กลไกที่มีการสำรวจเพิ่มเติมได้โดยใช้การวิเคราะห์องค์ประกอบ จำกัด mechanism was further explored using the finite element analysis for explaining the
สำหรับการอธิบายปฏิสัมพันธ์กลไฟฟ้าและผลกระทบของพวกเขาในการดูดซับเสียงทรัพย์สินelectro-mechanical interactions and their effect on the sound absorbing property.
2 รูปแบบ 2. DEAA model and measurement system
และระบบการวัดการวัดอะคูสติกได้ดำเนินการในท่อสี่เหลี่ยมที่มีภาคตัดขวางของThe acoustic measurement was conducted in a rectangle duct with a cross section of
160 รูปที่ ลำโพงมีการติดตั้งที่ปลายด้านหนึ่งของท่อและทำหน้าที่เป็นแหล่งกำเนิดเสียงที่จะสร้างคลื่นซายน์หรือเสียงสีขาว โช้ค กับโพรงหลังปิดผนึกมีการติดตั้งที่เป็นศูนย์กลางของท่อส่วนการทำงาน ดังแสดงในรูป 1, ควบคู่กับโพรงหลัง ความลึกของช่องคือ 160 mm 160 mm. Figure 1 shows the experimental setup. A loudspeaker is installed
at one end of the duct and acts as the sound source to generate sinusoidal wave or
white noise. The DE absorber with a sealed back cavity is installed at the centre of the
duct working section. As shown in Fig. 1, a duct silencer consists of a DE membrane
coupled with a back cavity. The depth of the cavity is 160 mm. The dimensions of the
DE membrane are 160 mm 135 mm. In order to avoid the wrinkle phenomenon, the
circular conductive electrode covers 25% of the whole DE membrane surface. Four
printed circuit board (PCB) array microphones of model 130E20 (PCB Piezotronics)
are used for measuring the sound pressure inside the duct. These microphones are
referred to as “Mic.1,” “Mic.2,” “Mic.3,” and “Mic.4.” A two-load method is used to
measure the transmission loss (TL) of the duct silencer;22 one of the advantages of this
method is that it does not need an absorption anechoic end, only the normal rigid and
acoustic foam end can be used for the measurements. The frequency range of the present
duct is from 50 to 1060 Hz due to the cross section of the duct. A Trek 10/40 A
(Trek) high voltage amplifier is used to generate both dc and alternating current high
voltage from 0 to 10 kV on the DE membrane. All the acquisition and control signals
were programmed using the NI PCI (National Instruments) platform.
A cavity installed on the wall of the duct, acting as an “acoustic resonator,”
can absorb acoustic energy around its resonance frequency. In the present experiment,
a cavity with depth h ¼ 160 mm, length l ¼ 135 mm, and width w ¼ 160 mm was installed
on one side of the duct. The TL of this cavity was measured using the TL measurement
system and plotted in Fig. 2. It is observed that the resonance frequency of
this cavity is at 466.3 Hz. There is only one resonance peak in the frequency ranges
from 50 to 1060 Hz. Without changing the dimension of the cavity itself, a porous
plate can be placed on the open end of the cavity to adjust the resonance peak of the
cavity. The couplings between the porous plates with the back cavity do change the
resonance frequency of the whole system as shown in the traditional acoustic treatment
designs. However, the resonance peaks are limited by the configurations of the holes
on the porous plate, such as the thickness of the plate, the diameters of the holes, and
the ratio of the holes on the surface. The disadvantage of this design is that the resonance
frequency of the system cannot be easily tuned without the support of addition
mechanical parts. Therefore, a membrane was used to replace the porous plate; in this
acoustic system the sound energy can transfer into the back cavity when they coincide
with the resonances of the membrane, and the sound energy converts into heat as the
membrane vibrates. The membrane and the back cavity can be regarded as an acoustic
resonator which can be considered as one part of the duct silencer. Following this line
of thinking, a membrane of DE was used to cover the open end of the cavity, thus the
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