Effectiveness of ANC Partition with Film Speaker
Yusuke MAKIYAMA(1) , Shun HIROSE(2) , Kohei OTO(3) , Yusuke KOMOTO(4) and Yoshinobu KAJIKAWA(5)(1) Kansai University, Japan, k494073@kansai-u.ac.jp(2) Kansai University, Japan, k458472@kansai-u.ac.jp(3) Nitto Denko Corporation, Japan, kohei.oto@nitto.com(4) Nitto Denko Corporation, Japan, yusuke.komoto@nitto.com(5) Kansai University, Japan, kaji@kansai-u.ac.jp

Abstract
In this paper, we design an ANC partition with ﬁlm speaker and demonstrate the effectiveness through experimental results. In a cubicle of public areas, like a reception desk inside bank, surrounding sound including
conversation and environment noise avoids smooth conversation and the privacy may not be protected due toleaking to the adjacent cubicles. In such a case, the partition should have not only passive sound control function
but also active sound control function. However, the ordinary loudspeaker (electrodynamic loudspeaker) may
not be implemented into the partition effectively and may not control enough region in the cubicle. In this paper,
we implement a ﬁlm speaker into the partition and realize active noise control (ANC) system. The proposed
ANC partition can achieve more than 10 dB noise reduction and wider zone of quiet compared with the ANC
partition using the ordinary loudspeaker.

1 INTRODUCTION
In recent years, when many people talk at the same time in an open place, there are problems such as
difﬁculty in conversation and information leakage such as TV and snoring disturb sleep in a hospital room,and conversations leak to people next to a bank window, a meeting room, and a shared ofﬁce. We therefore
examine a partition with active noise control (ANC) in order to solve the problem. Active noise control (ANC)
is a means of reducing noise. ANC is a system that can reduce noise by superimposing anti noise of the same
amplitude and opposite phase as the target noise (1-4).
As similar applications, ANC headrest for reducing broadband noise has been already proposed and examinedin the reference (5). In the ANC headrest, since the headrest part is surrounding the user’s head, this could
be thought one kind of ANC partitions. As another approach, an ANC partition for reducing snore noise in
bed rooms has been proposed in the reference (6). In this approach, the ANC partition is located between asnoring person and the partner, and then creates Zone of Quiet (ZoQ) for the partner. Either approach considers
creating ZoQ for one person who is sitting a chair with the ANC headrest or is exposed by snore noise from thepartner. However, this paper aims at controlling sound environments in a cubicle of public areas like a reception
desk inside band. In this case, one partition should reduce noise in not only one cubicle but also the adjacent
cubicle at the same time, and two loudspeakers must be consequently implemented at the same location on theboth sides of the partition as secondary sources. In such a situation, ordinary loudspeaker (e.g. electrodynamicloudspeaker) requires a thick partition to ensure a back cavity for the loudspeaker and such bulky partition
is not practical. Moreover, multiple loudspeakers with large diameter are needed to control wider area in the
cubicle and costly, bulky and complicated system is accordingly required. Furthermore, active noise controlbarriers have been studied by many researchers as a similar application (7-12). However, these studies aim atlarger sound barriers for road noise and surrounding noise around house, so that ordinary loudspeakers can beeasily installed for such ANC barriers unlike ANC partitions for small cubicle.
In this paper, we utilize a thin ﬁlm speaker instead of an ordinary loudspeaker as a secondary source. By
using thin ﬁlm speaker, the secondary sources can be implemented at the same location on both sides of a24

thin partition and the cost and space can be consequently saved. Moreover, this thin ﬁlm speaker can generate
similar sound wave surface as the diffraction sound with the partition from the noise source and can control
wider areas in the cubicle.

2 ANC PARTITION
ANC partition where secondary sources are installed on the partition can create zone of quiet (ZoQ) aroundthe user’s ears and multiple ANC partitions can create quiet sound environment in a cubicle surrounding by thepartitions. In this case, a multi-channel ANC is required to realize higher noise reduction while considering thecrosstalk paths. In the ANC partition, the error microphones are generally put on the partitions, so that ZoQ
cannot be created around user’s ears. One of solutions is to utilize ﬁxed noise control ﬁlters which are obtainedby setting the error microphones around the user’s ears and estimating the optimal ﬁlter coefﬁcients in advance.
In this paper, we realize an ANC partition based on the ﬁxed noise control ﬁlter. Moreover, we utilize two
ANC partitions to control sound near the user’s ears and apply CASE (1,2,2) ANC which has one reference
microphone, two secondary sources and two error microphones.

3 CASE (1, 2, 2) ANC SYSTEM
A block diagram of the CASE (1,2,2) ANC system is shown in Fig. 1. In Fig. 1, em (n) is an error signal,
yk (n) is an output signal of a noise control ﬁlter, and x(n) is a reference signal. Here, m(= 1, 2) represents
the channel of the error microphone, and k(= 1, 2) represents the channel of the secondary source. The ﬁlteredreference signal is given byrmk (n) = ŝmk ∗ x(n)(1)
using x(n) and the secondary path model ŝmk . Also, the noise control ﬁlters are updated by2

αr (n)em (n),2 mkβ+
rmk (n)
m=1

wk (n + 1) =wk (n) + ∑(2)

where wk (n) is the ﬁlter coefﬁcient vector, and rmk (n) is the ﬁltered reference signal expressed aswk (n) = [wk0 (n) wk1 (n) · · · wkM−1 (n)]T ,rmk (n) = [rmk (n) rmk (n − 1) · · · rmk (n − M + 1)]T ,(3)

where M is the tap length of the noise control ﬁlters, α is a step size parameter, and β is a regularization
parameter which prevents the divergence due to small reference signal, respectively.

4 EXPERIMENTAL RESULTS
The effectiveness of the ANC partition based on the CASE (1,2,2) ANC is examined through noise reduction
experiments using an actual system. In the experiments, we compare the error spectra at the error microphone
locations and the size of noise reduction areas between an ordinary loudspeaker and a ﬁlm speaker which areinstalled on the partitions respectively. A dynamic loudspeaker (P650K from FOSTEX) is used as an ordinary
loudspeaker and a ﬁlm speaker is made by Nitto Denko corporation. The experimental conditions are shown in
Table 1, the experimental environment is shown in Fig. 2(a), and the system arrangement is shown in Fig. 3,respectively. The experiments were conducted in a soundproof room (2.9 × 3.1 × 2.1m3 ). The sound pressurelevel of the noise was set to be 60 dB near the right ear (Ch. 1) of the HATS (Head and Torso Simulator).
Figure 4 shows the sound pressure distribution when the ANC is not operating.
Figures 5 and 6 show the error spectra at each error microphone (each ear) using the ordinary loudspeakers
and ﬁlm speakers as the secondary sources, respectively. It can be seen from Figs. 5 and 6 that the ANC

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x(n)

P1(z)
P2(z)

+d1(n)d2(n)y11' (n) y21' (n)S11(z)

W1(z)Ŝ11(z)
Ŝ21(z)

r11(n)+ e2(n)
∑- -

∑

e1(n)
-S21(z)y1(n)' (n) y12y22' (n)NLMSr21(n)

S22(z)
W2(z)Ŝ12(z)
Ŝ22(z)

r12(n)

S12(z)

y2(n)

NLMS

r22(n)

Figure 1. Block diagram of CASE(1, 2, 2) ANC system.
partition with the ordinary loudspeaker can reduce the noise more at the both error microphones (ears) than theANC partition with the ﬁlm speaker. However, the dynamic loudspeaker requires sufﬁcient thickness for thepartition, it is consequently difﬁcult to install it on the partition. Hence, the ﬁlm speaker is more suitable for
the ANC partition.
Next, Fig. 7 shows sound pressure level distributions after ANC inside the cubicle bounded by the two ANC
partitions. It can be seen from Fig. 7 that the ANC partition with the ﬁlm speaker can create wider noise
reduction area (ZoQ) than that with the ordinary loudspeaker. We measured the phase planes from noise source(diffraction wave due to the partition), the ordinary loudspeaker installed on the partition, and the ﬁlm speakerinstalled on the partition, respectively. Fig. 8 shows the phase planes when emitting a sinusoidal wave whose
frequency is 800 Hz. It can be seen from Fig. 8 (a) and (b) that the ﬁlm speaker can generate plane wave
rather than spherical wave unlike the dynamic loudspeaker. Moreover, it can be found from Fig. 8 (c) that thediffraction sound from the noise source has the same characteristics as the ﬁlm speaker. Hence, the ﬁlm speaker
can realize the similar sound wave surface as the diffraction sound from the noise source in wider areas, sothat the wider ZoQ can be created inside the space bounded by the partitions. From the above results, the ﬁlm
speaker is more suitable for the ANC partition.

Table 1. Measurement conditions in noise reduction experiments
Unwanted noiseWhite noise (500 - 800 Hz)
Tap length of noise control ﬁlter Wk200
Tap length of secondary path model Ŝmk70
Step size parameter α0.01
Regularization parameter β
1.0 × 10−6
Sampling frequency
4000 Hz
Cut-off frequency of analog low-pass ﬁlter
1000 Hz26

(a)Ordinary loudspeaker(b)Film speaker
Figure 2. Experiment environment

Ch. 1 Partition Ch. 2
Noise Source
17.5 cm
10 cm
Reference Microphone
70 cm

Ch. 1

Ch. 2

HATS

45 cm

Error Microphones
30 cm

12.5 cm

Figure 3. System arrangement in CASE(1, 2, 2) ANC system.

Figure 4. Sound pressure distribution at ANC off.

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ANC off
ANC on-60-80-100
400

500

600 700 800
Frequency [Hz]-40
Amplitude [dB]

Amplitude [dB]-40-60-80-100
400

900

ANC off
ANC on(a)Right ear (Ch. 1)

500

600 700 800
Frequency [Hz]900(b)Left ear (Ch. 2)

Figure 5. Comparison of error spectra at the error microphone locations in CASE(1, 2, 2) ANC system withordinary loudspeaker

ANC off
ANC on-60-80-100
400

500

600 700 800
Frequency [Hz](a)Right ear (Ch. 1)

900-40
Amplitude [dB]

Amplitude [dB]-40

ANC off
ANC on-60-80-100400500

600 700 800
Frequency [Hz]900(b)Left ear (Ch. 2)

Figure 6. Comparison of error spectra at the error microphone locations in CASE(1, 2, 2) ANC system withﬁlm speaker(a)Ordinary loudspeaker(b)Film speaker

Figure 7. Sound pressure distributions in CASE(1, 2, 2) ANC system.

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(a)Ordinary loudspeaker(b)Film speaker(c)Noise source

Figure 8. Comparison of phase planes from ordinary loudspeaker, ﬁlm speaker, and noise source.

5 CONCLUSION
In this paper, we developed an ANC partition using a ﬁlm speaker and demonstrate the effectiveness throughsome experiments. The ANC partition with the ﬁlm speaker can realize wider ZoQ than the ordinary (dynamic)
loudspeaker inside the space bounded by the partitions. This is because the ﬁlm speaker can generate similarsound wave surface as the diffraction sound with the partition from the noise source. Hence, the ﬁlm speaker ismore suitable for the ANC partition. In the future, we will develop an ANC partition which can control soundspaces of both sides of the partition.

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