There are three types in the frequency characteristics of the band pass filter, such as Ⅰ type (for simple measurement), Ⅱ type (for normal measurement) and Ⅲ type (for precision measurement). The moderateness of cutoff frequency is in order of Ⅰ>Ⅱ>Ⅲ. According to the JIS C 1513-1983, Ⅰ and Ⅱ types are applicable to the 1/1 octave band pass filter, and Ⅱ and Ⅲ types are applicable to the 1/3 octave band pass filter. It is also prescribed in the ANCI CLASS Ⅲ.
The band number, central frequency, and cutoff frequency (upper and lower frequency) can be obtained in the following formula, and results are described in the following table.
Calculation formula of the cutoff frequency
fm: Central frequency
f1: Lower limit of the cutoff frequency
f2: Upper limit of the cutoff frequency
(1) In the 1/1 octave band pass filter
f1 = fm / √2 ≒ fm÷1.4142
f2 = √2 ×fm ≒ 1.4142 × fm
f2 = 2 × f1
(2) In the 1/3 octave band pass filter
f1 = fm / 6√2 ≒ fm ÷ 1.1225
f2 = 6√2 × fm≒ 1.1225 × fm
f2 = 3√2 × f1 ≒ 1.2599 × f1
Band number |
1/1 octave (Hz) |
||
|---|---|---|---|
| Central frequency fm |
Lower limit of the frequency f1 |
Upper limit of the frequency f2 |
|
0 |
1 |
0.71 |
1.41 |
3 |
2 |
1.41 |
2.83 |
6 |
4 |
2.83 |
5.66 |
9 |
8 |
5.66 |
11.31 |
12 |
16 |
11.3 |
22.6 |
15 |
31.5 |
22.3 |
44.5 |
18 |
63 |
44.5 |
89.1 |
21 |
125 |
88.4 |
176.8 |
24 |
250 |
176.8 |
353.6 |
27 |
500 |
353.6 |
707.1 |
30 |
1000 |
707.1 |
1414.2 |
33 |
2000 |
1414.2 |
2828.4 |
36 |
4000 |
2828.5 |
5656.8 |
39 |
8000 |
5656.9 |
11313.6 |
42 |
16000 |
11313.8 |
22627.2 |
Band number |
1/3 octave (Hz) |
||
|---|---|---|---|
| Central frequency fm |
Lower limit of the frequency f1 |
Upper limit of the frequency f2 |
|
-2 |
0.63 |
0.56 |
0.71 |
-1 |
0.8 |
0.71 |
0.90 |
0 |
1 |
0.89 |
1.12 |
1 |
1.25 |
1.11 |
1.40 |
2 |
1.6 |
1.43 |
1.80 |
3 |
2 |
1.78 |
2.25 |
4 |
2.5 |
2.23 |
2.81 |
5 |
3.15 |
2.81 |
3.54 |
6 |
4 |
3.56 |
4.49 |
7 |
5 |
4.45 |
5.61 |
8 |
6.3 |
5.61 |
7.07 |
9 |
8 |
7.13 |
8.98 |
10 |
10 |
8.9 |
11.2 |
11 |
12.5 |
11.1 |
14.0 |
12 |
16 |
14.3 |
18.0 |
13 |
20 |
17.8 |
22.5 |
14 |
25 |
22.3 |
28.1 |
15 |
31.5 |
28.1 |
35.4 |
16 |
40 |
35.6 |
44.9 |
17 |
50 |
44.5 |
56.1 |
18 |
63 |
56.1 |
70.7 |
19 |
80 |
71.3 |
89.8 |
20 |
100 |
89.1 |
112.3 |
21 |
125 |
111.4 |
140.3 |
22 |
160 |
142.5 |
179.6 |
23 |
200 |
178.2 |
224.5 |
24 |
250 |
222.7 |
280.6 |
25 |
315 |
280.6 |
353.6 |
26 |
400 |
356.3 |
449.0 |
27 |
500 |
445.4 |
561.3 |
28 |
630 |
561.2 |
707.2 |
29 |
800 |
712.7 |
898.0 |
30 |
1000 |
890.9 |
1122.5 |
31 |
1250 |
1113.6 |
1403.1 |
32 |
1600 |
1425.4 |
1796.0 |
33 |
2000 |
1781.7 |
2245.0 |
34 |
2500 |
2227.2 |
2806.3 |
35 |
3150 |
2806.2 |
3535.9 |
36 |
4000 |
3563.5 |
4490.0 |
37 |
5000 |
4454.3 |
5612.5 |
38 |
6300 |
5612.5 |
7071.8 |
39 |
8000 |
7126.9 |
8980.0 |
40 |
10000 |
8908.7 |
11225.0 |
41 |
12500 |
11135.9 |
14031.3 |
42 |
16000 |
14253.9 |
17960.0 |
43 |
20000 |
17817.4 |
22450.0 |
44 |
25000 |
22271.7 |
28062.5 |
45 |
31500 |
28062.4 |
35358.8 |
46 |
40000 |
35634.7 |
44900.0 |
47 |
50000 |
44543.4 |
56125.0 |
48 |
63000 |
56124.7 |
70717.5 |
49 |
80000 |
71269.5 |
89800.0 |
50 |
100000 |
89086.9 |
112250. |
Revised:2002.06.17
