Study on the effect of vent on the electroacoustic absorber

Transcription

1 INTER-NOISE 016 Study on the effect of vent on the electroacoutic aborber Youngeun Cho 1 ; Semyung Wang 1, Gwangju Intitute of Science and Technology, Republic of Korea ABSTRACT Electroacoutic aborber (EA) with a ealed encloure ha limitation of ound aborbing performance due to the reonance characteritic of a loudpeaker that work a it actuator. Specifically, the ound aborbing performance of EA decreae at the lower and higher frequency range on the bai of the reonance frequency of the loudpeaker. To overcome thi limitation, it ugget to utilize a vented encloure rather than the ealed encloure in the EA ytem. Firt of all, the effect of the vent on the EA i analyzed through the related formula and imulation reult. Then, the correponding experiment i conducted to verify the aforementioned analytical reult. Finally, thi paper reveal that the vented encloure increae the performance of EA up to a certain point at frequencie below the reonance frequency of the loudpeaker. From the uer' point of view, thi paive method uing the vented encloure lead to put it to better ue. Keyword: electroacoutic aborber, vented encloure I-INCE Claification of Subject Number(): INTRODUCTION Thi paper deal with a method of EA aiming to reduce actively noie in an encloed ound field by matching the pecific acoutic impedance of a loudpeaker acting a an actuator of EA with that of air, rather than the method of active noie cancellation. The EA in the preceding tudie [1]-[4] ha following feature. The ound aborbing performance and pecific acoutic impedance of the EA decline in the low frequency and high frequency band with a reonance frequency of a loudpeaker acting a an actuator in whole EA ytem a the center. Thi i unavoidable phenomenon caued due to a limit to control the pecific acoutic impedance of the EA through the DIC technique. To overcome thi limitation, thi paper propoe to apply a vented encloure to the EA.. General EA with the ealed encloure.1 Dynamic modeling The mechanical dynamic of a loudpeaker i repreented a a ingle lumped model of ma-pring-damper baed on Newton econd law. Meanwhile, the electrical dynamic i baed on Kirchhoff law. Thee two dynamic can be expreed a (1). The direct impedance control voltage in () for the applied voltage in (1), it can be conidered a a total dynamic model of the EA. 1 SP () M m Rm V () BlI() Cmc E () Le ReI () BlV () (1) E () K P () K V() () c P V Baed on thi dynamic model, Fig. 1 how an equivalent circuit of an EA coupled with a ealed encloure. Next, an equation of the pecific acoutic admittance uing the mechanical impedance and the electrical impedance through the imple operation between (1) and () can be expreed a (3). 1 yecho@git.ac.kr mwang@git.ac.kr 56

2 INTER-NOISE 016 Figure 1 The equivalent circuit of the EA coupled with a ealed encloure V() SZ () K Bl Y () c c P () Z Z() ( Bl) KBl e P m e V (3) The pecific acoutic admittance of the typical loudpeaker can be derived by removing the term of KBl and P KBl in the numerator and denominator in (3) repectively. Finally, by ubtituting (4) V indicating a reflection coefficient () for the incident ound wave into (5), a ound aborption coefficient () indicating the ound aborbing performance of the EA can be calculated. 1 Y ( ) () (4) 1 Y ( ) () 1 () (5) Fig. i a imulation reult of the pecific acoutic admittance and ound aborption coefficient through (3)-(5) uing the nominal parameter of the loudpeaker ued in thi paper. Figure Simulation reult of the pecific acoutic admittance (left) and ound aborption coefficient (right) for the EA coupled with the ealed encloure In thi figure, in both cae, the ound aborption coefficient become maximum at near the reonance frequency of the loudpeaker. More important i that the performance gradation phenomenon occur in low and high frequency band. Thu, to overcome thi limitation, it i uggeted to apply a vented encloure, not a ealed encloure to the EA ytem.. Simulation Analyi for the Performance of EA with the vented encloure In thi paper, in order to account for the effect of a vented encloure on the EA, the equivalent circuit analyi baed on impedance model i ued. Comparing the equivalent circuit of Fig. 3 to the equivalent circuit of the EA coupled with vented encloure (Fig. 1), the following are noticed. A ingle equivalent impedance Z() v of the vented encloure i repreented a (6) uing an equivalent acoutical impedance Z ap () of vent itelf and another equivalent acoutical compliance C ab and the 57

3 INTER-NOISE 016 diaphragm effective area. Note that the formula for the equivalent acoutical element Map, Rap, C ab of the vented encloure are ummarized a (7) through the reference paper [5]. S Figure 3 The equivalent circuit of the EA coupled with a vented encloure Z () v S Map Rap MapCab RapCab 1 ( l 0.6 r ) w l V M, R, C v v v b av av ab rv rv rv c (6) (7) Next, in the ame manner with derivation of (3), the total pecific acoutic admittance of the EA coupled with a vented encloure can be obtained a (8). SZe() KPBl Yt () c Z Z Z Bl K Bl () () () ( ) m v e V a a a a c b b b b b b a3 CmLe MavCabS a CmLeRavCabS CmMavCabReS CmMavCabKpBl a1 CmLe S CmRe SRavCab Cm RavCabK pbl a0 CmRe S CmKpBl b5 MmCmLe MavCab b4 MmCmLe RavCab RmCm Le MavCab MmCm Re MavCab, b3 MmCmLe RmCmLe RavCab Le MavCab Le MavCmS MmCm Re RavCab... RmCmReM apcab CmM avcabbl CmM apcabkv b RmCmLe Le RavCab Le RavCmS MmCmRe RmCmRe RavCab Re MavCab... CmRe MavS CmRavCab Bl CmRavCab KV b1 Le Re RmCm Re RavCab Cm Re Rav S Cm Bl Cm KV b0 Re (8) The following can be deduced through the imulation reult of Fig. 4 baed on (8). The fact that a ound aborbing performance i improved in a low frequency range of approximately 0-3Hz where either the magnitude i increaed or the phae i decreaed in term of it pecific acoutic admittance, o a to enhance the degree of acoutic impedance matching with air, i confirmed. A oppoed to thi, there i alo a frequency range of approximately 3-50Hz where the degree of acoutic impedance matching with air i declined, and which lead to degrade the ound aborption coefficient. Conequently, it can be mentioned that there are both frequency range where the ound aborbing performance i clearly improved and lightly degraded due to the vented encloure in the EA. In other word, a kind of trade-off phenomenon occur. 58

4 INTER-NOISE 016 (a) (b) Figure 4 Simulation reult of the pecific acoutic admittance (left) and ound aborption coefficient (right) for the EA coupled with the vented encloure 3. EXPERIMENTAL RESULTS 3.1 Experimental Setup In thi ection, the imulation analyi of the influence of the vented encloure on the EA performance in previou ection i verified through the related experiment. For thi experimental verification, the experimental etup ued in thi paper i hown in Fig. 5. Loudpeaker of Peerle /4" PPB cone HDS woofer are ued a an actuator of the EA and a noie ource in the experiment etup. An audio amplifier of INTER-M QD 4480 i ued to upply the driving power to the 3 loudpeaker. The dimenion of the ealed encloure internal volume i made a mm with MDF material of 0mm thickne. A vented encloure i made by a way to produce a vent required for the experimental verification on the top face of the ealed encloure. The meaurement proce of the pecific acoutic admittance i conducted a follow. A noie ource loudpeaker generate a noie ignal received from NI cdaq. The noie hake a diaphragm of a control loudpeaker acting a an actuator of an EA and imultaneouly ha a dominant influence on a vicinity the diaphragm, propagating through a duct having 0.13m of diameter and 1.93m of length in the form of a plane wave. For meaurement of the pecific acoutic admittance repreenting the acoutic characteritic in the vicinity of the control loudpeaker diaphragm, the neighboring preure i meaured by a 1/ inch preure field microphone (B&K type 419) intalled in front of the diaphragm and the diaphragm velocity i meaured by a velocity enor (ESV-00 laer vibrometer) intalled outide of the duct, repectively. Figure 5 Schematic of experimental etup 59

5 INTER-NOISE Experimental Verification The feaibility for improvement of ound aborbing performance of the EA uing a vented encloure in a low frequency band i verified through the experiment reult of Fig. 6(a). A fact that thi experiment reult ha a imilar tendency with the imulation reult of Fig. 4(a) i confirmed. Next, Fig. 6(b) howing the experimental reult of the ound aborption coefficient i analyzed a follow. Thi experimental reult i alo checked to have a imilar tendency with the imulation reult of Fig. 4(b). (a) (b) Figure 6 Experimental reult of the pecific acoutic admittance (left) and ound aborption coefficient (right) for the EA coupled with the vented encloure 4. CONCLUSIONS In thi paper, it i uggeted to apply a vented encloure to an EA ytem intead of the conventional ealed encloure. It i theoretically and experimentally verified that the vented encloure can improve the ound aborbing performance in a low frequency band below the reonance frequency of the control loudpeaker by being coupled with the EA. ACKNOWLEDGEMENTS Thi work wa partially upported by a National Reearch Foundation of Korea (NRF) grant funded by the Korean government ( ) and wa alo partially upported by Minitry of Culture, Sport and Tourim(MCST) and Korea Creative Content Agency(KOCCA) in the Culture Technology(CT) Reearch Development Program 014. REFERENCES [1] M. Furto, D. Thenail, and M. A. Galland, Surface impedance control for ound aborption: direct and hybrid paive/active trategie, Journal of ound and vibration, vol. 03, no., pp , [] H. Liek and X.A. Meynial, preliminary tudy of an iodynamic tranducer for ue in active acoutic material, Applied Acoutic, vol. 64, no.9, pp , 003. [3] H. Liek, R. Boulandet, and R. Fleury, Electroacoutic aborber: bridging the gap between hunt loudpeaker and active ound aborption, The Journal of the Acoutical Society of America, vol. 19, no. 5, pp , 011. [4] Y. Cho, S. Wang and K. Park, Electroacoutic Aborber uing Diturbance-oberver-type Velocity Etimator, IEEE/ASME Tran. Meahctronic, vol. 1, no. 1, pp , 016. [5] M. Kleiner, Electroacoutic, CRC Pre,