TYPES OF NOISE
1.
Alternator noise
: This is the most common source of noise, and expresses
itself as a high-pitched whine, which increases and decreases in pitch with the
speed of the engine. Unfortunately for sound systems, the cable between the
alternator and the battery forms a beautiful antenna to transmit the alternator’s
noise to anything surrounding it.
2
. Ignition noise
: Ignition noise is formed by the primary and secondary ignition
systems in gas engines. It is characterized by a rapid ticking or popping noise
that increases or decreases with engine speed. The first form of ignition noise,
from the primary circuit, is caused by the points or solid-state circuitry that fires
the coil. These primary pulses can feed back through the ignition coil and into the
vehicle’s electrical system. The secondary ignition circuit is composed of the
ignition coil, the spark plug wires, and the spark plugs. Since the secondary
circuit operates at quite a high voltage, and since this voltage is pulsed, it forms a
nice radio (noise) station under the hood. This noise is often transmitted to the
vehicle’s wiring harness.
3.
Accessory noise:
Accessory noise is caused by the electrical noises formed
by the many electrical accessories in the vehicle. The most common noises are
the pops caused by high current switches (like the brake light switch) and
whirring noises caused by the various electrical motors in the vehicle (such as
the fuel pump or fan motor).
ENTRY METHODS
1.
Radiation
: Radiated noise is the most common problem found. As mentioned
earlier, the worst problem area is the wiring between the alternator and the
battery. The entire wiring harness can become contaminated if a portion of it
runs along side the alternator to battery cable.
2.
Ground Loops
: Ground loops are the most common way radiated noise gets
into a mobile stereo system. This is especially true of multiple amp systems.
They have more grounding points, and that means more possible locations
for ground loops to form. A ground loop is formed when any ground point is at
a different potential than at any other ground point in the system.
3.
Power Lead (+12V) Noise
: Since true power lead noise is the only noise that
isn’t radiated, and since the vehicle’s battery (if in good condition) provides
adequate filtering for alternator noise, then only ignition and accessory noise
could enter the system through power leads.
© 2008 Linear Power, Inc. - ALL RIGHTS RESERVED
LINEAR POWER
™
is a trademark of Linear Power, Inc.
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