1. Welcome to TalkBass 2014! If you're new here, we just went through a major site upgrade. Please post all concerns and bugs to the Forum Usage Issues forum. We will be monitoring that forum. Thank you for all of your feedback.

    The TalkBass iphone/android app is NOT WORKING currently. We're working on it. Tapatalk IS working, so if you need to use an app, use Tapatalk. Try using your browser though - TalkBass is now 100% responsive to your phone/tablet screen size ;)

    Please read the TalkBass 2014 FAQ for lots of great info on the new software.

running 8 ohm speakers with a 4 ohm amp?

Discussion in 'Amps [BG]' started by Lonesomedave, Jun 26, 2011.

  1. Lonesomedave

    Lonesomedave Supporting Member

    Joined:
    May 13, 2011
    Likes Received:
    0
    hi, guys,

    got another stupid question (or to quote Chris Berman of ESPN, "There are no stupid questions...only stupid people who ask questions.")

    actually 2 questions:

    1) what happens if you run an 8 ohm speaker with an amp with a 4 ohm output?

    2) what happens if you run a 4 ohm speaker with an amp with an 8 ohm output?

    essentially the same question, just reversed.

    for purposes of this question, let's presume it is a tube amp, say a sunn 2000s or marshall vba 400 for example.

    would it work? would it damage the amp? would it damage the speakers? would it sound like s**T?

    just wanted to know, as I have heard it is ok to run higher ohm speakers with a lower ohm amp, but not the reverse.

    thanks,

    /s/ Dave
  2. kosmicwizard

    kosmicwizard

    Joined:
    Nov 18, 2008
    Likes Received:
    0
    With all tube heads it is best to match impedance. I wouldn't play an SVT through an 8 Ohm cab and I wouldn't play a Mesa Bass 400 into a 2 Ohm load either. It won't affect tone but there are stresses that are causing damage that you can't see until something gives and you have to spend money to repair it. Cheers.
  3. Munjibunga

    Munjibunga Total Hyper-Elite Member Gold Supporting Member

    Joined:
    May 6, 2000
    Likes Received:
    8
    Disclosures:
    Independent Contractor to Bass San Diego
    For solid state amps (even with tube preamps):

    Running an 8-ohm cab from a 4-ohm-rated head is just fine. You'll typically get a little more than half the rated power of the amp, though.

    Running a 4-ohm cab from an 8-ohm-rated head would result in excessive current draw, and could damage the amplifier. Don't do it.

    For tube amps (tube power section):

    It's best to run cabs whose impedance is the same as the output impedance rating of the amp. You might be able to get away with running a cabinet with a lower impedance (kind of opposite of SS amps), but I wouldn't recommend it.

    I'm sure some of the tube guys will weigh in on this.

    Jimmy?
  4. recreate.me

    recreate.me

    Joined:
    Apr 2, 2010
    Likes Received:
    0
    I have run my old all tube Traynor YBA 3 for about a year on various 8 ohm cabs (its a 4 ohm head, i just didnt know that all year) i didnt know so i ran it at 8, never had a problem. I played a lot of shows and practices, it was on just about every day.

    I am sure its not ideal, but i doubt it will kill anything.
  5. JimmyM

    JimmyM Supporting Member

    Joined:
    Apr 11, 2005
    Likes Received:
    29
    Disclosures:
    Endorsing: Ampeg Amps, EMG Pickups
    Actually, I think it does affect tone to a degree. Tube amps not being run at their proper impedances always feel a little tighter and a little less tubey to me. It's not real noticeable but I do notice it. Anyway, I've done it with rentals at low volumes, and it's been fine, but with my own gear I would never do it! It can stress tubes and transformers. Won't happen overnight, especially if you don't play loud, but that kind of stuff can take its toll eventually, and I see no reason not to run stuff at their proper impedances.
  6. enricogaletta

    enricogaletta

    Joined:
    May 21, 2011
    Likes Received:
    0
    As Munjibunga told you that's basically what happen using 4-8 ohm amps-cabs.
    The 8ohm cab solution it will be more helpful if you have a powerful amp but you need to use a small cab for a small-medium gig, so you can just pick a any of the smaller cab out on the market now, like a 110, 112 or 210. It will be much better than use a combo ;-)
    Cheers. Enrico
    YouTube
    My Album
    WebSite
  7. anderbass

    anderbass

    Joined:
    Dec 20, 2005
    Likes Received:
    0
    Lonesomedave, What brand/model amp are you referring to here?
  8. Lonesomedave

    Lonesomedave Supporting Member

    Joined:
    May 13, 2011
    Likes Received:
    0
    well, in my original question, i posed a tube amp and gave a sunn 2000s or marshall vba 400 as examples

    /s/ Dave
  9. ggunn

    ggunn

    Joined:
    Aug 30, 2006
    Likes Received:
    0
    In general, if you must run a mismatch, for solid state amps it is better to run higher impedance than lower. Tube amps are the reverse. In either case, the harder you drive the amp, the more risk you take.
  10. Munjibunga

    Munjibunga Total Hyper-Elite Member Gold Supporting Member

    Joined:
    May 6, 2000
    Likes Received:
    8
    Disclosures:
    Independent Contractor to Bass San Diego
    With SS, there's no increased risk.
  11. Unrepresented

    Unrepresented Something Borderline Offensive Supporting Member

    Joined:
    Jul 1, 2006
    Likes Received:
    6
    I ran my SVT-II 4 ohm into an 8 ohm cab for years. Maybe I was lucky, but I never had any catastrophic failures during this time linked to the mismatch. I eventually upgraded cabs mostly because I figured I was pushing my luck.
  12. edbass

    edbass

    Joined:
    Nov 8, 2004
    Likes Received:
    0
    Tube amps are pretty resilient, and it’s not like impedance is an exacting science relative to the application being discussed here. There is a reason the term “nominal” is used in reference to a cab/driver’s impedance rating;, in actual use the load that any specific cab shows the output stage of an MI amp is all over the place.
    While a tube amp will perform its best* with the load impedance matched with the output stage, I think it’s generally accepted that a 100% mismatch is tolerable within the physical parameters of most quality tube amps.

    Now that’s refreshing; an actual first person example of the thread subject!
    At the risk of further breaking with the TB tradition of posting “common wisdom” hearsay and/or regurgitated, hyperbolized factoids from TB’s resident technical “armchair quarterbacks” as gospel, here’s another real world, first person example from the other side of the impedance mismatch fence:

    Before I bought it, one of my personal two cab 2000S rigs had begun life as part of an endorsement deal, toured multiple times in the 70’s; long hard road use/abuse… with a 2 ohm load on the 4 ohm OT tap. The original road tech for the rig told me that while he realized the situation wasn’t ideal, it was, well… an endorsement rig; they had backup, and the factory would air express another one anywhere they needed in an emergency.
    He said they changed tubes a lot but the unit never failed, other than its appetite for 6550A’s it was a rock.
    It’s still fine, original trannies still at stock spec. Of course a 2000S is an overbuilt boat anchor, way under rated as far as output vs. component potential, and a higher strung, higher output amp that stresses components more may not perform as well or as long.



    *As far as the design specification; what any particular individual considers tonally “best” is subjective, just listen to some of the clips linked here on TB… ;)
  13. Munjibunga

    Munjibunga Total Hyper-Elite Member Gold Supporting Member

    Joined:
    May 6, 2000
    Likes Received:
    8
    Disclosures:
    Independent Contractor to Bass San Diego
    I suppose that's fine if you accept anectodal examples as proof of something. Because you can cite two examples of not damaging a tube amp from mismatched cabinets doesn't negate the designers' recommendation not to mismatch impedances. You are ignoring any examples of disasters related to it. Also you seem to have ignored unrepresented's final comment: "I eventually upgraded cabs mostly because I figured I was pushing my luck."
  14. edbass

    edbass

    Joined:
    Nov 8, 2004
    Likes Received:
    0
    Actually, the point of my “poke” was that I generally don’t “accept anectodal examples as proof of something” and that I find actual first hand experiences refreshing as compared to the usual plethora of anecdotal advice on technical issues so readily volunteered on TB.
    For example; as far as mismatched impedance, maybe you can share one of your first hand, non anecdotal examples of “disasters related to it” that I ignored. Here’s one of mine, when I was about 14 I toasted a Gretsch 6154 by forgetting to reconnect the speakers and playing it, wondering why nothing was coming out until I smelled the “magic smoke” it was releasing.

    I didn’t mean to suggest that anyone should run their amp outside the manufacturer’s specifications; I certainly don’t, at least intentionally with my own gear. I was just pointing out two real world examples of impedance mismatches, one over and one under, in reference to the original thread topic.
    As I mentioned, my mismatched 2000S rig did have an abnormal appetite for output tubes, but I failed to mention that as with Unrepresented’s scenario I remedied the mismatch ASAP.

    Anyway, my apologies to anyone else who somehow misinterpreted my post as an endorsement of running mismatched loads on tube amps.
  15. Munjibunga

    Munjibunga Total Hyper-Elite Member Gold Supporting Member

    Joined:
    May 6, 2000
    Likes Received:
    8
    Disclosures:
    Independent Contractor to Bass San Diego
    Clearly you don't know what "anecdotal evidence" means.
  16. okcrum

    okcrum in your chest Supporting Member

    Joined:
    Oct 5, 2009
    Likes Received:
    2
    Disclosures:
    Endorsing Artist: Dark Horse strings
    That settles it, then. We have Cargo Cult Consensus.
  17. okcrum

    okcrum in your chest Supporting Member

    Joined:
    Oct 5, 2009
    Likes Received:
    2
    Disclosures:
    Endorsing Artist: Dark Horse strings
    Tell ya what. Why not start a thread where people who have actually had tube amp failures from speaker mismatches post. No anecdotes, no beliefs, no acid flashbacks, just 1st person examples. That should answer the OP's question.

    My guess is that it will be a very short (and short-lived) thread.
  18. coreyfyfe

    coreyfyfe Supporting Member

    Joined:
    Nov 19, 2007
    Likes Received:
    0
    Long technical answer here:

    A ton more information here.

    Emphasis added to sort-of-important parts, but it's all worth a read. I used my SVT-CL with a 5.3 ohm load for a while, over a year at least, with little effect, but that's not really all that far off from 4 ohms. If it were me, I'd always go for correct impedance. Ever seen an amp with a blown OT? Mismatch is a likely culprit.

    As far as tonal variance, when you have a mismatch, you're putting a different stress on the output tubes than they usually see, so really the difference is how the tubes are being driven and whether you're in their "sweet spot" range.
  19. okcrum

    okcrum in your chest Supporting Member

    Joined:
    Oct 5, 2009
    Likes Received:
    2
    Disclosures:
    Endorsing Artist: Dark Horse strings
    $0.20 worth of 1N4007 diodes takes care of the voltage spikes mentioned above. Look at a modern SVT schematic; they're in there. The SVT is pretty rugged when it comes to unusual conditions.
  20. Fender4Me

    Fender4Me

    Joined:
    Dec 2, 2008
    Likes Received:
    0
    I recently bought a 70's Acoustic 126 combo that someone had installed an 8 ohm JBL D-140 speaker in. The 126 has a 4 ohm output. The amp sounded fine with the 8 ohm JBL but sounds much fuller and a little louder with the correct 4 ohm speaker.

Share This Page