OHMS
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Ohms is an easy subject that I can quickly explain to you (I'm majoring in computer/electrical engineering 
).
First off, ohms measure resistance. In relation to car audio, your speakers and even all of the electrical wires throughout your car each have an independent resistance. How you combine these components determines the overall resistance for the circuit. The easiest circuit to analize is the series circuit shown below in figure1.bmp. Suppose we replace the resistor and put a 4 ohm speaker into that spot. Ignoring the negligable resistance of the wires and battery (almost 0), the entire circuit has a total resistance of just the speaker (4 ohms). Now lets say we add another speaker/resistor to the series circuit (see figure2.bmp). Adding a second speaker in series increases the circuit's overall resistance. The total resistance = resistance of speaker1 + resistance of speaker2. So, if you have two 4 ohm speakers in series, the the total resisatnce is 8 ohms. I f you have two 2-ohm speakers in series, the reisistance = 2 + 2 = 4 ohms. Pretty simple so far. Just remember, when wiring a series circuit, just add up all of the resistances that are present in the circuit. Also remember, your speakers are basically just resistors. Like any any resistor, they help restrict the amount of current flowing through the circuit. Given a particular voltage from your amp or H/U, a speaker that is 2 ohms will let more current through than a speaker that is 4 or 8-ohms. More current means more power (watts). Here are 3 simple formulas:
Voltage (V) = current (I) * total-resistance (R) : V = I*R
Power (watts) = current (I) * voltage (V) : P = I*V
Total-Resistance in series = R1 + R2 + R3....
Oh, I almost forgot to mention, resistors/speakers are able to "resist" or "restrict" the amount of current by giving off heat. This is the only way to dissipate the extra energy in the current. Heat is VERY bad in the 12 volt world. If the power wire leading from your battery to the amp (which by way has its own resitance) has alot of current flowing through it (because you're bumpin' your system), it can begin to heat up and possibly catch fire. That is why it is so important to use an extremely thick gauge wire in this application. Also, heat itself can cause the internal resistance of the wire/speaker/resistor to increase. Therefore, the more heat present in your circuit/system the more current and power you will be losing. If I were jam my system outside in the Nevada desert at temps around 120 degrees, compared to in canada at 10 degrees, my system will not produce as many watts in the desert as it will if I were in Canada due to external temps. Same as if I were to use a 32 gauge wire (pretty dang thin) compared to a 2 gauge wire (pretty friggin' huge in diameter) to wire my amp to the battery. Consider your wires like a hallway full of people moving in one direction. A small hallway (thin wire) is not going to allow very many people to flow through quickly when compared to a wide hallway. Therefore, a thin wire has a higher internal resistance and allows less current to pass ( and will probably catch fire), while a wider wire has lower resistance and allows higher current and more watts to pass.
Ok, we are now going to talk about parallel circuits/speaker wiring. (See figure3.bmp) Parallel cuircuits are different from series circuits in many different aspects.
Formulas for parallel ciruit:
Voltage (V) = current (I) * total-resistance (R) : V = I*R
1/(total resistance) = 1/R1 + 1/R2 + 1/R3..... therefore Total-resistance = 1/[ (1/R1) + (1/R2) + (1/R3)....]
There are many other formulas that need to be applied but we are only going to focus on the resistance [IMG]i/expressions/face-icon-small-tongue.gif[/IMG]
If you have two 4-ohm speakers wired in parallel as shown in figure3.bmp, the overall resistance (not including wires and heat) is 2 ohms.
Here is why: (skip this part if you are a math genius)
1/(4 ohms) + 1/(4 ohms) = 1/(2 ohms)
*using a caculator*
0.25 + 0.25 = 0.5
now take the recipricol of 0.5 to get 2: 1/0.5 = 2
Okay now lets suppose we have two speakers rated at 2 ohms apiece that are wired in parallel. After doing the math, the total current is now only 1 ohm. Two 8 ohm resistors/speakers in parallel = 4 ohms. Why is the overall resitance dropped you may ask?? Think of the circuit like a hallway again---better yet, think of it like a set of straws. If you have two straws when drinking your soda, you are able to drink at twice the rate than if you only had one straw. If you think of your speakers/resistors as straws in which power is sucked through, having two speakers running in parrallel to each other will draw twice the current and power from your system than just one speaker. Now, going back to the straw metaphor, if you were to connect the two straws from the end of one to the beginning of another (in series) you get one long @$$ straw which will restrict the amount of soda that you can suck up. Therefore, two speakers wired in series will only draw half the current/power from your amp/system.
Let's talk about bridging very briefly. When you bridge your amp, simply put, you are basically halving the total resistance of your circuit. (It's really a helluva alot more complicated, but I will spare us all the math) Thus, if you briddge two channels into one channel, then run that channel to a 4-ohm speaker, your system load is really 2 ohms. The easiest way IMO to calculate the overall system load in bridged applications is to first calculate the total resistance of you speaker configuration, then just halve that value. Sorry for the long post, but I hope this clears up a few things.
). First off, ohms measure resistance. In relation to car audio, your speakers and even all of the electrical wires throughout your car each have an independent resistance. How you combine these components determines the overall resistance for the circuit. The easiest circuit to analize is the series circuit shown below in figure1.bmp. Suppose we replace the resistor and put a 4 ohm speaker into that spot. Ignoring the negligable resistance of the wires and battery (almost 0), the entire circuit has a total resistance of just the speaker (4 ohms). Now lets say we add another speaker/resistor to the series circuit (see figure2.bmp). Adding a second speaker in series increases the circuit's overall resistance. The total resistance = resistance of speaker1 + resistance of speaker2. So, if you have two 4 ohm speakers in series, the the total resisatnce is 8 ohms. I f you have two 2-ohm speakers in series, the reisistance = 2 + 2 = 4 ohms. Pretty simple so far. Just remember, when wiring a series circuit, just add up all of the resistances that are present in the circuit. Also remember, your speakers are basically just resistors. Like any any resistor, they help restrict the amount of current flowing through the circuit. Given a particular voltage from your amp or H/U, a speaker that is 2 ohms will let more current through than a speaker that is 4 or 8-ohms. More current means more power (watts). Here are 3 simple formulas:
Voltage (V) = current (I) * total-resistance (R) : V = I*R
Power (watts) = current (I) * voltage (V) : P = I*V
Total-Resistance in series = R1 + R2 + R3....
Oh, I almost forgot to mention, resistors/speakers are able to "resist" or "restrict" the amount of current by giving off heat. This is the only way to dissipate the extra energy in the current. Heat is VERY bad in the 12 volt world. If the power wire leading from your battery to the amp (which by way has its own resitance) has alot of current flowing through it (because you're bumpin' your system), it can begin to heat up and possibly catch fire. That is why it is so important to use an extremely thick gauge wire in this application. Also, heat itself can cause the internal resistance of the wire/speaker/resistor to increase. Therefore, the more heat present in your circuit/system the more current and power you will be losing. If I were jam my system outside in the Nevada desert at temps around 120 degrees, compared to in canada at 10 degrees, my system will not produce as many watts in the desert as it will if I were in Canada due to external temps. Same as if I were to use a 32 gauge wire (pretty dang thin) compared to a 2 gauge wire (pretty friggin' huge in diameter) to wire my amp to the battery. Consider your wires like a hallway full of people moving in one direction. A small hallway (thin wire) is not going to allow very many people to flow through quickly when compared to a wide hallway. Therefore, a thin wire has a higher internal resistance and allows less current to pass ( and will probably catch fire), while a wider wire has lower resistance and allows higher current and more watts to pass.
Ok, we are now going to talk about parallel circuits/speaker wiring. (See figure3.bmp) Parallel cuircuits are different from series circuits in many different aspects.
Formulas for parallel ciruit:
Voltage (V) = current (I) * total-resistance (R) : V = I*R
1/(total resistance) = 1/R1 + 1/R2 + 1/R3..... therefore Total-resistance = 1/[ (1/R1) + (1/R2) + (1/R3)....]
There are many other formulas that need to be applied but we are only going to focus on the resistance [IMG]i/expressions/face-icon-small-tongue.gif[/IMG]
If you have two 4-ohm speakers wired in parallel as shown in figure3.bmp, the overall resistance (not including wires and heat) is 2 ohms.
Here is why: (skip this part if you are a math genius)
1/(4 ohms) + 1/(4 ohms) = 1/(2 ohms)
*using a caculator*
0.25 + 0.25 = 0.5
now take the recipricol of 0.5 to get 2: 1/0.5 = 2
Okay now lets suppose we have two speakers rated at 2 ohms apiece that are wired in parallel. After doing the math, the total current is now only 1 ohm. Two 8 ohm resistors/speakers in parallel = 4 ohms. Why is the overall resitance dropped you may ask?? Think of the circuit like a hallway again---better yet, think of it like a set of straws. If you have two straws when drinking your soda, you are able to drink at twice the rate than if you only had one straw. If you think of your speakers/resistors as straws in which power is sucked through, having two speakers running in parrallel to each other will draw twice the current and power from your system than just one speaker. Now, going back to the straw metaphor, if you were to connect the two straws from the end of one to the beginning of another (in series) you get one long @$$ straw which will restrict the amount of soda that you can suck up. Therefore, two speakers wired in series will only draw half the current/power from your amp/system.
Let's talk about bridging very briefly. When you bridge your amp, simply put, you are basically halving the total resistance of your circuit. (It's really a helluva alot more complicated, but I will spare us all the math) Thus, if you briddge two channels into one channel, then run that channel to a 4-ohm speaker, your system load is really 2 ohms. The easiest way IMO to calculate the overall system load in bridged applications is to first calculate the total resistance of you speaker configuration, then just halve that value. Sorry for the long post, but I hope this clears up a few things.
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