Department of Aerospace Engineering, The Pennsylvania State University, University Park, PA, 16802, United States
Popular version of 2aNSa3 – Multirotor broadband noise modulation
Presented at the 186th ASA Meeting
Read the abstract at https://doi.org/10.1121/10.0026987
–The research described in this Acoustics Lay Language Paper may not have yet been peer reviewed–
Picture yourself strolling through a quiet park. Suddenly, you are interrupted by the “buzz” of a multirotor drone. You ask yourself: why does this sound so annoying? Research demonstrates that a significant source is the time variation of broadband noise levels over a rotor revolution. These noise fluctuations have been found to be important for how we perceive sound. This research has found that these sound variations are significantly affected by the blade angle offsets (azimuthal phasing) between different rotors. This demonstrates the potential for synchronizing the rotors to reduce noise: a concept that has been studied extensively for tonal noise, but not broadband noise.
Sound consists of air pressure fluctuations. One major source of sound generated by rotors consists of the random air pressure fluctuations of turbulence, which encompass a wide range of frequencies. Accordingly, this sound is called broadband noise. A common example and model of broadband noise is white noise, shown in Figure 1, where the random nature characteristic of broadband noise is evident. Despite this randomness, we hear the noise of Figure 1 as having a nearly constant sound level.
Figure 1: White noise with a nearly constant sound level.
A better model of rotor noise is white noise with amplitude modulation (AM). Amplitude modulation is caused by the blades’ rotation: sound levels are louder when the blade moves towards the listener, and quieter when the blade moves away. This is called Doppler amplification, and is analogous to the Doppler effect that shifts sound frequency when a sound source travels towards or away from you. AM white noise is shown in Figure 2: the sound is still random, but has a sinusoidal “envelope” with a modulation frequency corresponding to the blade passage frequency. AM causes time-varying sound levels, as shown in Figure 3. This time variation is characterized by the modulation depth, the peak-to-trough amplitude in decibels (dB), as shown in Figure 3. A greater value for modulation depth typically corresponds to the noise sounding more annoying.
Figure 2: White noise with amplitude modulation (AM).
Figure 3: Time-varying sound levels of AM white noise.
Broadband noise modulation is known to be important for wind turbines, whose “swishing” is found to be annoying even at low sound levels. This contrasts with white noise, which is typically considered soothing when it has a constant sound level (i.e., no AM). This exemplifies the importance of considering time variation of sound levels for capturing human perception of sound. More recently, the importance of broadband noise modulation has been demonstrated for helicopters, as this chopping noise is what makes a helicopter sound like a realistic helicopter, even if it has low sound levels.
Researchers have not extensively studied broadband noise modulation for aircraft with many rotors. Computational studies in the literature predict that summing the broadband noise modulation of many rotors causes “destructive interference”, resulting in nearly no modulation. However, flight test measurements of a six-rotor drone showed that broadband noise modulation was significant. To investigate this discrepancy, changes in modulation depth were studied as the blade angle offset between rotors was varied. This offset is typically not considered in noise predictions and experiments. The results are shown in Figure 4. For each data point in Figure 4, the rotor rotation speeds are synchronized, but the value for the constant blade angle offset between rotors is different. The results of Figure 4 demonstrate the potential for synchronizing rotors to reduce broadband noise modulation. This synchronization controls the blade angle offset between rotors to be as constant as possible, and has been extensively studied for controlling tones (sounds at a single frequency), but not broadband noise modulation.
Figure 4: Modulation depth as a function of blade angle offset between two synchronized rotors.
If the rotors are not synchronized, which is typically the case, the flight controller continuously varies the rotors’ rotation speeds to stabilize or maneuver the drone. This causes the blade angle offsets between rotors to with vary with time, which in turn causes the summed noise to vary between different points in Figure 4. Measurements showed that all rotor blade angle offsets are equally likely (i.e., azimuthal phasing follows a uniform probability distribution). Therefore, multirotor broadband noise modulation can be characterized and predicted by constructing a plot like Figure 4, by adding copies of the broadband noise modulation of a single rotor.
École de technologie supérieure, Université du Québec, Montréal, Québec, H3C 1K3, Canada
Rachel Bouserhal, Valentin Pintat & Alexis Pinsonnault-Skvarenina
École de technologie supérieure, Université du Québec
Popular version of 1pNSb12 – Immersive Auditory Awareness: A Smart Earphones Platform for Education on Noise-Induced Hearing Risks
Presented at the 186th ASA Meeting
Read the abstract at https://doi.org/10.1121/10.0026825
–The research described in this Acoustics Lay Language Paper may not have yet been peer reviewed–
Ever thought about how your hearing might change in the future based on how much and how loudly you listen to music through earphones? And how would knowing this affect your music listening habits? We developed a tool called InteracSon, which is a digital earpiece you can wear to help you better understand the risks of losing your hearing from listening to loud music trough earphones.
In this interactive platform, you can first select your favourite song, and play it through a pair of earphones at your preferred listening volume. After providing InteracSon with the amount of time you usually spend listening to music, it calculates the “Age of Your Ears”. This tells you how much your ears have aged due to your music listening habits. So even if you’re, say, 25 years old, your ears might be like they’re 45 years old because of all that loud music!
Picture of the “InteracSon” platform during calibration on an acoustic manikin. Photo by V. Pintat, ÉTS/ CC BY
To really demonstrate what this means, InteracSon provides you with an immersive experience of what it’s like to have hearing loss. It has a mode where you can still hear what’s going on around you, but it filters sounds based on what your ears might be like with hearing loss. You can also hear what tinnitus, a ringing in the ears, sounds like, which is a common problem for people who listen to music too loudly. You can even listen to your favorite song again, but this time it would be altered to simulate your predicted hearing loss.
With more than 60% of adolescents listening to their music at unsafe levels, and nearly 50% of them reporting hearing-related problems, InteracSon is a powerful tool to teach them about the adverse effects of noise exposure on hearing and to promote awareness about how to prevent hearing loss.
Institute for Hearing Technology and Acoustics
RWTH Aachen University
Aachen, Northrhine-Westfalia 52064
Germany
– Christian Dreier (lead author, LinkedIn: Christian Dreier)
– Rouben Rehman
– Josep Llorca-Bofí (LinkedIn: Josep Llorca Bofí, X: @Josepllorcabofi, Instagram: @josep.llorca.bofi)
– Jonas Heck (LinkedIn: Jonas Heck)
– Michael Vorländer (LinkedIn: Michael Vorländer)
Popular version of 3aAAb9 – Perceptual study on combined real-time traffic sound auralization and visualization
Presented at the 186th ASA Meeting
Read the abstract at https://doi.org/10.1121/10.0027232
–The research described in this Acoustics Lay Language Paper may not have yet been peer reviewed–
“One man’s noise is another man’s signal”. This famous quote by Edward Ng from a 1990’s New York Times article breaks down a major learning from noise research. A rule of thumb within noise research states the community response to noise, when asked for “annoyance” ratings, is said to be statistically explained only to one third by acoustic factors (like the well-known A-weighted sound pressure level, which can be found on household devices as “dB(A)” information). Referring to Ng’s quote, another third is explained by non-acoustic, personal or social variables, whereas the last third cannot be explained according to the current state of research.
Noise reduction in built urban environments is an important goal for urban planners, as noise is not only a cause of cardio-vascular diseases, but also affects learning and work performance in schools and offices. To achieve this goal, a number of solutions are available, ranging from switching to electrified public transport, speed limits, traffic flow management or masking of annoyant noise by pleasant noise, for example fountains.
In our research, we develop a tool for making the sound of virtual urban scenery audible and visible. From its visual appearance, the result is comparable to a computer game, with the difference that the acoustic simulation is physics-based, a technique that is called auralization. The research software “Virtual Acoustics” simulates the entire physical “history” of a sound wave for producing an audible scene. Therefore, the sonic characteristics of traffic sound sources (cars, motorcycles, aircraft) are modeled, the sound wave’s interaction with different materials at building and ground surfaces are calculated, and human hearing is considered.
You might have recognized a lightning strike sounding dull when being far away and bright when being close, respectively. The same applies for aircraft sound too. In an according study, we auralized the sound of an aircraft for different weather conditions. A 360° video compares how the same aircraft typically sounds during summer, autumn and winter when the acoustical changes due to the weather conditions are considered (use headphones for full experience!)
In another work we prepared a freely available project template for using Virtual Acoustics. Therefore, we acoustically and graphically modeled the IHTApark, that is located next to the Institute for Hearing Technology and Acoustics (IHTA): https://www.openstreetmap.org/#map=18/50.78070/6.06680.
In our latest experiment, we focused on the perception of especially annoyant traffic sound events. Therefore, we presented the traffic situations by using virtual reality headsets and asked the participants to assess them. How (un)pleasant would be the drone for you during a walk in the IHTApark?
Dick Botteldooren and Paul Devos
Ghent University
Technology Campus, iGent, Technologiepark 126
Gent, Gent 9052
Belgium
Popular version of 2aNSb7 – Soundscape Augmentation for People with Dementia Requires Accounting for Disease-Induced Changes in Auditory Scene Analysis
Presented at the 186th ASA Meeting
Read the abstract at https://doi.org/10.1121/10.0026999
–The research described in this Acoustics Lay Language Paper may not have yet been peer reviewed–
Sensory stimuli are significant in guiding us through space and making us aware of time. Sound plays an essential role in this awareness. Soundscape is an acoustic environment as perceived and experienced by a person. A well-designed soundscape can make the experience pleasant and improve moods; in contrast, an unfamiliar and chaotic soundscape can increase anxiety and stress. We aim to discuss different auditory symptoms of dementia and introduce ways to design an augmented soundscape to foster individual auditory needs.
People with dementia suffer from a neurodegenerative disorder that leads to a progressive decline in cognitive health. Behavioural and psychological symptoms of dementia refer to a group of noncognitive behaviours that affect the prediction and control of dementia. Reducing the occurrence of these symptoms is one of the main goals of dementia care. Environmental intervention is the best nonpharmacological treatment to improve the behaviour of people with dementia.
People with severe dementia usually live in nursing homes, long-term care facilities, or memory care units where sensory perception is unfamiliar. Strange sensory stimuli add to residents’ anxiety and distress, as care facilities are often not customized based on individual needs. Studies show that incorporating pleasant sounds into the environment, known as an ‘augmented soundscape,’ positively impacts behaviour and reduces the psychological syndrome of dementia. Sound augmentation can also help a person navigate through space and identify the time of the day. By implementing sound augmentation as part of the design, we can enhance mood, reduce apathy, lower anxiety and stress, and promote health. People with dementia experience changes in perception, including misperceptions, misidentifications, hallucinations, delusions, and time-shifting. Sound augmentation can support a better understanding of the environment and help with daily navigation. In the previous study by the research team, implementing soundscape in nursing homes and dementia care units showed a promising result in reducing the psychological symptoms of dementia.
It’s crucial to recognize that dementia is not a singular entity but a complex spectrum of degenerative diseases. For example, environmental sound agnosia—the difficulty in understanding non-speech environmental sounds—is common in some with frontotemporal dementia. Therefore, sound augmentation should be focused on non-complicated sounds. Amusia, another type of dementia, is when a person cannot recognize music; thus, playing music is not recommended for this group.
Each type of dementia presents with its unique set of symptoms, including a variety of auditory manifestations. These can range from auditory hallucinations and disorientation to heightened sound sensitivity, agnosia for environmental sounds, auditory agnosia, amusia, and musicophilia. Understanding these diverse syndromes of auditory perception is critical when designing a soundscape augmentation for individuals with dementia.
Swedish National Road and Transport Research Institute (VTI), Linkoping, -, SE-58195, Sweden
Popular version of 1pNSb9 – Acoustic labelling of tires, road vehicles and road pavements: A vision for substantially improved procedures
Presented at the 185th ASA Meeting
Read the abstract at https://doi.org/10.1121/10.0022814
Please keep in mind that the research described in this Lay Language Paper may not have yet been peer reviewed.
Not many vehicle owners know that they can contribute to reducing traffic noise by making an informed choice of their tires, while not sacrificing safety or economy. At least you can do so in Europe, where there is a regulation requiring tires be labelled with noise level (among others). But it has substantial flaws for which we propose solutions by applying state-of-the-art and innovative solutions.
It is here where consumer labels come in. In most parts of the world, we have consumer labels including noise levels on household appliances, lawn mowers, printers, etc. But when it comes to vehicles, tires, and road pavements, a noise label on the product is rare. So far, it is mandatory only on tires sold in the European Union, and it took a lot of efforts of noise researchers to get it accepted along with the more “popular” labels for energy (rolling resistance), and wet grip (skid resistance). Figure 1 shows and explains the European label.
Figure 1: The present European tire label, which must be attached to all tires sold in the European Union, here supplemented by explanations.
Why so much focus on tires? Figure 2 illustrates how much of the noise energy that comes from European car tires compared to the “propulsion noise”; i.e. noise from engine, exhaust, transmission, and fans. For speeds above 50 km/h (31 mph) over 80 % of the noise comes from tires. For trucks and busses, the picture is similar although above 50 km/h it may be 50-80 % from the tires. For electric powered vehicles, of course, the tires are almost entirely dominating as a noise source at all speeds. Thus, already now but even more in the future, consumer choices favouring lower noise tires will have an impact on traffic noise exposure. To achieve this progress, tire labels including noise are needed, and they must be fair and discriminate between the quiet and the noisy.
Figure 2: Distribution of tire/road vs propulsion noise. Calculated for typical traffic with 8 % heavy vehicles in Switzerland [Heutschi et al., 2018].
The EU label is a good start, but there are some problems. When we have purchased tires and made noise measurements on them (in A-weighted dB), there is almost no correlation between the noise labels and our measured dB levels. To identify the cause of the problem and suggest improvements, the European Road Administrations (CEDR) funded a project named STEER (Strengthening the Effect of quieter tyres on European Roads), also supplemented by a supporting project by the Swedish Road Administration. STEER found that there were two severe problems in the noise measuring procedure: (1) the test track pavement defined in an ISO standard showed rather large variations from test site to test site, and (2) in many cases only the noisiest tires were measured, and all other tires of the same type (“family”) were labelled with the same value although they could be up to 6 dB quieter. Such “families” may include over 100 different dimensions, as well as load and speed ratings. Consequently, the full potential of the labelling system is far from being used.
The author’s presentation at Acoustics 2023 will deal with the noise labelling problem and suggest in more detail how the measurement procedures may be made much more reproducible and representative. This includes using special reference tires for calibrating test track surfaces, production of such test track surfaces by additive manufacturing (3D printing) from digitally described originals, and calculating the noise levels by digital simulations, modelling, and using AI. Most if not all the noise measurements can go indoors, see an existing facility in Figure 3, to be conducted in laboratories that have large steel drums. Also in such a case a drum surface made by 3D printing is needed.
Figure 3: Laboratory drum facility for measurement of both rolling resistance and noise emission of tires (both for cars and trucks). Note the microphones. The tire is loaded and rolled against one of the three surfaces on the drum. Photo from the Gdansk University of Technology, courtesy of Dr P Mioduszewski.
Kent L. Gee – kentgee@byu.edu
Twitter (x): @KentLGee
Instagram: @gee.kent
Brigham Young University, Provo, UT, 84602, United States
Logan T. Mathews, Bradley McLaughlin, Mark C. Anderson (@AerospaceMark), Grant W. Hart
Brigham Young University, Utah, USA
@BYU_PASCAL
@BYUAcoustics
Daniel Edgington-Mitchell
Monash University, Victoria, Australia
@MonashUni
Popular version of 5PNSa1 – Rocket noise: What does it mean for Australian spaceports?
Presented at the 185th ASA Meeting
Read the abstract at https://doi.org/10.1121/10.0023749
Please keep in mind that the research described in this Lay Language Paper may not have yet been peer reviewed.
The global space industry is rapidly expanding. Rockets are being launched from a greater number of spaceports and a recent exponential increase in annual global orbital launches (Figure 1) has surpassed numbers seen during the 1960s’ Space Race. While about 75% of rockets are currently launched from the United States and the People’s Republic of China, an increasing number of countries are tapping into a global space launch services market projected to reach USD 33.4 billion in 2028. The Australian Space Agency was created in 2018 to support the growth of Australia’s space industry and the use of space across the broader economy. Australia is well-situated for launching payloads to a variety of orbits and multiple spaceports are being constructed or planned.
Figure 1. Global orbital launches by year.
The power generated by rockets during liftoff and ascent generates lots of noise, which can cause possibly damaging vibration of the payload, rocket, and launchpad structures. Farther away, the noise may have short and long-term impacts on communities and the environment, although these impacts are at present poorly understood.
Rocket noise is generated by the high-speed turbulent exhaust plume mixing with the outside air. Although less than 1% of the plume’s mechanical power is turned into sound during liftoff, even a small orbital rocket creates several times more sound power than a military jet aircraft at afterburner. The most powerful orbital rocket, NASA’s Space Launch System (SLS), generates sound power equal to nearly 900 T-7A aircraft.
Near-term, orbital rockets that will launch from Australian spaceports are relatively small. From U.S.-based Phantom Space’s Daytona rocket to Gilmour Space Technologies’ Australian-built Eris rocket, these vehicles will have a much smaller noise footprint than SLS or SpaceX’s oft-launched rocket, the Falcon 9 (see Fig. 2.) However, peak noise levels within several meters of these rockets will still exceed 180 dB and maximum sound levels tens of kilometers away will be above typical background noise, particularly at low frequencies. For example, Figure 3 is a maximum sound level map from a small rocket launched to the east over the Great Barrier Reef. Maximum launch levels along portions of the reef are predicted to be 70-75 dB, not including the ascent sonic boom, which can be significantly louder.
Figure 2. Near-term orbital launch vehicles to be launched from Australia are significantly smaller than the well-known Falcon 9.
Figure 3. RUMBLE-predicted maximum sound level footprint over the Great Barrier Reef for a small orbital rocket launch from the Bowen Orbital Spaceport.
Will launches from Australian soil create damaging vibrations or harmful environmental noise impacts? That is a complex question that depends on vehicle size and design, launch cadence, distance to structures, habitats, and communities, weather patterns, and other factors. Continued study of the multiple facets of generation, propagation, and reception of rocket noise will help find answers and improve our access to space, from Australia and worldwide.
Figure 1: White noise with a nearly constant sound level.
Figure 1: White noise with a nearly constant sound level.
Figure 2: White noise with amplitude modulation (AM).
Figure 2: White noise with amplitude modulation (AM).
Figure 3: Time-varying sound levels of AM white noise.
Figure 3: Time-varying sound levels of AM white noise.
Figure 4: Modulation depth as a function of blade angle offset between two synchronized rotors.
Figure 4: Modulation depth as a function of blade angle offset between two synchronized rotors.
Picture of the “InteracSon” platform during calibration on an acoustic manikin. Photo by V. Pintat, ÉTS/ CC BY
Figure 1: The present European tire label, which must be attached to all tires sold in the European Union, here supplemented by explanations.
Figure 2: Distribution of tire/road vs propulsion noise. Calculated for typical traffic with 8 % heavy vehicles in Switzerland [Heutschi et al., 2018].
Figure 3: Laboratory drum facility for measurement of both rolling resistance and noise emission of tires (both for cars and trucks). Note the microphones. The tire is loaded and rolled against one of the three surfaces on the drum. Photo from the Gdansk University of Technology, courtesy of Dr P Mioduszewski.
Figure 1. Global orbital launches by year.
Figure 2. Near-term orbital launch vehicles to be launched from Australia are significantly smaller than the well-known Falcon 9.
Figure 3. RUMBLE-predicted maximum sound level footprint over the Great Barrier Reef for a small orbital rocket launch from the Bowen Orbital Spaceport.