Technical Note
11/15
www.rohm.com
2010.10 - Rev.
© 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)
2RC
(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
GAIN
FREQUENCY
Fc
G=5dB
(Constant)
3dB
