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

Soundscape engineering of a promenade on Namsan Mountain Parkby noise, sound, and preference maps
Jisu YOO1; Jae Kwan LEE1; Seo Il CHANG1
1

Environment Engineering, University of Seoul, Republic of Korea

ABSTRACT
Namsan Mountain is a 262m-high mountain located in the center of Seoul. It functions as a park rather than amountain and has a 7.5km-long promenade around it with a moderate slope. Some sections of the promenade
are accompanied by trees and rills, which provide a good sonic environment, but the other sections areinfluenced acoustically by shuttle buses, road-traffic and various noise sources. Noise map for theroad-traffic was generated to find the spatial distribution of the noise over the mountain including thepromenade. It shows that the promenade of Namsan Mountain is exposed to the noise levels ranging from55dB(A) to 75dB(A). The natural sound which was identified most frequently by visitors was rill sound andrill-sound map was generated. Individual responses from 4 acousticians and 6 non-acoustic people werecollected from on-site questionnaire about sonic environment along the promenade at 37 evaluating spots.
The results of questionnaire were used to generate preference map. Separate and combined analyses of thethree maps were performed and the addition of the rill sound was proposed to improve the sonic environment.
To determine the levels of the rill sound a listening experiment was conducted and the adjusted levels of rillsound were incorporated into the noise map.
Keywords: Soundscape, Noise Map, Sound Map, Preference Map, Soundwalk, Psycho-acoustic Experiment

1. INTRODUCTION
Namsan Mountain is a 262m high mountain located in the center of Seoul. Its easy accessibility andtourist attractions such as a cable car and a tall tower on the top allure native and foreign people. Itfunctions as a park rather than a mountain and has a 7.5 km promenade around it with a moderate slope
where even the old and weak enjoy walking. Some parts of the promenade. Some sections of thepromenade are surrounded by trees and flowing waters but the other sections are influenced by various
un-wanted sound sources such as shuttle buses, roundabout road-traffic and several machines toprovide inadequate soundscape on the promenade Therefore, appropriate measures are needed to
improve the soundscape that can provide positive effects such as stress relief for Namsan Mountain'svisitors.
In this study, noise maps for the sources were generated to find the spatial distribution of the noiseover the mountain including the promenade and also sound maps were generated using the naturalsound including mainly water streaming sound were identified by along the promenade. Individual
responses collected during Soundwalk and these results used to generate the preference map.
Separate and combined analyses of the three acoustic maps were performed to propose some locations
to need to improve the soundscape. Through the listening experiment, the levels and types of watersound determined to improve the soundscape to make Namsan Mountain' visitors satisfy.

2. STUDY AREA
Namsan Mountain is a 262m-high mountain located in the center of Seoul. It functions as a parkrather than a mountain and has a 7.5km- long promenade around it with a moderate slope. Somesections of the promenade are accompanied by trees and rills, which provide a good sonic environment,
but the other sections are influenced acoustically by shuttle buses, road-traffic and various noise
sources. Figure 2.1 shows the satellite map of Namsan Mountain and its promenade.

1

luvxjisu@gmail.com

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Figure 2.1 – The satellite map of Namsan Mountain (OpenStreetMap) and its promenade

3. NOISE MAP, SOUND MAP AND PREFERENCE MAP
3.1 NOISE MAP
Noise maps were calculated using the noise-mapping software SoundPLAN(ver.7.4), according tothe RLS-90 road-traffic estimation model(1). Some sections of the promenade are influenced
acoustically by shuttle buses, road-traffic and various noise sources. In order to calculate the noisemap, the internal and external noise sources that can affect the promenade on Namsan Mountain’soundscape have examined.
Sound levels, traffic volumes, vehicle speed and classifications were measured at the roads within
500 meter from the promenade and other data were provided from the report from Seoul website.
GIS information about the ground surfaces, buildings and roads were obtained from government
websites.
Noise map was calculated with A-weighted equivalent noise level(LAeq) and Figure 3 shows the noise
map of the Namsan Mountain. As expected, most of the study area results to be exposed to more than
65 dB with a few spots falling in the 55 – 60 dB range(2).

Figure 3.1 - Noise map of Namsan Mountain (2D (left) and 3D (right))
3.2 SOUND MAP
Noise map are largely used to assess exposures to un-wanted sounds (i.e. road traffic noise)(3).
In order to evaluate the overall soundscape of the promenade, sound map using water sounds alsoneeded to assess the soundscape.

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The rill was selected as water sound source to make a sound map Only the northern part of thepromenade has the water sound and it has 1.0~1.5m wide and flows along the promenade. Rill isclassified into two types: Rill with no step and steps. Figure 4 shows the image of the two types of
the rill on the promenade on Namsan Mountain. The rill sound sources were measured at 1m fromthe center of the source for a minute and it was analyzed using ArtemiS, an acoustic and vibration
analysis program.
The sound map was again calculated in SoundPLAN(ver.7.4) and the rill sound sources weretreated as a surface source with a continuous operating time and 1/3-octave band spectra(125~4000Hz, dB(A)) were considered to be representative(7).

Figure 3.2 – Two types of the rill with no step(left) and steps(right) on the promenade

3.3 SOUNDWALK AND FIELD SURVEY
Field surveys were performed in total of 37 spots on the promenade. These spots were chosen by
dividing the total length of Namsan by 200m intervals.
The field survey continued for 2 hours, with 10 subjects (one female and nine males) aged 20-30.
All the participants conducted the soundwalk at the same time and they were led by an experimenter
who walked the promenade and stopped at 37 evaluating spots. For each spot, participants wererequired to listen to the sonic environment for one minute and to fill in a structured questionnaire. At
the same time, a non-participant operator carried out the sound-pressure level measurements for one
minute by means of a calibrated sound level meter.
3.3.1 Questionnaire
The questionnaire included questions about: demographic information of the participant (age,gender, etc.), suitability of the spots for promenade (preference related to the sound environment andappropriateness of the sound environment), noticeability of different sound sources’ types and theirpreference(4).
Two questions were selected for the purpose of this study: [Q1] “Overall, how would you ratesound environment of the present spot using given adjectives such as bad/good, noisy/calm, etc.?”
and [Q2] “Overall, “What types of sound can you perceive here?”For Q1 questions, a seven-point scale was used, ranging from “Very unfavorable” (-3) to “Veryfavorable” (+3) and various sound source options such as water sound, birdsong, etc. were provided
and their preference was evaluated using 5-scale for Q2.
3.4 PREFERENCE MAP
In order to calculate the preference map, the mean individual assessments of two question(Bad/Good and Noisy/Calm) in Q1 were selected. The individual responses collected at 376695

evaluating spots were averaged over the 10 soundwalk’ participants. Those values were thenuploaded to a GIS software (ArcGIS pro) and used to generate a prediction surface based on “IDW
(Inverse Distance weighted)” method(5). Figure 3.3 shows the preference maps for the overall
assessment of soundscape on the promenade. From the maps’ observation, it emerges that some partson the promenade are characterized by a poor individual assessment, for both “Bad/Good” and“Noisy/Calm”. This is likely due to the spots are influenced by high roundabout road-traffic or
non-existence of the water sound, leading to poor preference that result in contrast with the visual
scenario (park or mountain).

3.5 COMBINE ANALYSIS OF NOISE MAP, SOUND MAP AND PREFRERNCE MAP
Separate and combined analyses of the three maps were performed and the results showed not
only the presence or absence of the water sounds improve the preference of promenade but also
seven evaluating spots need to improve the soundscape. Thus, the addition of the water sounds in thelaboratory experiment was proposed to improve the sonic environment. To determine the levels andtypes of the water sound, a listening experiment was conducted and the adjusted levels and type ofwater sound were proposed.

4. LABORATORY EXPERIMENT: ENHANCEMENT OF SOUNDSCAPE USINGWATER SOUNDSIn Sec 3.5, seven evaluating spots determined that need to improve the soundscape. Thus, alistening experiment was designed to determine which the levels and types of water sounds were able
to improve the soundscape for each seven spots(6).
Water sounds selected from a commercial sound effects CD (Sony Pictures Sound Effects Series),
which included sounds called “Small Stream”,” Medium Stream”, “Small Waterfall”, “MediumWaterfall”, “Steady Fountain” and “Rhythmic Fountain” and also two types of rill sound thatmeasured from the promenade included. Spectral characteristics of water sounds were not modified,
but their levels were adjusted for the experiments. During the Soundwalk, the background sound ofeach seven spots recorded was used into auditory experiments.
4.1. Preferred the types of water soundIn the first part, the preference to types of water sounds was evaluated. The sound levels of watersound were adjusted to be equal to the sound levels of the background of each seven spots, andadjusted water sounds were combined with each background sound. The duration of the combinedsounds with adjusted water sound and background sound was 5s, and their LAeq varied from 50 to65 dBA. Ten subjects aged 20-30 participated in this experiment, and the stimuli were presented
through headphones in a hearing laboratory. Subjects rated their preference when the combinedsounds were presented to them. They were informed about the purpose of the experiments andinstructed about how to use 7-point scale. They were asked to respond to the following question:
Which stimuli do you prefer if you were exposed to it on the promenade? The stimuli were presented
to the subjects simultaneously. A visual image of each seven spots was shown to the subjects before
the listening tests began.

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Figure 4.1 – Participants in the listening experiment4.1.1 Results and discussions
The results of this auditory experiment are shown in Figure 4.2, where a larger value indicates ahigher preference. As shown in Figure 8.1, the small stream or medium stream were highly preferredwith background sounds, which measured at the seven spots.
3Prefernce ratings

2,52
1,5
10,50

Noise
only

Small
streamMediumstreamOnsitenostepOnsitewithsteps

Smallwaterfall

Mediumwaterfall

Steadyfountain

Rhythmic
fountain

Types of water soundFigure 4.2 – Preferred water sounds at spots where sound environment are recommended to improve

4.2 Preferred the sound levels of water soundEven though speciﬁc water sounds were determined as preferable sounds in urban spaces, adetailed difference in sound level between the water sound and the urban noise was needed toimprove the soundscape for promenade. Therefore, the preference to sound levels of water soundwas evaluated in the second part. The SPLs of each water sounds were adjusted. For example, TheSPLs of water sound varied from 44.4 to 56.4 dBA in a step of 3 dB in the case of the backgroundsound of.50.4 dBA. Thus, a total of 280 combined sound sources with water sound and backgroundsound was used for the listening test to evaluate. These stimuli were presented randomly throughheadphones and subjects were asked to respond to the following sentence: Please rate the sounds on
your preference according to the 7-point scale. A visual image of each seven spots was shown to thesubjects during the listening tests began.

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4.2.1 Results and discussions
The scale value of preference is shown in Figure 4.3. As shown in Figure 4.3, the mean scalevalue was the highest when the relative SPL of Small stream and Medium stream was 0 dB comparedto the background sound. In other words, the results suggest that the water sounds are most effective toenhance the promenade soundscape when the water sound is with the same level or 3 dB lower than thebackground sound. It is interesting to note that the preference decreased when the sound level of the watersound increased, perhaps due to the increase in the total sound level.

3Preference ratings

2,52
1,510,50-6-30

Relative SPL (dB)36

Figure 4.3 – Preference rating according to relative presentation level of sounds of waters and backgroundsound.

5. CONCLUSIONS
Separate and combined analysis of the three acoustic maps were performed to propose somemeasures to improve the soundscape of the promenade through listening experiment. The main
conclusions are as follows:
1. The noise map of surrounding road-traffic and crossing shuttle buses shows that the noise
can affect visitors and ecology and most of the study area results to be exposed to more than
65 dB with a few spots falling in the 55 – 60 dB range.
2. The sound map was calculated with the rill sound sources which were treated as a surface
source with continuous operating time and is shown for the rill sound sources’ spatial
distribution.
3. Preference map calculated by individual responses during Soundwalk. The results presented
the spots are influenced by high roundabout road-traffic or non-existence of the water sound,leading to poor preference.
4. Separate and combined analyses of the three maps were performed and the results proposedthat seven evaluation spots need to improve the soundscape.
5. From the results of listening experiment, the water sounds such as “Small Stream” and“Medium Stream” sounds were selected as preferred natural sound to improve soundscape.
The appropriate level of the water sounds should be similar to or not less than 3 dB below
the level of the background sounds on the promenade of Namsan Mountain.

ACKNOWLEDGEMENTS
This research was supported by Basic Science Research Program through the National Research
Foundation of Korea (NRF) funded by the Ministry of Education (NRF-2015R1D1A1A01060891)

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