Technical Note

11/15

www.rohm.com

2010.10 - Rev.A

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

BD3870FS,BD3871FS,BD3872FS,BD3873FS

1)Sound generation using Loud Speaker Equalizer (BD3872FS)

Using external components, one of the following two functions can be established; one having an effect to localize the

vocal forward and enhance it (Loud Speaker Equalizer) and the other having an effect to clarify the vocal quality and

improve the Articulation Index (Cinema Surround). Those characteristic values can be adjusted by choosing the external

components with desirable constants. Details of above two functions are described below:

◎

Cinema Surround

Constructing the external components as shown below allows the vocals to be moved forward and enhanced.

Surround effect with enhanced vocal is achieved by turning on the built-in surround simultaneously.

Merging this effect, while playing movies on a DVD player, will make vocal listening clearer and surround effect

more impactful.

Fig.10

◎

Loud Speaker Equalizer (SEQ)

BOOM BOX and Micro-sound systems are often restricted to using small-diameter speakers because of location space.

These speakers, where the vocal range are attenuated, may give an impression of having a muffled vocal sound

with respect to its audibility. Using the Loud Speaker Equalizer, the vocal quality which degrades in small-diameter

speakers, can be improved and the Articulation Index is also increased.

Fig.11

・

C1 can be selected to determine the frequency where the phase should be inverted.

C1

Frequency where the phase is inverted

Larger value

Set to the lower frequency side

Smaller value

Set to the higher frequency side

・

C2 can be selected to determine the HPF cut-off frequency fc. The SEQ gain remains constant.

1

fc =

(Hz)

2

RC

(Where R is a built-in resistance of 10kΩ)

Fig.12

32

Loud speaker

equalizer1

Loud speaker

equalizer2

31

30

29

HPF

C2

SOUT (29. 31pin)

Phase Shifter

C1

SEQ (30, 32pin)

IN

OUT

FREQUENCY

Fc

G=5dB

(Constant)

3dB