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I was an audio newbie a few months ago but I think I've learned enough about it through these boards and other boards that I can have an intelligent conversation about it now. But I still don't know what it means when it says when an amp or speaker is 2 or 4 ohms. And I don't understand how can you change the ohms? FOr example, an amps specs could say it is X Watts at 2 ohms and Y watts at 4 ohms. How do you change the ohms on an amp?
 

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Speakers are rated in ohms, some smart asses will say "its not a resistor!" but ignore them.

A 4 ohm speaker will have a DC resistance of a little under 4. A dual voice coil 4 ohm speaker will have two voice coils each 4 ohms. If you wire them in series, it'll be 8 ohms, wire them in parallel it'll be 2 ohms.

Now, lets say you have an amp rated at 300 watts x 1 at 2 ohms. If you take your dual voice coil sub, wire the coils in parallel it'll appear to be a 2 ohm sub. Connect this to your amp and each coil will get 150 watts.

Take the same amp, assume its rated at 150 watts x 1 at 4 ohms. Take your single voice coil 4 ohm sub and wire it to the amp. It is now getting 150 watts to the coil.

Basically, if its 300 watts at 2 ohms, and you connect a 2 ohm sub to it, the amp can output 300 watts. If you connect up a 4 ohm load to it, it won't be able to output as much power.
 

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Yes, the smartass say it's an IMPEDANCE not a resistance :D

But basicly, Noggin explain you the hole thing right... only diff is audio signal is AC current, not DC. And speakers will not only consume current (the resistor role) but also induct some current (the coil role). This will affect a bit the real resistance value at the end but anyway, amp and speakers are rated with ohms impedance value, not resistance value. That's why if you take an ohmmeter it will never read the value marked on the speaker. Like if the speaker say 4 ohms, an ohmmeter may read like 3.2ohms.
 
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