Sound level meter - Frequently Asked Questions
Question number FAQ-0162
The upper and lower cutoff frequencies for 1/1 and 1/3 octave bands are
Bandpass filters have three types of frequency characteristics, classified by the degree of cutoff: Type I (for simple measurements), Type II (for general measurements), and Type III (for precision measurements). JISC 1513-1983 specifies that Type I and Type II are used for 1/1 octave bandpass filters, and Type II and Type III are used for 1/3 octave bandpass filters. Similarly, ANCI CLASS III specifies the same classifications.
The table shows the band number, center frequency, and cutoff frequencies (upper and lower limits) calculated using the following formula.
■ Formula for calculating cutoff frequency
f m: center frequency f1: Lower cutoff frequency f2: Upper cutoff frequency
(1) In 1/1 octave
f1 = fm／√2 ≒ fm÷1．4142
f2 =√2×fm ≒ 1．4142 × fm
f2 = 2 × f1
(2) 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