[Mariachi]

On Feb 26, 11:34 am, Matt Ion wrote:
Mariachi wrote:
On Feb 25, 4:22 pm, Matt Ion wrote:

Mariachi wrote:

On Feb 25, 4:01 pm, Matt Ion wrote:

Mathematically, there may be a theoretical difference... REALISTICALLY you can
be 99.9% sure the difference would barely be measurable in your deck's output,
and certainly not audible or noticeable, especially when you factor in the
ambient noise and the fact that your HU's built-in amp isn't actually giving you
anywhere near 25W/ch.

Mariachi wrote:

At any rate, you'd have to know the length of the wire--there's
nothing magical about the gauge of the wire, it's all a matter of the
total resistance that wire has. So, would be fine with 1" of 18 AWG on
a 750 Watt amplifier, but you'd be in really bad shape if you had to
go 15 feet with the same wire on that same amp. :-)

yes I agree...

Resistance of the wire = Resistivity * Length / Area
R(wire) = p * (L/A)

If you lower the wire by 3 gauges then you have a cross sectional area
increase by a factor of 2.
Therefore, the total resistance decreases by a factor of 2 given that
the resistivity and length are still the same.

So if you want to make a power wire twice as long, you need to
increase A by 2 times also. Therefore it would be the same ratio and
therefore it would be the same total resistance.

So if I have positive power wire with a length 2 meters with a 16
guage cross sectional area...
Resistivity of copper = 1.7 microohm/cm = 1.7 microohm/cm * (1 *
10^(-6) ohms / 1 microohm) * (1 m / 100 cm) = 0.000000017 ohm/m
L = 2 meters
A (16 gauge)= 0.8107 m^2

R(16 GWG wire) = (1.7e-8)*(2/.8107) ohms = 4.194e-8 ohms
R(14 GWG wire) = (1.7e-8)*(2/1.291) ohms = 2.634e-8 ohms

4.194 / 2.634 = 1.59

Resistance decreased by 1.59 times

R(16 GWG) / R(13 GWG) = 2
R(16 GWG) / R(14 GWG) = 1.6

my head unit is rated to get a continuous power at 24 Watts per
speaker, but with a 5% THD. It gets 17 Watts per each speaker with a .
01 % THD.

Yes, but "rated" with what test criteria? This is the problem with car audio,
there are no real solid "standards" for testing and specifying power output (I
understand there have been some ad-hoc standards introduced that are adhered to
*voluntarily* by SOME manufacturers, but even that is borderline meaningless).

Your ACTUAL output will vary more with your RPM and alternator output voltage
than it will with increased wire size to your HU, and even then, you're not
usually going to hear the difference between 12.5V and 14.5V, let alone with the
few fractions of a volt difference you'll see with the larger wire

It doesn't really depend on the rpm's of the engine or the alternator
if your battery is properly charged... you're talking about subwoofer
systems that need 300 Watts or more that constantly requires the
battery to be recharged... i'm just talking about around 80 Watts
total. Unless you have a crappy battery maybe it would depend more on
your alternator than usual. But still, it's a head unit amp... sure
it can drain the battery but not as quick as a 800 Watt amplifier. It
takes about 4 hours of music playing to kill my battery and that's
with the stereo running at full blast. If you are running a higher
voltage battery, you are able to get more voltage to the head unit and
therefore more power. Of course the head unit amp has it's limits...
but with a higher voltage battery you can help the head unit amp reach
those limits. That's why they say 22 Watts RMS per 4 ohm speaker
"using a 14.4 V battery". I wouldn't put a 14.4 V battery in my car,
but I do like to provide good connections for all the audio equipment
in my car in order to get the most out of what I have.

Er... dude, you're WAY out to lunch here.

Your battery is ALWAYS 12V (give or take a bit). Your ALTERNATOR can output
anywhere between 12 to 15 volts depending on load and RPM. You have little to
no control over it (unless you use an ACCUVOLT like MOSFET).

In normal operation, with the engine running, NOTHING should be drawing on the
battery - the alternator should be providing ALL your car's power needs (yeah
yeah, the battery filters power, yada yada - semantics).

Unless your amp is running a regulated power supply (which your head unit likely
isn't), your max output power will vary with the power input voltage, and most
manufacturers will test and spec their amps at 14.5V because that gives higher
numbers - it's marketing, plain and simple.- Hide quoted text -

- Show quoted text -


why would it use the alternator??? You might be talking about the
engine.. but the stereo uses the battery. It uses the alternator
indirectly because the battery get's energy from the alternator.
wow... this is why your amplifiers are connected to the battery, so
they get power from the battery, not the alternator. The alternator
is not a stable power source, the battery is. Otherwise you would be
getting alternating current into your amplifier and resulting in
noise. This is why audio equipment uses DC voltage, not AC voltage
(like your alternator). Don't you know this?