Sound absorptive light comprising nanofibrous resonant membrane applicable in room acoustics

2017 ◽  
Vol 39 (3) ◽  
pp. 362-370 ◽  
Author(s):  
Klara Kalinova
Keyword(s):  
Broad Band ◽  
Low Frequency ◽  
Acoustic Power ◽  
Acoustic Properties ◽  
Room Acoustics ◽  
Sound Waves ◽  
Final Thickness ◽  
Low Frequencies ◽  
Perforated Sheet ◽  
Lower Frequencies

Room acoustic solutions are based on measurements of the acoustic power of the room and acoustic elements with different functions (absorption tiles, absorption ceilings, absorption bodies, diffusers, barriers). This work is focused only on absorption elements with an emphasis on addressing lower-middle frequencies. The design of the material is based on broad band noise. Damping of lower frequencies is restricted to a certain extent by the final thickness of the acoustic material. Nanofibrous resonant membranes will be used in the design to achieve higher sound absorption at lower frequencies in comparison with commercially available materials. The principle of the acoustic system is to use combination of a perforated sheet covered by a nanofibrous resonant membrane, which is brought into forced vibration upon impact of sound waves of low frequency. Practical application:To absorb sounds of high frequencies, porous materials are used. To absorb sounds of low frequencies, resonant membranes are employed. However, these structures absorb only sounds of certain frequency. Nanofibrous layers have unique acoustic properties due to the large specific surface area of the nanofibres, where viscous losses may occur, and also the ability to resonate at its own frequency. The advantage of this technology is the space between the acoustic element with a thickness of 1–2 mm and the wall/ceiling, which can be used for the installation of lighting/audio speakers, etc. The acoustic light prototype has been made.

A nanofibrous acoustic system based on the cavity/membrane resonance principle

2016 ◽  
Vol 88 (6) ◽  
pp. 644-653 ◽  
Author(s):  
Klara Kalinova
Keyword(s):  
Sound Absorption ◽  
Perforated Plate ◽  
Cavity Resonator ◽  
Acoustic Power ◽  
Broadband Noise ◽  
Sound Waves ◽  
Acoustic System ◽  
Optimal Arrangement ◽  
Final Thickness ◽  
Lower Frequencies

Room acoustic solutions are based on measurements of the acoustic power of the room and acoustic elements with different functions (absorption tiles, absorption ceilings, absorption bodies, diffusers, barriers). This work is focused only on absorption elements, with an emphasis on addressing lower frequencies. The goal of this research is achieved by sound absorbing means which contains a cavity resonator with a nanofibrous resonant membrane, which overlaps orifices of the cavity resonator. The design of the material is based on broadband noise. Absorption of lower frequencies is restricted to a certain extent by the final thickness of the acoustic material. A two-microphone impedance tube for determining the sound absorption coefficient was used to measure the limited frequency spectrum 100–1600 Hz. These frequencies, however, cover the area particularly focusing on middle and lower frequencies. The principle of the acoustic system consists in using combination of a cavity resonator, by which the air or other material contained in its cavities is forced into vibration upon impact of sound waves of high frequency, and a nanofibrous resonant membrane, which is forced into vibration upon impact of sound waves of low frequency. The optimal arrangement of holes inside the perforated plate, according to broadband sound absorption, has been found.

scholarly journals Low frequency sound field reconstruction in a non-rectangular room using a small number of microphones

Acta Acustica ◽  
2020 ◽  
Vol 4 (2) ◽  
pp. 5 ◽  
Author(s):  
Thach Pham Vu ◽  
Hervé Lissek
Keyword(s):  
Low Frequency ◽  
Sound Field ◽  
Acoustic Properties ◽  
Room Acoustics ◽  
Low Frequencies ◽  
Reverberation Chamber ◽  
Sound Fields ◽  
Accurate Knowledge ◽  
Sound Field Reconstruction ◽  
Rectangular Room

An accurate knowledge of the sound field distribution inside a room is required to identify and optimally locate corrective measures for room acoustics. However, the spatial recovery of the sound field would result in an impractically high number of microphones in the room. Fortunately, at low frequencies, the possibility to rely on a sparse description of sound fields can help reduce the total number of measurement points without affecting the accuracy of the reconstruction. In this paper, the use of Greedy algorithm and Global curve-fitting techniques are proposed, in order to first recover the modal parameters of the room, and then to reconstruct the entire enclosed sound field at low frequencies, using a reasonably low set of measurements. First, numerical investigations are conducted on a non-rectangular room configuration, with different acoustic properties, in order to analyze various aspects of the reconstruction frameworks such as accuracy and robustness. The model is then validated with an experimental study in an actual reverberation chamber. The study yields promising results in which the enclosed sound field can be faithfully reconstructed using a practically feasible number of microphones, even in complex-shaped and damped rooms.

Fiber Metal Acoustic Material for Gas Turbine Exhaust Environments

1989 ◽  
Vol 111 (1) ◽  
pp. 181-185
Author(s):  
M. S. Beaton
Keyword(s):  
Gas Turbine ◽  
Power Unit ◽  
Broad Band ◽  
Acoustic Energy ◽  
Acoustic Properties ◽  
Roll Forming ◽  
Sound Waves ◽  
Auxiliary Power Unit ◽  
Auxiliary Power ◽  
Fiber Metal

FELTMETAL® fiber metal acoustic materials function as broad band acoustic absorbers. Their acoustic energy absorbance occurs through viscous flow losses as sound waves pass through the tortuous pore structure of the material. A new FELTMETAL® fiber metal acoustic material has been designed for use in gas turbine auxiliary power unit exhaust environments without supplemental cooling. The physical and acoustic properties of FM 827 are discussed. Exposure tests were conducted under conditions that simulated auxiliary power unit operation. Weight gain and tensile strength data as a function of time of exposure at 650°C (1202°F) are reported. Fabrication of components with fiber metal acoustic materials is easily accomplished using standard roll forming and gas tungsten arc welding practices.

The Use of Optimally Shaped Piezo-electric Film Sensors in the Active Control of Free Field Structural Radiation, Part 2: Feedback Control

1996 ◽  
Vol 118 (1) ◽  
pp. 112-121 ◽  
Author(s):  
S. D. Snyder ◽  
N. Tanaka ◽  
Y. Kikushima
Keyword(s):  
Feedback Control ◽  
Control Strategies ◽  
Free Field ◽  
Low Frequency ◽  
Acoustic Power ◽  
State Equations ◽  
Subsequent Increase ◽  
Low Frequencies ◽  
Control Approach ◽  
Iir Filters

Feedback control of free field structural radiation is considered. State equations are formulated with a transformation which decouples the acoustic power error criterion. Using the resultant equations, expressed in terms of “transformed mode” states, the order of the state equations can be significantly reduced at low frequencies. Two experimental implementations of feedback control strategies using shaped piezoelectric polymer film sensors to measure the transformed system states are described. The first of these is a simple analog implementation. The second implementation is in discrete time, where an adaptive algorithm for optimizing the weights of IIR filters for practical use is described. It is shown that by using the outlined control approach significant levels of low frequency acoustic power attenuation can be obtained with no control spillover and subsequent increase in higher frequency acoustic power output.

Research on local resonance and Bragg scattering coexistence in phononic crystal

2017 ◽  
Vol 31 (11) ◽  
pp. 1750127 ◽  
Author(s):  
Yake Dong ◽  
Hong Yao ◽  
Jun Du ◽  
Jingbo Zhao ◽  
Jiulong Jiang
Keyword(s):  
Band Gap ◽  
Mass Density ◽  
Resonance Effect ◽  
Phononic Crystal ◽  
Broad Band ◽  
Low Frequency ◽  
Bragg Scattering ◽  
Low Frequencies ◽  
Local Resonance ◽  
Resonance Band

Based on the finite element method (FEM), characteristics of the local resonance band gap and the Bragg scattering band gap of two periodically-distributed vibrator structures are studied. Conditions of original anti-resonance generation are theoretically derived. The original anti-resonance effect leads to localization of vibration. Factors which influence original anti-resonance band gap are analyzed. The band gap width and the mass ratio between two vibrators are closely correlated to each other. Results show that the original anti-resonance band gap has few influencing factors. In the locally resonant structure, the Bragg scattering band gap is found. The mass density of the elastic medium and the elasticity modulus have an important impact on the Bragg band gap. The coexistence of the two mechanisms makes the band gap larger. The band gap covered 90% of the low frequencies below 2000 Hz. All in all, the research could provide references for studying the low-frequency and broad band gap of phononic crystal.

Receptivity to free-stream vorticity of flow past a flat plate with elliptic leading edge

2010 ◽  
Vol 653 ◽  
pp. 245-271 ◽  
Author(s):  
L.-U. SCHRADER ◽  
L. BRANDT ◽  
C. MAVRIPLIS ◽  
D. S. HENNINGSON
Keyword(s):  
Boundary Layer ◽  
Flat Plate ◽  
Free Stream ◽  
Three Dimensional ◽  
Low Frequency ◽  
Leading Edge ◽  
Sound Waves ◽  
Streamwise Vorticity ◽  
Low Frequencies ◽  
Free Stream Turbulence

Receptivity of the two-dimensional boundary layer on a flat plate with elliptic leading edge is studied by numerical simulation. Vortical perturbations in the oncoming free stream are considered, impinging on two leading edges with different aspect ratio to identify the effect of bluntness. The relevance of the three vorticity components of natural free-stream turbulence is illuminated by considering axial, vertical and spanwise vorticity separately at different angular frequencies. The boundary layer is most receptive to zero-frequency axial vorticity, triggering a streaky pattern of alternating positive and negative streamwise disturbance velocity. This is in line with earlier numerical studies on non-modal growth of elongated structures in the Blasius boundary layer. We find that the effect of leading-edge bluntness is insignificant for axial free-stream vortices alone. On the other hand, vertical free-stream vorticity is also able to excite non-modal instability in particular at zero and low frequencies. This mechanism relies on the generation of streamwise vorticity through stretching and tilting of the vertical vortex columns at the leading edge and is significantly stronger when the leading edge is blunt. It can thus be concluded that the non-modal boundary-layer response to a free-stream turbulence field with three-dimensional vorticity is enhanced in the presence of a blunt leading edge. At high frequencies of the disturbances the boundary layer becomes receptive to spanwise free-stream vorticity, triggering Tollmien–Schlichting (T-S) modes and receptivity increases with leading-edge bluntness. The receptivity coefficients to free-stream vortices are found to be about 15% of those to sound waves reported in the literature. For the boundary layers and free-stream perturbations considered, the amplitude of the T-S waves remains small compared with the low-frequency streak amplitudes.

Near-field observations and source parameters of central California earthquakes

1974 ◽  
Vol 64 (6) ◽  
pp. 1855-1886 ◽  
Author(s):  
Lane R. Johnson ◽  
Thomas V. McEvilly
Keyword(s):  
San Andreas Fault ◽  
Strong Dependence ◽  
Source Parameters ◽  
Broad Band ◽  
Low Frequency ◽  
Corner Frequency ◽  
Fault Plane Solutions ◽  
Low Frequencies ◽  
Central California ◽  
San Andreas

abstract This is a study of source characteristics of 13 earthquakes with magnitudes between 2.4 and 5.1 located near the San Andreas fault in central California. On the basis of hypocentral locations and fault-plane solutions the earthquakes separate into two source groups, one group clearly related to the throughgoing northwest-trending San Andreas fault zone and the other apparently associated with generally north-trending bifurcations such as the Calaveras fault. The basic data consist of broad-band recordings (0.03 to 10 Hz) of these earthquakes at two sites of the San Andreas Geophysical Observatory (SAGO). Epicentral distances range between 2 and 40 km, and maximum ground displacements from 4 to 4000 microns were recorded. The whole-record spectra computed from the seismograms lend themselves to source parameter studies in that they can be interpreted in terms of low-frequency level, corner frequency, and high-frequency slope. Synthetic seismograms have also been used to estimate source parameters in both the time domain and frequency domain, and the results compare favorably with those estimated directly from the spectra. The influences of tilts and nonlinear response of the seismometer were considered in the interpretation of the low frequencies. Seismic source moments estimated from the low-frequency levels of the spectra show a linear dependence on magnitude with a slope slightly greater than 1. The geology at the recording site can contribute an uncertainty factor of at least 3 to the estimated moments. Observed corner frequencies are only weakly dependent on magnitude. Interpreted in terms of source dimension, these corner frequencies imply values of 1 to 2 km for the earthquakes of this study. The corner frequencies may also be interpreted in terms of the rise time source function, yielding values in the range 0.5 to 1.0 sec. The data indicate that the earthquakes of this study are all surprisingly similar in their fundamental source parameters, with only the seismic moment showing a strong dependence on magnitude.

Dynamic Mechanical Properties of Cross-Linked Rubbers. II. Effects of Crosslink Spacing and Initial Molecular Weight in Polybutadiene

1966 ◽  
Vol 39 (4) ◽  
pp. 905-914
Author(s):  
Etsuji Maekawa ◽  
Ralph G. Mancke ◽  
John D. Ferry
Keyword(s):  
Molecular Weight ◽  
Crosslink Density ◽  
Low Frequency ◽  
Dynamic Mechanical Properties ◽  
Cross Linking ◽  
Loss Mechanism ◽  
Low Frequencies ◽  
Molecular Weights ◽  
Monomeric Friction Coefficient ◽  
Lower Frequencies

Abstract The complex shear compliances of eight samples of polybutadiene crosslinked by cumyl peroxide and four samples crosslinked by sulfur have been measured over a frequency range from 0.2 to 2 cps at temperatures from − 6 to 45° C by a torsion pendulum. On four of the samples, measurements were extended by the Fitzgerald transducer from 45 to 600 cps at temperatures from − 71 to 55°. The vulcanizates had been prepared from polymers of two different molecular weights (180,000 and 510,000) with sharp molecular weight distribution; the physical crosslink density ranged from 0.57 to 2.68×10−4 mole/cm3, and the chemical crosslink density calculated following Kraus ranged from 0.22 to 1.49×10−4 mole/cm3. The mechanical data were all reduced to T0=298° K by shift factors calculated from the equation log aT=−3.64(T−T0)/(186.5+T−T0). In the transition zone of frequencies, the viscoelastic functions of the cumyl peroxide vulcanizates were closely similar, except for a shift toward lower frequencies with increasing crosslinking, corresponding to a small but unexpected increase in the monomeric friction coefficient. Cross-linking by sulfur caused a somewhat larger shift toward lower frequencies at a comparable crosslink density. In the rubbery zone, the sample with least cross-linking exhibited a substantial secondary loss mechanism at very low frequencies. The low-frequency losses are evident in all the samples, but their magnitude falls rapidly with increasing crosslink density as previously found for natural rubber. It also falls somewhat with increasing initial molecular weight, indicating a contribution from network strands with loose ends. The possible relation of the low-frequency losses to trapped entanglements is discussed.

3D printed multifunctional, load-bearing, low-frequency sound absorbers

2021 ◽  
Vol 263 (1) ◽  
pp. 5605-5610
Author(s):  
William Johnston ◽  
Pulitha Godakawela Kankanamalage ◽  
Bhisham Sharma
Keyword(s):  
Mechanical Performance ◽  
Low Frequency ◽  
Normal Incidence ◽  
Acoustic Properties ◽  
Low Frequencies ◽  
Load Bearing ◽  
Fibrous Network ◽  
Size Limitation ◽  
Porous Architecture ◽  
3D Printed

Cellular porous materials are an attractive choice for lightweight structural design. However, though their open porous architecture is ideally suited for multifunctional applications, their use is typically limited by the pore sizes achievable by traditional as well as advanced fabrication processes. Here, we present an alternative route towards overcoming this pore size limitation by leveraging our recent success in printing fibrous structures. This is achieved by superimposing a fibrous network on a load-bearing, open-celled porous architecture. The multifunctional structure is 3D printed using a novel technique that enables us to simultaneously print a load-bearing scaffold and the necessary fibrous network. The acoustic properties of the printed structures are tested using a normal-incidence impedance tube method. Our results show that such structures can provide very high absorption at low frequencies while retaining the mechanical performance of the underlying architected structure.

Study of the Acoustic Properties of Lighting Systems Based on Hollow Mirrored Tubular Light Guides

2021 ◽  
pp. 32-38
Author(s):  
Sergei Yu. Pleshkov ◽  
Gennaro Bracale ◽  
Alexander L. Kuznetsov
Keyword(s):  
High Frequency ◽  
High Reliability ◽  
Low Frequency ◽  
Scientific Work ◽  
Acoustic Properties ◽  
Sound Waves ◽  
Natural Lighting ◽  
Lighting Systems ◽  
Pass Through ◽  
Light Guides

This scientific work presents test results of energy efficient lighting systems based on mirrored hollow tubular light guides when sound waves of various intensities of low-frequency, mid-frequency and high-frequency ranges pass through them. Technological changes in design of natural lighting systems, which were carried out in order to increase their vibration resistance and noise absorption, are shown here. Studies have proved high reliability of lighting systems in terms of their soundproofing, especially in mid-frequency and high-frequency ranges, which can significantly reduce harmful effects of noise on human body.

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