2. Introduction
The noise and vibration of cars have become
increasingly important. The predominant sources of
interior noise in cars are engine and wheel vibrations,
which propagate as structure-borne sound through the
car body and finally radiate as airborne sound into the
cabin. In order to reduce the noise and make it tolerable
and negligible we use noise cancellation techniques
1.Vibration Control
Passive Vibration Control
Active Vibration Control
2. Noise Control
Passive Noise Control or Active Noise Reduction
Active Noise Control
3. Active vibration control
The sensor is a
piezoelectric
accelerometer that
senses the
excitation of the
passive engine
mount.
The controller
generates a
canceling signal
that is fed to a
power amplifier.
The amplifier
converts the
controller's low-
voltage signal to an
actuator current.
The force generated
by the actuator
cancels the primary
disturbance signal
resulting in near
zero chassis
vibration.
6. Active Noise Cancellation
Most road noise comes from the sound of tires
contacting the road, but the vehicles' engines also
play a significant role
The frequency of road noise is around 1,000 Hz.
Researchers have documented road noise as low
as 700 Hz and as high as 1,300 Hz.
7. Sound Wave
Y(t) = A*Sin(2π*f*t+ϕ) (sine wave form)
A - Amplitude or Magnitude(decibels)
f – Natural Frequency
t – Time
φ – Phase angle
We consider 40db for all the sound waves for
easier assumption.
8. Road Noise at a average Frequency of 1000Hz
t=(0:0.00001:0.003);
y1=40*sin(2000*pi*t);
plot(t,y1);
0 0.5 1 1.5 2 2.5 3
x 10
-3
-50
-40
-30
-20
-10
0
10
20
30
40
50
Time(t)
dba
9. Cancellation Input at 1000Hz frequency
t=(0:0.00001:0.003);
y2=-40*sin(2000*pi*t);
plot(t,y2);
0 0.5 1 1.5 2 2.5 3
x 10
-3
-40
-30
-20
-10
0
10
20
30
40
Time(t)
dba
11. Active Noise Cancellation
Most road noise comes from the sound of tires
contacting the road, but the vehicles' engines also
play a significant role
The frequency of road noise is around 1,000 Hz.
Researchers have documented road noise as low
as 700 Hz and as high as 1,300 Hz.
The voiced speech of a typical adult male will
have a fundamental frequency from 85 to 180 Hz,
and that of a typical adult female from 165 to 255
Hz.
12. Female voice at a average of 200Hz frequency
t=(0:0.00001:0.01);
y3=40*sin(400*pi*t);
plot(t,y3);
0 0.001 0.002 0.003 0.004 0.005 0.006 0.007 0.008 0.009 0.01
-50
-40
-30
-20
-10
0
10
20
30
40
50
Time(t)
dba
17. Conclusion
Although describing the system like that is
relatively simple, the acoustics inside a car made
getting it right a challenge.
Unlike headphones, the in-car system has to deal
with both direct noise and its echo when it
bounces off interior walls.
The technology required for clear identification of
the appropriate sound waves with certain
frequencies requires a lot of skill and money.
