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Old 10-18-2002, 09:06 PM   #1
AmIGrand
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Impedance and Ohms, etc....

Questions regarding ohms and wiring are frequent, so here we go - the simplified version according to me. We're trying to help the newbies here, both to the site and to the 12-volt environment, so please keep things on topic and helpful. This means I will NOT be addressing the fact that ohms can in fact affect sound, the actual impedance curve of a voicecoil over time/space, notch filters, or anything other than nominal impedance and basic series/parallel wiring. There are dedicated sites for that stuff, this is Impedance 101.

This right from the start - ohms have nothing to do with how loud a speaker can play, how much power they can handle, what kind of box they need, or ANYTHING other than what amp you should use and how things should be wired. Please direct anyone who tells you otherwise to read this post or stop talking.

An "ohm" is a unit of measure - just like a degree or an inch or a liter or a second. All these things are used to measure something. An ohm is a measure of resistance in a circuit. It doesn't even have to be electrical - ohms are used to measure the resistance of air in a tube when designing a flute. But we'll stick to electricity 'cuz we're talking about car audio speakers and I don't want to scare you away. The scale they measure ranges from 0 (a dead short) to infinity (a perfect insulator). The lower the # of ohms, the closer you are to a dead short - and we all know what happens to most amps at a dead short, right?

When you design an amplifier (or anything that will react with something else), you have to know the resistance of the circuit your piece of equipment will be driving. A standard is generally agreed upon so everyone knows that their product will work with other products. In the car audio world, 4 ohms is the standard. Most amps are designed to run lower than that for reasons we'll leave alone, but let it suffice to say that everything currently (bad pun) being done could be done just as well or better if all amps only ran a 4 ohm load. The only reason speakers are made in any other impedance (ohms) is so you can use different #'s of them and get the impedance you want. Which leads us to -

You can change the impedence (I'm not going to keep adding "ohms" here, I hope you've figured it out) by wiring the speakers in series or parallel. Series means adding resistance to go higher, parallel means decreasing resistance to go lower. Here's how you do it.

To wire speakers in parallel, you simply make all the positive and negative terminals into one + and one -. In more direct physical terms, this means connect all the positive terminals together, leading to one positive wire running to the amp - than connect all the negative terminals together, leading to one negative wire running to the amp. You can jump the wires from woofer to woofer, you can run a seperate wire from each woofer to a central point and crimp them all together with one bigger one, or you can run a seperate wire from each terminal and stack them on top of each other at the amp - it doesn't matter, as long as you end up with all the positives connected to one positive output, and all the negatives connected to one negative output. The idea here is that the power leaves the amp, and splits up to all the coils simultaneously.

Now for the math: To find out your final impedence (or "load") when running in parallel, take the impedance you're working with, and divide it by the number of coils you've got. Four 4-ohm speakers, or 2 dual 4-ohm voicecoil speakers, with everything in parallel = 4 divided by 4, a 1 ohm load. Three 4 ohm coils in parallel = 4 divided by 3, a 1.33333.... ohm load. Pretty simple. If your speaker has more than one coil, just treat them as different speakers - there's no difference.

Series is slightly more complicated. Where parallel turns all the coils into one big connection to divide up the impedence, series makes the power run through all the coils one at a time, adding resistance each time. Keeping in mind that the end goal here is to make the power go through them all one at a time, what appears to be complex wiring begins to make sense. You connect the coils + to -, down the line. It's easiest to picture using two single voicecoil speakers, but it's the same no matter what. Connect one of the +'s on one speaker to one of the -'s on the other one. Now you have a wire connecting them, with a free + on one and a free - on the other to go to the amp. For 3 or 4 or 100 speakers, it's the same - daisy chain positive on one to negative on the next, the last connection on each end become the + and - for your amp to connect to.

The math for series is even easier than for parallel - just add 'em up. Two 4-ohm speakers in series is an 8-ohm load. A dual 4-ohm voicecoil woofer wired in series is also an 8-ohm load. Three 4 ohm speakers in series is a 12 ohm load. Again, different soeakers or multiple coils on one speaker makes no difference here, we're counting voicecoils, not speaker cones.

If I did my job right, you're wondering how it all seemed so hard before. You may need to read through this a couple times, easy or not - if it's new you gotta study it. But the overall concept and wiring is actually quite simple if you know what's going on and why.

So one more curveball to ruin your day after reading all this, then I'll address how different amplifiers handle all this crap and I'll go away.

Sometimes you have to combine series and parallel to get where you wanna be. Say for instance you have three dual 6-ohm coil speakers, and you want to run your amp bridged to 4-ohms. I'm using dual 6's because I just got you used to 4 ohms and I want to be mean. Well, if we run them all parallel, we get 1-ohm, not what we're after. If we series all the coils together, it's somewhere near 36 ohms, and that would mean not much power, so we'll avoid that too. But if we series the two coils on each woofer however, we get three 12-ohm speakers (6+6=12). And three 12-ohm speakers run in parallel is a 4-ohm load (12/3=4), right? SO here's how it gets done, with three or any number of subs in this situation. Connect one of the +'s on each speaker to the opposite - on the same speaker. Now you have one + and one - left on each speaker - run those terminals in parallel by connecting the positives together, and same for the negatives. Not so hard!

Note that you should never mix different impedence woofers together - some would get more power than others, and it would suck, trust me. Make sure they're all the same, (preferably the same speakers, not just impedences) or if you MUST mix & match speakers (because somebody is threatening to do very evil things if you don't, there is no other possible reason to do this) put them in different boxes.

Ok, now for different amps, and why they are rated into ridiculous ohm loads.

Basicly, if the all was right in the world, all amps would put max power into 4 ohms, and all woofers would be made only in impedences that divided into 4, i.e. 4, 8, or 12. But when car audio competition got to be big, the different classes were seperated by rated amplifier power. The rules said that whatever your amp was rated to put out at four ohms stereo was it's rated power. So companies started making amps than ran ridiculously close to a short to put out more power - so they made 25x2 into 4 ohms, but 400 watts by 2 into 1/4 of an ohm. Here's how that works -

Remember that ohms measure resistance. Well, if you lower resistance, current flows more easily. So if you lower the resistance an amp sees, it puts out more power. The downside here is that this creates more heat, and draws more current from the charging system. Keep in mind - a dead short is a bad thing here, heat and limtited availability of current are the main reason. The closer we get to a short, the more current we need, and the more heat we develope. Anyway -

Some bright fellow figured out that if you put one whole side of an amp to the positive swing and one whole side to the negative, it's the same as reducing the impedence, and makes more power - if the amp can handle the low resistance. Note here that bridging an amp makes it think the speakers are parallel, so the amp "sees" 1/2 the actual load - bridging an amp to a single 4 ohm driver = a 2 ohm load as far as the amp is concerned. Anyway, this led to a huge mess where everyone makes amps that bridge to make more power instead of just cranking up the rail voltage to make more in the first place. I won't go into that, it'd get really long. But now we have amps rated to put more power into different loads, as if just getting to 4 ohms with different #'s of speakers wasn't enough to keep up with.

Just keep this in mind - most amps that are stable onto less than 2 ohms (with a few exceptions) don't actually make more power at the lower impedances, they just don't blow up. The closer to 4 you are, the better off your system is - no matter how well that amp was designed to play into 1 ohm, it's still gonna make more heat, and heat is never good in this arena. Keep it at 4, 2 for monoblock amps (Again, they could make them full power into 4, they just don't, 'cause some competitions still rate with the stupid watt thing), if you have a choice between an amp that makes 1000 watts into 4 or 10000 watts into 2 or 1, go with the 4 ohm scenario. The lower resistance only makes it hotter, adds distortion, and lowers damping factor. None of these things is good.

I can expound more on the amp thing later as questions are asked, I think I've gone off too much as it is on that, and I want to go to bed.

I hope this has made the whole ohm thing a little less daunting. Work with it for a while, and it'll be second nature, you won't even have to think about it. Until then, ask questions!
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Old 10-22-2002, 10:47 PM   #2
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I'd like to post this wiring diagram up for people to use. This diagram includes wiring for 1-4 SVC or DVC Subwoofers using 2, 4, or 6 ohm voice coils.
http://www.maaudio.com/techsupport/b...ubwoofers.html
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Old 10-23-2002, 08:14 PM   #3
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Great link, very helpfull! Thanx!
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Old 10-29-2002, 03:42 PM   #4
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I found this one today it might be helpfull also.

http://www.audiobahninc.com/tech/par...lel-dual-4.gif
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Old 11-27-2002, 02:39 AM   #5
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you know i had this whole ohm thing figured out till i figured i am gonna amp my interior speakers....... OK DARNIT! i have a JBL 1200.1 amp running 2 kicker L5's. each sub has dual coils at 2 ohms. i remember runing each coil in series and parallel each speaker to the amp. so that is 4 ohm load on each speaker... so if i have 2 speakers with a 4 ohm load on a single channel amp, that means that i am running each speaker at a 4ohms? i remember that it is 2ohms but i dont remember why. each coil is 2ohms, in series = 4 ohms. now i have 2 4ohm loads going to one channel. the single channel sees an 8ohm load? then divides it in half wich equals 4ohms. because in parallel :brain fart: its..... golly i cant think of what it is. but if i have 2 4ohm loads going to 1 channel HOW DOES THAT COME TO 2ohms? unless the single channel is seeing 2 different 4 ohm loads THEN dividing each one, to make 2 but i dont see wtf it would do that. and now im wondering if my amp is powering the correct ohm load on my speakers. im getting newbie syndrome all over again.

next, my interiors have a single 4 ohm coil.... if i wire that to a multi channel amp parallel each channel sees only a 4ohm load right? which is what i want right? i am 80% sure on that, if i am an idiot call me one cuz i sure feel like one again.
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Old 11-27-2002, 09:25 AM   #6
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for your subs, you need to wire the subs vc's in series and then wire the subs in parallel. vc in series = 2 4 ohm subs.. then when you parallel them you get a mono 2 ohm load. thus giving each sub 600 rms.

now onto your interiors.. are you amping front and rear or just front? do you have a 4 channel amp? if so bridge the channels into 2 channels and run each front speaker off a channel. i would prolly just use all your power to amp your fronts and then just run rear speakers off the head unit.
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Old 11-27-2002, 10:07 AM   #7
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well the way you explained the subs is the way i have them but what i am having a hard time grasping is this, if it is only one channel and there are 2 speakers with a 4ohm load why does it see a 2 ohm load to each speaker?

and i would LIKE to amp all my interiors, i dont have an amp yet, but i was gonna get like a 50 watt 4 channel amp. all my interiors are rated over 50 watts, the rears more then the fronts, but i figure that should be enough power for them.
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Old 11-27-2002, 03:32 PM   #8
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it doesnt actually give a 2 ohm load to the speakers.. its the other way around. you have the jbl 1200.1 so heres how you could do this. series each sub. the jbl has two sets of + and - for ease of wiring. if you hook up each sub to its own set of + and -, (providing the amp with a 4 ohm load on each "channel", the jbl will automatically combine the two "channels" into one (parallel them) when you parallel, you drop the ohm that the amp sees by 2.
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Old 11-27-2002, 03:40 PM   #9
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in simple terms. if you have one channel and a 4 ohm sub, the amp will see a 4 ohm load. now everytime you add another 4 ohm load to the same channel, the ohm load that it see's will keep dropping. the lower the ohm, the more power to an extent if its not regulated. so if you had only one l5 connected, the amp would see a 4 ohm load. now if you added another 4 ohm load to the amp and since its a mono block amp, it will drop the ohm load to 2 ohms. if you still dont undersatnd.. lemme know.. hehe.
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Old 11-27-2002, 05:32 PM   #10
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yea i get it now (again) but im sure i'll lose it again so stick around and see how one mans brain can turn to mush in a matter of months.
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Old 12-01-2002, 01:27 PM   #11
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Thanx everyone for helpin' out while I was gone, good replies here!

GTkid - You'll get the hang of it, don't stress. After you've been in the game a while, it'll be second nature to you.
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Old 03-29-2003, 12:39 PM   #12
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Ok so if i am going with 2 dual voice coil speakers and i wanted them to run at 4 ohms they would need to be dual 4 ohm subs. If i did this correct. Because you have 2 dual 4's when run in parallel and series would be 8/2=4 correct. Am i correct in assuming this.
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Old 03-29-2003, 12:45 PM   #13
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Quote:
Originally posted by Vinaashak
Ok so if i am going with 2 dual voice coil speakers and i wanted them to run at 4 ohms they would need to be dual 4 ohm subs. If i did this correct. Because you have 2 dual 4's when run in parallel and series would be 8/2=4 correct. Am i correct in assuming this.
2 4 ohm DVC subs would give you your 4 ohm load via wiring the VC in series and the subs in parallel.
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Old 03-02-2005, 07:44 AM   #14
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Here's another link:

http://www.rockfordfosgate.com/rftech/wiringwizard.asp

I've been a member of the Rockford forum for over a year now, and find the most valuable car audio questions answered there. If anyone ever joins, I'm Team_RF_2005
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