Preferred Frequencies for Acoustical Measurements

The ISO R 266 recommendation contains a table of preferred frequencies of acoustic measurements. As basis for all series of preferred frequencies, the frequency 1,000 Hz is chosen because of its great importance in acoustics. Because most commonly a constant percentage increment in frequency is used in acoustic measurements the present recommendation deals with geometric series and is not intended to apply where a constant frequency increment, or other particular spacing would be more suitable.

In the case of bandbass filters or bands of sound, the frequencies listed in the table below are known as Nominal Center Frequencies and correspond to the geometric center frequencies of the band. Because of the way their center frequencies are generated, third-octave filters are often referred to as one-tenth decade filters. Crossover frequencies are calculated from 10n/10 0.5.


Table 1: Third-Octave and Octave Passbands

Band No.

Frequency

(Hz)

Third-Octave

Passband

(Hz)

Octave

Passband

(Hz)

1

1.25

1.12 - 1.41

---

2

1.6

1.41 - 1.78

---

3

2

1.78 - 2.24

1.41 - 2.82

4

2.5

2.24 - 2.82

---

5

3.15

2.82 - 3.55

---

6

4

3.55 - 4.47

2.82 - 5.62

7

5

4.47 - 5.62

---

8

6.3

5.62 - 7.08

---

9

8

7.08 - 8.91

5.62 - 11.2

10

10

8.91 - 11.2

---

11

12.5

11.2 - 14.1

---

12

16

14.1 - 17.8

11.2 - 22.4

13

20

17.8 - 22.4

---

14

25

22.4 - 28.2

---

15

31.5

28.2 - 35.5

22.4 - 44.7

16

40

35.5 - 44.7

---

17

50

44.7 - 56.2

---

18

63

56.2 - 70.8

44.7 - 89.1

19

80

70.8 - 89.1

---

20

100

89.1 - 112

---

21

125

112 - 141

89.1 - 178

22

160

141 - 178

---

23

200

178 - 224

---

24

250

224 - 282

178 - 355

25

315

282 - 355

---

26

400

355 - 447

---

27

500

447 - 562

355 - 708

28

630

562 - 708

---

29

800

708 - 891

---

30

1000

891 - 1120

708 - 1410

31

1250

1120 - 1410

---

32

1600

1410 - 1780

---

33

2000

1780 - 2240

1410 - 2820

34

2500

2240 - 2820

---

35

3150

2820 - 3550

---

36

4000

3550 - 4470

2820 - 5620

37

5000

4470 - 5620

---

38

6300

5620 - 7080

---

39

8000

7080 - 8910

5620 - 11200

40

10000

8910 - 11200

---

41

12500

11200 - 14100

---

42

16000

14100 - 17800

11200 - 22400

43

20000

17800 - 22400

---


Although nominal frequencies are used to identify the filters, the true center frequencies of third-octave filters are calculated from 10n/10 where n is the band number.

Band Number

Exact Frequency

Band Number

Exact Frequency

0

1

6

3.9811

1

1.2589

7

5.0119

2

1.5849

8

6.3096

3

1.9953

9

7.9433

4

2.5119

10

10

5

3.1623

11

12.589