PROCEEDINGS of the
23rd International Congress on Acoustics
9 to 13 September 2019 in Aachen, Germany

Sound quality improvement of operation sounds emitted by MFPs
Masao YAMAGUCHI1
1

Toshiba Tec Corporation, Japan

ABSTRACTMultifunctional peripherals (MFPs) integrating multiple functions including copying, printing, scanning, andfaxing functions in one unit are now widely used in offices. In MFPs there are many sound sources which
generate steady sounds such as noises emitted by motors and fans, and transient sounds such as collision
noises between parts. It is difficult to identify sound sources for sound quality improvement, because of thevariety of sounds when in operation. In this study, we proposed a method to efficiently improve the soundquality of the operation sounds emitted by MFPs. First we performed a subjective sound quality evaluationof the operation sounds using the SD method. Then, we derived an equation (PSI) representing pleasantness,based on the subjective sound quality evaluation and the psychoacoustic parameters. We also examined theinfluence of each sound on a pleasantness scale of the operation sounds. In the examination we performed asensitivity analysis by calculating the contribution of each sound to the pleasantness by using the PSI. Finally,
we took steps to modify the sounds that were high in contribution to the improvement in sound quality.
Consequently, we efficiently achieved an improvement in sound quality to the operation sound emitted by the
MFP.
Keywords: Sound quality, Multifunctional peripheral, Psychoacoustic parameter

1. INTRODUCTION
These days, multifunctional peripherals (MFPs) integrating multiple functions including copying,printing, scanning, and faxing functions in one unit are now widely used in offices. In addition, thenumber of parts of MFPs has increased compared to a single purpose machine. Additionally, there is agreat demand for MFPs to achieve high-speed and small-size, and also to produce images anddocuments in high-resolution. As a result, operation sound becomes a problem due to the further
increase in the number of parts, the complicating of the mechanism, and the speeding up driving parts.
Furthermore, quietness of offices has progressed due to the improvement of noise reduction technologies
in buildings. Therefore, the operation sounds from the office equipment in offices have become easierto hear than before. Consequently, a pleasant sound emitted by the MFP is desirable.
There are many kinds of sound sources in MFPs. Some examples are: motors, gears, papers,
clutches, and other sound sources. Moreover, the sound includes steady sounds and transient sounds.
These are the features of MFPs. One of the steady sounds is noise from the motor, and one of thetransient sounds is the collision sound between parts. The sound qua lity emitted by products has
become very important in addition to the reduction of sound pressure (1, 2). However, the soundquality improvement of the operation sound emitted by the MFP is difficult, because the soundincludes many sound sources and is non-steady (3, 4). Therefore, it is difficult to identify soundsources for an improvement in sound quality. If the part of the sound that makes a high contribution to
the sound quality is identified, the sound quality improvement can be made efficiently.
In this study, we proposed a method to efficiently improve the sound quality of the operation sounds
emitted by MFPs. First we performed a subjective sound quality evaluation of the operati on sounds
using the SD method. Then, we derived an equation representing pleasantness, based on the subjective
sound quality evaluation and the psychoacoustic parameters. We also examined the influence of eachsound on a pleasantness scale of the operation sounds. In the examination we performed a sensitivity
analysis by calculating the contribution of each sound to the pleasantness by using the equation we
derived. Finally, we took steps to modify the sounds that were high in contribution to the sound quality
improvement of the operation sound.
1

Masao_Yamaguchi@toshibatec.co.jp8009

2. ACOUSTIC CHARACTERISTICS OF OPERATION SOUNDS EMITTED BY MFPS
2.1 Configuration of MFP
Figure 1 (a) shows the MFP which is a Toshiba Tec product, whose configuration is only the main
body. Figure 1 (b) shows the main body of the MFP and an optional finisher. The finisher is attached tothe main body, and has functions such as stapling, sorting, punching holes, and folding documents,
after printing has been performed by the main body.
Finisher(a) Main body(b) Main body and finisher
Figure 1 – Appearance of MFP

2.2 Frequency Characteristics of Operation Sounds Emitted by MFPs
First, we measured the characteristics of the sounds emitted by the MFPs during consecutive page
printing in color mode. Figure 2 (a) and (b) show color maps of the frequency characteristics of sounds
emitted by the MFPs, whose configurations are the main body alone and the main body with thefinisher attached, respectively. Figure 3 shows a comparison of each frequency characterist ic.
In the Figures the printing speed of the MFP is 50 Pages Per Minute (PPM) in consecutive color
printing mode, and the operation mode of the finisher is two sheets two staples mode whose sound isloudest. A microphone is placed at 1 m in front of the machine’s front surface. The microphone’s
position is supposed to represent the position of a bystander.
As shown in Figure 2 and 3, many kinds of transient sounds and steady sounds are included.
Moreover, when the finisher is attached, the number of transient sounds and steady sounds increases,
and the peak frequency sound is louder. As a result, the sound pressure level of the configuration islarger than that of the main body alone. In Figure 2, the cyclic period is continuously repeated duringconsecutive page printing. From these characteristics, in this study, we have focused on the operation
sound emitted by the MFP whose configuration is the main body with the finisher attached.
1 cyclic part
Frequency (Hz)Frequency (Hz)

0
0

10k

10

Time (s)00Time (s)10Sound pressure level (dB)

1 cyclic part
10k

Sound pressure level (dBA)(a) Main body(b) Main body and finisher
Figure 2 – Color maps of frequency characteristics of operation sounds emitted by MFPs
60
Main body
Main body and finisher

50
40
30

20
10
0

0

200

600
400
Frequency (Hz)

800

1000

Figure 3 – Comparison of frequency characteristics of operation sounds emitted by MFPs

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60
50
40
30
20
10
0

3. SUBJECTIVE SOUND QUALITY EVALUATION
3.1 Sound Quality Evaluation Using Semantic Differential (SD) Method
We performed a subjective sound quality evaluation of the operation sounds emitted by the MFPs
whose configurations were the main body with the finisher attached. We prepared five evaluation sounds
which were recorded operation sounds. The printing speeds of the MFPs were from 47.5 to 60 PPM inconsecutive color printing, and the operation mode of the finisher was two sheets two staples mode. The
microphone for recording sound was placed in the same way as previously mentioned in 2.2.
28 Japanese subjects aged between 22 and 55 participated in the sound quality evaluation usi ng the
SD method. The subject sat on a chair and listened to the evaluation sounds from a speaker in themeeting room, then answered the impression of evaluation sound on a scale of one to seven using theform as shown in Figure 4. After that, we performed a factor analysis using the data of the SD method.
Very

Quiet
SmoothLike
Pleasant

NeitherQuite Slightly Nor Slightly Quite

Very

1

2

3

4

5

6

7

1

2

3

4

5

6

7

1

2

3

4

5

6

7

1

2

3

4

5

6

7

Clamorous
Spiky
Dislike

Unpleasant

14 bipolar adjective pairs

Figure 4 – Questionnaire form for SD method
3.2 Result of Sound Quality Evaluation
Table 1 shows the result of the factor analysis. A pleasant factor such as “Pleasant - Unpleasant”, ametallic factor such as “Metallic - Moist” and a powerful factor such as “Powerful - Weak” are classified.
Figure 5 (a) and (b) show the scatter diagrams of the factor scores. In Figure 5 (a), the plotted
data on the horizontal axis represents the factor score of a pleasant factor which indicates that
operation sound is more pleasant in the upper direction. The plotted data on the vertical axis
represents the factor score of a metallic factor which indicates that operation sound is more metallic
in the lower direction. In Figure 5 (b), the plotted data on the horizontal axis represents the factor
score of a pleasant factor which is the same as Figure 5 (a). The plotted data on the vertical axis
represents that of a powerful factor which indicates that operation sound is more powerful in thelower direction. In these Figures, the five operation sounds emitted by the MFPs are defined as
MFP1- MFP5, respectively.
Table 1 – Result of factor analysis of operation sounds emitted by MFPs
Adjective pairs

Pleasant factor

Metallic factor

Powerful factor

Pleasant – Unpleasant

-0.82

-0.30

-0.23

Like – Dislike

-0.79

-0.34

-0.09
-0.27

Beautiful – Dirty

-0.76

-0.32

Cheap – Luxurious

0.70

0.41

0.01

Quiet – Clamorous

-0.68

-0.37

-0.37

Restless – Calm

0.66

0.39

0.37

Cracked – Smooth

0.63

0.49

0.17

Round – Square

-0.57

-0.53

-0.17

Metallic – Moist

0.35

0.78

0.16

Gruff – Delicate

0.50

0.74

0.20

Hard – Soft

0.51

0.61

0.39

Powerful – Weak

0.37

0.30

0.77

Contribution ratio

0.36

0.22

0.11

Cumulative
contribution ratio

0.36

0.58

0.69

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0

1.0

MFP2
MFP3
MFP5

Powerful factor

Metallic factor

1.0

MFP1

-1.0
-1.0

MFP4
0
Pleasant factor

MFP3 MFP5
0

MFP4
MFP1

-1.0
-1.0

1.0

(a) Metallic factor vs. Pleasant factor

MFP20
Pleasant factor

1.0(b) Powerful factor vs. Pleasant factor

Figure 5 – Scatter diagrams of factor scores
Figure 5 (a) indicates that when an auditory impression of the sound is metallic, the sound is felt
unpleasant. Figure 5 (b) indicates that when an auditory impression of the sound is powerful, the soundis felt unpleasant. In order to identify the sound that was deteriorating sound quality, we asked thesubjects which sound felt metallic and powerful. The comment of the subjects was that the impulsive
sounds in evaluation sound were metallic and powerful, and the motor sounds were metallic.
Therefore, it may be stated that the impulsive sounds and the motor sounds affect an impression of theoperation sounds emitted by the MFPs whose configurations are the main body with the finisher attached.

4. DERIVING EQUATION REPRESENTING PLEASANTNESS
4.1 Significance of Deriving Equation Representing Pleasantness
We derived an equation representing pleasantness using psychoacoustic parameters. The significanceof derivation is as follows:
It is possible to:(a) Quantify the sound quality without performing the subjective sound quality evaluation.
(b) Clarify the target value of the sound quality by representing it quantitatively.
(c) Easily identify the part of the sound that makes a high contribution to the sound quality, andpredict the effect of the improvement in sound quality, before making a prototy pe with steps
to improve sound quality.
Therefore, the sound quality improvement can be made efficiently, so the duration and the cost of
product development can be reduced.
4.2 Deriving Equation Representing Pleasantness Using Multiple Regression Analysis
In order to derive the equation, we performed a multiple regression analysis based on thepleasantness factor score obtained by the factor analysis as previously mentioned in 3.2, and on thepsychoacoustic parameters as shown in Table 2. In performing a multiple regression analysis, theobjective variable is the pleasantness of the sound, and the explanatory variable is the psychoacoustic
parameters. We defined the objective variable of a multiple regression analysis as Pleasant Sound
Index (PSI). The equation obtained by a multiple regression analysis is as follows:
PSI = - 0.358 * Loudness - 1.364 * Sharpness - 2.026 * Roughness + 8.036

Table 2 – Psychoacoustic parameters of each MFP

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Loudness(sone)

Sharpness(acum)

Roughness(asper)

MFP1

13.6

1.456

0.929

MFP2

11.8

1.182

0.870

MFP3

12.4

1.491

0.650

MFP4

13.1

1.599

0.912

MFP5

11.0

1.501

0.657

(1)

Value of pleasantness

1.0

Subjective evaluation
Calculated value using PSI

0

-1.0

MFP1

MFP2

MFP3

MFP4

MFP5

Figure 6 – Difference in value of pleasantness between subjective evaluation and calculated PSI
Figure 6 shows the values of the pleasantness factor score obtained by the subjective evaluationand calculated PSI. Figure 6 indicates that the calculated values using PSI concur with the factor
score obtained by the subjective evaluation. The correlation coefficient between the values of thepleasantness by calculating PSI and the subjective evaluation is 0.992. From this result, it may bestated that the precision of the equation (PSI) we derived is high, and it is possible to use PSI toevaluate the pleasantness of operation sounds emitted by MFPs. Additionally, by quantifying thesound quality using the PSI, it is possible to clarify the target value of the sound quality.

5. IDENTIFYING SOUND THAT MAKES HIGH CONTRIBUTION TO SOUND QUALITY
5.1 Influence of Each Sound on Impression of Operation Sound
If the part of the sound which makes a high contribution to the sound quality is identified, thesound quality improvement can be made efficiently (5). Therefore, we examined an influence of eachsound on an impression of the operation sound emitted by the MFP4. In order to obtain the value of theinfluence, we performed the sensitivity analysis by calculating the contribution of each sound to thesound quality improvement of the operation sounds, using the PSI we derived. In performing thesensitivity analysis, we prepared sounds which were edited sounds that consisted of only part oforiginal sound was changed, and then we calculated the pleasantness of each edited sound using PSI.
Figure 7 and 8 show how the evaluation sounds were edited from the original sound using acoustic
simulation (6).
1. The transient sound 13 (T13) was edited by replacing it with the steady part as shown in Figure 7
which shows one cyclic part of the operation sound.
2. The peak sounds of the frequency characteristic (363 Hz and 1494 Hz) were cut off with anotch filter as shown in Figure 8.
T5

T6

T7

T8 T9

T10

T11 T12 T13

00Time (s)2.4Sound pressure level (dB)

T460

Sound pressure level (dB)Frequency (Hz)T1 T2 T3
20k

60

50
40

30
20
10
0

Frequency (Hz)(a) Original sound
20k

0
0

Time (s)

2.4

50
40
30
20
10
0

(b) Edited sound with T13 removed
Figure 7 – Original sound and edited sound with one transient sound removed

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50

1494Hz

363Hz

40
30
20
10
0

0

1000
500
1500
Frequency (Hz)60

Sound pressure level (dBA)

Sound pressure level (dBA)



60

363Hz

50

1494HzNotch filter

40
30
20
10
0

2000

1000
500
1500
Frequency (Hz)

0

2000

  (a) Original steady sound(b) Edited steady soundFigure 8 – Original steady sound and edited steady sound with peak frequency sounds cut off

We prepared 14 edited sounds, which consisted 13 transient sounds and one steady sound whosesound sources were in the finisher, because in this study we have focused on the operation soundemitted by the finisher. We defined transient sound 1-13 as T1-T13, respectively.
5.2 Result of Sensitivity Analysis
Figure 9 shows the result of the sensitivity analysis by calculating the contribution of each soundto the improvement in pleasantness. In Figure 9 the bar graph data of the calculated improvement
value of pleasantness is shown on the left vertical axis, which indicates that the improvement effectof removing transient sound and cutting off peak frequency sound is larger in the upper direction. In
this calculation, the PSI of the original sound was subtracted from each calculated PSI of edited
sound which had each transient sound removed and the peak frequency sound cut off. The plotted
data of the calculated reduction value of sound pressure level is shown on the right vertical axis,
which indicates that the reduction effect of removing transient sound and cutting off peak frequency
sound is larger in the upper direction. In this calculation, each sound pressure level of the edited
sound was subtracted from that of the original sound.

Improvement valueof pleasantness

0.25
0.25

0.5
0.5

0.2
0.20

0.4
0.4

0.15
0.15

0.3
0.3

0.1
0.10

0.2
0.2

0.05
0.05

0.1
0.1

0.45
0.35
0.25

0.15
0.05

00

T1

T2

T3

T4

T5

T6

T7

T8

T9

T10

T11

T12

T13 Steady
sound

00

Reduction value of soundpressure level (dBA)

Cutting off
peak frequency soundRemoving transient soundFigure 9 – Sensitivity analysis by calculating contribution of each sound to sound quality improvement

6. SOUND QUALITY IMPROVEMENT OF OPERATION SOUND EMITTED BY MFP
6.1 Taking Steps to Improve Sound Quality
We modified the MFP4 and made a prototype that took steps to improve the sound quality. We
accomplished this by using the following policy.
We did not allow:(1) Major design changes. In other words, we aimed to achieve the sound quality improvement by
taking simple steps.
(2) A significant cost increase.
(3) Specification changes to the MFP. The reason behind this is that loudness of the operation soundcan be reduced by slowing down driving parts. However, printing speed will also be slowed down,
and as a result, specifications need to be changed.
We took steps to modify the top nine sounds that are high in contribution to the improvement insound quality as shown in Table 3.

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Table 3 – Steps to improve sound quality of operation sound emitted by MFP4
Sounds which taken steps

Causes of sounds

Steps

Effects

T1, T4, T5, T6, T11, T13

Backlash between parts

Reducing gap between parts- Reducing loudness of sound- Reducing reverberation

T13

Collision between parts

Reducing impact force throughinstallation of shock absorbing material- Reducing loudness of sound- Reducing reverberation

T4

Shock due to rapid speed
fluctuations in operation of part

Smoothing operation of part throughsmoothing motor control accelerationand deceleration- Reducing impulsive sound- Reducing reverberation

Steady soundVibration caused by drive pulse

Replacing stepping motor withDC motor- Reducing loudness of peakfrequency soundMain target sounds: T7, T10
This step is effective for all
soundsSound leakage from the gap

Reducing opening of parts- Improving sound insulation

6.2 Result of Sound Quality Improvement
Figure 10 and 11 show the frequency characteristics of the original operation sound emitted by
the MFP4 and that of the modified MFP4 for which we have taken steps to improve the pleasantness.
Figure 12 shows the values of pleasantness and the sound pressure levels of the operation sounds. In
Figure 12, the bar graph data of the calculated value of pleasantness using PSI is shown on the left
vertical axis, which indicates that the operation sound is more pleasant in the upper direction. The
plotted data of the sound pressure level is shown on the right vertical axis.
These figures show that the pleasantness of the operation sound emitted by the modified MFP4
significantly improved compared to the original MFP4 by taking simple steps. However, the value ofthe pleasantness of the modified MFP4 is lower than that of the MFP5, even though the soundpressure level of the modified MFP4 is lower than that of the MFP5.
T5

T6

T7

T8 T9

T10

T11 T12 T13

20k

0
0

2.4

Time (s)Sound pressure level (dB)

T460

Sound pressure level (dB)Frequency (Hz)T1 T2 T3

60

50

40
30
20

10
0

20k

0
0

2.4

Time (s)

50
40
30
20
10
0

(b) After improvement
Figure 10 – Color maps of frequency characteristics of operation soundSound pressure level (dBA)

Frequency (Hz)(a) Before improvement60

Before improvement
After improvement

50
40
30
20
10
0

0

1000
500
1500
Frequency (Hz)2000

Figure 11 – Comparison of frequency characteristics between original sound and after improvement

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Sound pressure level (dBA)

Value of pleasantness

1
1.0

58.00
57

0.5
0.5

57.00
56

00

55

56.00
55.00

-0.5
-0.5

-1.0
-1

54
54.00
MFP1

MFP2

MFP3

MFP4

MFP5

After improvementof MFP4

53
53.00

Figure 12 – Comparison of operation sounds emitted by MFPs, including improvement effect of MFP4
As a result of further investigation into the MFPs, it was found that the sound insulation of the
MFP5 was higher in value with the cost increase. The sound insulation effect of the MFP5 was foundto be 34% higher in sound power than that of the MFP4. Therefore, further improvement in thepleasantness of the modified MFP4 can be expected just by improving the sound insulation.
Furthermore, we have clarified the steps to improve the sound quality of the transient sound emitted
by the main body. As a result, further improvement in the pleasantness of the modified MFP4 can be
expected by taking steps to the main body. Consequently, it may be stated that the sound quality
improvement can be made efficiently using the method we carried out.

7. CONCLUSIONSIn this study, we proposed a method to efficiently improve the sound quality of the operation
sounds emitted by MFPs. It is difficult to identify the sound which leads to the improvement. In themethod, in order to quantify the pleasantness of operation sound emitted by MFPs, we derived theequation (PSI) representing the pleasantness. It has been confirmed that the correlation coefficient
between the calculated value of the pleasantness using PSI and the pleasant factor score obtained by
the subjective evaluation is high. Therefore, it may be stated that the precision of the PSI which
represents the pleasantness is high. Then, we examined the influence of each sound on thepleasantness scale of the operation sounds. In the examination we performed the sensitivity analysis bycalculating the contribution of each sound to the pleasantness by using the PSI. After that, in order tomodify the MFP, we made a prototype that took simple steps to improve the sound quality. As aresult, the sound quality of the operation sound emitted by the modified MFP was improved.
By using the PSI, it is possible to quantify the sound quality without performing the subjective
sound quality evaluation, and to clarify the target value of sound quality as well. Moreover, we caneasily identify the part of the sound that makes a high contribution to sound quality. We also can
predict the effect of the improvement in sound quality before making a prototype with steps toimprove sound quality. Therefore, we can efficiently achieve the improvement in so und quality tothe operation sounds emitted by the MFP using the method we carried out, which will lead to a
reduction in the duration and the cost of development of MFPs.

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