looking to buy a new sub for the jeep, but im not sure what the difference beteween (4ohm + 4ohm) and (2ohm + 2ohm) is? can someone explain?

that means you have a dual voice coil sub. you can wire the 4 + 4 ohm two ways. one way you will get 2 ohms and one way you will get 8 ohms. make sure your amp can handle a 2 ohm load!!

so it's a power output issue?

V=I*R

Smaller R (Resistance), bigger current AMP at given same voltage.

P=I^2*R (I think)

Bigger I (current), MORE POWER

uh... :confused:

so it's a power output issue?



Sort of......


Your amplifier makes power into a load*. The load is identified as a number. Every speaker has a number on it. The number may be 2, 4, 8-ohms, or something above, below, or in-between. Welcome to the Wild World of Audio! (*Load is also called impedance. Impedance is expressed in a value of resistance called "ohms".)

Think of you amplifier as having eyes. It wants to "see" a certain speaker load in order to function optimally. A dual voice-coil woofer can wired up so it has 2 different mono loads. You would pick an ampifier that performs best into one of those loads. If the amplifier is rated for 4-ohm mono, you'd select a woofer that reflects a 4-ohm load back to it.

How about if you want to use 2 woofers with the same amp so that it sees the same 4-ohm load again? You could use 2x 2-ohm woofers connected in series for 4-ohm load (a "so so" alternative) or use 2x 8-ohm woofers connected in parallel for 4-ohm load (a better way to go).

It really comes down to what you have, or are going to buy, and making sure that it is all compatible with one another. You've asked a pretty basic question too. For more of this to make sense, I'd start here:

Car Audio FAQ (http://www.mobileaudio.com/rac-faq/)

speaker

It's to give you more possibilities with wiring and amp selection. A dual 4ohm sub (4 + 4) can be wired in parallel to 2ohm or series to 8ohm. A dual 2ohm sub (2 + 2) can be wired in parallel to 1ohm or series to 4ohm.

So you need to pick an amp, if it puts out full power into 1ohm or 4ohm then you'll want a dual 2ohm sub, if it puts out full power into 2ohm then you'll want a dual 4ohm sub. This is if you just have one of those subs, if you have a pair of them then things are a little different.

What TJRCS was saying is that power is equal to the voltage the amp puts out at the speaker terminals squared and divided by the impedance of the speaker you have attached to it (P=V^2/R). If you cut the resistance in half, you get double the power, if you double the resistance, you cut the power in half. This is true if you're looking at running the same amp at 1ohm vs 2ohm (1ohm will have twice, or nearly twice the power as 2ohm will), but if you're looking at an amp that puts out full power into 1ohm vs a different amp that puts out full power into 2ohm, those equations mean nothing so just ignore them.

well im purchasing this amp 400 watts RMS x 1 at 4 ohms

320 watts RMS x 1 at 2 ohms

requires 8-gauge power and ground leads — wiring and hardware not included with amplifier

variable 40-500 Hz low-pass crossover, 12 dB/octave

variable bass boost (0-12 dB) at 45 Hz

preamp- and speaker-level inputs

12-9/16"W x 2-1/16"H x 9-13/16"D

Mono amplifier with two 20-amp fuses inserted in chassis



and i wanted to pair it with a subwoofer, but the description says that it's 4ohm + 4 ohm.

So I guess my question is, what kind of subwoofer would work with this amplifier?

well im purchasing this amp 400 watts RMS x 1 at 4 ohms

320 watts RMS x 1 at 2 ohms


The amp puts out less power at 2 ohms than at 4 ohms?!? That's either a typo or a very...interesting...amplifier.


So I guess my question is, what kind of subwoofer would work with this amplifier?

OK, here's the thing: you need to make sure that the resistance (= ohms) of your speakers is equal to or greater than the resistance supported by your amp.

With a single speaker (or voice coil), this is easy: you just compare the numbers. So if your amp will handle 2 ohms and you buy a 4 ohm speaker, you're fine.

Things get more interesting if you want to connect two (or more) speakers or voice coils to an amp that only has one connection. In this case, there are two ways to do it:

1) Wire the speakers in series. To compute the resistance, you simply add up all of the ohms. If your woofer has two 4 ohm voice coils, the resistance would be:

R = 4 + 4 = 8

Take the total value you get and compare it to the number from your amp.

2) Wire the speakers in parallel. Here, the formula is a bit more complex. Let's assume that the speakers are called R1 and R2. The formula is then:

R = (R1 x R2)/(R1+R2)

So, in your case if you wire the two 4 ohm voice coils wired in parallel:

R = (4 x 4)/(4 + 4) = 16 / 8 = 2 ohms

Again, you take this number and compare it to what your amp supports.

FYI, it sounds like you might want to do some reading at bcae1.com (http://www.bcae1.com)...

i did a little reading, so this means i want to find a sub that performs well at 4ohms then?