Noise Control of a Chamber Core Cylinder Using Cylindrical Helmholtz Resonators

2003 ◽  
Author(s):  
Deyu Li ◽  
Jeffrey S. Vipperman
Keyword(s):  
Resonant Frequency ◽  
Noise Level ◽  
Noise Control ◽  
Low Frequencies ◽  
Optimal Position ◽  
Cylindrical Structure ◽  
Helmholtz Resonators ◽  
Resonator Design ◽  
Frequency Calculation ◽  
Cavity Resonances

Previous investigations have determined that the noise transmission into a finite cylindrical structure at low frequencies is dominated by the cavity resonances. Therefore, noise control at the first several cavity resonances for a Chamber Core cylinder can significantly reduce the noise level at low frequencies inside the cylinder. This work explores the feasibility of noise control for the Chamber Core cylinder using cylindrical Helmholtz resonators. The targeted frequencies are the first four cavity resonances. Detailed considerations of the resonant frequency calculation, resonator design, and experimental verification are presented. The effects on the noise reduction spectrum of two closely spaced resonators are experimentally studied. The optimal position of the resonators is also discussed. The noise control results indicate that the Helmholtz resonators can significantly attenuate the noise level at the targeted frequency bands.

scholarly journals Development of acoustic metamaterials for efficient sound control noise mitigation

2021 ◽  
Author(s):  
◽  
Huy Nguyen
Keyword(s):  
Fano Resonance ◽  
High Performance ◽  
Noise Control ◽  
Single Layer ◽  
Acoustic Metamaterials ◽  
Noise Mitigation ◽  
Short Channel ◽  
Low Frequencies ◽  
Helmholtz Resonators ◽  
Unit Cells

Acoustic metamaterials have been studied intensively recently since they can expose unnatural-born properties, potentially breaking the capacity limits of conventional acoustic materials. Since these interesting properties are mostly observed around metamaterials' local resonances/anti-resonance, resonance-based acoustic metamaterials are most popular in developing metamaterials. Employing resonance-based unnatural born properties such as effective negative mass density, effective negative bulk modulus, and acoustic hyper-damping on designing noise control solutions can give excellent devices showing such high performance that conventional acoustic material cannot achieve. This dissertation is an effort to employ acoustic metamaterials in designing efficient noise control. First, membrane-type acoustic metamaterials (MAM) will be employed to design a lightweight acoustic panel with high sound transmission loss (STL) in broadband at low frequencies. Negative density at around the anti-resonance of MAM gives it high capability on blocking sound. A double MAM-layer structure is proposed to double the STL performance of unit cells theoretically. Therein, simulation by using COMSOL Multiphysics is the main tool to optimize the unit cell design, panel structure, and effect of panel frame's vibration. Fabrication of the optimal design and experiments are also conducted to verify the calculation and simulation predictions. In addition to the acoustic panel, MAM is used to design a highly efficient acoustic energy harvester working at low frequencies. A magnet coin is deployed close to a magnet coil attached to the mass of MAM. The maximum oscillation of the coil due to MAM's first local resonance will induce a strong electric current inside the coil. Hence, energy can be harvested by an external resistor representing loads of harvesting devices. A complete theoretical model of the harvester is also developed in order to optimize its performance. Multiphysics simulation is conducted to verify the theoretical predictions. Besides MAM, Helmholtz has been used to design a high-performance and broadband acoustic silencer. Specifically, five slit-type Helmholtz resonators, which possess a massive viscous area, are packed together to create a single-layer silencer. In turn, two single-layer silencers are combined to form a double-layer silencer, which in theory double performance on noise blocking of the single-layer silencer. Theoretical models of slit-type Helmholtz resonators and silencers are developed completely and well validated with simulation and experimental results. Finally, Fano resonance resulting from the coupling between resonant and non-resonant channels will be explored and employed to design an ultra-broadband acoustic barrier with high ventilation. The resonant channel is generally represented a space-coiling channel, and the non-resonant channel represents ventilation or a straight and short channel. First, the formation of coupling Fano resonance will be theoretically addressed. Subsequently, acoustic hyper-damping is proposed by integrating thin acoustic foams into velocity anti-nodes in the resonant channel. In the end, an ultra-broadband acoustic barrier with high ventilation and STL is designed by employing three rows of hyper-dampened unit cells. Fabrication and experiment also are conducted to verify the simulation prediction.

Multi-tonal low frequency noise control using Helmholtz resonators with complex cavity designs for aircraft cabin noise improvement

2021 ◽  
Vol 263 (2) ◽  
pp. 3975-3986
Author(s):  
Tenon Charly Kone ◽  
Sebastian Ghinet ◽  
Raymond Panneton ◽  
Thomas Dupont ◽  
Anant Grewal
Keyword(s):  
Noise Control ◽  
Transmission Loss ◽  
Low Frequency ◽  
Helmholtz Resonator ◽  
Sound Insulation ◽  
Frequency Noise ◽  
Low Frequency Noise ◽  
Low Frequencies ◽  
Helmholtz Resonators ◽  
Resonance Frequencies

The noise control at multiple tonal frequencies simultaneously, in the low frequency range, is a challenge for aerospace, ground transportation and building industries. In the past few decades, various low frequency noise control solutions based on acoustic metamaterial designs have been presented in the literature. These solutions showed promising performance and are considered a better alternative to conventional sound insulation materials. In the present investigation, it was noticed that subdividing the cavity of a Helmholtz resonator allowed the control of multi-tonal noise at several resonance frequencies simultaneously and a shift of the resonance peaks towards the low frequencies. This paper proposes concepts of Helmholtz resonators with subdivided cavities to improve the sound transmission loss (STL) performance and simultaneously control the noise at several tonal frequencies. HRs with cylindrical shaped cavities were embedded in a layer of porous material. The STL of the metamaterial noise insulation configuration was predicted using serial and parallel assemblies of transfer matrices (TMM) incorporating a thermo-viscous-acoustic approach to accurately account for the viscous and thermal losses of acoustic wave propagation within the metamaterial. The STL calculated using the proposed TMM approach were observed to be in excellent agreement with the finite element method (FEM) numerical results.

Noise control of outdoor unit of split type air-conditioner using periodic scatterers made with array of Helmholtz resonators

2021 ◽  
Vol 179 ◽  
pp. 108054
Author(s):  
J. Dandsena ◽  
K. Mohapatra ◽  
A.K. Satapathy ◽  
D.P. Jena
Keyword(s):  
Noise Control ◽  
Air Conditioner ◽  
Helmholtz Resonators

scholarly journals THE PECULIARITIES OF THE SOUND FIELD ENERGY DECAY IN A ROOM WITH THE USE OF DIFFERENT PULSED SOUND SOURCES/GARSO LAUKO ENERGIJOS SLOPIMO PATALPOJE YPATUMAI, NAUDOJANT SKIRTINGUS IMPULSINIUS GARSO ŠALTINIUS

1999 ◽  
Vol 5 (2) ◽  
pp. 135-140
Author(s):  
Vytautas Stauskis
Keyword(s):  
Noise Level ◽  
Sound Field ◽  
Maximum Energy ◽  
Reverberation Time ◽  
Frequency Range ◽  
Sound Sources ◽  
Low Frequencies ◽  
High Frequencies ◽  
The Difference ◽  
Field Decay

The paper deals with the differences between the energy created by four different pulsed sound sources, ie a sound gun, a start gun, a toy gun, and a hunting gun. A knowledge of the differences between the maximum energy and the minimum energy, or the signal-noise ratio, is necessary to correctly calculate the frequency dependence of reverberation time. It has been established by investigations that the maximum energy excited by the sound gun is within the frequency range of 250 to 2000 Hz. It decreases by about 28 dB at the low frequencies. The character of change in the energy created by the hunting gun differs from that of the sound gun. There is no change in the maximum energy within the frequency range of 63–100 Hz, whereas afterwards it increases with the increase in frequency but only to the limit of 2000 Hz. In the frequency range of 63–500 Hz, the energy excited by the hunting gun is lower by 15–30 dB than that of the sound gun. As frequency increases the difference is reduced and amounts to 5–10 dB. The maximum energy of the start gun is lower by 4–5 dB than that of the hunting gun in the frequency range of up to 1000 Hz, while afterwards the difference is insignificant. In the frequency range of 125–250 Hz, the maximum energy generated by the sound gun exceeds that generated by the hunting gun by 20 dB, that by the start gun by 25 dB, and that by the toy gun—by as much as 35 dB. The maximum energy emitted by it occupies a wide frequency range of 250 to 2000 Hz. Thus, the sound gun has an advantage over the other three sound sources from the point of view of maximum energy. Up until 500 Hz the character of change in the direct sound energy is similar for all types of sources. The maximum energy of direct sound is also created by the sound gun and it increases along with frequency, the maximum values being reached at 500 Hz and 1000 Hz. The maximum energy of the hunting gun in the frequency range of 125—500 Hz is lower by about 20 dB than that of the sound gun, while the maximum energy of the toy gun is lower by about 25 dB. The maximum of the direct sound energy generated by the hunting gun, the start gun and the toy gun is found at high frequencies, ie at 1000 Hz and 2000 Hz, while the sound gun generates the maximum energy at 500 Hz and 1000 Hz. Thus, the best results are obtained when the energy is emitted by the sound gun. When the sound field is generated by the sound gun, the difference between the maximum energy and the noise level is about 35 dB at 63 Hz, while the use of the hunting gun reduces the difference to about 20–22 dB. The start gun emits only small quantities of low frequencies and is not suitable for room's acoustical analysis at 63 Hz. At the frequency of 80 Hz, the difference between the maximum energy and the noise level makes up about 50 dB, when the sound field is generated by the sound gun, and about 27 dB, when it is generated by the hunting gun. When the start gun is used, the difference between the maximum signal and the noise level is as small as 20 dB, which is not sufficient to make a reverberation time analysis correctly. At the frequency of 100 Hz, the difference of about 55 dB between the maximum energy and the noise level is only achieved by the sound gun. The hunting gun, the start gun and the toy gun create the decrease of about 25 dB, which is not sufficient for the calculation of the reverberation time. At the frequency of 125 Hz, a sufficiently large difference in the sound field decay amounting to about 40 dB is created by the sound gun, the hunting gun and the start gun, though the character of the sound field curve decay of the latter is different from the former two. At 250 Hz, the sound gun produces a field decay difference of almost 60 dB, the hunting gun almost 50 dB, the start gun almost 40 dB, and the toy gun about 45 dB. At 500 Hz, the sound field decay is sufficient when any of the four sound sources is used. The energy difference created by the sound gun is as large as 70 dB, by the hunting gun 50 dB, by the start gun 52 dB, and by the toy gun 48 dB. Such energy differences are sufficient for the analysis of acoustic indicators. At the high frequencies of 1000 to 4000 Hz, all the four sound sources used, even the toy gun, produce a good difference of the sound field decay and in all cases it is possible to analyse the reverberation process at varied intervals of the sound level decay.

scholarly journals Acoustic notch filtering earmuff utilizing Helmholtz resonator arrays

PLoS ONE ◽  
2021 ◽  
Vol 16 (10) ◽  
pp. e0258842
Author(s):  
Fumiya Mizukoshi ◽  
Hidetoshi Takahashi
Keyword(s):  
Resonant Frequency ◽  
Noise Control ◽  
Active Noise Control ◽  
Low Frequency ◽  
Helmholtz Resonator ◽  
Honeycomb Structure ◽  
Sound Insulation ◽  
Frequency Noise ◽  
Target Frequency ◽  
Notch Filtering

In recent years, noisy bustling environments have created situations in which earmuffs must soundproof only specific noise while transmitting significant sounds, such as voices, for work safety and efficiency. Two sound insulation technologies have been utilized: passive noise control (PNC) and active noise control (ANC). However, PNC is incapable of insulating selective frequencies of noise, and ANC is limited to low-frequency sounds. Thus, it has been difficult for traditional earmuffs to cancel out only high-frequency noise that people feel uncomfortable hearing. Here, we propose an acoustic notch filtering earmuff utilizing Helmholtz resonator (HR) arrays that provides a sound attenuation effect around the tuneable resonant frequency. A sheet-like sound insulating plate comprising HR arrays is realized in a honeycomb structure. Since the resonant frequency is determined by the geometry of the HR arrays, a highly audible sound region can be designed as the target frequency. In this research, the acoustic notch filtering performance of the proposed HR array plate is investigated in both simulations and experiments. Furthermore, the fabricated earmuffs using the novel HR array plates achieve a sound insulation performance exceeding 40 dB at the target frequency, which is sufficiently high compared to that of conventional earmuffs. The experimental results confirm that the proposed device is a useful approach for insulating frequency-selective sound.

Using noise control principles when evaluating the acoustic impacts of face coverings during the coronavirus pandemic

2021 ◽  
Vol 263 (3) ◽  
pp. 3554-3561
Author(s):  
Richard Ruhala ◽  
Laura Ruhala
Keyword(s):  
Classroom Environment ◽  
Noise Control ◽  
Experimental Tests ◽  
Analytical Models ◽  
Octave Band ◽  
Interference Level ◽  
Cavity Resonances ◽  
The Face ◽  
Clear Plastic ◽  
Stiffness And Damping

Several different combinations of face masks and shields are evaluated for their acoustic performance using a head and torso simulator (HATS). The HATS is used as a controlled and repeatable artificial sound source using white noise in a classroom environment. Sound pressure levels at octave band frequencies due to the face coverings are evaluated at a location of 2.0 meters from the HATS which is within the direct field to reduce the room acoustical effects. The problem is modeled as a barrier separating a source and receiver using fundamental noise control principles. Fabric material properties are used such as thickness, density, stiffness, and damping. The results are compared with experimental tests. The face shield with clear plastic barrier produces a resonance in the 1000 Hz octave band. Analytical models of cavity resonances, standing wave resonances, or plate resonances are calculated and compared with the experimental resonance. The speech interference level is used to determine the frequency content that is most likely to cause hearing difficulties and compared with A-weighted differences between the unmasked condition and masked.

Measurement of total respiratory impedance in calves by the forced oscillation technique

1988 ◽  
Vol 64 (5) ◽  
pp. 1786-1791 ◽  
Author(s):  
P. Gustin ◽  
A. R. Dhem ◽  
F. Lomba ◽  
P. Lekeux ◽  
K. P. Van de Woestijne ◽  
...  
Keyword(s):  
Resonant Frequency ◽  
Fourier Analysis ◽  
Respiratory System ◽  
Pressure Wave ◽  
Forced Oscillation ◽  
Forced Oscillation Technique ◽  
Respiratory Impedance ◽  
Upper Airways ◽  
Low Frequencies ◽  
Spontaneously Breathing

We have determined the resistance (Rrs) and the reactance (Xrs) of the total respiratory system in unsedated spontaneously breathing calves at various frequencies. A pseudorandom noise pressure wave was produced at the nostrils of the animals by means of a loudspeaker adapted to the nose by a tightly fitting mask. A Fourier analysis of the pressure in the nostrils and flow signals yielded mean Rrs and Xrs, over 16 s, at frequencies of 2–26 Hz. A good correlation was found between values of pulmonary resistances measured by the isovolume method at the respiratory frequency of animals and values obtained at a frequency of 6 Hz by use of our technique. The linearity of the respiratory system, the reproducibility of the technique, and the effects of upper airways on results have been studied. In healthy calves, Rrs increases with frequency. Mean resonant frequency is 7.5 Hz. Bronchospasm was induced in six calves by administration of intravenous organophosphates. Rrs tended to decrease with increasing frequency. Resonant frequency exceeded 26 Hz. All parameters returned to initial values after administration of atropine. In healthy calves, atropine produces a decrease in Rrs, especially at low frequencies. Values of resonant frequency are not modified.

Phase Reversal Barriers for Better Noise Control at Low Frequencies: Laboratory Versus Field Measurements

1987 ◽  
Vol 28 (1) ◽  
pp. 16 ◽  
Author(s):  
Maurice Amram ◽  
Vick J. Chvojka ◽  
Laurent Droin
Keyword(s):  
Noise Control ◽  
Field Measurements ◽  
Low Frequencies ◽  
Phase Reversal
Sign in / Sign up

Export Citation Format

Share Document