ohm
12-01-2003, 01:56 PM
#6
Guest
Posts: n/a
12-01-2003, 07:39 PM
#10
50 Watt CAFz'r
Join Date: Oct 2003
Posts: 113
Originally posted by dantheman:
no i mean like what does ohm do?
no i mean like what does ohm do?
Resistance against current flow.
"Ohms law" states:
voltage = current x resistance
Voltage is just "potential energy", essentially.
Like a car battery, sitting on a shelf.
It's got potential to do "work".. but without a circuit to do work through (and "loads" in that circuit), nothing will happen, no current will flow...
Current is the actual "kinetic energy" if you will.
You have your voltage source, and you have your circuit...
In the case of car audio -
Your amplifier is your voltage source, and your speaker has a certain amount of resistance (or, since an audio signal is AC electricity, we call it "impedance").
You hook wires up between the amp and the subwoofer, to create a circuit, between the amp's + and - terminals, with the speaker being the resistive "load" on that voltage source.
Per ohms law up there:
Voltage = current x resistance.
and with a little manipulation, you get:
current = voltage / resistance
Another one to know is:
Power is voltage x current.
OK.. to get started-
Our amplifier is essentially a constant voltage source (well, it really varies up and down, with our volume ****
).So we have some number for voltage.. higher wattage amps will have higher voltage numbers (given that they are stable to the same impedance). It's a constant.
So we can calculate current using formula #2 up there.
You'll note that as you hook up lower impedance speakers, you'll make more current flow in the circuit.
And we can easily then calculate power, once we know current, using formula #3.
Example:
Let's say we had an amplifier that was a 20v source for our speakers.
If we hooked up a 4 ohm subwoofer to it:
current = 20 / 4 = 5 amps of current
power = 20 * 5 = 100 watts
If we hooked up a 2 ohm subwoofer to it:
current = 20 / 2 = 10 amps of current
power = 20 * 10 = 200 watts
If we hooked up a 1 ohm subwoofer to it:
current = 20 / 1 = 20 amps of current
power = 20 * 20 = 400 watts
You'll see that every time you cut the impedance in half, the amplifier will double it's power..
Not because voltage changes, but because more current naturally flows through a lower impedance.
"So hey! I'll just run the lowest impedance I can, and get MONSTER POWER out of my amp!"
It doesn't work that way.
The actual limits of much of the componentry inside amplifiers is actually rated in terms of how much current can flow through it.
When current flows through a component, heat is generated... and if too much heat is generated, the componentry will melt.
Which is why you'll see amps are only "stable" down to a certain impedance.
Try to run the amp any lower, trying to wring more power out of the amp, and it'll go up in smoke.
Also, you can wire subwoofers (or voice coils - some subs have more than 1 to play with) in series (into one, out the other side, into the next, out the other side), or in parallel (jumper wires connecting all the + together, and all the - together).
When you wire subs in parallel, you'll reduce the impedance that the amp sees, by a factor of how many subs you are parallelling (never mix impedances of subs together!).
When you wire subs in series, the total impedance is the sum of the impedances of all the subs (again, never mix impedances).
Hope that helps you understand what an Ohm "is"...
