AVAS Sound Specification

1

5-7 December 2011

JASIC

Three vehicle manufacturers provide their AVAS for EV and HEV in Japanese market. This report shows sound characteristics according to QRTV informal group discussion.

2

Specifications (discussed in QRTV)

1 Over all sound level(a) Stopped condition

(b) 10 km/h cruise

2 Frequency component

3 Frequency shift

4 Modulation

Test vehicles

EV/HEV with AVAS Vehicle-A, -B, -C

ICE vehicle Vehicle-D

Summary of Sound Characteristics

EV/HEV with AVAS ICE vehicle

A B C D

1

Over all

sound level

[dB(A)]

(a) stopped

conditionNot generated 45.9

(b)

10 km/h

cruise

Avg. 54.0 54.3 54.6 55.8

Max. 54.1 55.0 54.8 56.4

Min. 53.8 53.4 54.4 55.4

2Frequency

component

Band [Hz] 250 2k 630 2.5k 500 2.5k - -

Level

[dB(A)]

Avg. 44.5 48.7 49.0 44.1 47.5 47.8 - -

Max. 46.3 49.1 51.0 45.3 50.4 50.7 - -

Min. 41.1 48.2 47.4 43.3 44.6 44.1 - -

3Frequency shift [%]

(from 10 to 20 km/h)21 14 8

4 Modulation With With Without

3

“Avg.”, “Max.” and “Min.” levels correspond to the averaged, maximum and minimum values in 4 measurement results, respectively.

1. Over all sound level measurement

according to SAE J2889-1: 2011

(a) Stopped condition

(b) 10 km/h cruise

4

(a) Stopped condition @semi-anechoic room (defined by SAE J2889-1:2011)

1.2 m

2.0 m

2.0 m

Microphone

D-range, Brake on

40

45

50

55

0 2 4 6 8 10

A-w

eig

hte

d s

ound

p

ressure

leve

l [d

B]

Time [s]

40

45

50

55

0 2 4 6 8 10

A-w

eig

hte

d s

ound

p

ressure

leve

l [d

B]

Time [s]

Min.

Right

Min.

Left

Lstop = Min(left, right)

5

Semi-anechoic room

(b) 10 km/h cruise @ISO test track (defined by SAE J2889-1:2011)

ISO test track

2 m

2 m

Microphone (h = 1.2 m)

AA'PP'

6

V = 10 km/h (constant speed)

45

50

55

60

-4 -2 0 2 4

A-w

eig

hte

d s

ound

p

ressure

leve

l [d

B]

Time [s]

45

50

55

60

-4 -2 0 2 4

A-w

eig

hte

d s

ound

p

ressure

leve

l [d

B]

Time [s]

Max. (AA'-PP')

Max. (AA'-PP')

Right

Left

Lcrs = Min(left, right)

Measurement results

Minimum sound level [dB]

EV/HEV with AVAS ICE vehicle

A B C D

Lstop Avg. Not generated 45.9

Lcrs

Max. 54.1 55.0 54.8 56.4

Min. 53.8 53.4 54.4 55.4

Avg. 54.0 54.3 54.6 55.8

7

similar level to ICE vehicleLcrs(Avg.) is

“Avg.”, “Max.” and “Min.” levels correspond to the averaged, maximum and

minimum values in 4 measurement results, respectively.

2. Frequency component measurement

according to SAE J2889-1: 2011

8

0

10

20

30

40

50

60

63 125 250 500 1k 2k 4k 8k

A-w

eig

hte

d s

ound

p

ressure

leve

l [d

B]

1/3 octave band center frequency [Hz]

The example of frequency component：10 km/h cruise @ISO test track

9

1/3 octave band spectrum

of minimum sound level @10 km/h cruise

Tonal component band

from 160 Hz to 3.15 kHz

(1)(2)

(1) (2)

Frequency

band [Hz]630 2.5k

Level [dB] 49.0 44.1

(Vehicle-B with AVAS)

0

10

20

30

40

50

60

63 125 250 500 1k 2k 4k 8k

A-w

eig

hte

d s

ound

p

ressure

leve

l [d

B]

1/3 octave band center frequency [Hz]

0

10

20

30

40

50

60

63 125 250 500 1k 2k 4k 8k

A-w

eig

hte

d s

ound

p

ressure

leve

l [d

B]

1/3 octave band center frequency [Hz]

without AVAS

with AVAS

0

10

20

30

40

50

60

63 125 250 500 1k 2k 4k 8k

A-w

eig

hte

d s

ound

p

ressure

leve

l [d

B]

1/3 octave band center frequency [Hz]

without AVAS

with AVAS

0

10

20

30

40

50

60

63 125 250 500 1k 2k 4k 8k

A-w

eig

hte

d s

ound

p

ressure

leve

l [d

B]

1/3 octave band center frequency [Hz]

without AVAS

with AVAS

Measurement results：10 km/h cruise @ISO test track

10

Vehicle-A Vehicle-B

Vehicle-C Vehicle-D

(2)(1) (1)

(2)

(2) (1)

(1), (2): Tonal component band from 160 Hz to 3.15 kHz

Measurement results：10 km/h cruise @ISO test track

Frequency componentEV/HEV with AVAS ICE vehicle

A B C D

Tonal

component

(1), (2)

Frequency

band [Hz]250 2k 630 2.5k 500 2.5k - -

Level

[dB]

Avg. 44.5 48.7 49.0 44.1 47.5 47.8 - -

Max. 46.3 49.1 51.0 45.3 50.4 50.7 - -

Min. 41.1 48.2 47.4 43.3 44.6 44.1 - -

Max. - Min.

5.2 0.9 3.6 2.0 5.8 6.6 - -

11

In case where the levels of frequency components are specified, it is necessary

to consider the following items:

• Dispersion of each measurement

• Errors which are made in 1/3 octave band frequency analysis

• Variation of frequency characteristics in loudspeakers

“Avg.”, “Max.” and “Min.” levels correspond to the averaged, maximum and

minimum values in 4 measurement results, respectively.

0

2

4

6

8

10

12

0

10

20

30

40

50

60

63 125 250 500 1k 2k 4k 8k OA

Le

vel

de

ffe

rence

[dB

]

A-w

eig

hte

d s

ound

p

ressure

leve

l [d

B]

1/3 octave band center frequency [Hz]

0

2

4

6

8

10

12

0

10

20

30

40

50

60

63 125 250 500 1k 2k 4k 8k OA

Le

vel

de

ffe

rence

[dB

]

A-w

eig

hte

d s

ound

p

ressure

leve

l [d

B]

1/3 octave band center frequency [Hz]

0

2

4

6

8

10

12

0

10

20

30

40

50

60

63 125 250 500 1k 2k 4k 8k OA

Le

vel

de

ffe

rence

[dB

]

A-w

eig

hte

d s

ound

p

ressure

leve

l [d

B]

1/3 octave band center frequency [Hz]

The figures indicate the maximum,

minimum and averaged levels, and the

differences between the maximum and

the minimum levels for 4 measurements

in 1/3 octave band.

Dispersions of sound level in 1/3 octave

band (0.3~7.2 dB) are larger than those

in overall levels (0.3~1.6 dB).

Example of dispersion in each measurement：10 km/h cruise @ISO test

track

12

Vehicle-A with AVAS (n=4) Vehicle-B with AVAS (n=4)

Vehicle-C with AVAS (n=4)

Max. Min. Avg. Difference

So

und

pre

ssure

leve

l [d

B]

Frequency [Hz]

Case-1

Case-2

Case-3

The errors occurred in 1/3 octave band frequency analysis

13

1/3 octave band frequency [Hz]

Sound p

ressure

level [d

B]

An example of AVAS sound

:1/3 octave band filter (1)

1/3 octave band

A B

Case-1 X dB

Case-2 X-3 dB X-3 dB

Case-3 X dB

Band A Band B

On the process of 1/3 octave band

frequency analysis, the AVAS sound

level at specific frequency may result

in 3 dB lower than the level where

the frequency is at center of

frequency band.

X dB X-3 dB X dB

(1): defined by IEC 61260, ANSI S1.11

3. Frequency shift measurement

in reference to SAE J2889-1 draft: 20xx

14

0 2 4 6 8 10

A-w

eig

hte

d s

ound

p

ressure

leve

l [d

B]

Time [s]

1 dB

Frequency shift measurement @ chassis dynamometer in semi-anechoic room

0.5 m

1.0 m

Microphone

15

Chassis dynamometer in semi-anechoic room

FFT analysis

(next slide)

1.0 m

(Vehicle-B with AVAS)

It is difficult to drive stably at less than 10 km/h.

--> The measurements were conducted from 10 km/h to 20 km/h (every 2 km/h).

V = 10 to 20 km/h (every 2 km/h)

0 500 1000 1500 2000 2500 3000 3500

A-w

eig

hte

d s

ound

p

ressure

leve

l [d

B]

Frequency [Hz]

with AVAS without AVAS

10 dB

0 500 1000 1500 2000 2500 3000 3500

A-w

eig

hte

d s

ound

p

ressure

leve

l [d

B]

Frequency [Hz]

with AVAS without AVAS

10 dB

0 500 1000 1500 2000 2500 3000 3500

A-w

eig

hte

d s

ound

p

ressure

leve

l [d

B]

Frequency [Hz]

with AVAS without AVAS

10 dB

0 2 4 6 8 10

A-w

eig

hte

d s

ound

p

ressure

leve

l [d

B]

Time [s]

1 dB

0 2 4 6 8 10

A-w

eig

hte

d s

ound

p

ressure

leve

l [d

B]

Time [s]

1 dB

0 2 4 6 8 10

A-w

eig

hte

d s

ound

p

ressure

leve

l [d

B]

Time [s]

1 dB

Examples of frequency shift measurements：10 km/h

16

Vehicle-B with AVAS

Vehicle-A with AVAS

Vehicle-C with AVAS

FFT analysis

Sample rate 48 kHz

Number of

data points

32768

(215)

Frequency

resolution1.46 Hz

Frequency

range18.75 kHz

Window Hanning

Overlap 75 %

Average10 s

(55 times)

Vehicle-B

Vehicle-A

Vehicle-C

0 500 1000 1500 2000 2500 3000 3500

A-w

eig

hte

d s

ound

p

ressure

leve

l [d

B]

Frequency [Hz]

with AVAS without AVAS

10 dB

0 500 1000 1500 2000 2500 3000 3500

A-w

eig

hte

d s

ound

p

ressure

leve

l [d

B]

with AVAS without AVAS

10 dB

0 500 1000 1500 2000 2500 3000 3500

A-w

eig

hte

d s

ound

p

ressure

leve

l [d

B]

Frequency [Hz]

with AVAS without AVAS

10 dB

R² = 0.9996

2400

2600

2800

3000

5 10 15 20 25

Fre

que

ncy

[Hz]

Speed [km/h]

Examples of frequency shift measurements：From 10 to 20 km/h (every 2 km/h)

17

10 km/h

12 km/h

20 km/h

� Identify the predominant

frequency of AVAS sound

�Read the shifting frequencies

�Calculate the frequency shift (fs)

from 10 to 20 km/h

fs = (f20 - f10) / f10 x 100 [%]

Vehicle-B

Measurement results of frequency shift

EV/HEV with AVAS

A B C

Frequency shift

from 10 to 20 km/h21 % 14 % 8 %

e.g.)

Frequency of

AVAS sound

@10 km/h 1086 Hz 2531 Hz 2247 Hz

@20 km/h 1313 Hz 2879 Hz 2435 Hz

18

• It is difficult to drive stably at less than 10 km/h.

• Frequency shifts from 10 to 20 km/h are in the range of 8 - 21 %.

4. Study of modulation

19

0 1 2 3 4 5 6 7 8 9 10

A-w

eig

hte

d s

ou

nd

p

ressu

re le

ve

l [d

B]

Time [s]

1 dB

Study of modulation for AVAS sound

0.5 m

1.0 m

Microphone

20

Chassis dynamometer in semi-anechoic room

1.0 m

V = 10 km/h

(Vehicle-B with AVAS)

（A microphone was set at the same position as the frequency shift measurement）

Sound pressure waveform and

A-weighted sound pressure

level were measured.

Intention of AVAS sound design

EV/HEV with AVAS

A B C

Modulation with with without

21

Time variation of sound pressure waveform

22

Vehicle-A with AVAS

(display time <--> 2 sec)

with modulation

Vehicle-B with AVAS

with modulation

Vehicle-C with AVAS

without modulation

Vehicle-D (ICE vehicle)

Time variation of sound pressure waveform

23

Vehicle-A with AVAS

(display time <--> 0.5 sec)

with modulation

Vehicle-B with AVAS

with modulation

Vehicle-C with AVAS

without modulation

Vehicle-D (ICE vehicle)

Investigation into modulation of AVAS sound

24

• With or without modulation, clear distinction is not found in the time domain of sound pressure waveform and A-weighted sound pressure level.

• It is difficult to define and to evaluate the modulation.

EV/HEV with AVAS

A B C

Modulation（Intention of

sound design）with with without

Summary (1)

25

The sound characteristics of AVAS that are introduced in Japan and our experiences of measurements are as follows;

1. Minimum A-weighted sound pressure level

• AVAS sound is not generated in stopped condition.

• Sound level of cruising EV/HEV with AVAS is equivalent to that of ICE vehicle.

2. Frequency componentWe observe a lot of uncertainties in sound level on frequency base. In case where the levels of frequency components are specified, it is necessary to consider the following uncertainties:

- Dispersion of each measurement- Errors which are made in 1/3 octave band frequency analysis

- Variation of frequency characteristics in loudspeakers

Summary (2)

26

3. Frequency shift

• It is difficult to drive stably at less than 10 km/h.

• Frequency shifts between 10 and 20 km/h are from 8 to 21 %.

4. Modulation

• With or without modulation, clear distinction is not found in the time domain of sound pressure waveform and A-weighted sound pressure level.

• It is difficult to define and to evaluate the modulation.

5. Others

• From the viewpoint of authorities who grant approval or inspectors, practical method should be considered.