014 – Acoustics — Soundscape Part 1 : Definition and conceptual framework,” ISO, 2014.
5. D. Botteldooren, C. Lavandier, and A. Preis, “Understanding urban and natural soundscapes,” in Forum Acusticum 2011, 2011, vol. 1, no. c, pp. 2047–2052.
Many around the world are experiencing life with very low noise levels due to restrictions as we are confined to our home and there is a decrease in the industrial, transportation and leisure activity. This provides a wonderful opportunity to quantify and record for the future the lower noise levels of our soundscapes. With the reduction in shipping there is also a change in the underwater soundscapes.
Nowadays there are a high number of noise monitoring systems (noise monitoring terminals, city wide systems, underwater systems etc.) installed all over the world which will capture this information for the future. However, there are many acousticians working from home with access to a sound level meter that can be used to capture the soundscape from their balcony or from their garden and compare the before and after the restrictions.
The IYS 2020 committee has provided a central contact between a number around the world who were thinking similarly that there would be some benefit in coordination and a little standardization in the capture of the data. Marçal Serra from CESVA has taken a lead to set up a LinkedIn group COVID-19 Noise Reduction (at www.linkedin.com/groups/13844820/) and with hashtag #COVID19NoiseReduction for any posts.
The following is a general structure for those who wish to participate and share their data in the future. But do not break your confinement to report this data!
Place: Country and city (e.g., Spain village near Barcelona)
Primary noise source: (e.g., Traffic noise: note number of lanes per direction or Social noise: note if café/bar/restaurant/sporting)
Noise measuring system: The noise measuring system used to measure Lduring, Lbefore, and Lafter
Noise level during COVID-19 confinement:Lduring, expressed as a weighted overall level (preferably LAeq,1 hour), spectrum or psychoacoustic metrics as Loudness. It could also be reported as an image of the noise time history or a weekly color map and/or compiled into a report/article/conference paper with the measurement details and the comparison data
Noise level before & after COVID-19 confinement:Lbefore & Lafter, expressed in the same way as Lduring and over the same time period.
Most industrial activities create noise that can be harmful to the environment as well as to their workers. To minimize this effect, governments, associations, and companies have created regulations, standards, and codes to set the allowable noise both inside the sites, that can be harmful to the workers, as well as to the environment. In a lot of cases, during the planning phase, the plant owner and project management want to be sure that the noise levels are acceptable. Since the plant is not built yet, what can be done is creating a noise model to simulate the plant, so that the noise levels can be predicted. In this article, we will explore how we can do so.
The first thing we must know is how much noise does the noise sources inside of the plant will emit. The noise source is usually described in two ways which is Sound Power Level (Lw or SWL), and Sound Pressure Level (Lp or SPL) in certain distance, most commonly Lp in 1 m distance. There are multiple ways to get this information for certain noise sources. First, if the equipment type and model have been chosen, the equipment manufacturer will normally report the noise level in their datasheet. However, this is not usually the case with most of noise predictions since the noise study is normally done before the equipment suppliers are appointed. So, the second way to be able to predict the noise emission is by following empirical formulas that are developed by researchers. You can find such formulas in some textbooks, journals, and papers. For rotating parts, you will need its rated power and rotational speed to be able to estimate the noise emission.
For example, in the speed range of 3000-3600 rpm, the noise level of a pump with drive motor power above 75 kW can be predicted using the following equation:
Suppose a pump with rotational speed of 3000 rpm and 100 kW, according to the formula, it can be estimated that the noise level at 1 m from the pump would be 92 dB. And suppose the noise source can be considered as point source on the ground (hemisphere propagation), the sound power level of the pump can be calculated using the following formula:
Where r is the distance from source to receiver
And in this case, the predicted Lw would be 100 dB.
Thirds, noise measurement to a similar equipment can also be an option to be able to determine the noise level of the new equipment. Another option, in some countries, there are noise emission limit for certain equipment, you can use that limit if it is applicable for your project.
After the Lw of all noise sources is obtained, we want to calculate the noise levels (the Lp) at the receivers. There are some standards which procedure can be followed to calculate this. Few of which are ISO 9613-2, NORD 2000, CNOSSOS EU, and many others. Most of the standards consider some factors to the calculation such as distance, atmospheric absorption, ground reflection, screening effect (from barriers and obstacles) and other factors such as volume absorption from vegetation, industrial site, etc. Most consultants and projects will require a software such as SoundPLAN to do this calculation.
Depending the project, there are few types of noise limit which compliance will need to be ensured. The most common ones are environmental noise limit, noise exposure limit, area noise limit and absolute noise limit. Besides, the noise level during emergency is also modelled so that the information can be used for safety and PAGA (Public Address and General Alarm) study.
Environmental noise limit is usually calculated for the plant’s contribution to the plant’s boundary as well as to the nearest sensitive receiver such as residential and school near the plant. How this is accessed depends on the regulation applicable on the plant area. In Indonesia for example, the noise limit for residential area is Lsm 55 dBA and industrial area is Lsm 70 dBA. Lsm is a measure like Ldn, but the night noise level addition is 5 dB instead of the 10 dB addition that most other countries, especially Europeans use. To ensure compliance with this regulation, the noise level at fence should be less than Lsm 70 dBA, and suppose there is a residential area nearby, the contribution from the site should be less than 55 dBA. It is also advisable to measure the existing noise level at the sensitive receivers to make the study more relevant to the situation.
Noise exposure limit is the maximum exposure to noise that the workers get during their working period. In Indonesia, the noise exposure limit is 85 dBA for 8 working hours. To change the working hours, 3 dB exchange rate is used. For example, if the noise level in the plant is 88 dBA, then the workers can only work there for 4 hours, if it is 91 dBA, then the time limit is 2 hours, and so on. To extend the working hours on a noisy area, the options are to actually reduce the noise level by reducing the noise emission from the source or noise control at transmission (for example using barrier), or by usage of Hearing Protection Device (HPD) for the workers such as ear plugs and ear muffs. The noise exposure of workers after usage of HPD can be calculated using the following formula:
Where NRR is the noise reduction rating of the HPD in dB.
Different area might have different noise level limits, and therefore area noise limits are useful. For example, in an unmanned mechanical room, the noise level can be high, for instance 110 dBA. However, inside of the site office, the allowable noise level is much lower, for example 50 dBA. This noise level shall be calculated to ensure compliance with the noise limit. Different companies might have different limits for this to ensure their employees’ health and productivity. If the area is indoor and the noise source is outdoor, then the interior noise level can be estimated using standards such as ISO 12354-3.
The absolute noise limit is the highest noise level allowable at the plant, and shall not be exceeded at any times, including emergency. In most cases, the absolute noise limit for impulsive sound is 140 dBA. To ensure compliance with this requirement, potential high-level noise shall be calculated, for example safety valves.
During emergency, different noise sources than normal situation will be activated, such as flare, blowdown valves, fire pumps, and other equipment. In such cases, the sound from the alarm and Public Address system must be able to be heard by the workers inside of the plant. Normally the target for the SPL from the PAGA system should be higher than 10 dB above the noise level. Therefore, the noise level during emergency in each area should be well-known.
The COVID-19 lockdown could become an unprecedented natural experiment in noise pollution. Some of the world’s most vocal animals — birds and whales — might already be benefiting from a quieter environment.
According to the World Health Organization (WHO), noise pollution affects over 100 million people across Europe and, in Western Europe alone, road traffic accounts for premature deaths equivalent to the loss of roughly “1.6 million healthy years of life.”
Take the disturbance to human health out of the equation, and noise remains a big source of pollution for the other inhabitants of the planet as well, namely, animals.
But how much have animals in countries on lockdown really benefited from the drop in noise levels? Turns out, that’s a very difficult question to answer.
Birds will benefit the most
Birds — by far the most visible animals found in cities, and the most vocal — stand to be among the biggest beneficiaries of quieter streets and parks.
The signals birds send each other through song is a means of survival. Without the ability to sing, hear and be heard, birds would have a difficult time finding a mate or defending their territory from predators.
Human activity influences bird behavior, even prompting them to communicate at less ‘busy’ times of day
The swift rise of human-made noise — also known as anthropogenic noise — over the past century has made this harder for birds.
Just like humans who have to speak up in a loud setting, birds, too, have to sing louder to communicate properly in today’s noisy world, according to ornithologist Henrik Brumm, who heads the research group for the communication and social behavior of birds at the Max Planck Institute for Ornithology near Munich.
“This happens really fast,” Brumm told DW. “We found out that it takes roughly 300 milliseconds, so less than 1 second, for birds to readjust when the level of noise rises. So, when their surroundings become louder, they sing louder, too.”
Are birds getting quieter? Maybe.
Birds are already known to sing more quietly in the early morning hours of the weekends, says Brumm. The reason: there’s less traffic to compete with.
With Europe on lockdown, Germany for its part, has seen passenger air travel slashed by over 90%. Moreover, car traffic has dropped by more than 50% and trains are running at less 25% their usual rates.
A recent study from the Max Planck Institute also suggests that chronic traffic noise can have a negative effect on embryo mortality and growth in zebra finches. This, in turn, could mean that the current lockdowns coinciding with mating season could lead to not only more, but also healthier hatchlings. That is, as long as their parents choose a spot that’s still safe from humans after the lockdown ends.
Though it’s difficult to speculate without real-time data, Brumm says, it stands to reason that the current period of quiet could mean birds might be singing more softly than usual, which would already be a huge benefit.
At land or sea, noise is bad news for animals
Birds aren’t the only animals that stand to benefit from less noise. According to a recent study published in the journal Biology Letters, noise pollution affects any number of creatures ranging from frogs, to shrimp, to fish, mammals, mussels and snakes.
In fact, another habitat garnering more and more attention for noise pollution is the ocean. As bioacoustics expert Christopher Clark described it in with Yale’s environmental magazine, the din from oil and gas activity, for example, is filling entire ocean basins with “one big storm of noise.”
While research on noise pollution and marine life, just like with ornithology, is in its early stages, a landmark study conducted in the days after 9/11 found that less shipping traffic seemed to make whales calmer.
Examining the feces of right whales — a species of baleen whale that can reach 15 meters in length and weigh up to 70 tons — researchers found that fewer ships in the waters along the US-Canadian coast correlated with lower stress hormones.
The noise levels from shipping traffic, whose 20–200 Hz hum disturbs sea life despite being a low frequency, decreased by 6 decibels, with a significant reduction below 150Hz .
An unprecedented time for researchers
Just like ornithologists, marine life researchers have also found correlations between noise and interruptions in behaviors like foraging and mating. Whales, like birds, also “mask.” That is to say, they sing louder to be heard over noise disturbances, be they high or low frequency sounds.
“It’s really a huge footprint that these activities have in the ocean,” according to Nathan Merchant, an expert on noise and bioacoustics at the UK’s Centre for Environment, Fisheries and Aquaculture Science (CEFAS).
And the sources of noise pollution — ranging from shipping, to wind farms, to the sequence of powerful blasts from seismic air gun tests used to locate oil and gas deposits in the ocean deep — are even harder to escape in the ocean than on land.
“It has a lot to do with how sound travels under water. Sound can travel much further and much faster than in air,” Merchant told DW.
Instruments off the coast of North America, for example, can detect seismic air gun testing as far away as the Brazilian coast.
With many cruises suspended, oil freighter traffic impacted by an oil price crash and rig activity being run by skeleton crews to curb the spread of COVID-19, marine biologists could potentially find a treasure trove of data once they’re allowed to go back into the field.
“We have underwater noise recorders at sea as we speak, but they aren’t cabled to land. So, we’ll find out when get out on a ship in several months’ time and get the data back,” Merchant said.
The more interesting question by that point might be how marine life responds to a sudden reintroduction of the human cacophony after an unexpected period of rest.
Binaural hearing allows for localizing the source of the sound, suppressing noise, example to better understand speech. To localize sound there is an important aspect of auditory perception that allows us to adjust to the room, namely spatial hearing. There are two processes in localizing sounds in humans, monaural cues and different cues.
Monaural cues are how each ear translates the captured sound signal. Monaural cues are the result of a convolution of sound sources with head-related transfer function (HRTF) impulses. Head-Related Transfer Function (HRTFs) is a form of transformation of sound wave propagation from the source to the ear or Head-Related Impulse Response (HRIR). HRTF is also defined as a form of modification of a sound from a certain direction that reaches the ear. This transformation involves diffraction and reflection from the anatomy of the ear. HRTF also depends on the location of the sound source relative to the listener so that it can determine the sound source.
Difference cues are how the difference between two ears translates to sound signals. These differences cues contain information on International Time Difference (ITD) and Interaural Level Difference (ILD). ITD is the difference in the arrival time of the left and right ear sound waves while ILD is the difference in pressure level between the left and right ears. Based on Duplex Theory, ITD values are used for localizing sounds at low frequencies, which is below 1.5 kHz while ILD is used for localizing sounds at high frequencies, which is above 1.5 kHz. Environmental sounds are in the range of low frequency and high frequency so that the human auditory system uses ITD and ILD.
The basic principles in ITD are illustrated in Figure 1
When the sound source is sound waves with low frequency, the propagation of sound waves will reach both ears without decreasing the sound pressure level. This is because the wavelength of sound is smaller than the dimensions of the head. However, there is a time difference received between the two ears. Therefore, sound waves at low frequencies are related to ITD.
The basic principles of ILD are illustrated in Figure 2. The ILD value is influenced by the size of the head and for sources that are very close to the head. When the sound source is in the high-frequency range where the wavelength of the sound is smaller than the dimensions of the head, the sound will reach the ears closer to the sound source. When will reach the other ear, the sound will be held up or there is a failure of propagation of sound waves for a while, this phenomenon is called an acoustic shadow. The sound that finally reaches the other ear will experience a decrease in the level of sound pressure caused by the phenomenon of acoustic shadow.
T. Potisk, “Head-Related Transfer Function,” 2015.
X. Zhong and B. Xie, “Head-Related Transfer Functions and Virtual Auditory Display,” Soundscape Semiot. – Localis. Categ., 2014
W. György, “HRTFs in Human Localization : Measurement , Spectral Evaluation and Practical Use in Virtual Audio Environment,” 2002.
K. Carlsson, “Objective Localisation Measures in Ambisonic Surround- sound,” 2004.
Doctors have used focused ultrasound to destroy tumors in the body without invasive surgery for some time. However, the therapeutic ultrasound used in clinics today indiscriminately damages cancer and healthy cells alike.
Most forms of ultrasound-based therapies either use high-intensity beams to heat and destroy cells or special contrast agents that are injected prior to ultrasound, which can shatter nearby cells. Heat can harm healthy cells as well as cancer cells, and contrast agents only work for a minority of tumors.
Researchers at the California Institute of Technology and City of Hope Beckman Research Institute have developed a low-intensity ultrasound approach that exploits the unique physical and structural properties of tumor cells to target them and provide a more selective, safer option. By scaling down the intensity and carefully tuning the frequency to match the target cells, the group was able to break apart several types of cancer cells without harming healthy blood cells.Their findings, reported in Applied Physics Letters, from AIP Publishing, are a new step in the emerging field called oncotripsy, the singling out and killing of cancer cells based on their physical properties.
“This project shows that ultrasound can be used to target cancer cells based on their mechanical properties,” said David Mittelstein, lead author on the paper. “This is an exciting proof of concept for a new kind of cancer therapy that doesn’t require the cancer to have unique molecular markers or to be located separately from healthy cells to be targeted.”
A solid mechanics lab at Caltech first developed the theory of oncotripsy, based on the idea that cells are vulnerable to ultrasound at specific frequencies — like how a trained singer can shatter a wine glass by singing a specific note.
The Caltech team found at certain frequencies, low-intensity ultrasound caused the cellular skeleton of cancer cells to break down, while nearby healthy cells were unscathed.
“Just by tuning the frequency of stimulation, we saw a dramatic difference in how cancer and healthy cells responded,” Mittelstein said. “There are many questions left to investigate about the precise mechanism, but our findings are very encouraging.”The researchers hope their work will inspire others to explore oncotripsy as a treatment that could one day be used alongside chemotherapy, immunotherapy, radiation and surgery. They plan to gain a better understanding of what specifically occurs in a cell impacted by this form of ultrasound.