a Speaker has a Voice coil,
this produces the sound for your speaker,
Each voice coil has a Impedance rating,
in the case of a single voice coil, most have a Rating of 4 Ohm Impedance and or resistance.
If you take a look at the ratings on your amps, then you will notice they are rated at X Amount of power at 4 Ohm, X amount of power at 2 ohm, and if it's a D class, or really high end amp it will have a Rating at 1 Ohm, or even lower.
Most amplifiers can handle 4 Ohm Loads as standard, for this reason almost all car speakers at standard 4 Ohm,
Eg: a Amp that puts out 50 Watts at 4 Ohm loading, in most cases puts out 100 Watts at 2 Ohms, because it is half the load, but this is not always the case, and often depends on the Amplifier design.
This being said, Not all amps can cope with a 2 Ohm load and even less often a 1 Ohm Load. Often Amplifiers will be able to cope with a 2Ohm Load in stereo, but not in bridged mono.
EG: A 2 x 50 Watt amp, can also put out 2 x 100 at 2 Ohm, but when you bridge it to a Single Channel, MONO it puts out 200 Watts x 1 but at 4 Ohm. Putting a 2 Ohm load on this amp, will not neccessarily make 400 Watts, and often will damage or destroy the amp if you do so while it is bridged.
what does all this have to do with Subs and how many voice coils it has?
Simple, if you have 1 Voice coil, and it's rated at 4 Ohm, you plug it into a amp, it has a 4 ohm load, and thats that.
However a Dual Voice coil sub has 2 voice coils, Often they are Rated at Dual 4 Ohm Voice coils.
Now you must connect BOTH voice coils to your amp, to avoid damaging the subwoofer, and they must be wired correctly or it won't work.
Now lets say you have a Dual 4 Ohm voice Coil Sub, you have 2 Specific ways you can Wire it.
You can wire it in Series or Parralel..
Series will actually produce a 8 Ohm Load for your amp, EG: if your amp is rated at 100 watts at 4 Ohm, putting a 8 Ohm loading on your amp will cause it's output to drop to around 50 watts (again depending on the amp design).
While this all might seem bad, a 8 Ohm loading can often produce more dynamic bass, and better quality sound as long as power is not dropped too much, For this reason 8 and 16 Ohm is often/normally used in Home Audio.
wiring your 2 voice coils in Parralel, given they are both 4 ohm, will cause a 2 Ohm Load on your amp, EG: making your 100 Watt amp rated at 4 Ohm output 200 Watts.
To make a series wiring,
Start by plugging on end of your wire into the negative - input in the amp, then run it to the new negative wire to lets say left voice coil mounts Negative terminal, then lets run a short cable from the left voice coil positive + to the Right voice coil mount Negative -, then from the right voice coil mount positive + to the Positive + on the amp.
Your sub is now wired in series, and it's dual 4 Ohm voice coil, is producing a 8 Ohm load,
That being said, if you have a Dual 2 Ohm voice coil, series produces a 4 Ohm Load, and a Dual 8 Ohm voice coil would produce a 16 Ohm load ect ect.
Now with Parralel.
start by wiring your wire to the negative on the amp, then run it to the Left negative on the sub, then run a wire from your left negative on the sub to the Right negative (supposing your voice coil wiring mounts are opposite each other, you can also call it voice coil 1 and voice coil 2 if you like).
Now get a new wire, and run it from the positive on your amp to the positive on your left voice coil, then run another wire from the positive on your left voice coil to your right voice coil.
Now you have wired your sub in parralel, given that it's a Dual 4 ohm sub, you will have a 2 ohm load, or if it's a dual 2 ohm you will get a 1 ohm load,
and ect ect..
So what the hells the point of all this?
Imagine you want to run your Amp Bridged, and you can only run a 4 Ohm load, No lower.
Now lets go buy 2 12" Single voice coil subs.. you have 2 wiring options parrallel and series, one produces 8 ohm and one 2 ohm, but neither 4 ohm, unfortunatly to get the most power from your amp, you need a 4 ohm load.. so your stuffed! because you only have 2 4 Ohm Voice coils.
Now lets say you had 2 Dual 4 Ohm Voice coils.
Now we have 4, 4 ohm voice coils, we can run them in either series parrallel or parrallel series, and both will give us a 4 Ohm loading to our amp.
Rather than explain it.. get yourself a piece of paper out and draw up a series and parrallel circuit like i explained, and try to design a parrallel/series or series/parrallel circuit for your 2 subs.
with 4 4 ohm voice coils you all of a sudden have wiring options,
1 Ohm, 4 ohm and 16 Ohm loadings.
Keep this simple thing in mind, parrallel creates a reduced load, giving my amp more power, a series creates a increased load reducing my amps power.
This being said, Reducing your load, may increase your power to your amp, However your amp may produce ALOT more distortion, and it will loose some of it's control over the sub. Both of these things reducing their capability to produce nice quality sound, so always wire your subs to the reccomended loading, to avoid 1. Blowing your amp up and 2. creating crap bass.
Personally I run a 8 Ohm load, simply because the amp has alot more control over the subwoofer, and my bass become more accurate and dynamic, agreed it doesn't Pump and blow my windows out, but is just sounds plain nice and I'm not risking ruining both my sub and my amp.
the Higher the load, the less power you have, however the cooler and more effecient your amp runs, (draws less current)
Running a lower load than reccomended, might make your amp draw excessive current, which can damage your alternator, your batterys and even overheat the wiring your using if it's not good enough and finally damage your amp, if not do that first! not to mention overheat your sub voice coils and destroy your sub.
Keep in mind, this Highly depends on your Amp, and the type and design it is.
Some amplifiers, like D Class Subwoofer amps, are designed to run at 1 and 2 ohm loads. Some of the Older style A Class amps could cope with up to 1/4 Ohm loads, a feeble 25 x 2 amp could produce amazing power like 2000 Watts RMS! however that was the old days.. when 6 batterys and a 300 Amp alternator where required to get huge power!
Choose the amount and type of subs, to suit the amplifiers you plan to use.
and or vice versa, always make sure you have a big enough power system available for the subs and amps you want to run.
if you have anymore q's don't hesitate to email me.
regards
Juls
julsisere@hotmail.com