Car Stereo deck power is very deceiving! Many head units
have HUGE power ratings on the Boxes or right on the front of the units! The
highest head unit power I have ever actually tested was 13 watts (at a half way
decent THD)... So even if the head unit says 35Watts or 40 watts per channel on
it don't ever expect for it to really be more than 15! Just cant happen!
Real amplifiers use massive power supplies in them with
toroidal transformers to "step up" the voltage so that large amounts
of power can be made! Head units just don't have room in them For the large
transformers that are needed for large power supplies, so don't expect more
than 15 watts per Speaker out of the unit's built-in amplifier circuitry. Some
of the more reputable head units might print high power ratings on the boxes
but If you read the small print in the spec sheets in the owners manual they
might admit to the 15 watt figure! Alpine's V-Drive head units are stated to
put out 60 watts per channel, using a direct 10AWG power line directly from the
car battery's positive terminal, but once you read the fine print, you'll see
that the actual power output is a maximum of 26 watts per channel continuous.
This is still one of the most powerful head units on the market... at 26 watts.
Most high power stereos use a bridged output (also called
floating ground or push pull), units use an IC chip that makes both speaker
wires to each speaker work together with one pushing while the other pulls (so
to speak) just like a real amplifier does when you bridge it. Unlike a real
amplifier however, most car stereos cannot be un-bridged. Even still, having no
transformer in the head unit limits it severely and your output will be around
12 to 13 watts per speaker.
How can they print these specs if they aren't true? Well,
for starters, car audio is not regulated like home audio. The Federal Trade
Commission several years ago required home audio manufacturers to print
accurate power ratings based on a standard testing procedure. Car audio did not
yet exist (much), so this requirement was not worded to include car audio. As a
result, less scrupulous manufacturers will print the peak power rating, as
opposed to the RMS. A peak power rating (usually called "maximum"
because it sounds better) is a measure of what the amplifier can do for just a
very short time. RMS (often called "continuous", because it sounds
better) is a more true measurement. This is how much power an amplifier can continue
to put out for longer periods. Accurate peak and RMS measurements give a good
view of an amplifier's capability (the peak measurement is required to produce
the heart pounding bass, which requires much more power than the continuous
music, which needs RMS power). However, there is no standard for measuring peak
power among manufacturers, so it can't be trusted for most equipment.
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