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分貝(decibel,符號:dB)係一個對數單位用嚟表達兩個物理量嘅比,通常用喺功率同強度上,亦會用喺場嘅幅度。十分貝等於一貝爾(bel),貝爾都係表達兩個物理量嘅比嘅單位,但冇人會用貝爾,只會用分貝。貝爾個名嚟自美籍蘇格蘭發明家、電話發明人亞歷山大·貝爾(Alexander Graham Bell)。
dB | 功率比 | 幅度比 | ||
---|---|---|---|---|
100 | 10 000 000 000 | 100 000 | ||
90 | 1 000 000 000 | 31 623 | ||
80 | 100 000 000 | 10 000 | ||
70 | 10 000 000 | 3 162 | ||
60 | 1 000 000 | 1 000 | ||
50 | 100 000 | 316 | .2 | |
40 | 10 000 | 100 | ||
30 | 1 000 | 31 | .62 | |
20 | 100 | 10 | ||
10 | 10 | 3 | .162 | |
6 | 3 | .981 | 1 | .995 (~2) |
3 | 1 | .995 (~2) | 1 | .413 |
1 | 1 | .259 | 1 | .122 |
0 | 1 | 1 | ||
-3 | 0 | .501 (~1/2) | 0 | .708 |
-6 | 0 | .251 | 0 | .501 (~1/2) |
-10 | 0 | .1 | 0 | .316 2 |
-20 | 0 | .01 | 0 | .1 |
-30 | 0 | .001 | 0 | .031 62 |
-40 | 0 | .000 1 | 0 | .01 |
-50 | 0 | .000 01 | 0 | .003 162 |
-60 | 0 | .000 001 | 0 | .001 |
-70 | 0 | .000 000 1 | 0 | .000 316 2 |
-80 | 0 | .000 000 01 | 0 | .000 1 |
-90 | 0 | .000 000 001 | 0 | .000 031 62 |
-100 | 0 | .000 000 000 1 | 0 | .000 01 |
分貝 dB、功率比 x 同幅度比 √x 比較。 |
用喺功率比同強度比,分貝用以下公式計算[1]:
由於功率係同場嘅幅度(電流或電壓)平方成正比,分貝係用嚟表示兩個幅度嘅平方比,用以下公式計算[1]:
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