4 ohm vs. 2 ohm discussion

[kiteman]

so the front speakers and rear speakers come in a different ohms, right? one is 4 ohms and the other 2 ohms or something...

i'm wondering when people hook up the JL or any other amp via the FARK, how exactly does the amp handle two different ohm settings? does it take the front and play them using 2 ohms and the rear using 4 ohms (or vice versa), or does it convert all of them to 4 ohms? would any amp capable of doing 4 channels at 2 or 4 ohms be able to play both simultaneously if that is what the JL amp is doing? i am confused by this concept. thanks for the help.

[DraggnFrameGMC]

It doesnt convert them. The lower the ohm load, the more power they will pull. The front speakers are most liekly a 4 ohm load because they parallel with the factory tweeter and create a 2 ohm load. All 4 channel amps i've ever seen are 2 ohm stable, so thats not a problem at all. But its not a bad thing they run at 2 ohm because they are getting more juice to them. And like I said, if you put a meter on the combo of the factory door speaker and the tweeter, its probably at 2 ohm also.

[2K11SS]

Buy a JL audio XD 400/4 and a subthump harness. The harness allows for a simple hookup and the XD 400 fits right in the stock amps spot and is class D so it runs cool since the stock location does not allow for ample cooling. As far as the 2 ohm 4 ohm question, the amp will play in both loads so it will not affect the amp (actually no speaker is exactly X ohms through its entire frequency range. The impedance (ohms) will move up and down as the frequency changes). Technically the 2 ohm will receive twice as much power to it but you can adjust out any difference by using your fader. Many amps are stable down to 1 ohm (note: 0 ohms is a short circuit) you just have to check to see what each individual amp is capable of.

[Steve@Subthump]

The front door speakers are 2ohms and the tweeters are 4ohms. The wiring is simply split off. Part of it goes to the mid and the other part goes to the tweeter. The tweeter has a capicitor onboard that filters out the highs but it remains a 2ohm nominal impedence.

The rear speakers are also 2ohm with a 4ohm tweeter, but wired separately (ie bi-amped--not on the same line). Guys that are using our FARK to replace their amp can essentially hook the rears up just like the fronts are hooked up by adding filters ie caps or bass blockers to the extra leads. This puts the tweeter in series for a 2ohm nominal impedence. If you look at most coaxial speakers, this is how they are typically built.

[kiteman]

Originally Posted by Steve@Subthump

The front door speakers are 2ohms

The rear speakers are also 2ohm

aha, so herein lies the question: the FARK allows those 4 speakers you mentioned in your quote to be powered by an aftermarket amp. if we are assuming that aftermarket amp is in fact the JL XD400, then each speaker is getting 100w @ 2ohms (the rated JL specs). do i understand that right?

i assume the front tweeters are being powered by the head unit? and if you splice in bass blockers to the rear 6x9s, what is happening then...is the 6x9 mid getting 50w and the tweeter getting 50w? i'm just trying to understand exactly how much power each speaker gets and where it is going. thank you.

[kiteman]

can anyone answer? is the amp providing power at 2 ohms or 4 ohms to the speakers in our car via the FARK?

[DraggnFrameGMC]

It should be 2 ohm. I've never used one before, but I just looked at it on their site and theres nothing in the harness to change the resistance of the speakers.

[Zach@ExtremePerformance]

Originally Posted by kiteman

i assume the front tweeters are being powered by the head unit? and if you splice in bass blockers to the rear 6x9s, what is happening then...is the 6x9 mid getting 50w and the tweeter getting 50w? i'm just trying to understand exactly how much power each speaker gets and where it is going. thank you.

Yes, no, maybe. As texas mentioned, the load (resistance, impedance, whathaveyou) of a speaker actually changes somewhat based on the frequency/combination of frequencies its playing at any given moment. Hence the "nominal 2ohm rating." And, even more fun, the frequency that a crossover (the cap on the tweet is a 6db/oct high pass filter) kicks in at changes as the impedance "behind" it changes.
Now, take the split second of music you are feeding through the amp to the speakers. In this case we have the amp seeing 2 ohms below, say, 4k (I'm making an educated guess at what the tweet is capped at, haven't had the urge to actually check so it may be slightly different!) and theoretically 1.34 above 4k since the tweeter would normally be PARALLELED with the mid (if you DO series wire it, it'd be a 6ohm load) but since the tweet is only going to draw so much power, you will typically not reach the current limit on the amp's output stage and run it into protection. Based on that piece of music's spectral content, and level, you may have any amount of power going to either - or both- driver within the amp's 100w capability. There's no hard and fast division of power.
Also note that the actual power delivered fluctuates radically on an instant by instant basis at any given frequency, depending on what instruments are playing what notes (and how loud) at any moment. Dynamic range compression lessens this some, but you might need gobs of power at say 300Hz as a kick drum mallet hits the drum head but be essentially dead from 500-2k 'cause no one else is playing or singing yet; with another decent but lesser demand up say 8k as the drummer works a cymbal.
Clear as mud? Sorry...

[Shu71]

If you have two four ohm impedance speaks wired in parallel, you end up with a 2 ohm load to the amp. On the fronts they run 4 ohms for the tweet and 2 ohms for the mids. So you take 4 x 2 / 4 + 2 = 8/6 = 1.33 ohms. So if your amp is stable to 1 ohm and powers to 100W @ 2 ohms, then it would actually power the fronts speaker combination at about 150W. Adding the X2A Subthump harness on the rear would put the rear 6x9 mid and tweeter at the same impedance as the fronts (1.33 ohms) and thus allowing the amp to produce 150W to those as well. If you do not use the X2A harness then your rear 6x9 mids (tweeters disabled) would have 2 ohm impedance and thus the amp would power to 100W thus would also add to those who are using more rear fader to their system to balance the sound stage (in addition to the accoustics of the cabin design). I can not find in writting the XD400 is stable at one ohm but since so many are using it with the stock speakers and it is working well, I'd assume it is. All this is to the best of my knowledge and hopefully right as this is how I have learned it...if I'm wrong, someone please set me straight.

[kiteman]

Originally Posted by Zach@ExtremePerformance

Also note that the actual power delivered fluctuates radically on an instant by instant basis at any given frequency,

i do understand this, but the ohm load should not fluctuate.

Originally Posted by Shu71

If you have two four ohm impedance speaks wired in parallel, you end up with a 2 ohm load to the amp. On the fronts they run 4 ohms for the tweet and 2 ohms for the mids. So you take 4 x 2 / 4 + 2 = 8/6 = 1.33 ohms.

wow, 1.33 ohms, really? i don't think the XD is stable at that level.

i really wish we could know for certain what the ohm load is for the stock speakers via the FARK. good discussion nonetheless, thanks for the input guys!

[DraggnFrameGMC]

Ohm load does fluctuate. Test a speaker with a system off, then turn the radio and re-test and it will be bouncing all over the place.

I cant see the door speaker combo being at 1.33ohms. Every person with an aftermarket amp on their doors would be going into thermal/protect mode. Its not common at all for a 4ch amp to ne 1ohm stable.

[Zach@ExtremePerformance]

Originally Posted by Shu71

If you have two four ohm impedance speaks wired in parallel, you end up with a 2 ohm load to the amp. On the fronts they run 4 ohms for the tweet and 2 ohms for the mids. So you take 4 x 2 / 4 + 2 = 8/6 = 1.33 ohms. So if your amp is stable to 1 ohm and powers to 100W @ 2 ohms, then it would actually power the fronts speaker combination at about 150W. Adding the X2A Subthump harness on the rear would put the rear 6x9 mid and tweeter at the same impedance as the fronts (1.33 ohms) and thus allowing the amp to produce 150W to those as well. If you do not use the X2A harness then your rear 6x9 mids (tweeters disabled) would have 2 ohm impedance and thus the amp would power to 100W thus would also add to those who are using more rear fader to their system to balance the sound stage (in addition to the accoustics of the cabin design). I can not find in writting the XD400 is stable at one ohm but since so many are using it with the stock speakers and it is working well, I'd assume it is. All this is to the best of my knowledge and hopefully right as this is how I have learned it...if I'm wrong, someone please set me straight.

Not sure where you get the 150w number from? But yes, the amp is theoretically seeing 1.34 at the frequencies where the mid and the tweeter are both operating*.
The amp jumps from 75w/p/c at 4ohms to 100w/p/c at 2; or a 33% increase. So you'd get at best another 33% going from 2 to 1ohm. Ohms Law says the current output should double as impedance halves...but an amp's ability to actually DO this often falls short.

Originally Posted by Zach@ExtremePerformance

Now, take the split second of music you are feeding through the amp to the speakers. In this case we have the amp seeing 2 ohms below, say, 4k (I'm making an educated guess at what the tweet is capped at, haven't had the urge to actually check so it may be slightly different!) and theoretically 1.34 above 4k since the tweeter would normally be PARALLELED with the mid (if you DO series wire it, it'd be a 6ohm load) but since the tweet is only going to draw so much power, you will typically not reach the current limit on the amp's output stage and run it into protection.

NOMINALLY, it is indeed at that load, above the tweeter's high pass frequency. But the amp won't go into protection until you ask it to exceed it's ability to deliver current; the tweet won't do this unless you are really leaning on the volume and at that point you're running it into clipping anyway. Below the tweeter's crossover frequency, it and it's cap (that leg of the circuit, if you will) show an increase in resistance, so an amp is at the woofer's 2ohm load where most of the music is. This is why it doesn't shut down.

*a passive crossover works by adding an increasing resistance above/below (as appropriate) it's crossover point. Or, a cap serving as a 3kHz high pass on a tweet, causes the amp to see more and more resistance below 3k, increasing as frequency decreases. This causes the amp to produce 6dB worth of power less for each octave you go below 3k, to the tweeter. So, even though your multi-meter sees the aggregate impedance of all the drivers hooked up to a passive crossover, the amplifier sees the actual impedance at any given frequency, which will vary based on the speaker/speakers resistances at those frequencies, the actions of the passive filters, etc.

[kiteman]

zach, thanks for the info. so you agree the fronts are seeing about 1.33 ohms and the rears 2 ohms (no tweeters)? so if your amp is pushing 100w @ 4ohm, and 200w @ 2ohm, then the fronts might be seeing 266w and the rears 200w? is that peak or RMS? i guess i'm just curiously trying to figure out that if you used an amp with those ratings i just mentioned, what the RMS power would be to the front and rear speakers...

[Agent WD-40]

Originally Posted by Steve@Subthump

The front door speakers are 2ohms and the tweeters are 4ohms. The wiring is simply split off. Part of it goes to the mid and the other part goes to the tweeter. The tweeter has a capicitor onboard that filters out the highs but it remains a 2ohm nominal impedence.

The rear speakers are also 2ohm with a 4ohm tweeter, but wired separately (ie bi-amped--not on the same line). Guys that are using our FARK to replace their amp can essentially hook the rears up just like the fronts are hooked up by adding filters ie caps or bass blockers to the extra leads. This puts the tweeter in series for a 2ohm nominal impedence. If you look at most coaxial speakers, this is how they are typically built.

Steve- Do you have a recommendation on what size cap to use as a filter on the rear tweeters?

[Steve@Subthump]

non-polarized electrolytic capacitor rated at 25 volts with a value of 10uf for a cutoff frequency of about 4kHz.

[2010SLVRBULIT]

question of resistance, higher# having more resistance, and lower# having more power delivered due to lower impedance/resistance, drawing more power from the amp. Depending on the amps ability to drive those speakers at that impedance is the question.

[Zach@ExtremePerformance]

Originally Posted by kiteman

zach, thanks for the info. so you agree the fronts are seeing about 1.33 ohms and the rears 2 ohms (no tweeters)? so if your amp is pushing 100w @ 4ohm, and 200w @ 2ohm, then the fronts might be seeing 266w and the rears 200w? is that peak or RMS? i guess i'm just curiously trying to figure out that if you used an amp with those ratings i just mentioned, what the RMS power would be to the front and rear speakers...

Okay, on an amp (I'm guessing you mean a theoretical amp, not the JL XD400/4) that truly doubles from 4ohms to 2, then you would be up around 66% into a 1.33ohm load (again, within the limits of the amp's power supply to make current and the output stage to deliver it).
Now, note, you are only at 1.33ohms at and above the tweet's crossover point. Below that the amp only sees the woofer and delivers it it's 2ohm allotment of power. At and above, it sees the woofer (still) and continues to deliver the 2ohm level of power. It ALSO sees the tweeter, delivering IT it's 4ohm level of power. Below the tweeter's crossover point, the crossover shows a resistance that increases more and more as you get lower and lower below that crossover point, so the amp is still doing whatever is dictated to the woofer, but the tweeter side of the circuit gets less and less power (with a cap, at a rate of 6dB/oct, or a 4 times less power each time the frequency cuts in half).
In the very-oversimplified example below, even though both speakers are the same impedance (the theoretical ones in the diagram, not the actual JL speakers!), of say, 4ohms, and even though they are parelleled...the amp sees.... a 4ohm load! The tweeter's circuit becomes a higher and higher impedance drawing less and less power below 4kiloHertz, and the woofer does the same thing above 4k. Realistically, there is somewhat of a fluctuation where the speakers overlap (notice the crossover doesn't STOP power out of band, just decreases it) and as the speaker's individual overall impedance changes, the crossover points change (which changes the overlap, and where phase issues happen...et cetera) but this gives you an idea.
The crossover doesn't "divide power" so much as tell power associated with a given frequency where to go. How much goes where is based on what the music itself requires at any given instant.

[Zach@ExtremePerformance]

Now, instead of the flat 20 -20k test tone, since no one listens to the "pipe organs" on their CleanSweep CD or the sine sweep on their Bit One/Ten CD, play music. Here are two pics where I set my analyzer to update on each sample, played a track (YYZ from Rush's Moving Pictures album, if you gave a hoot, which you probably don't!) and froze it at random.
Look at the two snapshots of a track's spectral content, and mentally overlay that with the crossover's breakout in the diagram above and you'll see what I mean. One, there isn't nearly as much up in the tweeter range (in terms of energy required from the amp), which is why you're amp doesn't freak out running a stock Camaro's front stage.
Two, where the power is changes radically instant to instant! The nature of the track, the recording engineer, all kinds of things will affect the specific distribution of power by frequency; and on a more dynamically compressed track you won't have as deep of valleys or as high of peaks, but you'll still have things all over the map.

Okay, wake up, I'll leave off now.

[Agent WD-40]

Originally Posted by Steve@Subthump

non-polarized electrolytic capacitor rated at 25 volts with a value of 10uf for a cutoff frequency of about 4kHz.

Thanks. This got me thinking though... Can you recommend a resistor I can wire in series with my rear Boston spekers to make them a higher impedance (so the amp sees it as a 4-8 ohm load)? I would like to increase the impedance so they run at a lower volume. I was thinking if I hooked up the rear tweeters it may sound more balanced but I really just want to quiet my rear speakers down.

I'm using the FARK kit to hook my aftermarket 5 channel amp into the system. I replaced my front speakers (which are now 4 ohm) and the stock Boston rear speakers are 2 ohm. Because the factory head unit has such strong signal input I don't have the sort of control with the gains on the amp I would like (my rears are already at the lowest gain setting).

I have been using the fader to move the sound more to the front but I would like to have it more centered on the dial and not have the rear speakers play as loud.

Any advice on what sort of resistor I can use? Thanks!

[Steve@Subthump]

Originally Posted by Agent WD-40

Thanks. This got me thinking though... Can you recommend a resistor I can wire in series with my rear Boston spekers to make them a higher impedance (so the amp sees it as a 4-8 ohm load)? I would like to increase the impedance so they run at a lower volume. I was thinking if I hooked up the rear tweeters it may sound more balanced but I really just want to quiet my rear speakers down.

I'm using the FARK kit to hook my aftermarket 5 channel amp into the system. I replaced my front speakers (which are now 4 ohm) and the stock Boston rear speakers are 2 ohm. Because the factory head unit has such strong signal input I don't have the sort of control with the gains on the amp I would like (my rears are already at the lowest gain setting).

I have been using the fader to move the sound more to the front but I would like to have it more centered on the dial and not have the rear speakers play as loud.

Any advice on what sort of resistor I can use? Thanks!

You could wire a loc onto the rear inputs of the x3. I think that would reduce the input signal enough for you without resistors and that sort of thing.

[Agent WD-40]

Originally Posted by Steve@Subthump

You could wire a loc onto the rear inputs of the x3. I think that would reduce the input signal enough for you without resistors and that sort of thing.

Thanks! That is a good idea and I didn't think of that... I'm pretty sure I have a spare LOC floating around that I can try. I also have an AudioControl EQX from my last setup I could use but that is a bit more complicated that I think I want to make it right now.

I was originally thinking a resistor because the harness that goes between the stock rears and the factory harness is probably the easiest wire for me to access in my trunk without having to pull anything apart. I'm going to give the LOC a try but if it doesn't work out for me any idea what sort of resistor I would wan to use?