Please 'Boom' Responsibly As most of you have noticed, the noise ordinances have become much tougher lately. Most of this is due to idiots, yes IDIOTS, who drive through residential areas with their windows down while their system is playing at full power. To make things worse, the music they listen to has all sorts of foul language that's not suitable for small children, (who may be playing outside). There are even a few people, who are even beyond idiot status, that play their systems at full power through residential areas after 10:00 PM (when many people go to bed). I don't believe that this type of behavior is good for the industry. If the fines get too stiff, people will stop buying large systems. If this happens, more people will get out of car audio (who wants a mediocre system). People get interested in things because they're exciting. A deck and four 6.5" speakers are not going to interest many of the younger car audio enthusiasts. If car audio enthusiasts keep annoying more and more people, the fines will keep getting tougher. All of this will only reduce interest in the equipment that fuels the industry. If you want to listen to your system at full volume, get out on the highway where there's little chance of bothering anyone. When you get to a red light, turn it down. If the only thing attractive about you is your 'system', you have some work to do. Bottom line... Think about what you're doing. Think about other people. It's not the end of the world if you have to turn the volume down for a little while. |
| Balanced
Line Drivers Overview: When audio is transferred from one audio component to another by electrical cables (not fiber optic cable), sometimes the cable will act as a lossy transformer and pick up some of the noise in the vehicle. This problem becomes worse when the electrical 'environment' is especially noisy or the cable length is really long. A balanced line driver takes an unbalanced signal and converts it to a balanced signal. The balanced signal makes it easier to cancel out the noise, leaving a 'clean' signal. If you run your preamp cables next to your power wire (like the diagram below), you're more likely to pick up noise with an unbalanced signal line than with a balanced signal line.
Signal Types Unbalanced signal: In
the diagram below, you can see that the center conductor
has a signal (a sine wave in this case) on it and the
shield is connected to ground (which means it has no
signal on it). Balanced signal: A
balanced signal will have, in virtually all cases,
signals that are the same in all respects except for the
fact that one is a mirror image of the other. In the
diagram below, you can see that the center conductor AND
the outer shield have signals on them. These signals
originate from identical drive circuits (they'll have the
same output impedance and drive capabilities). There is
also a third connection which is usually connected to
ground. If the line driver uses RCA type connectors the
ground connection is the chassis/power ground. If the
connector is a mini DIN connector, the cable's shield is
the ground conductor. Other types of connectors will have
dedicated ground connections. Unbalanced to
balanced signal: In the diagram below, you can see that
the line driver takes in an unbalanced
signal and converts it to a balanced signal. It actually
takes the input signal, inverts it and applies the
inverted signal to the shield conductor. Line Driver and Receiver: Some line drivers are designed to be used with a dedicated receiver. The balanced line receiver is necessary when the next device in the audio chain can not handle a balanced input signal. The balanced line receiver will simply convert the balanced signal into an unbalanced signal. The following diagram shows the signal as it pass from one component to the next. You can see that the signal starts off unbalanced. Then it's converted to a balanced signal by the line driver. And finally it's converted back into an unbalanced signal by the receiver. If there's a gain/level control on the driver there will likely be gain/level controls on the receiver.
Doubled output
voltage: In this diagram, as with all noise canceling
inputs used in car audio, the line driver's input
signal is the difference of potential
(voltage) between the center conductor and the shield.
This voltage is the difference of
potential between any point on the sine wave and the
reference. At the white line, this would be the
instantaneous voltages labeled point A
and point B. This input signal is the same signal that
your amplifier would receive without
the line driver. At the line driver's output, you can see
that the difference of potential between points C
and D is twice the difference of potential between
points A and B. This translates into a 6dB increase in
the signal level. This will allow you to reduce the gain
settings on your amplifier or other signal processors
which will effectively increase the system's S/N ratio by
6dB. Noise rejection: One benefit of the balanced line system is an ability to reject noise which may be induced into the audio signal path between two audio components. Earlier we said that an audio device uses the difference of potential between the shield and the center conductor as the audio signal (with RCA type connectors). With an unbalanced signal the shield is grounded and is unlikely to pick up noise along the signal line because it has a very low output impedance (large conductor connected to ground). The center conductor, however, is not grounded and is more likely to pick up noise (it's output impedance may be as low as 50 ohms or as high as 600 ohms). If the audio signal is considered to be the difference between the voltages on the shield and the center conductor and the noise is only induced into the center conductor, the induced noise will become part of the signal. In a balanced signal system, the noise would be induced into the center conductor's and the shield's signal equally but the noise is canceled out because the noise is on both of the signal lines and the signal used by the amplifier (or balanced receiver) is the difference between the two signal lines. If the noise has a magnitude of 1.5 volts, the amplifier 'sees' 1.5 volts minus 1.5 volts which is 0 volts (if I'm not mistaken). In the following drawing you can see a 100hz sine wave mixed with a 5khz sine wave. The 5khz tone simulates 'engine noise'. You can also see how the engine noise is in phase on both signal lines (look at the dashed vertical line for a reference) while the audio signal is 180º out of phase (inverted).
When the amplifier or balanced line receiver receives the signal, it will subtract the two signals from one another. This means that the engine noise will cancel itself out while the 100hz part of the signals will double. This is the resultant output.
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