sound level meter Frequently Asked Questions
Question number FAQ-0162
The upper and lower cutoff frequencies of the 1/1 and 1/3 octave bands are
The frequency characteristics of bandpass filters are categorized into three types based on the smoothness of the cutoff characteristics: Type I (for simple measurements), Type II (for general measurements), and Type III (for precise measurements). According to JISC 1513-1983, Type I and Type II are used for 1/1 octave bandpass filters, while Type II and Type III are adopted for 1/3 octave bandpass filters. Similarly, this is also stipulated in ANCI CLASS III.
The table shows the values obtained from the following formula for the band number, center frequency, and cutoff frequencies (upper and lower limits).
Formula for Cut-off Frequency
f m: center frequency f 1: lower cutoff frequency f 2: upper cutoff frequency
In a 1/1 octave
f1 = fm／√2 ≒ fm÷1．4142
f2 =√2×fm ≒ 1．4142 × fm
f2 = 2 × f1
In 1/3 octave.
f1 = fm／6√2 ≒ fm ÷1．1225
f2 = 6√2 × fm≒1．1225 × fm
f2 = 3√2 × f1 ≒ 1．2599 × f1
| Band No. | 1/1 octave (Hz) | ||
|---|---|---|---|
| Center frequency f m | Lower limit frequency f 1 | Upper limit frequency f 2 | |
| 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 No. | 1/3 octave (Hz) | ||
|---|---|---|---|
| Center frequency f m | Lower limit frequency f 1 | Upper limit frequency f 2 | |
| -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. |
Last updated: 2002-06-17