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Boundary Cancellation and Room Modes

 

If you have a cancellation at a given frequency, this chart will tell you the distance from the speaker to the boundary that is causing the cancellation. In addition, if you measure the distance from a speaker to a boundary, this chart will tell you the frequency at which that boundary will cause a cancellation.

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

Freq

10

15

20

25

30

35

40

45

50

55

60

65

70

75

80

85

90

95

100

105

Feet

28.25

18.83

14.13

11.30

9.42

8.07

7.06

6.28

5.65

5.14

4.71

4.35

4.04

3.77

3.53

3.32

3.14

2.97

2.83

2.69

Inches

339.00

226.00

169.50

135.60

113.00

96.86

84.75

75.33

67.80

61.64

56.50

52.15

48.43

45.20

42.38

39.88

37.67

35.68

33.90

32.29

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

Freq

110

115

120

125

130

135

140

145

150

155

160

165

170

175

180

185

190

195

200

205

Feet

2.57

2.46

2.35

2.26

2.17

2.09

2.02

1.95

1.88

1.82

1.77

1.71

1.66

1.61

1.57

1.53

1.49

1.45

1.41

1.38

Inches

30.82

29.48

28.25

27.12

26.08

25.11

24.21

23.38

22.60

21.87

21.19

20.55

19.94

19.37

18.83

18.32

17.84

17.38

16.95

16.54

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

Freq

210

215

220

225

230

235

240

245

250

255

260

265

270

275

280

285

290

295

300

305

Feet

1.35

1.31

1.28

1.26

1.23

1.20

1.18

1.15

1.13

1.11

1.09

1.07

1.05

1.03

1.01

0.99

0.97

0.96

0.94

0.93

Inches

16.14

15.77

15.41

15.07

14.74

14.43

14.13

13.84

13.56

13.29

13.04

12.79

12.56

12.33

12.11

11.89

11.69

11.49

11.30

11.11

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

Freq

310

315

320

325

330

335

340

345

350

355

360

365

370

375

380

385

390

395

400

405

Feet

0.91

0.90

0.88

0.87

0.86

0.84

0.83

0.82

0.81

0.80

0.78

0.77

0.76

0.75

0.74

0.73

0.72

0.72

0.71

0.70

Inches

10.94

10.76

10.59

10.43

10.27

10.12

9.97

9.83

9.69

9.55

9.42

9.29

9.16

9.04

8.92

8.81

8.69

8.58

8.48

8.37

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

Freq

410

415

420

425

430

435

440

445

450

455

460

465

470

475

480

485

490

495

500

505

Feet

0.69

0.68

0.67

0.66

0.66

0.65

0.64

0.63

0.63

0.62

0.61

0.61

0.60

0.59

0.59

0.58

0.58

0.57

0.57

0.56

Inches

8.27

8.17

8.07

7.98

7.88

7.79

7.70

7.62

7.53

7.45

7.37

7.29

7.21

7.14

7.06

6.99

6.92

6.85

6.78

6.71

 

Every enclosed space has natural resonances, called Room Modes. This chart will tell you the frequency at which a given dimension will resonate. Note that each given dimension will also resonate 2x, 4x, 8x, etc. the frequency of the main mode. (It's actually much more complicated than this - see the calculator javascript at http://www.mcsquared.com/modecalc.htm or http://www.mcsquared.com/metricmodes.htm)

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

Feet

70

69

68

67

66

65

64

63

62

61

60

59

58

57

56

55

54

53

52

51

Freq

8.07

8.19

8.31

8.43

8.56

8.69

8.83

8.97

9.11

9.26

9.42

9.58

9.74

9.91

10.09

10.27

10.46

10.66

10.87

11.08

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

Feet

50

49

48

47

46

45

44

43

42

41

40

39

38

37

36

35

34

33

32

31

Freq

11.30

11.53

11.77

12.02

12.28

12.56

12.84

13.14

13.45

13.78

14.13

14.49

14.87

15.27

15.69

16.14

16.62

17.12

17.66

18.23

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

Feet

30

29

28

27

26

25

24

23

22

21

20

19

18

17

16.5

16

15.5

15

14.5

14

Freq

18.83

19.48

20.18

20.93

21.73

22.60

23.54

24.57

25.68

26.90

28.25

29.74

31.39

33.24

34.24

35.31

36.45

37.67

38.97

40.36

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

Feet

13.5

13

12.5

12

11.5

11

10.5

10

9.5

9

8.5

8

7.5

7

6.5

6

5.5

5

4.5

4

Freq

41.85

43.46

45.20

47.08

49.13

51.36

53.81

56.50

59.47

62.78

66.47

70.63

75.33

80.71

86.92

94.17

102.73

113.00

125.56

141.25

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

What use is all this? Say you have a boom at about 70 Hz. This is the first mode of 8', a common ceiling height. (And the octave of the first mode of ~16'.) Looking at the Boundary Cancellation Charts, we find that a 70Hz cancellation occurs at ~ 48.5". Put the bass driver(s) at 48.5" from a boundary and see what happens.

 

Going the other way, say we cannot place the bass drivers against a boundary, but we have some choice as to where they can go. Try a spot whose boundary cancellation matches a resonance mode. Say we have a 12' ceiling. The first mode will be at 47Hz. The cancellation distance for 47Hz is ~6'. If the drivers can go 6' from the wall or floor, try them there.

 

 

 

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