Technical Note

10/15

www.rohm.com

2010.10 - Rev.A

© 2010 ROHM Co., Ltd. All rights reserved.

BD3870FS,BD3871FS,BD3872FS,BD3873FS

2) Treble filter

Fig.7

Standard values of R1, R2 (reference)

Treble Boost Cut Amount

Resistance (kΩ) * Typ.

R1

R2

0dB

0

36.28

2dB

7.46

28.82

4dB

13.39

22.89

6dB

18.10

18.18

8dB

21.84

14.44

10dB

24.81

11.47

12dB

27.20

9.08

14dB (BD3872FS only)

29.04

7.24

* The actual boost cut amount may deviate from the standard values in some degree.

3) Matrix surround

Fig.9

Matrix surround is constructed as shown above. Gains are defined as follows:

In-phase Gain: Gains obtained on OUT1 and OUT2 against IN1 when inputting a signal of the equivalent level and

in-phase (L=R) to IN1 and IN2.

1

L

L

2

2.14

L

2

4.14

IN2

OUT2

IN1

OUT1





















(dB)

0

20log1



Single-phase Gain: Gains obtained on OUT1 and OUT2 against IN1 when inputting a signal to IN1 and AC-grounding IN2

(R=0).

2,07

L

L

2

4.14

IN1

OUT1





1.07

L

L

2

2.14

IN1

OUT2









(dB)

6.3

20log2.07



(dB)

0.59

1.07

20log





Opposite-phase Gain: Gains obtained on OUT1 and OUT2 against IN1 when inputting signals of the equivalent level and

opposite-phase (L-R) to IN1 and IN2.

fc =

(Hz)

G (boost) = 20log

(dB)

G (cut) = 20log

(dB)

Zc =

(Ω)

2πR2C

1

R2+Zc

R1+R2+Zc

R1+R2+Zc

R2+Zc

jωc

1

R2

IN

OUT

C

+

-

R1

+

+

-

×1/2

×1/2

+

L

R

IN1

IN2

+

-

×2.14

(4.14L/2 - 2.14R/2)

OUT1

OUT2

(4.14R/2 - 2.14L/2)

+

+

+

3.14

L

L

2

2.14

L

2

4.14

IN2

OUT2

IN1

OUT1





















(dB)

10

20log3.14



Fig.8

G

f

fc

G

3dB

G

3dB