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???????????????????????????????????????????????????к??壬????????????? ?????????????????????????????????????????????????????????????????????? ???????????????????????????棬??????????????????????????? ??????????Щ ????????????????????????????ξ?????????????????????
?????????????????
????????????????н?10???????????????????????????????????3?????????????? ??????????????????????????????????????????????0.5%??г???????????????? ????????????????????????
0dBSPL=2??10-5Pa
???????????????????????y???????????????????????????????????? ?档?????????????????????????????????????????????
1.?????
????????????λ????????????????????????????????λ??mV/Pa??????·?е?? ???????￡??????????????????????????????λdBm??dBV?????
0dBm=1mW/Pa??????1Pa??????????600???????????1mW????????????0dB??
0dBV=1V/??bar??????1??bar????????2?????1V???????????0dB??
????????????λdB??????
0dB??=0.775V/Pa??????1Pa???????????0.775V???????????0dB(????????????????? ????????????????????·?????????0dB??=0.775V????ο???λ)??
????????????????α??????????????????dB??????????????????Pa?????λ??
???磺NEUMANNU89????????????8mV/Pa?????????
20lg[(0.008V/Pa)??(0.775V/Pa)]
?ó??????????-40dB???
???磺AKGC414???????????-60dBV????
0dBV=1V/??bar=10V/Pa
?????1Pa?????-60dBV????????X??
20lg[(XV/Pa)??(10V/Pa)]=-60
?ó?X=0.01(V)??????????????10mV/Pa???????
20lg[(0.01V/Pa)??(0.775V/Pa)]
????????????-37dB??
2.?????????
??????????????????μ????????????????????????????????????????????????? ????????????????????????????????????????????????????????????????????? ????????????????????????????????????????
????NEUMANNU89????????????????8mV/Pa???????????????134dBSPL(??10dB?????????)???? ???????????????????????????????????????????????0dBSPL=2??10-5Pa?????????????? X????
134dBSPL=20lgX/2??10-5Pa
?ó?X=100(Pa)?????????8mV/Pa???100Pa????????800mV????????????????
20lg[(0.8V/Pa)??(0.775V/Pa)]
??0dB??????U89?????????????????????????????????????????10dB?????(??? ??????????)??????????????????????U89??????????????????????????λ?μ? 124dBSPL??????????????????????????0dB???
?????????????????????
?????????????????????????????????????????????????趨?????????????????涨??( ????й???????????????????????????)?????????????????г??????????????? ??0dB????????ε????Χ????????
???????????????????????????????????????????????????????????????????? ????????????????????????????????????????????????????(??????)?????????棻 ????????μ????????????????????????
??????????????????????U89?????AMEKRemBandt????????????????????????????? 70cm?????????????????112dBSPL(?????A???)???????????????????????????124dB?????? ????8mV/Pa??????
112dBSPL=20lgX/2??10-5
???112dB?????????8Pa???????????8Pa??8mV/Pa=64mV?????????????е???????
20lg[(0.064V/Pa)??(0.775V/Pa)]=-22dB??
???????????70dB???????桢?????????????????г???????0.017%??12dB?????????(?? ???????·????????????28dB??)????+12dB???????????34dB??????(+12dB-(-22dB)=34dB)?? ????????????е????????档???????????????????????
???????У???????????????????????г????????0.017%????????????????????????? ????????????????????·???????????????????????????????????????????????????0dB?? ??λ????????????????????????????????????????????????????併??????????