bro, ive been researching this also since am also a newbie when it comes to setting up car audios.
i would like to share this with you. medyo mahaba pero worth reading to understand how impedance affects amps power output. speaker wire connection to amp also affects power output.
For most car speakers, impedance isn’t usually a concern because almost all
of them have a 4-ohm impedance. But with subwoofers, impedance plays a
very crucial role. Impedance is a measure of how much resistance a subwoofer
presents to the power flowing from the amplifier, and is often referred
to as the load a sub places on an amp. Another way to think of impedance
is how much a speaker restricts flow of power from an amplifier. The higher
the impedance, the more the power from the amplifier is restricted, and the
lower the impedance, the less the power from the amplifier is restricted.
Impedance is an important subwoofer spec because, depending on a subwoofer’s
impedance and the way the subwoofer is wired to an amplifier, it
causes the amp to increase or decrease its power output. In general, most car
audio amps produce more power with every halving of impedance — up to a
point, that is.
For example, if a two-channel or stereo amplifier produces 60 watts x 2 into a
4-ohm load, it may produce around 75 watts into a 2-ohm load. When the two
channels are bridged to form a single channel, meaning the two separate
stereo channels are combined into one mono channel, the power more than
doubles to about 150 watts.
But the amplifier has to be stable at that load, meaning it has been designed
to operate at that impedance. Otherwise, the amp is being asked to perform
beyond its design capabilities and either shuts down (if it has protection circuitry)
or it fries (if it does not). Some amps, called high current amps, can
drive loads as low as half an ohm (although these are usually specialized for
sound-off competitors who are trying to squeeze every last drop of power
out of their systems, and they often require an upgrade of a car’s charging
The various ways in which subs can be wired to an amplifier are the determining
factors of the final impedance at the amplifier’s outputs, and therefore
the ultimate power output of the amp. That’s why you see amplifiers rated at
different impedances. For example, the same 120-watt stereo amplifier mentioned
earlier may have power ratings that look like this:
60 watts x 2 into 4 ohms
75 watts x 2 into 2 ohms
150 watts x 1 into 4 ohms
Almost all car audio amplifiers are designed to produce their optimum power
output into a specific impedance. If the impedance goes up past that optimum
point, the amp performs less powerfully and you’re not getting all the
power you paid for. If the amp is driven into a lower impedance than it’s capable
of handling, it could either shut down, if built-in protection circuitry kicks
in, or become damaged, if it does not.
Another important thing to know about amplifiers in relation to subwoofers
is that subs are almost always driven in mono as opposed to stereo. That’s
because stereo separation cannot be detected at low frequencies. That’s why
it’s common to bridge two channels of a stereo amp or a mutichannel amp to
form a single mono channel to power a sub, and why mono block subwoofer
amps are often used to power subwoofers. (Mono block is just a fancy way of
describing a single-channel amplifier, and the terminology came from the highend
home audio world, in which mono block amps are preferred for powering
As mentioned earlier, a single bridged channel of an amp is usually
about twice as powerful as two separate stereo channels if all are driving
the same load, which is a good thing because subwoofers require roughly
twice the power of other speakers.