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.
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.
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.
Mountain bicycle (MTB) is one the most favorite vehicles in the globe. MTB comfort, in consequence, has then become a challenge issue to the manufacturers since MTB nowadays is not only being used for sports and exercises, but also for daily activities. One of the simplest methods to assess vehicle comfort is by evaluating their vibration level. Thus, this paper presents an experimental assessment on the road transmitted vibration on a MTB through a field test subjected to different road surface conditions and tire sizes. The result shows that the cycling comfort is significantly affected by the road roughness condition and tire size. As the road is rougher, higher force excitation is generated to the bike which is then generating higher vibration. Similarly, as the contact area between the tire and the road is increased, bike vibration is also significantly increased.
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