PROCEEDINGS of the23rd International Congress on Acoustics
9 to 13 September 2019 in Aachen, Germany

Improvement of construction machine noise
Takeo HASHIMOTO 1; Shigeko HATANO 2
1

Seikei University, Japan2

Seikei University, JapanABSTRACTThis Study deals with the improvement of booming sensation inside the compartment of construction
machine. Booming sensation is the hearing sensation caused by the existence of low frequency component
below 500Hz and due to this component our ear drums are pressurized and feel pressurized feeling that isuncomfortable. In the first place, 6 construction machines were tested their degree of booming sensationand the worst one for this ranking is selected for improvement. Then, several factors are selected for
improvement of booming sensation. Selected factors are fun noise, intake and exhaust noises. In order totest the effect of these factors to the reduction of booming sensation, each component noise was eliminatedby the lead cover method. As a result, reduction of fan noise was most effective counter measure for theimprovement.
Keywords: Booming sensation, Low frequency sound, Improvement, Fun noise

1. INTRODUCTION
At the construction site of buildings and that for the development of city area for example, manyconstruction machines are used for moving earth and to move heavy materials for the constructions.
Due to this, the inhabitants near the construction cite exposed to the noise emitted from themachines(1). In these days, the noise emitted from these machines becomes quieter and quieter inorder not to affect the residents near the construction site. Together with the noise emitted to theoutside, the compartment noise inside the cabin must be improved for the operators inside(2).
Especially, if low frequency content of sound below 500Hz dominates inside the cabin, then thebooming sensation reveals to the operator’s hearing and felt annoyed. This paper describes the way
how we reduce booming sensation that is felt uncomfortable inside the compartment.
For this purpose, we have conducted subjective experiment by using 6 medium size construction
machine noises for the evaluation of booming sensation to decide the ranking of booming sensation.
Then, to pick up the sound with worst ranking for booming sensation, we have conducted the second
experiment for the improvement of booming sensation by modifying the original sound in variousways. The countermeasure introduced were reductions of cooling fun noise, intake and exhaust
noises. And these effects were tested subjectively in a separate manor on one hand and the combined
effects are also examined.
As a result, to reduce cooling fun noise for cooling the Diesel engine equipped for the power toactivate oil pressure for the construction machine is most effective countermeasure for reducing
booming sensation.

2. EXPERIMENT FOR RANKING OF BOOMING SENSATION
2.1 Test Sounds, Subject and Test method
Test sounds are 6 construction machine noises at no load and high idle condition for medium size
construction machines, their weights are similar and 20tons class. Subjects participated thisexperiment were 19males and 2 females aged between 21 and 62 with normal hearings. Test wasconducted inside the sound proof room and subject sits in front of the screen set 2m apart from the128048

hashimotf@st.seikei.ac.jp
hatano@st.seikei.ac.jp

subject. In the first place, video image of the construction machine is projected on the screen by theLCD projector and construction machine noise was reproduced by the equalized headphone andwoofer set in front of the subject to strengthen the low frequency sound with realistic impression. In
this stage, subjects were asked to just watch the image and hear the sound. Then, next session, only
sounds were reproduced with no image and subjects were asked to evaluate the booming sensation
using score seat. They are asked to evaluate booming sensation in seven categories from 1 to 7 thatare relates to not booming at all to strong booming.
2.2 Test result
The result was shown in Figure 1. as is shown in this figure, sound B is more booming among the6 sounds. And the relation between the test result and booming index(3) was shown in Figure 2. The
relation between the test result in booming sensation and booming index is good and the correlation
is 0.903. On the other hand, relation between booming sensation and loudness(4) is not so highcompared with that with the booming index In this case, correlation is r=0.617.

Figure - 1 result of ranking on booming sensation for 6 construction machines

Figure – 2 booming sensation and booming index

Figure -3 booming sensation and loudness

2.3 Select of the sound to improve
As a result of this experiment, we have chosen the sound B as the one to modify its boomingsensation because this sound is more booming among the 6 sounds..

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3. IMPROVEMENT OF BOOMING SENSATION ON SOUND “B”
3.1 Method for Improvement
As was shown in the previous chapter 2, test sound B is most booming sound among the 6 test
sounds. In order to make sound B with less booming sensation, the original test sound was modified
at the recording stage. The way we modified the sound B is as follows.
ձ Original sound without modification
ղ Elimination of cooling fun noise by elongation of inlet horse at the original fun position andthe introduction of lead metal cover for the reduction of fun noise.
ճ Elimination of exhaust noise by the lead metal cover of the exhaust muffler area.
մ Elimination of intake noise by the lead metal cover of the intake muffler area
յ Elimination of fun and exhaust noisesն Elimination of fun and intake noisesշ Elimination of intake and exhaust noisesո Elimination of fun noise and intake and exhaust noises.
FFT spectra of original sound B, and that of the elimination of fun noise is shown in Figure – 4. By
the elimination of fun noise, broad band level reduction effect is observed according to see Figure -4.
We could expect more effect for the improvement of booming sensation by this treatment.

Figure – 4 FFT spectra of sound B and that of the elimination of fun noise

Figure – 5 FFT spectra of sound B and that of the elimination of exhaust noise8050

Figure – 6 FFT spectra of sound B and that of the elimination of intake noise
From Figure -5, we could two peaks around 100 and 150 Hz reduce their peak values by theelimination of exhaust noise. And by the elimination of intake noise, peak at the 200Hz reduced its
peak significantly and as is shown in Figure – 6.
3.2 Subjective Evaluation of Sound B and its Variations
The method to represent sound to the subjects is the same as in the first test for the presentationof sound alone condition. And the subjects participated in this experiment are the same as in the firstexperiment. Again, subjects were asked to evaluate the booming sensation of test sounds in 7
categories from one to seven that related to not booming and booming.
Result of evaluation in booming sensation for the variation of sound B including its original was
shown in Figure – 7.

Figure – 7 Evaluation of booming sensation of sound B and its variations
According to the test result, if one countermeasure is selected, then elimination of fun noise is8051

most effective for the reduction of booming sensation(ձ) and the second one is elimination of intake
noise(մ) and the last one is elimination of exhaust noise(ճ). Combined effect by the several
treatments taking together is the most for the elimination of fun and intake noise together(ն) andthis is close to the three treatments together(ո), namely the elimination of fun, intake and exhaust
noise. The least effect is observed by the combined effect of the elimination of intake and exhaust
noises together(շ) elimination of fun and exhaust noise together is close to the elimination of funnoise alone(յ).
The relation between booming sensation of test sounds and booming index is shown in Figure – 8and that with the loudness is shown in Figure – 9.

Figure – 8 relation between booming sensation of test sound and booming index

Figure – 9 relation between booming sensation of test sounds and loudness
The evaluation of booming sensation of the test sounds, namely, sound B and its variations arewell collated with the booming index and loudness.
The result of evaluation on booming sensation is compared with the sound energy ratio, namely,sound energy of the sound variations were divided by that of the original sound B. We could havehigh correlation with this expression, r=0.9246. Namely with the treatment of sound B, sound energyof the treated sound reduced and if the energy reduction is more then the sound becomes lessbooming.

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Figure – 10 relation between booming sensation of test sounds and sound energy ratio

4. CONCLUSIONSThe evaluation of booming sensation of cabin noise of medium size construction machines wasconducted under the condition of high idle no load condition. In the beginning of the experimental
stage, we have compared 6 construction machine noises for the ranking of booming sensation to pickup most booming sound among the six test sounds. Then, the most booming sound was selected forimprovement.
In order to find the way to reduce booming sensation of cabin noise inside the compartment ofconstruction machine, three treatments were selected, namely, elimination of cooling fun noise,elimination of intake noise and that of exhaust noise. We also tested combined effect of thesimultaneous treatments such as elimination of fun and intake noises etc.
As a result, following conclusions were obtained..
1. Result of booming evaluation obtained for ranking which sound is more booming with the others
related well with the booming index. Our current result shows that correlation between
evaluation and booming index is 0.903 while the that with the loudness is 0.617.
2. For the improvement of booming sensation of cabin noise inside the compartment, we haveintroduced three treatments, i.e. elimination of cooling fun noise, eliminations of intake noise
and that of exhaust noise from the original sound.
3. As a result, elimination of fun noise is the most effective counter measure for the reduction ofbooming sensation.
4. The reason why this effect is obtained is that this treatment realizes broadband level reduction
effect along the frequency band from 20Hz up to 500Hz.
5. Elimination of intake noise is second effective countermeasure for the reduction of booming
sensation.
6. The least effect is observed for the treatment of exhaust noise elimination but it still has someeffect.
7. Combined effect by introducing two or three counter measure simultaneously is more effective
for the reduction of booming sensation. Especially, the most efficient combined effect isobserved by the combination of fun noise and intake noise eliminations.

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8. The result obtained by introducing 3 treatments correlated well with the energy ratio value. Thismeans that by the treatment, the modified sound reduces it sound energy to some extent.

REFERENCES
1. Shigeko Hatano, Takeo Hashimoto, Yasuo Kimura, Toshimitsu Tanaka. Sound Quality Evaluation ofconstruction machine. Proc. 7th ICA, No.5233, Rome, Italy; 2000.
2. Takeo Hashimoto, Shigeko Hatano. Evaluation of noise emitted from construction machine. Proc.
Inter-noise 2018, Illinois, USA; 2018.
3. Shigeko Hatano, Takeo Hashimoto. Booming index as a measure for booming sensation. Prc.
Inter-noise 2000, No.233, 1-6, Nice France 2000.
4. Hugo Fastl, Eberhard Zwicker. Psycho-Acoustics; Facts and Models. Chap. 8, Springer, Berin,Heidelberg, New York 20078054