Destructive interference using sound waves can cancel out sound to create silence
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Multiple scientific sources confirm that destructive interference of sound waves, generated by introducing an out-of-phase wave of equal amplitude, is used to cancel or attenuate sound.
In this project, I tried to build a noise-cancellation system using DSK. Two microphones and one speaker were used in the system: the first microphone is to sample unexpected noises from the outside and the second microphone is to collect all the sounds, including both the desire sounds and unexpected noises. The second microphone detects and evaluates how well the noise cancelation works. I used Least Mean Square algorithm to implement Noise Cancellation system. The output of the adaptive filters in LMS algorithm would be phase shifted by 180 degrees and sent to a speaker to generate the anti-noise sound, which would cancel noises. Introduction This Noise Cancellation system is motivated to improve passengers’ comforts in the aircraft industry, such as Bose. There are a lot of noise source in an aircraft from its engine or the friction created between aircraft and air. Those noises can hurt passengers’ ears. As the one property of sound, sound can be destructed by inverting and adding it to the same sound. The result of inverting and adding sound is shown in Figure 1. But, this approach should have a perfect distance of microphone and speaker, or it can generate a greater noise if there is some time lag. In the worst case, noise can be twice larger than the original noise. Figure 1: A sound cancellation with destructive interference. A better method for noise cancellation system can be implemented by using adaptive filters. Adaptive filter is a filter that adjusts coefficients of its transfer function by itself, according to the optimization algorithm driven by an error signal. This method, which reduces undesired noises gradually, is called Active Noise Cancellation. Actually, there are two ways for noise cancellation: passive and active noise cancellation. Passive noise cancellation cancels noise with using some material, which can block the sound. Oppositely, active noise cancellation cancels noise, generating 180 degree phase shifted sound. The benefit of active noise cancellation is more efficient in low frequency and possible to block noise signal selectively. Most industries use both passive and active noise cancellation system to optimize the whole system. In this project, I used Least Mean Square algorithm, which is active noise cancellation algorithm and one of adaptive filters algorithm to reduce noise. This report will demonstrate the approaches that I use for this project. Background Usually, noises are random and have some characteristics of amplitude, phase, and speed of sound. To control this random noise well, the active noise control system should be used. Adaptive filter algorithm adjusts its internal filter coefficients to minimize error signals between unknown system and adaptive filter. The least-mean-squares algorithm is one of adaptive filters algorithm; the LMS algorithm and its relatives are all adaptive filtering algorithms. The basic block diagram is shown in Figure 2 and Figure 3. Figure 2: A block diagram of the whole system Figure 3: A block diagram of an adaptive filter part in x[n] is the input to the system y[n] is the output of the unknown system ŷ[n] is the output of the adaptive filter d[n] = y[n] + v[n] e[n] = d[n] − ŷ[n] μ is the “step size” or “learning rate” Definition of symbols LMS algorithm and collects noise H(z). It can be any desire signal. Ĥ(z), which has adaptive filter coefficients The basic performance of adaptive algorithm is to make Ĥ(z) as similar as the unknown system H(z) by the calculation of equations shown below. 1. Y(n) =H x X(n) for filtering 2. E(n)=D(n)-Y(n) for error estimation 3. H (n + 1) =H (n) + 2μ * E(n) x X(n) for updating filter coefficients As time goes on, the last equation, shown above, lets the adaptive filter coefficients will be updated to be the same as coefficients of the unknown filter. Therefore, the error between the unknown filter and adaptive filter will be minimized because those two filters get more similar as time goes on. Requirements The
As the virtual reality market has grown, implementing an optimized virtual environment has become more important. Three-dimensional audio rendering is a crucial aspect of virtual reality. External interference, such as acoustic noise, should be minimized to build a system where users can fully immerse themselves in the virtual world. Active noise cancellation allows users to analyze and process the noise in real time. Recently, audio signal processing methods that use deep learning have been widely studied. However, utilizing deep learning models at runtime can be challenging, thus requiring a suitable external simulation environment, including hardware accelerators. In this paper, we propose a Tcl-based active noise cancellation platform for the removal of three-dimensional noise components. This platform constructs a noise library using temporal convolutional networks and selects filter weights to remove various types of noise. The experimental results show that it is possible to construct a library with a minimum delay of 10ms and a size of 36 bytes. This allowed for real time noise cancellation with short delay time and low memory requirement. In addition, various noise environments were experimented with using FPGA, and it was demonstrated that the signal-to-noise ratio improved by an average of 3.8dB.
Monitoring the fetus during pregnancy is crucial for identifying factors that could adversely affect fetal health, preventing intrauterine deaths or causing permanent harm to the fetus. Diverse approaches including fetal electrocardiography (fECG), fetal phonocardiography (fPCG), fetal echocardiography (fECHO), fetal magnetocardiography (fMCG) and cardiotocography (CTG) utilizing Doppler ultrasound are utilized in the surveillance of fetal well-being. The fECG method has been employed for extracting fetal signals. However, proper signal processing is imperative during pregnancy due to contamination by maternal components and disturbances encompassing biological elements such as maternal and fetal movements, breathing, muscle activity, uterine contractions, and technical interferences like electrostatic potentials and network disruptions contribute to the overall noise. This study focuses on the technique of extracting fetal electrocardiogram (fECG) using Active Noise Cancellation (ANC). The application of destructive interference principles is used to isolate the fetal heart signal from surrounding maternal and environmental noise. An adaptive filter is designed using three prominent algorithms: the Gradient Descent method, the Least Mean Square (LMS) Algorithm, and the Normalized Least Mean Square (NLMS) algorithm. A MATLAB Graphical User Interface (GUI) is developed to implement these algorithms, allowing the variation of parameters such as filter length and learning rate for each algorithm. The GUI provides graphical visualization of the results, facilitating a comprehensive comparison of all three algorithms. The presented research contributes to enhancing the accuracy of fetal monitoring and signal extraction during pregnancy.
<h4>Objective</h4>Environmental noise poses a major barrier to the accuracy of self-administered hearing tests conducted outside clinical settings. There is a pressing need for effective noise control solutions to enable reliable hearing threshold measurements in everyday environments. This study introduces an optimized active noise cancellation (ANC) technique based on auditory masking characteristics.<h4>Method</h4>The method was implemented in a mobile hearing test system using calibrated true wireless Bluetooth earphones. Electroacoustic validation and clinical testing were conducted across four ANC scenarios: normal, generic ANC off, generic ANC on, and optimized ANC on in 65 dB(A) pink noise.<h4>Results</h4>A total of 50 participants completed hearing tests at eight frequencies (0.25-8 kHz), and results were compared to standard audiometry. The optimized ANC yielded the highest signal-to-noise ratio in noisy conditions and demonstrated strong agreement with standard hearing thresholds (r = 0.99, p <.01) in normal environments. Under 65 dB(A) noise, the proposed method significantly outperformed generic ANC with smaller hearing measurement error, improving threshold accuracy across most frequencies.<h4>Conclusion</h4>The proposed ANC technique enhances hearing test reliability in noisy conditions, supporting accurate, self-administered hearing assessments outside clinical settings. This technology has strong potential for home or community-based hearing healthcare applications.
Abstract : The objective of this project was to investigate global noise attenuation of narrow band fan noise in an air duct through the use of magnetic bearings. An axial flow fan creates tonal noise related to its rotational rate. Additional noise exists due to harmonics of this frequency as well as turbulent airflow. In addition to conventional brush bearings to support the fan shaft radially, this project used an active magnetic thrust bearing to control axial movement. The thrust bearing primarily functioned as an active sound control actuator. Active sound control is the method of achieving destructive interference of sound waves by outputting a secondary wave of equal amplitude and frequency, but 180 degrees out of phase with the primary wave. An error microphone was positioned in the duct to provide feedback to a Digital Signal Processor (DSP), which contained the active sound control program, while a performance microphone tested for global sound control at various points along the duct. Instead of using a secondary speaker, this project used the fan itself to collate the primary and secondary sound sources. Therefore, global sound control throughout the duct was theoretically possible. This project demonstrated this global control of noise experimentally.
"anti-phase destructive interference generator."[citation needed] The process duplicates the sound waves generated by the muzzle blast and then uses them to create
A silencer, also known as a sound suppressor, suppressor, or sound moderator, is a muzzle device that suppresses the blast created when a gun (firearm or airgun) is discharged, thereby reducing the acoustic intensity of the muzzle report (sound of a gunshot) and jump, by modulating the speed and pressure of the propellant gas released from the muzzle. Like other muzzle devices, a silencer can be a
In addition to containing and slowly releasing the gas pressure associated with muzzle blast or reducing pressure through the use of coolant mediums, advanced silencer designs attempt to modify the properties of the sound waves generated by the muzzle blast. In these designs, effects known as frequency shifting and phase cancellation (or destructive interference) are used in an attempt to make the suppressor quieter. These effects are achieved by separating the flow of gases and causing them to collide with one another or by venting them through precision-made holes. The intended effect of frequency shifting is to shift audible sound waves frequencies into ultrasound (above 20 kHz), beyond the range of human hearing. The Russian AN-94 assault rifle has a muzzle attachment that claims apparent noise reduction by venting some gases through a "dog-whistle" type channel. Phase cancellation occurs when similar sound waves encounter one another 180° out of phase, cancelling the amplitude of the wave and eliminating the pressure variations perceived as sound.
An alternate method under development is called an "anti-phase destructive interference generator." The process duplicates the sound waves generated by the muzzle blast and then uses them to create an anti-phase auditory signal. Currently, this is a muzzle attached device and is only being tested to cancel out the gunshot sound of the firearm. The devices tested incorporate multiple microphones, speakers, and an auditory processor. The first shot fired is recorded, and then played back precisely out of sync (180 degrees out of phase) with each subsequent shot. This has proven successful with small caliber (.17-.22) rifles, but the amplitude has not been matched efficiently with larger cartridges. With the use of subsonic ammunition, the resultant sound waves effectively cancel out one another, and with the exception of the sound of the action cycling, eliminate any gunshot sound. In the current development stage, this has worked only in close proximity to the shooter, and the pressure wave (p-wave) can still be felt. Each time a different type of ammunition or firearm is used, the device needs…
Ultrasound application has been reported to assist chemical processes as a result of various physiochemical effects during acoustic cavitation phenomena in a liquid. In this study, acoustic pressure distribution in ethanol solution induced by ultrasonic waves in a sonoreactor was investigated using COMSOL Multiphysics software. The variations of acoustic pressure distribution in ethanol liquid were investigated through a single-phase incompressible model developed by varying the frequency of an ultrasonic transducer. The simulation in COMSOL Multiphysics shows that the acoustic wave emitted from the bottom of the sonoreactor generated multiple layers of high acoustic pressure distribution. The fluctuating pressure magnitude along the sonoreactor shows that constructive interference produced high acoustic pressure region whereas destructive interference resulted in low acoustic pressure. Meanwhile, the distance over sound wave can travel before attenuation occurs is much further at 60 kHz. These results support the theory that wave attenuation is strongly frequency dependent.
dates to the early 20th century. In 1936, German physicist Paul Lueg patented a theoretical system for cancelling sound waves through destructive interference
Noise-cancelling headphones are headphones that reduce unwanted ambient sounds using active noise control (ANC), a technology that electronically minimizes external noise by generating sound waves that interfere destructively with incoming sounds. They are commonly used in environments with persistent background noise, including aircraft cabins, trains, offices, industrial workplaces, and urban en
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The main aim of our research is to design a Muffler for four stroke diesel engine. Muffler is a device which is used for reducing the amount of noise emitted by the exhaust of an internal combustion engine. In this research baffle arrangement are used to resist the flow of the exhaust from the engine. An exhaust pipe must be carefully designed to carry toxic and/or noxious gases away from the users of the machine .Indoor generators and furnaces can quickly fill an enclosed space with carbon monoxide or other poisonous exhaust gases if they are not properly vented to the outdoors. Also, the gases from most types of machine are very hot; the pipe must be heat resistant and it must not pass through or near anything that can burn or damaged by the heat. A chimney serves as an exhaust pipe in a stationary structure. For the internal combustion engine it is important to have the exhaust system “tuned” optimal efficiency. Mufflers are installed within the exhaust system of most internal combustion engines, although the muffler is not designed to serve any primary exhaust function. The muffler is engineered as an acoustic soundproofing device designed to reduce the loudness of the sound pressure created by the engine by way of acoustic quieting. The majority of the sound pressure produced by the engine is emanated out of the vehicle using the same piping used by the silent exhaust gases absorbed by a series of passages. And chambers lined with roving fibre glass insulation and/or res
Active noise control (ANC) is the application of the principle of the superposition of waves to noise attenuation problems. Much progress has been made toward applying ANC to narrow-band, low-frequency noise in confined spaces. During this same period, the application of ANC to broad-band noise or noise in three-dimensional spaces has seen little progress because of the recent quantification of serious physical limitations, most importantly, noncausality, stability, spatial mismatch, and the infinite gain controller requirement. ANC employs superposition to induce destructive interference to affect the attenuation of noise. ANC was believed to utilize the mechanism of phase cancellation to achieve the desired attenuation. However, current literature points to other mechanisms that may be operating in ANC. Categories of ANC are one-dimensional field and duct noise, enclosed spaces and interior noise, noise in three-dimensional spaces, and personal hearing protection. Development of active noise control stems from potential advantages in cost, size, and effectiveness. There are two approaches to ANC. In the first, the original sound is processed and injected back into the sound field in antiphase. The second approach is to synthesize a cancelling waveform. ANC of turbulent flow in pipes and ducts is the largest area in the field. Much work into the actual mechanism involved and the causal versus noncausal aspects of system controllers has been done. Fan and propeller noise can be divided into two categories: noise generated directly as the blade passing tones and noise generated as a result of blade tip turbulence inducing vibration in structures. Three-dimensional spaces present a noise environment where physical limitations are magnified and the infinite gain controller requirement is confronted. Personal hearing protection has been shown to be best suited to the control of periodic, low-frequency noise.
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