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4ohm vs 8ohm; do they SOUND the same?

Discussion in 'Amps and Cabs [BG]' started by keyboardguy, Feb 22, 2008.

  1. keyboardguy

    keyboardguy Supporting Member

    May 11, 2005
    Hi folks,

    There's plenty of info here on TB on 4 and 8 ohm speakers that got me wondering:

    Say you had 2 identical speakers from the same manufacturer, in 2 identical cabinets;

    cabinet #1 having one 4 ohm speaker (same model #)
    cabinet #2 having one 8 ohm speaker (same model #)

    Would they sound EXACTLY the same? Has anyone ever tested/evaluated this?

    Just wondering.....

  2. onlyclave


    Oct 28, 2005
    In my experience if you A/B'd a 4 and 8 ohm cabinet on the same amplifier you would get almost twice as much power with the 4 ohm (BUT loudess = not very much more) but there would be more distortion and heat generated by the amp.
  3. keyboardguy

    keyboardguy Supporting Member

    May 11, 2005
    "there would be more distortion and heat generated by the amp"

    But I'm talking about an amp that can handle it, ie. my Carvin B800 and B1500.

    If you have a decent size amp that's not going to distort, would you HEAR any difference between the 4 and 8 ohm?
  4. Bass sounds better at 4 Ohms. Not really any better just louder. 8 Ohms is fine, just not as loud. Not good to run at 2 Ohms for any length of time.
  5. The difference would be about 3dB with a SS amp. Tonally, i dont believe there is any difference.
  6. Says who?

    If the amp is designed to work at 2 ohms, there is no issue. I sure havent had any with either of my amps at 2 ohms.
  7. MarkMyWordsXx


    May 17, 2006
    any evidence to support this wild claim?
  8. bassman639


    Dec 23, 2006
    northeast ,pa
    if you have the same cabs,but one is 4 o and one is 8, the diff is watts going into it ,e.g. your cabs are 300 watt cabs first off, now you have a head that at 8 ohms gives you 200 watts ,but at 4 ohms gives you 350 watts same head, you see the diff? just more headroom, and the result of it the head gives off more heat, but you have 350 watts not two, you might want to push the 200 watt,now you're clipping, i always thought you should match as close as you can to the watts and ohms, also with 8 ohm cabs you can add more cabs up to 4 cabs if your head goes to two ohms, you can't do that, with 4 ohms, just 2 cabs and the spl is minor its only about 2 db spl, where as another cab will give maybe 3 db plus xtra watt== louder
  9. 4 Ohms gives more power without hurting the amp and of course at 2 Ohms you are taking risk even when they claim that the amp can handle it. Not worth it.
  10. That is mostly correct except modern amps will usually function fine at 4 or 8. I believe the SPL variance is around 6 dB at the top of the power range, so you probably would not notice it.

    I select impedance based solely on how I intend to hook them up later. I am currently running 2 8 ohm boxes off a 2 channel PA amp, but they were originally bought for a Behringer power amp that had 2 outs that were paralleled when use together. The amp said it was good to 2 ohms, but I never push the limit of my equipment.
  11. RobbieNuke


    Jan 22, 2008
    Theoretically, with all other things being equal (i.e. bass/amp/cables), there should be no difference in sound quality (i.e. tone). There may be a volume difference... the 4 Ohm may sound louder since there is less resistance/impedance for the amp to overcome.

    Some (tube) amps have multi-tap output transformers that match the load to the amp. Lets say the amp (head or combo) came with an 8-Ohm cabinet you would plug it into the speaker out marked "main". Plugging a second 8-Ohm cabinet into the "Extension" or "Aux" cabinet output jack would switch to a 4-Ohm tap on the output transformer so there would not be any mismatch of impedance. In this case the actual output power would be the same, but you would have twice as many speakers moving twice as much air sounding louder but using the same amount power.

    Solid state amps do not have an output transformer and so as you loaded on more speakers the output section would see less resistance/impedance and would produce more power RMS (i.e. 100 WRMS may become 150 WRMS). Of course you can only go so far with this... you can not hook up 20 cabinets and expect to get 5,000 watts, you would exceed the transistor operating parameters.

    I usually suggest using one amp/one cabinet for most situations. If there is a need for a second cabinet it's usually as a monitor for someone else on the far end of the stage (keyboard player in my case) so tone/volume are't a big thing. But I still keep in mind the total load.
  12. figuredbass

    figuredbass Supporting Member

    Jul 11, 2007
    NYC vicinity
    Good question! I wondered about this myself, and when auditioning a UL310 (with 16 ohm drivers) and a 4 ohm version UL210 (with 8 ohm drivers) I asked Nick Epifani if there was an actual sonic difference between the two drivers. Recalling as best as I can, he said, "If you were to closely A/B both drivers side by side you would hear a slight difference, but as far as the overall cabinet sound and voicing goes you wouldn't." I agree with this. I did hear what I believe to be a small driver difference (and not a cabinet voicing difference) between the two, and slightly preferred the 16 ohm drivers in the UL310. This is not to say they were/are better, just that I picked one over the other. Someone else may feel the complete opposite as I do. Please bear in mind that this was not a completely valid test because I did not compare a 4 ohm UL210 against an 8 ohm UL210.

    Cabinet designers can go through great lengths to keep the drivers of different impedances sounding as close as possible. If done well the differences can be so small as to be negligible overall.
  13. Chuck78


    Feb 16, 2008
    columbus, oh
    So basically you are saying, that if the amp is rated for 2 ohms, don't chance it, run at 4 ohms. This would also translate into you saying, "If your head is rated at 4 ohms, you're running the risk of blowing it up with a 4 ohm cab if you push it, so you'd better not chance it and just stick to 8 ohms and baby the thing so that it will definitely last a long time."

    Not true whatsoever. I have 4 amplifiers rated to a 2 ohm load, all are from 1968 to 1978, all are still SCREAMING today. Those are 30 to 40 year old power sections! We play EXCESSIVELY LOUD, and at 2 ohms always.

    If the amp is quality, and you treat it right, it will handle the rated load just fine.
  14. jtc_hunter


    Feb 16, 2007
    Ok Flamers get your flamethrowers out and aim them at me, cause here is what I think:

    If you have 2 identical cabs ,except 1 is 4ohm and the other 8 ohm,
    A. The tone will be pretty much the same
    B. The 4 ohm cab will be louder, but not twice as loud as the 8ohm.
    C. 2 -8 ohm cabs will be louder than 1 -4 ohm
    D. relatively, if you gave the cabs a volume level/loudness/rating, 1-8 ohm at say level 2, the 1-4 ohm would be 3, but 2-8 ohm would be 5.

    Ok , let er fly---
  15. A) correct

    B) correct, everything being equal it will be 3 dB (dont know how i managed to hit 5 earlier)

    C) two 8 ohm cabs (of the same format + brand etc 4 ohm) will double speaker area, while recieving the same power as the 4 ohm cab, resulting in the 2x 8 ohm cabs being 3db louder

    D) I'd say it would be more like Level 2, level 3 and level 4 respectivley (each expressing an incremental increase of 3dB). However, I dare say, depending on circumstance, using two cabs (Ie stacked 4x10s) could bring speakers closer to ear level, making it easier to hear, but this would only be the case when stacking smaller cabs together. i.e. it wouldnt have an effect on using two 8x10s

    Pretty much on the mark mate!
  16. greenboy


    Dec 18, 2000
    remote mountain cabin Montana
    greenboy designs: fEARful, bassic, dually, crazy88 etc
    It really depends how the manufacturer/designer arrived at their 4-ohm version of the 8-ohm driver. Sometimes it involves shortening the active area of the voice coil some, so that's going to be an xmax issue, and other changes will also be reflected in the Theile-Small parameters. That's why there's a separate datasheet for any responsible manufacturer's 4-ohm product. The best can be very close indeed, but for the designer it's not a process with a magic wand solution that means both are essentially going to be sound-alikes. It takes effort to arrive at a facsimile.

    As for the LOUDER bit, not necessarily. There could be a difference in sensitivity if expressed in terms of 2.83 volts, but in real use, the main difference is that it presents a different load to an amp. But that does not mean it has a higher displacement (often just the opposite as covered above), or a higher thermal ("RMS") rating - being a 4-ohm driver does not magically impart higher power handling.
  17. keyboardguy

    keyboardguy Supporting Member

    May 11, 2005
    To clarify, I'm not interested in which cab is louder/softer.

    I'm asking about TONE ONLY.

    Is there any difference?
  18. greenboy


    Dec 18, 2000
    remote mountain cabin Montana
    greenboy designs: fEARful, bassic, dually, crazy88 etc
    Since 4-ohm versions have different electrical and electro-mechanical properties, there's bound to be some differences. If the designers have really tried hard to duplicate the sound of their 8-ohm version of the same model the differences couold be slight enough that one would have trouble hearing those differences once mounted in a cab. Or not. It depends how significant the differences are.
  19. seamonkey


    Aug 6, 2004
    What is "TONE"?
    The ability to accurately reproduce the signal fed to it? You probably would not be able to hear any difference. But let's say the cable resistance was high. then the 8 ohms would be more accurate.
    Here's a chart: http://www.roger-russell.com/wire/wire.htm#resistancehigh
    It's the same as putting a resistor in series with the speaker, the frequency response will end up following the impedance curve of the speaker.
    You can actually play with this by putting a resistor in series with your speaker, power will drop to it, but not equally across the frequency spectrum.

    So if all parameters were otherwise equal, the 8 ohm would have a higher voltage across it and be more accurate.
  20. billfitzmaurice

    billfitzmaurice Commercial User

    Sep 15, 2004
    New Hampshire
    Owner, Bill Fitzmaurice Loudspeaker Design
    No. A 4 ohm versus 8 ohm driver will have different voice coils, and when you alter one driver component you alter to some degree all of the driver parameters. Most by very small amounts, but it's still enough that they won't sound identical.

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