The Significance of the Incident Sound Field on the Sound Transmission Loss of a Finite Panel

2005 ◽  
Vol 12 (4) ◽  
pp. 225-235 ◽  
Author(s):  
Jeremy W. Trevathan ◽  
John R. Pearse
Keyword(s):  
Plane Wave ◽  
Transmission Loss ◽  
Sound Transmission ◽  
Sound Field ◽  
Normal Incidence ◽  
Angle Of Incidence ◽  
Sound Transmission Loss ◽  
Wave Source ◽  
Integration Limit ◽  
Definition Of

Results are presented for the numerically predicted sound transmission loss of a finite panel excited by plane wave sources at various angles of incidence. It is shown that the limitation commonly imposed upon the integration of the ‘mass law’ is not arbitrary. Rather, it is the upper integration limit at which a function dependent on cos2 (the ‘mass law’), when integrated, becomes equal to a function dependent on cos (the method used in this study, the ISO 140 experimental method) which has been integrated from zero to 90 degrees. The current definition of sound transmission loss implicitly assumes that a plane wave sound source at normal incidence to the panel surface will produce the highest level of excitation in the panel, and as the angle of incidence is increased the panel will experience decreasing levels of excitation. However, it is shown here that the excitation experienced by a panel due to a plane wave source is almost independent of the angle of incidence.

An improved approach for normal-incidence sound transmission loss measurement using a four-microphone impedance tube

2020 ◽  
pp. 107754632092690
Author(s):  
Zechao Li ◽  
Sizhong Chen ◽  
Zhicheng Wu ◽  
Lin Yang
Keyword(s):  
Transfer Matrix ◽  
Sound Absorption ◽  
Transmission Loss ◽  
Sound Transmission ◽  
Normal Incidence ◽  
Sound Insulation ◽  
Sound Transmission Loss ◽  
The Common ◽  
Wavefield Decomposition ◽  
Insulation Performance

The main aim of this study is to introduce an improved method for determining the sound properties of acoustic materials which is more precise than the common wavefield decomposition method and simpler than the common transfer matrix method. In the first part of the article, a group of formulae for calculating sound transmission loss is represented by combining the wavefield decomposition and transfer matrix methods. Subsequently, a formula for calculating sound absorption coefficients is derived from these formulae by definition. Furthermore, the present formulae are validated by comparing the experimental results achieved with the present formulae and those results obtained by other methods recorded in published articles. Eventually, it is demonstrated that the method can accurately measure the sound insulation performance of materials and the sound absorption properties of limp and lightweight materials.

scholarly journals Normal Incidence of Sound Transmission Loss of a Double-Leaf Partition Inserted with a Microperforated Panel

2013 ◽  
Vol 2013 ◽  
pp. 1-8 ◽  
Author(s):  
A. Putra ◽  
A. Y. Ismail ◽  
R. Ramlan ◽  
Md. R. Ayob ◽  
M. S. Py
Keyword(s):  
Mathematical Model ◽  
Transmission Loss ◽  
Low Frequency ◽  
Sound Transmission ◽  
Normal Incidence ◽  
Sound Transmission Loss ◽  
Engineering Structures ◽  
Air Mass ◽  
Noise Barrier ◽  
The Mathematical Model

A double-leaf partition in engineering structures has been widely applied for its advantages, that is, in terms of its mechanical strength as well as its lightweight property. In noise control, the double-leaf also serves as an effective noise barrier. Unfortunately at low frequency, the sound transmission loss reduces significantly due to the coupling between the panels and the air between them. This paper studies the effect of a microperforated panel (MPP) inserted inside a double-leaf partition on the sound transmission loss performance of the system. The MPP insertion is proposed to provide a hygienic double-leaf noise insulator replacing the classical abrasive porous materials between the panels. It is found that the transmission loss improves at the troublesome mass-air-mass resonant frequency if the MPP is located closer to the solid panel. The mathematical model is derived for normal incidence of acoustic loading.

scholarly journals SOUND TRANSMISSION LOSS OF A DOUBLE-LEAF SOLID-MICROPERFORATED PARTITION UNDER NORMAL INCIDENCE OF ACOUSTIC LOADING

2011 ◽  
Vol 12 (3) ◽  
Author(s):  
Ahmad Yusuf Ismail
Keyword(s):  
Transmission Loss ◽  
Noise Source ◽  
Sound Transmission ◽  
Normal Incidence ◽  
Acoustic Excitation ◽  
Sound Transmission Loss ◽  
Low Frequencies ◽  
Vehicle Cabin ◽  
Preliminary Study ◽  
The Mathematical Model

The micro-perforated panel (MPP) is recently well-known as an alternative ‘green‘ sound absorber replacing the conventional porous materials. Constructed from a solid panel which provides a non-abrassive structure and also an optically attractive surface, there gives a feasibility to implement such a panel inside a vehicle cabin. This paper is the preliminary study to investigate the sound transmission loss (TL) of a solid panel coupled with a micro-perforated panel to form a doube-leaf partition which is already known as a lightweigth stucture for noise insulation in vehicles and buildings. The mathematical model for the TL subjected to normal incidence of acoustic excitation is derived. The results show that its performance substantially improves at the troublesome frequency of mass-air-mass resonance which occurs in the conventional double-leaf solid partition. This is important particularly for the noise source predominant at low frequencies. This can also be controlled by tuning the hole size and number as well as the air gap between the panels.  ABSTRAK: Panel bertebuk mikro (micro-perforated panel (MPP)) kebelakangan ini dikenali sebagai alternatif penyerap bunyi yang mesra alam menggantikan bahan berliang lazim. Dibina daripada satu panel padu yang memberikan satu struktur tak lelas dan juga satu permukaan yang menarik, ia memberikan kemungkinan penggunaan panel tersebut di dalam kabin kenderaan. Tesis ini merupakan kajian permulaan dalam mengkaji hilang pancaran bunyi (sound transmission loss (TL)) oleh satu panel padu yang digandingkan dengan satu panel bertebuk mikro. Kaedah ini menghasilkan satu sekatan lembar kembar yang sememangnya dikenali sebagai struktur ringan penebat bunyi di dalam kenderaan dan bangunan. Model matematik diterbitkan untuk TL tersebut dengan menjalankan pengujaan akustik yang tuju normal. Keputusan menunjukkan bahawa prestasi meningkat dengan ketara pada frekuensi yang susah semasa resonans jisim-udara-jisim berlaku di dalam sekatan padu lembar kembar  lazim. Ini penting terutamanya untuk sumber bunyi yang pradominan pada frekuensi rendah. Ia juga boleh dikawal dengan menalakan saiz dan jumlah lubang serta luang udara di antara panel-panel  tersebut.

Noise reduction of plenum window with add-in dual staggered sound scatterer arrays

2021 ◽  
Vol 263 (5) ◽  
pp. 1539-1547
Author(s):  
Xiaolong LI ◽  
Shiu Keung Tang ◽  
Shiu-Keung, Tang
Keyword(s):  
Noise Reduction ◽  
Transmission Loss ◽  
Computational Simulation ◽  
Sound Transmission ◽  
Sound Field ◽  
Model Space ◽  
Sound Transmission Loss ◽  
Sound Energy ◽  
Window System ◽  
Sonic Crystal

In present study, a 1:4 scaled down model was used to explore the noise reduction across the plenum window with add-in dual staggered scatterer arrays (sonic-crystal). Reverberation time inside the model space was measured firstly to eliminate the effect of the possible reverberation variation on the sound transmission loss of the plenum window. Two sonic-crystal arrays, the two-by-two and two-by-three scatterer arrangements, were adopted for measurement. A total of four arrays was thus tested after the staggering. Computational simulation was conducted for the sound field inside the plenum chamber to study the noise reduction mechanism of the present window system. Results show that the noise reduction of the plenum window was improved by varying degrees due to the placement of the dual staggered sonic-crystal. The Installation of the dual staggered sonic-crystal increased the sound energy reflections out of the plenum window inlet and decreased the sound energy that passed through the plenum window cavity. At the same time, the resonances inside the window cavity also contributed to the sound transmission loss of the plenum window. The noise reduction across the plenum window was enhanced. The improvement was between ~2 to ~2.7 dBA.

scholarly journals On the Frequency Up-Conversion Mechanism in Metamaterials-Inspired Vibro-Impact Structures

Acoustics ◽  
2019 ◽  
Vol 1 (1) ◽  
pp. 156-173 ◽  
Author(s):  
Anuj Rekhy ◽  
Robert Snyder ◽  
James Manimala
Keyword(s):  
Transmission Loss ◽  
Sound Transmission ◽  
Normal Incidence ◽  
Large Mass ◽  
Dominant Frequency ◽  
Energy Transfer Mechanism ◽  
Sound Transmission Loss ◽  
Low Frequencies ◽  
Limited Effectiveness ◽  
The Impact

Conventional acoustic absorbers like foams, fiberglass or liners are used commonly in structures for industrial, infrastructural, automotive and aerospace applications to mitigate noise. However, these have limited effectiveness for low-frequencies (LF, <~500 Hz) due to impractically large mass or volume requirements. LF content being less evanescent is a major contributor to environmental noise pollution and induces undesirable structural responses causing diminished efficiency, comfort, payload integrity and mission capabilities. There is, therefore a need to develop lightweight, compact, structurally-integrated solutions to mitigate LF noise in several applications. Inspired by metamaterials, tuned mass-loaded membranes as vibro-impact attachments on a baseline structure are considered to investigate their performance as an LF acoustic barrier. LF incident waves are up-converted via impact to higher modes in the baseline structure which may then be effectively mitigated using conventional means. Such Metamaterials-Inspired Vibro-Impact Structures (MIVIS) could be tuned to match the dominant frequency content of LF acoustic sources. Prototype MIVIS unit cells were designed and tested to study energy transfer mechanism via impact-induced frequency up-conversion and sound transmission loss. Structural acoustic simulations were done to predict responses using models based on normal incidence transmission loss tests. Simulations were validated using experiments and utilized to optimize the energy up-conversion mechanism using parametric studies. Up to 36 dB of sound transmission loss increase is observed at the anti-resonance frequency (326 Hz) within a tunable LF bandwidth of about 300 Hz for the MIVS under white noise excitation. Whereas, it is found that under monotonic excitations, the impact-induced up-conversion redistributes the incident LF monotone to the back plate’s first mode in the transmitted spectrum. This up-conversion could enable further broadband transmission loss via subsequent dissipation in conventional absorbers. Moreover, this approach while minimizing parasitic mass addition retains or could conceivably augment primary functionalities of the baseline structure. Successful transition to applications could enable new mission capabilities for aerospace and military vehicles and help create quieter built environments.

scholarly journals Normal Incidence of Sound Transmission Loss from Perforated Plates with Micro and Macro Size Holes

2014 ◽  
Vol 2014 ◽  
pp. 1-12 ◽  
Author(s):  
A. Putra ◽  
A. Y. Ismail
Keyword(s):  
Transmission Loss ◽  
Measurement Data ◽  
Sound Transmission ◽  
Normal Incidence ◽  
Hole Diameter ◽  
Sound Insulation ◽  
Sound Transmission Loss ◽  
Fluid Behavior ◽  
Micro Holes ◽  
Analytical Formulae

This paper studies the sound transmission loss of perforated panels and investigates the effect of the hole diameter on the sound insulation performance under normal incidence of acoustic loading. The hole diameters are distinguished into micro (submillimeter) and macro (millimeter) sizes. In general, the transmission loss reduces as the perforation ratio is increased. However, by retaining the perforation ratio, it is found that the transmission loss increases as the hole diameter is reduced for a perforate with micro holes due to the effect of resistive part in the hole impedance, which is contrary to the results for those with the macro holes. Both show similar trend at high frequency where the fluid behavior inside the hole is inertial. Simple analytical formulae for engineering purpose are provided. Validation of the models with measurement data also gives good agreement.

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