Sound absorption performance of various nickel foam-base multi-layer structures in range of low frequency

Commercial3D reticular nickel foam and its composite structure were investigated on the sound absorption at200-2000Hz.The absorption performance of foam plates1?5layers(1-layer thickness:2.3mm;porosity:89%;average pore-diameter:0.57mm)was found to be poor,and could be improved by adding backed cavum or front perforated thin sheet.The absorption coefficient could reach about0.4at1000-1600Hz for the composite structure of5-layer foam with a backed5mm-thick cavum,and even0.68at about1000Hz for that of2-layer foam with the same cavum and a perforated plate closely in front of the foam.

Low frequency acoustic properties of bilayer membrane acoustic metamaterial with magnetic oscillator

A bilayer membrane acoustic metamaterial was proposed to overcome the influence of the mass law on traditional acoustic materials and obtain a lightweight thin-layer structure that can effectively isolate low frequency noise. The finite element analysis（FEA） results agree well with the experimental results.It is proved that the sound transmission losses（STLs） of the proposed structures are higher than those of same surface density acoustic materials. The introduction of the magnetic mass block is different from the traditional design method, in which only a passive mass block is fixed on the membrane. The magnetic force will cause tension in the membrane, increase membrane prestress, and improve overall structural stiffness. The effects of the geometry size on the STLs are discussed in detail. The kind of method presented in this paper can provide a new means for engineering noise control.

Sound absorption of several various nickel foam multilayer structures at aural frequencies sensitive for human ears

Using the three-dimensional reticular nickel foam as experimental material, the sound absorption performance was investigated for several various multilayer structures in the frequency range of 2000-4000 Hz, which is aurally sensitive for human ears. The results showed that the 7.5 mm-thick foam sample, which was formed by piling of 5-layer foam plate（thickness： 1.5 mm; porosity： 96%; average pore-diameter： 0.65 mm） could exhibit an excellent sound absorption effect at 4000 Hz, with the absorption coefficient about 0.8. Constituting alternate air gap with the total thickness of about 18.5 mm can greatly improve the absorption performance at relatively low frequencies of 2000-3150 Hz, with the absorption coefficient up to about 0.5 or more. In addition, the research showed that alternate piling up the perforated plate inside the foam plates can also achieve a quite good effect of sound absorption at relatively low frequencies.

Sound absorption characteristic of micro-helix metamaterial by 3D printing

We present the design of micro-helix metamaterial supporting high sound absorption characteristic by 3D printing. The sample structure which is fabricated out of polylactide （PLA） material, many micro-helix are arranged by periodic arrays on XY plane. Experiment measurement results show that different geometrical dimensions of helix vestibule and cavity depth have a great effect on sound absorption coefficient. Physical mechanism depends on the friction and viscosity between the air and the helix vestibule. This work shows great potential of micro-structure metamaterial in noise control applications require light weight and large rigid of sound absorption.

Neurodynamics analysis of cochlear hair cell activity

There have been many studies on the effect of cochlea basal membrane movement on the resolution of different frequencies and intensities.However,these studies did not take into account the influence of power and energy consumption of the hair cells in the process of the electromotility movement,as well as the neurodynamic mechanism that produced this effect.This makes previous studies unable to fully clarify the function of outer hair cells(OHCs)and the mechanism of sound amplification.To this end,we introduce the gate conductance characteristics of the hair cells in the mechanical process of increasing frequency selectivity.The research finds that the low attenuation of OHCs membrane potential and the high gain in OHC power and energy consumption caused that OHC amplification is driven by electromotility.The research results show that the amplification of the OHCs is driven by low attenuation of membrane potential and high gain of power and energy consumption.This conclusion profoundly reveals the physiological mechanism of the electromotility movement.

Cochlear and Vestibular Functional Study in Patients with Sudden Deafness and Lyme Disease

Lyme disease (LD) and idiopathic sudden deafness (ISD) are supposed to be different diseases with different aetiologies. In an attempt to confirm this assumption, 10 patients with confirmed LD and 12 patients with ISD were consecutively included into the study. Further to the laboratory and audio logical investigation, a low frequency sound (LFS) stimulation on posturography was performed and evaluated. Patients with ISD had higher pure tone average (PTA) than patients with LD (PTA ISD/LD was 72 decibel (dB)/23 dB). There was no difference of vertigo between LD and ISD patients. Patients with ISD have more body sway velocity during the first stimulation than patients with LD. We conclude that the cochlear organ is more affected in ISD patients than in patients with LD. However, the vestibular organ seems to be affected in both diseases. ISD and LD are two different disease entities with different aetiologies but with common otological clinical signs.

Acoustic transfer function of cavity and its application to rapid evaluation of sound field at low frequency band

A new method to obtain numerical solution of Acoustic Transfer Function (ATF) by BEM is presented. For a simply supported panel backed by a rectangular cavity at low frequency band (0-200 Hz), the frequency property of ATF is analyzed. The relation between the accuracy of the rapid evaluation of sound field and the discretization schemes of the vibrational panel is discussed. The result shows that the method to obtain ATF and the rapid evaluation of sound field using the ATF is suitable to low frequency band. If an appropriate discretization scheme is choosed based on the frequency involved and the effort to obtain ATF, the accuracy of the rapid evaluation of sound field is acceptable.

DISCREPANCY IN SOUND POWER DETERMINATION AT LOW FREQUENCIES

The determination of the sound power of a source is simple in a reverberation chamber , but usually lower valves are obtained at low frequencies than the free - space value . It is shown that the sound power determined in a reverberation chamber depends not only on its free - space power , but also on the positions of the source and the reveiver , as well as the way the measurements are made and averaged . Exact and statistical formulas are derived to account for these factors . The results explain the discrepancy and agree well with earlier experiments . Based on the theory ,parcticable techniques of sound power determination are proposed and correct power formulas presented .