Free Shipping on Everything.
60-Day Money-Back Guarantee | Lifetime Tech Support

4 Ohm vs. 2 Ohm

Car Audio, Video, & GPS

Car Audio, Video, & GPS
Talk about stereos, navigation, amps, subs, and all things car audio

4 Ohm vs. 2 Ohm

This question is answered

Hi,

I was recently reading up on how a 2 ohm stereo setup generates up to 40% more power than a 4 ohm setup.  As I was shopping around for new car audio equipment I noticed that some car receivers had pre-amp outputs that supported 4 ohm and others that supported 2 ohms. 

I looked into it a little further and noticed how most amps will support a 2 ohm setup if you configure the speaker wires coming from your amp in such a way that will make the amp work under 2 ohms, therefore boosting the wattage going to the speakers.

When I searched a bit further, I noticed that many car speakers (not sub-woofers) support a 4 ohm configuration.  Assuming they're rated to support that much wattage, if I have a stereo receiver that supports a 2 ohm setup and I wire my amp to work under 2 ohms will my 4 ohm speakers support the 2 ohm configuration?

What if I had a stereo receiver that had pre-amp outputs that supported 4 ohm, if I wired my amp to run on 2 ohms would I still get the increased wattage output from the amp as a result?

 

Thanks in advance for your answers

Verified Answer
  • I think you're thinking about this all wrong.

    The impedance (2ohm, 4ohm, etc) is determined by two things, and two things only:

    1. The drivers (speakers, subs, etc) that you use (ie, 4ohm)
    2. How you wire the drivers to the amp (series, parallel, stereo, etc)

     

    Amazing1
    When I searched a bit further, I noticed that many car speakers (not sub-woofers) support a 4 ohm configuration.

    They don't support it, they are 4ohms. Think of impedance (in this case 4ohms) like any other physical property. Just as a 5" speaker will always be 5", a 4ohm speaker will always be 4ohms. You can wire different speakers together to create a different total impedance, but the impedance of individual speakers will not change.

    This is essentially the case for all single voice coil drivers. Similarly, voice coils can be wired together to create a different total impedance, but the impedance of the individual voice coils will not change.

    Amazing1
    [...] if I have a stereo receiver that supports a 2 ohm setup and I wire my amp to work under 2 ohms will my 4 ohm speakers support the 2 ohm configuration?

    If I understand you question correctly, you would actually be wiring the speakers to create a 2ohm load, not wiring the amp to accept a 2ohm load.

    Like I said before, you can wire the speakers together any way that you want as long as they can handle the resultant power output from the amp, and the amp can handle the impedance load.

    Amazing1
    What if I had a stereo receiver that had pre-amp outputs that supported 4 ohm, if I wired my amp to run on 2 ohms would I still get the increased wattage output from the amp as a result?

    Like I said before, if you wired the speakers at 2ohms, you would be fine as long as your amp was stable at 2ohms, and your speakers could handle the power.

     

    Long story short, your amp will see whatever impedance you wire your speakers at.

    If you connect a 2ohm (minimum) stable amp to a pair of 4ohm speakers wired in parallel, the speakers will be wired at 2ohms, and everything is fine.

    If you connect a 4ohm (minimum) stable amp to a pair of 4ohm speakers wired in parallel, the speakers will be wired at 2ohms, but the amp will only support 4ohms, so you have a problem.

    If you connect a 4ohm (minimum) stable amp to a pair of 4ohm speakers wired in series, the speakers will be wired at 8ohms, and everything is fine. You probably won't get as much power from the amp, but everything will be stable.

     

    Keep in mind that when you wire two speakers to a single channel of an amp, at a lower impedance, the total power may go up, but it is split between two speakers now. For instance, say you have an amp that outputs 100W @ 4ohms, and 200W @ 2ohms. If you wire one 4ohm speaker to that amp, you will have a 4ohm load, and get 100W. If you wire two 4ohm speakers in parallel, you will have a 2ohm total load, and get 200W. However, that 200W is now split between two speakers, so each speaker will still only see 100W each.

     

    Additionally, power output is not the only thing to be thinking about when wiring speakers. I always keep speakers on separate channels to get stereo separation. If you connect two speakers to the same channel (ie wiring two 4ohm speakers in parallel on one channel of an amp to get more power) those speakers will output the same signal, ie you will hear only mono, and will lose the differences between left and right channels.

     

    Probably more than you were asking for, but hope this explanation helps. Let us know if you have any other questions.

    (And yes, I know I made a few simplifications to disregard complex impedance, driver displacement, etc. for the sake of clarity)

    02 BMW 330Ci

    Alpine DVA-9965, and a mix of stuff

    12 Ford F-150

    In progress: Pioneer DEH-80PRS HU -> DLS RA40 amp -> Seas G18RNX woofers & SB Acoustics SB29 tweeters

All Replies
  • I think you're thinking about this all wrong.

    The impedance (2ohm, 4ohm, etc) is determined by two things, and two things only:

    1. The drivers (speakers, subs, etc) that you use (ie, 4ohm)
    2. How you wire the drivers to the amp (series, parallel, stereo, etc)

     

    Amazing1
    When I searched a bit further, I noticed that many car speakers (not sub-woofers) support a 4 ohm configuration.

    They don't support it, they are 4ohms. Think of impedance (in this case 4ohms) like any other physical property. Just as a 5" speaker will always be 5", a 4ohm speaker will always be 4ohms. You can wire different speakers together to create a different total impedance, but the impedance of individual speakers will not change.

    This is essentially the case for all single voice coil drivers. Similarly, voice coils can be wired together to create a different total impedance, but the impedance of the individual voice coils will not change.

    Amazing1
    [...] if I have a stereo receiver that supports a 2 ohm setup and I wire my amp to work under 2 ohms will my 4 ohm speakers support the 2 ohm configuration?

    If I understand you question correctly, you would actually be wiring the speakers to create a 2ohm load, not wiring the amp to accept a 2ohm load.

    Like I said before, you can wire the speakers together any way that you want as long as they can handle the resultant power output from the amp, and the amp can handle the impedance load.

    Amazing1
    What if I had a stereo receiver that had pre-amp outputs that supported 4 ohm, if I wired my amp to run on 2 ohms would I still get the increased wattage output from the amp as a result?

    Like I said before, if you wired the speakers at 2ohms, you would be fine as long as your amp was stable at 2ohms, and your speakers could handle the power.

     

    Long story short, your amp will see whatever impedance you wire your speakers at.

    If you connect a 2ohm (minimum) stable amp to a pair of 4ohm speakers wired in parallel, the speakers will be wired at 2ohms, and everything is fine.

    If you connect a 4ohm (minimum) stable amp to a pair of 4ohm speakers wired in parallel, the speakers will be wired at 2ohms, but the amp will only support 4ohms, so you have a problem.

    If you connect a 4ohm (minimum) stable amp to a pair of 4ohm speakers wired in series, the speakers will be wired at 8ohms, and everything is fine. You probably won't get as much power from the amp, but everything will be stable.

     

    Keep in mind that when you wire two speakers to a single channel of an amp, at a lower impedance, the total power may go up, but it is split between two speakers now. For instance, say you have an amp that outputs 100W @ 4ohms, and 200W @ 2ohms. If you wire one 4ohm speaker to that amp, you will have a 4ohm load, and get 100W. If you wire two 4ohm speakers in parallel, you will have a 2ohm total load, and get 200W. However, that 200W is now split between two speakers, so each speaker will still only see 100W each.

     

    Additionally, power output is not the only thing to be thinking about when wiring speakers. I always keep speakers on separate channels to get stereo separation. If you connect two speakers to the same channel (ie wiring two 4ohm speakers in parallel on one channel of an amp to get more power) those speakers will output the same signal, ie you will hear only mono, and will lose the differences between left and right channels.

     

    Probably more than you were asking for, but hope this explanation helps. Let us know if you have any other questions.

    (And yes, I know I made a few simplifications to disregard complex impedance, driver displacement, etc. for the sake of clarity)

    02 BMW 330Ci

    Alpine DVA-9965, and a mix of stuff

    12 Ford F-150

    In progress: Pioneer DEH-80PRS HU -> DLS RA40 amp -> Seas G18RNX woofers & SB Acoustics SB29 tweeters

  • Well said - Ninja ... A few things that were missed ...

    Amazing1
    I was recently reading up on how a 2 ohm stereo setup generates up to 40% more power than a 4 ohm setup.

    Pretty general and misleading setup.

    In theory, a 2-ohm stereo setup should generate 100% more power than a 4-ohm setup.  (i.e. a true linear amp will be 100W RMS at 4-ohms and 200W RMS at 2-ohms - so with a 2-ohm load connected, it makes twice as much power).

    Also confusing is that a few companies (Infinity, JBL, Polk) are marketing speakers at 2-ohms when they are truly closer to 3-ohms and throwing out other confusing factoids as well, but we won't address that here.

    Amazing1
    As I was shopping around for new car audio equipment I noticed that some car receivers had pre-amp outputs that supported 4 ohm and others that supported 2 ohms.

    I think you read that wrong as well - pre-amp outputs don't see any ohm load and don't car what ohm load is connected to the amp.  Some car receivers have 2-Volt and some have 4-Volt (or 5-Volt or 6-Volt) which I suspect you are referring to.  Higher voltage RCA's are less likely to pick up noise and allow lower gain settings on the amp, but it shouldn't be a determining factor on the head unit decision.

    Amazing1
    I looked into it a little further and noticed how most amps will support a 2 ohm setup if you configure the speaker wires coming from your amp in such a way that will make the amp work under 2 ohms, therefore boosting the wattage going to the speakers.

    Most amps will support 2-ohms stereo and 4-ohms bridged. Most amps will make more power at 2-ohms than 4-ohms, but not all amps will.

    Amazing1
    When I searched a bit further, I noticed that many car speakers (not sub-woofers) support a 4 ohm configuration.  Assuming they're rated to support that much wattage, if I have a stereo receiver that supports a 2 ohm setup and I wire my amp to work under 2 ohms will my 4 ohm speakers support the 2 ohm configuration?

    This got all confused - most car speakers ARE 4-ohms.  If you wire two of them in parallel to present 2-ohms at the amp, the amp puts out the 2-ohm wattage and the speakers split that.  Also - most amps are 2-ohms stable stereo - most car stereo receivers (head units) are NOT!!!!

    Amazing1
    What if I had a stereo receiver that had pre-amp outputs that supported 4 ohm, if I wired my amp to run on 2 ohms would I still get the increased wattage output from the amp as a result?

    As mentioned earlier - the pre-amp outputs don't care what is wired to the amp, except that you might have to re-adjust the gain on the amp if you wire the amp differently.

    Hope This Helps!!!

    Anyone else have suggestions?

     



    [edited by: TigerHeli at 1:44 PM (GMT -5) on Tue, Jan 4 2011]

    2002 Ford Focus JVC KD-A815 Sony CDX-GT410u Sony XT-100HD HD Tuner Stock speakers, no amp, no subs