Signal Processing - November 2016 - 68

Acoustic
Pressure (dB)

control system. The cost of implementation was quite high
and the resulting level of noise reduction was not deemed to
Front Seats
Rear Seats
be significant. Therefore, at the time, it was not generally
accepted as a useful technology.
In addition to engine booming noise reduction, research
has also been actively carried out on road noise reduction
10 dB
10 dB
since the early 1990s [28], [29]. In 2000, Honda introduced
600 1,200 1,800 2,400 600 1,200 1,800 2,400
ANC for low-frequency narrowband road noise control. It was
(r/min)
(r/min)
was applied as standard equipment in a station wagon, where a
fixed feedback controller based on control engineering theory
Figure 8. Noise reduction levels of the HONDA ANC system at (a) front
was utilized [5].
seats and (b) rear seats. (Figure adapted from [36] and [35] and used
Nearly a decade after Nissan's attempt, commercial
courtesy of Honda.)
interest in engine booming noise reduction started regaining attention due to the integration of the ANC system to
the vehicle's built-in audio system. In 2003, Honda introextended up to 500 Hz, revealing the potential advantages of
duced ANC for booming noise caused by the Honda V6
regional control systems.
engine model, which employed the variable cylinder management (VCM) technology to improve fuel economy by
Commercial systems
providing three-cylinder operation [30], [31]. This ANC
In the commercial automotive space, noise control is still presystem employed an adaptive notch filter-based MIMO
dominantly achieved via passive control. However, to overcome
feedforward controller and was combined with an active
limitations related to passive control, more companies are
control engine mount (ACM) to reduce vibrations. Curincreasingly applying active control to mass production. Comrently all VCM engine models from Honda are equipped
mercial active control systems are typically applied for both
with ANC and ACM. In 2006, Honda combined an ASC
noise and vibration control. While ANC utilizes an acoustic
system with their existing ANC solution
system, AVC typically comprises an active
for engine booming noise control. The
engine mount (ACM), which not only reducWe present the
ASC system was introduced to improve
es vibrations but also reduces noise inside
chronological
the internal cabin sound by synthesizing
the cabin. More recently, the concept of
advancement of active
engine acceleration sounds for speeds
active sound control (ASC) was introduced
control in commercial
above 2,500 r/minute such that it delivers
to commercial automotive solutions, which
automotive applications
a sporty feel to the driver [32]. In 2008,
improves the driving experience by synthewith the main focus
both Toyota [33] and GM introduced
sizing certain sounds that are essential for
ANC for booming noise in a midsize car
the perceptual sound quality inside/outside
on ANC.
and a midsize SUV, respectively. Both
the car. This process, which is similar to
solutions were based on adaptive MIMO feedforward conANC, typically uses adaptive algorithms to change the coeftrollers. Soon after in 2009, Nissan reintroduced a MIMO
ficients of a set of digital filters such that not only are some
ANC system based on adaptive feedforward control for
selected frequencies canceled by secondary loudspeaker(s)
engine booming noise in a midsize car [34]. In 2011, Honda
generating an inverse disturbance signal(s), but others are conintroduced commercial solutions for low-frequency road
trolled to a predetermined level, or even enhanced [12], [23].
noise by integrating an extra feedback controller (adapIn this section, we present the chronological advancement of
tive notch filter) to their existing booming noise controller
active control in commercial automotive applications with the
(MIMO feedforward) [35]. In the frequency range below
main focus on ANC.
100 Hz, this system is claimed to achieve 10 dB reduction
Research and development of ANC became popular in
of noise level inside a midsize car [36] (see Figure 8). The
the latter half of 1980 [1]. The earliest ANC systems were
aforementioned road noise controller by Honda was updatfeedforward arrangements based on MIMO FXLMS for
ed in 2015 with an expanded low-frequency range [37].
tonal engine noise (or booming noise) control inside cars [24].
In addition to the ANC solutions provided by automobile
Implementation of such a system was initially carried out in
manufacturers, leading audio system developers such as Bose
collaboration with the University of Southampton and Lotus
and Harman have also developed noise management soluEngineering, where four loudspeakers were adjusted at the
tions for automobiles. The Bose Active Sound Management
engine's firing frequency and its harmonics to minimize the
System (ASM) is an example for such a solution [38]. The
mean-square pressure at eight error microphones located on
main technologies used in ASM are Bose Engine Harmonic
the headrests [25], [26]. ANC in mass-produced vehicles was
Cancelation (EHC), Bose Engine Harmonic Enhancement
first introduced by Nissan in 1991 [27] for booming noise,
(EHE), and Bose Rapid Mode Transition (RMT). The
where a limited grade Nissan midsize car was optionally
EHC technology is an ANC solution that minimizes boominstalled with a separate ANC system that consisted of addiing noise utilizing a feedforward control system [39]. The
tional loudspeakers, microphones, and a MIMO FXLMS
68

IEEE SIgnal ProcESSIng MagazInE

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November 2016

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Table of Contents for the Digital Edition of Signal Processing - November 2016

Signal Processing - November 2016 - Cover1
Signal Processing - November 2016 - Cover2
Signal Processing - November 2016 - 1
Signal Processing - November 2016 - 2
Signal Processing - November 2016 - 3
Signal Processing - November 2016 - 4
Signal Processing - November 2016 - 5
Signal Processing - November 2016 - 6
Signal Processing - November 2016 - 7
Signal Processing - November 2016 - 8
Signal Processing - November 2016 - 9
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Signal Processing - November 2016 - 16
Signal Processing - November 2016 - 17
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Signal Processing - November 2016 - 19
Signal Processing - November 2016 - 20
Signal Processing - November 2016 - 21
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Signal Processing - November 2016 - 24
Signal Processing - November 2016 - 25
Signal Processing - November 2016 - 26
Signal Processing - November 2016 - 27
Signal Processing - November 2016 - 28
Signal Processing - November 2016 - 29
Signal Processing - November 2016 - 30
Signal Processing - November 2016 - 31
Signal Processing - November 2016 - 32
Signal Processing - November 2016 - 33
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Signal Processing - November 2016 - 100
Signal Processing - November 2016 - 101
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Signal Processing - November 2016 - 131
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Signal Processing - November 2016 - 133
Signal Processing - November 2016 - 134
Signal Processing - November 2016 - 135
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Signal Processing - November 2016 - 137
Signal Processing - November 2016 - 138
Signal Processing - November 2016 - 139
Signal Processing - November 2016 - 140
Signal Processing - November 2016 - 141
Signal Processing - November 2016 - 142
Signal Processing - November 2016 - 143
Signal Processing - November 2016 - 144
Signal Processing - November 2016 - 145
Signal Processing - November 2016 - 146
Signal Processing - November 2016 - 147
Signal Processing - November 2016 - 148
Signal Processing - November 2016 - Cover3
Signal Processing - November 2016 - Cover4
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