Prediction of outdoor sound propagation by applying ...odeon.dk/civimail/presentation_with_comments.pdfby applying geometrical sound simulation technique . Junichi Mori* Daisuke Yoshino*

Prediction of outdoor sound propagation

by applying geometrical sound simulation technique

Junichi Mori*

Daisuke Yoshino*

Fumiaki Satoh**

Hideki Tachibana**

*Graduate Student, Chiba Institute of Technology

**Chiba Institute of Technology



Junichi Mori*

Daisuke Yoshino*

Fumiaki Satoh**

Hideki Tachibana**



Prediction of outdoor sound propagation by applying geometrical sound simulation technique

Public address system for disaster prevention in Japan

Introduction of public address system

Conducting a study of such an outdoor sound propagation

Aim of the system

Disaster prevention Evacuation order Crime prevention

Junichi Mori

Gul seddel

Public-address system is being widely used for disaster prevention, evacuation order crime prevention and so on in Japan. In the system, loudspeaker as shown in this picture is used. The loudspeakers are set at some points in the city, from there, the announcements are conveyed all at once. We are conducting a study of such an outdoor sound propagation.



Junichi Mori*

Daisuke Yoshino*

Fumiaki Satoh**

Hideki Tachibana**




Acoustics problem of the public address system

Public address system for disaster prevention in Japan

Propagation sound from

loudspeakers covering other arias

Reflection sound from

surrounding buildings

Deterioration of speech intelligibility

affected by long pass echoes

Junichi Mori

Speaker

Of course, the system is an important information feeding system, but it has an acoustics problem. The problem is the deterioration of speech intelligibility affected by long pass echoes such as the propagation sound from loudspeakers covering other areas and the reflection sound from surrounding buildings.



Junichi Mori*

Daisuke Yoshino*

Fumiaki Satoh**

Hideki Tachibana**




Comparison study between

the simulation technique and field measurements

The simulation technique applied in this paper

Geometrical acoustics simulation technique


Aim of the simulation technique

Accuracy of the simulation technique in outdoor sound field

The point at issue

Application of sound simulation technique

Junichi Mori

Gul seddel

To design such a system, the sound simulation technique for predict the outdoor sound propagation is needed. For the aim, we applied the simulation technique based on geometrical acoustics. In order to see the accuracy of the simulation technique, we compared with field measurements.



Junichi Mori*

Daisuke Yoshino*

Fumiaki Satoh**

Hideki Tachibana**




Modeling of buildings for the calculation

Geometrical acoustics simulation technique -ODEON-

・Buildings position : Layout drawings

Setting the sound source

・Buildings height : Simplified survey

Setting the absorption coefficient of the surfaces Surfaces Building surfaces Ground surfaces Surrounding boundaries

Absorption coefficient 2.5% 10% 100%

・Number of rays : 10 million

・Directive : Directive corresponding to the field measurements

・Approximation with combinations of hexahedrons

Junichi Mori

Gul seddel

In this paper, we used ODEON as the simulation technique. In modeling the buildings for the calculation, the building shapes were approximated with combinations of hexahedrons based on the value of layout drawing and simplified survey. The absorption coefficient of the surfaces were assumed to the value as shown in this table. And, the frequency characteristics were flat. In setting the sound source, the number of rays was set at 10 million. And, directive was selected from database of ODEON corresponding to the field measurements.



Junichi Mori*

Daisuke Yoshino*

Fumiaki Satoh**

Hideki Tachibana**




Comparison study 1

Comparison with field measurement

using Swept-Sine signal

Comparison study 2


using on-site announcement signal

The field measurements for comparison with the simulation technique

Junichi Mori

Gul seddel

The field measurements for comparison with the simulation technique were carried out by two types. One was conducted by using Swept-Sine signal. The other was conducted by using on-site announcement signal. First, I'd like to talk about comparison study 1.



Junichi Mori*

Daisuke Yoshino*

Fumiaki Satoh**

Hideki Tachibana**




Summary of examination sites

Comparison study with measurement using Swept-Sine signal

Campus 1 Campus 2

Source position :Ground level

Receiving position :Ground level

Source position :Balcony

Receiving position :Ground level

(Ninth floor of the Building C)

Disposition of buildings :

Relatively simple

Disposition of buildings :

Somewhat complicate

Junichi Mori

Gul seddel

We carried out the studies in two campuses of our institute. As the disposition of buildings, Campus 1 is relatively simple while Campus 2 is somewhat complicated. In Campus 1, the position of the sound source and the receiving system were set on the ground level. In Campus 2, the sound source system was set on the balcony of the ninth floor of Building C to simulate the real P.A. system. And, the receiving system was set on the ground level.



Junichi Mori*

Daisuke Yoshino*

Fumiaki Satoh**

Hideki Tachibana**




・Sound source system : Dodecahedral loudspeaker (Height：1.5m)

・Source signal : Swept-Sine signal

(Duration time：8 s, Frequency ：2 octave bands of 500Hz and 1kHz)

・Receiving system : Sound level meter and digital data recorder

(Height : 1.2m)


Summary of the field measurement

Campus 2 Campus 1

Junichi Mori

Gul seddel

About the field measurements in both campuses, dodecahedral loudspeaker was used as the sound source system. From there, the Swept-Sine signal of 8 seconds was emitted. The frequency of the signal was 2 octave band of 500Hz and 1000Hz. We received the sound with sound-level mater and digital data recorder.



Junichi Mori*

Daisuke Yoshino*

Fumiaki Satoh**

Hideki Tachibana**




B A

C


Comparison results（2 octave band of 500 Hz and 1k Hz）-Campus 1-

Junichi Mori

Gul seddel

These are the results in Campus 1. The upper figure is a squared wave form of impulse response obtained by simulation and measurement. And, the lower figure is Figure of 3D ray tracing obtained by simulation. From the figure of 3D ray tracing, Reflection A appeared on the simulation result was that from Building A, [slide 10] B was that from Building B, [slide 11] and C was that from Building C, and [slide 12] Reflection D was that via Building B and C.



Junichi Mori*

Daisuke Yoshino*

Fumiaki Satoh**

Hideki Tachibana**




B A

C





Junichi Mori*

Daisuke Yoshino*

Fumiaki Satoh**

Hideki Tachibana**




B A

C





Junichi Mori*

Daisuke Yoshino*

Fumiaki Satoh**

Hideki Tachibana**




B A

C





Junichi Mori*

Daisuke Yoshino*

Fumiaki Satoh**

Hideki Tachibana**






・Reflection energy was not corresponded

・Arriving times of dominant reflections were in fairly good agreement

B A

C

Junichi Mori

Gul seddel

In comparison with the measurement result, the reflection energy was not corresponded, but the arriving times of the reflections were in fairly good agreement.



Junichi Mori*

Daisuke Yoshino*

Fumiaki Satoh**

Hideki Tachibana**




B

A C



Junichi Mori

Gul seddel

These are the results in Campus 2. The arriving times of Reflection A, and [slide 15] B appeared on the simulation result also were in fairly good agreement with the measurement results.



Junichi Mori*

Daisuke Yoshino*

Fumiaki Satoh**

Hideki Tachibana**




B

A C



Arriving times of dominant reflections were in fairly good agreement



Junichi Mori*

Daisuke Yoshino*

Fumiaki Satoh**

Hideki Tachibana**




B

A C



Fine reflections were not detected by the simulation technique

Junichi Mori

Gul seddel

However, this fine reflections appeared on the measurement result were not detected by the simulation technique.



Junichi Mori*

Daisuke Yoshino*

Fumiaki Satoh**

Hideki Tachibana**




Before

After

Calculation again by modeling the details

About the discrepancy


Modeling to the balcony

Junichi Mori

Gul seddel

As for the cause, the neglect of modeling about the balcony of Building C was suspected. So, we performed the calculation again by modeling the detail of the building facade.



Junichi Mori*

Daisuke Yoshino*

Fumiaki Satoh**

Hideki Tachibana**




Before

After

Fine reflections have appeared



Junichi Mori

Gul seddel

This is the result. It was found that the fine reflections were appeared by modeling the balcony.



Junichi Mori*

Daisuke Yoshino*

Fumiaki Satoh**

Hideki Tachibana**




Before

After

Fine reflections have appeared



Study about modeling of buildings

Arriving times of dominant reflections

were in fairly good agreement

Junichi Mori

Gul seddel

This fact indicates that study about modeling of buildings is needed. In any case, it was found that the arriving times of dominant reflections calculated by the simulation model were in fairly good agreement with the measurement results.



Junichi Mori*

Daisuke Yoshino*

Fumiaki Satoh**

Hideki Tachibana**




Comparison study 1


using Swept-Sine signal

Comparison study 2


using on-site announcement signal

Field measurements for comparison with the simulation technique

Junichi Mori

Gul seddel

Next, I'd like to talk about comparison study 2.



Junichi Mori*

Daisuke Yoshino*

Fumiaki Satoh**

Hideki Tachibana**




Summary of examination

Comparison study with measurements using on-site announcement signal

・Target announcement

P.A. announcement made at 5 P.M. every day in Narashino City

(Campus 2 is located)

【Contents of announcement (Female speech with BGM)】

“This is Narashino City. It will soon be 5 P.M.. Time for the children to

go home with care. May the local residents keep an eye on them please.”

Mic.

Loudspeakers for P.A. system

Junichi Mori

Gul seddel

In Narashino City where Campus 2 is located, an announcement is made at 5 P.M. every day. The announcement is conveyed with this content. We tried a field measurement by using this on-site announcement signal. That is, we obtained the echo-time pattern by calculating the cross correlation between the original source signal and the received sound.



Junichi Mori*

Daisuke Yoshino*

Fumiaki Satoh**

Hideki Tachibana**




・loudspeaker position : Rooftop of a Building B (Four horn-type)

・Receiving position : Ground level in the campus

(M1 / Direct sound is obtained , M2 / Direct sound is blocked )

・Processing method : Cross-Spectrum method

(The original source signal was obtained from Narashino City)

Summary of field measurement


0 50 METERS

B

C

A

D

Commercial

building Campus site E

M2

M1

SP1 (Rooftop)

Junichi Mori

Gul seddel

The left figure shows a wide area map in Narashino City. The SP marks in the figure are the position of the loudspeakers for P.A. system. We performed the field measurement in around Campus 2. The loudspeaker system nearest the campus was set on the rooftop of a commercial building adjacent to the campus. The system is comprised of four horn-type loudspeakers. The announcement sent out from there was recorded at two positions of the ground level in the campus. M1 was set at the position where direct sound was obtainable, while M2 was set at the position where direct sound was blocked. The echo-time patterns were calculated by using Cross-Spectrum method. The original source signal for the calculation was obtained from Narashino City.



Junichi Mori*

Daisuke Yoshino*

Fumiaki Satoh**

Hideki Tachibana**




B A


Comparison results（2 octave band of 500 Hz and 1k Hz）-M1-

E

Junichi Mori

Gul seddel

These are the results in M1. The frequency was 2 octave band of 500Hz and 1000 Hz. The arriving times of Reflection A, [slide 24] B [slide 25] and C appeared on the simulation result were in fairly good agreement with the measurement results.



Junichi Mori*

Daisuke Yoshino*

Fumiaki Satoh**

Hideki Tachibana**




B A



E



Junichi Mori*

Daisuke Yoshino*

Fumiaki Satoh**

Hideki Tachibana**




B A




E



Junichi Mori*

Daisuke Yoshino*

Fumiaki Satoh**

Hideki Tachibana**






B A

E

Junichi Mori

Gul seddel

These are the results in M2. The receiving position was under inferior condition with blocking of direct sound, but Reflection A, B, C, [slide 27]E [slide 28] and F appeared on the simulation result were in fairly good agreement with the measurement results.



Junichi Mori*

Daisuke Yoshino*

Fumiaki Satoh**

Hideki Tachibana**






B A

E



Junichi Mori*

Daisuke Yoshino*

Fumiaki Satoh**

Hideki Tachibana**







B A

E



Junichi Mori*

Daisuke Yoshino*

Fumiaki Satoh**

Hideki Tachibana**






Reflection D was not detected by the simulation technique

B A

E

Junichi Mori

Gul seddel

However, Reflection D appeared on the measurement result was not detected by the simulation technique.



Junichi Mori*

Daisuke Yoshino*

Fumiaki Satoh**

Hideki Tachibana**




Calculation again by modeling the details

About of the discrepancy


Before

After Modeling to the eaves

Junichi Mori

Gul seddel

As for the cause, the neglect of modeling about the eaves of Building E was suspected. So, we performed the calculation again by modeling the detail of the building facade.



Junichi Mori*

Daisuke Yoshino*

Fumiaki Satoh**

Hideki Tachibana**




Before

After Reflection D have appeared



Junichi Mori

Gul seddel

This is the result. It was found that the reflection regarded as Reflection D was appeared by modeling the eaves.



Junichi Mori*

Daisuke Yoshino*

Fumiaki Satoh**

Hideki Tachibana**




Before

After Reflection D have appeared




The simulation technique might be

effectively applied

Junichi Mori

Gul seddel

This fact also indicates that study about modeling of buildings is needed. In any case, it has been found that the simulation model might be effectively applied as the design tools of the P.A. system.



Junichi Mori*

Daisuke Yoshino*

Fumiaki Satoh**

Hideki Tachibana**




Summary

Develop of simulation technique that predict the outdoor sound propagation

Aim in this paper

Accuracy of the simulation technique in outdoor sound field

The point at issue

Application of geometrical acoustics simulation technique

Comparison study between the simulation technique and the field measurements

Might be effectively applicable as the design tools of the P.A. system

Through the study


Problem and prospect

Applications to design for the P.A. system

Junichi Mori

Gul seddel

Finally, I'd like to summarize the key points of this paper. The aim in this paper was to develop a simulation technique that can predict the outdoor sound propagation. For the aim, we applied a sound simulation technique based on the geometrical acoustics. To see the accuracy, we carried out the comparison studies between the simulation technique and the field measurements. As a result, it has been found that this simulation model might be effectively applied as the design tools of the P.A. system. In the future, we will perform the study on modeling of buildings. Furthermore, we intend to apply the simulation technique to the design of the P.A. system for disaster prevention. Thank you very much for your attention.

Documents

Prediction of outdoor sound propagation by applying ...odeon.dk/civimail/presentation_with_comments.pdfby applying geometrical sound simulation technique . Junichi Mori* Daisuke Yoshino*