麥克風的技術指標!
麥克風的靈敏度
指麥克(ke)風(feng)的(de)開(kai)路電壓(ya)(ya)(ya)與作用(yong)(yong)在其(qi)膜片(pian)上(shang)的(de)聲(sheng)(sheng)(sheng)(sheng)壓(ya)(ya)(ya)之比。實(shi)際(ji)上(shang),麥克(ke)風(feng)在聲(sheng)(sheng)(sheng)(sheng)場(chang)(chang)必然會(hui)引(yin)起聲(sheng)(sheng)(sheng)(sheng)場(chang)(chang)散射,所以(yi)靈(ling)(ling)(ling)敏度(du)(du)(du)(du)有兩種定義。一種是實(shi)際(ji)作用(yong)(yong)于膜片(pian)上(shang)的(de)聲(sheng)(sheng)(sheng)(sheng)壓(ya)(ya)(ya),稱為(wei)聲(sheng)(sheng)(sheng)(sheng)壓(ya)(ya)(ya)靈(ling)(ling)(ling)敏度(du)(du)(du)(du),另(ling)一種是指麥克(ke)風(feng)未置入聲(sheng)(sheng)(sheng)(sheng)場(chang)(chang)的(de)聲(sheng)(sheng)(sheng)(sheng)場(chang)(chang)聲(sheng)(sheng)(sheng)(sheng)壓(ya)(ya)(ya),稱為(wei)聲(sheng)(sheng)(sheng)(sheng)場(chang)(chang)靈(ling)(ling)(ling)敏度(du)(du)(du)(du),其(qi)中(zhong)聲(sheng)(sheng)(sheng)(sheng)場(chang)(chang)靈(ling)(ling)(ling)敏度(du)(du)(du)(du)又分(fen)為(wei)自由(you)場(chang)(chang)靈(ling)(ling)(ling)敏度(du)(du)(du)(du)和擴(kuo)散場(chang)(chang)靈(ling)(ling)(ling)敏度(du)(du)(du)(du)。通常錄音(yin)用(yong)(yong)麥克(ke)風(feng)給出聲(sheng)(sheng)(sheng)(sheng)壓(ya)(ya)(ya)靈(ling)(ling)(ling)敏度(du)(du)(du)(du),測量用(yong)(yong)麥克(ke)風(feng)因應(ying)用(yong)(yong)類型給出聲(sheng)(sheng)(sheng)(sheng)壓(ya)(ya)(ya)或聲(sheng)(sheng)(sheng)(sheng)場(chang)(chang)靈(ling)(ling)(ling)敏度(du)(du)(du)(du)。
麥克風的頻率響應
是指麥克(ke)風接受到不同頻(pin)率聲音(yin)時,輸(shu)(shu)出信(xin)號會(hui)隨著頻(pin)率的(de)(de)變化而發生放(fang)大(da)或衰(shuai)減(jian)(jian)(jian)。最理(li)想的(de)(de)頻(pin)率響應(ying)曲線(xian)為(wei)一條水平(ping)線(xian),代表輸(shu)(shu)出信(xin)號能直實呈(cheng)現(xian)原始聲音(yin)的(de)(de)特性(xing),但(dan)這種理(li)想情況不容易實現(xian)。一般來說,電容式(shi)麥克(ke)風的(de)(de)頻(pin)率響應(ying)曲線(xian)會(hui)比動圈式(shi)的(de)(de)來得平(ping)坦。常見的(de)(de)麥克(ke)風頻(pin)率響應(ying)曲線(xian)大(da)多為(wei)高(gao)低頻(pin)衰(shuai)減(jian)(jian)(jian),而中(zhong)高(gao)頻(pin)略為(wei)放(fang)大(da);低頻(pin)衰(shuai)減(jian)(jian)(jian)可以(yi)減(jian)(jian)(jian)少錄音(yin)環境周遭(zao)低頻(pin)噪音(yin)的(de)(de)干(gan)擾。
麥克風的阻抗
在麥克風規格中,都會列出阻抗值(單位為歐姆),根據最大功率傳輸定理(Maximum Power Transfer Theorem),當負載阻抗和麥克風阻抗匹配時,負載的功率將達到最大值。不過在大部份阻抗不匹配的情況下,麥克風依然能使用,也因此造成這項規格并未受到太大的重視。一般而言,低于600歐姆為低阻抗;介于600至10,000歐姆為中阻抗;高于10,000歐姆為高阻抗。例如像Shure SM58這支麥克風的阻抗值為300歐姆。