Since I've got a free minute, I figure I'll elaborate a little on the ohm ratings/impedence/resistance issue....as it is very important to car audio and I feel that everyone who wants a nice system aught to have a basic knowledge.
A speaker is a resistor. Sending an audio signal to a speaker requires power (from the amp) and the speaker, depending on its rated resistance will limit the AMOUNT of power that can pass through it. Think of it as a door to a busy supermarket. There's a lot of people outside that want to get inside (power), but the door is only so big (resistance)....it can only let so many people (power) through at one time.
So, in simple terms, a speaker's resistance (given in the measurement of OHMS, ie, 2 or 4 or 8 ohms) will essentially determine the power of your amp. A lower resistance speaker will be putting out more watts than a higher resistance speaker all else being equal.
But, we have to take into account the power ratings of your amp. MOST amps are rated to produce the highest wattage at 2 ohms per channel (ie, per speaker hookup). So, if you hook up a 4 ohm speaker, you cut your wattage in half. So for instance, you have a two channel amp (so it has two speaker hookups) and it is 1200 watts total, 600 per channel at 2 ohms per channel. If you get two 4 ohm speakers and hook one up to each speaker input, each speaker will only utilize half that (300 watts per channel, so only 600 watts total). That is leaving a lot of potential power from your amp untapped. So, in this case, you'd want to get two 2 ohm speakers to get the fully rated power.
Now, if you offer LESS resistance than what the amp recommends, then you run the risk of frying your amp, because now you are drawing even MORE POWER from your amp than it is rated to produce at a stable level. For instance, your amp is rated to produce its max stable power at 2 ohms per channel, and you give it 1 ohm per channel. Expect your amp to go up in smoke.
That seems fairly straighforward, but it gets more confusing when we are talking about different speaker combos and different types of amp, etc. For instance, let's say you have a single channel amp (ie, it has only a single speaker hookup), and this amp is rated to put out its max stable power at 4ohm from that one channel. BUT...you want to run TWO speakers off this single channel amp. It can be done, but you have to apply a little physics to make sure it is done right. We now have to BRIDGE the speakers/amp so that we achieve the proper resistance for the amp. This means that basically, we are connecting TWO speakers to a single channel (speaker hookup).
There are TWO ways to do this: in series, and in parralel. Let's go back to the "door to a busy supermarket" analogy. You want to get those people in and out quicker. What happens if you put one door in front of the other (ie, you must walk through one set of doors, and then another to get in/out)? You INCREASE the resistance and slow down the flow of people (power)....this is equivalent to bridging two speakers in SERIES. If you place the doors side by side, then people can go through either set of doors and eneter/exit faster, because you have lowered the resistance.....this is equivalent to bridging two speakers in PARRALLEL.
That's all well and good, but how do you figure out what your total resistance is going to be when bridging to speakers?
There are simple formulas for both parralel and series applications.
For series, it is simple addition: R(total) = R1 + R2 .....etc (so the total resistance equals the resistance of all speakers in the series added together, so two 2 ohm speakers in series produce a total resistance of 4 ohms).
For parrallel, it's a tad more complicated, but nothing major: 1/R(total) = 1/R1 + 1/R2 .....etc. So, if you run two 4 ohm speakers in parrallel, you get a total resistance of 2 ohm.
So back to that hypothetical of hooking up two subs to a single channel amp rated to produce max stable power at 4 ohms for that channel. How would we want to run our subs, and what resistance would we want? From the examples above, we know that two 2 ohm subs run in series would give us what we want (4 ohms total). So, we would buy our speakers accordingly.
But what does it mean to run speakers in series versus parralel. For a series application, you'd have the negative lead of ONE speaker attached to the negative input on the amp, then you'd attach to positive lead of the same speaker to the negative lead of the SECOND speaker. You'd finish it off by connecting the positive lead of the second speaker to the positive input of the amp.
For parralel wiring, you'd attach both negative leads from both speakers to the negative input on the amp, and then both positive leads from both speakers to the positive input.
Here's a graphical representation:
Now here's where it gets EVEN TRICKIER. The speakers you posted are DUAL VOICE COIL speakers....that means, instead of each speaker being a single resistor, each speaker is actually TWO resistors in one. That means that the individual voice coils of the speakers can be bridged in either series or parralel to produce a single resistor of different resistances.
For example, you posted dual voice coil speakers that are 4 ohms PER voice coil. So, each voice coil could be bridged in series, producing a speaker that is a total of 8 ohms of resistance. Or, each voice coil could be bridged in parrallel to produce a speaker that is a total of 2 ohms of resistance.
Continuing with the products you posted as examples, if you want to get the maximum power out of your amp, you'd get two of these speakers, and bridge the voice coils in parrallel so that each speaker was a total of 2 ohms. That way, you get the maximum power per channel from your amp (600 watts to each speaker).
This taken from the specs on the amp you posted:
Max Power Watts per Channel (4 Ohms) 300 x 2
Max Power Watts per Channel (2 Ohms) 600 x 2
Max Power Watts per Channel (4 Ohms Bridged) 1200
What happens if you run each in series? Well, you get 8 ohms of resistance per speaker/amp channel....and you get nowhere near the maximum power from your amp.
That's confusing enough for now......I won't get into multiple channel, multiple speaker combos (ie, if you wanted to run 3 subs off a 2 channel amp).
Anyway...hopefully you were able to at least begin to grasp the concept of resistance and its importance to proper car audio install and performance after this novel of a post.
KiL
Last edited by FeedUsYourFetus (2007-04-23 13:24:42)