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Thread: 16 Ohm Speaker in a 8 Ohm Amp?

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    Tone Member aaronl's Avatar
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    Default 16 Ohm Speaker in a 8 Ohm Amp?

    OK I am sure this has been asked before, but is it ok to use a 16 ohm speaker in a 8 ohm amp?

    Speaker is a Celestion G12T75 16 Ohm
    Amp is Crate V50 with a 8ohm in it now.

    Thanks for any help!
    "...Strange brew -- kill what's inside of you..."

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    Fuzzy. Guitars the guy who invented fire's Avatar
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    Default Re: 16 Ohm Speaker in a 8 Ohm Amp?

    It won't cause any damage right away, and might never but if you runit really hard for long periods of times it could hurt the amp
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    neonderthalotonalogist Dr.Mavashi's Avatar
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    Default Re: 16 Ohm Speaker in a 8 Ohm Amp?

    Quote Originally Posted by aaronl View Post
    Speaker is a Celestion G12T75 16 Ohm
    Why?
    “My Singal:
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  4. #4
    supernosher
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    Default Re: 16 Ohm Speaker in a 8 Ohm Amp?

    Depends on the amp. Generally with a tube amp it's OK (better than a lower impedance speaker), but with a SS it's not. I might be a liar regarding the SS circuits, tho.

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    Tone Member Thermionik's Avatar
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    Default Re: 16 Ohm Speaker in a 8 Ohm Amp?

    With a tube amp 2x either way is bearable.
    Ideally you want to match impedance, but if you MUST mismatch, try to have the speaker LOWER in impedance than the amp rather than HIGHER in impedance.

    HIGHER is nearer to NO speaker - reflected emf can fry the OT.
    LOWER works the tubes, but doesn't stress the OT nearly as much.

    Just compare the costs of tubes -v- transformers.
    Or check the extension speaker wiring on Fender tube amps.....
    .....they will go closed-circuit rather than open-circuit if you screw up.
    Last edited by Thermionik; 05-17-2009 at 03:02 AM. Reason: embarassing inability to spell.....
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    HomeGrownToneBrewologist Rich_S's Avatar
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    Default Re: 16 Ohm Speaker in a 8 Ohm Amp?

    +1

    Thank you, Thermionik, for typing that out for everybody to read. It used to be my job, but I was getting tired of typing the same answer over and over again.
    Tra-la-laa, lala-la-laa!
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    Fuzzy. Guitars the guy who invented fire's Avatar
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    Default Re: 16 Ohm Speaker in a 8 Ohm Amp?

    Let me be really clear on this...

    With MOST tube amps the amp can handle a 100% mismatch w/o too many (often times no) issues...meaning if the amp wants to see 8 ohms the speaker or cab could be 4 ohms or 16 ohms but no more than 100%, meaning if the amp wants to see 8 ohms don't even think about trying to run 2 ohms or 32 ohms!

    Now, all that said a LOT of new amps are built with junk parts and are built to much lower standards than amps from yesterday...saddest of all a lot of HIGH DOLLAR amps are still built with junk. So, if you take your amp and run it in a situation where your impedence is mismatched and it cooks don't hop on here yelling about how The Guy Who Invented Fire said it was OK...

    Anytime you do someting the factory says not to do you run the risk of breaking something, if that wasn't true the factory wouldn't say not to do it!

    My personal suggestion is that if you don;t understand how the insides of an amp work they run them just like the handbook says to run them...my other advise is not to trust people on internet forums!
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    Tone Member Thermionik's Avatar
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    Default Re: 16 Ohm Speaker in a 8 Ohm Amp?

    Yup - that's 2x either way.

    2x 8ohms is 16ohms
    8ohms /2 is 4ohms

    Double or Half.

    But not 100%. Down 100% from 8ohms is NO ohms.

    But like they said up there, ideally, match impedances for best results.
    Best sound and best OT life expectancy.

    Oh, and Rich_S - my pleasure mate.
    Last edited by Thermionik; 05-17-2009 at 08:58 AM. Reason: to say hi to Rich_S.....
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    Ultimate Tone Member lastwinj's Avatar
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    Default Re: 16 Ohm Speaker in a 8 Ohm Amp?

    16ohm speaker into an 8ohm tap will yield lower output as well. maybe a bit squishier and more distorted as well.
    personally, i have never worried about mipedance mismatches with lower power amps.
    Jeremy Ledford
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    Bullet Proof Toneologist kevlar3000's Avatar
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    Default Re: 16 Ohm Speaker in a 8 Ohm Amp?

    I have been running my 8 ohm heads into 16 ohm cabs for nearly 7 yrs now, never had an issue.

  11. #11
    supernosher
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    Default Re: 16 Ohm Speaker in a 8 Ohm Amp?

    Quote Originally Posted by Thermionik View Post
    HIGHER is nearer to NO speaker - reflected emf can fry the OT.
    since when is 16 ohms near 16,000,000 ohms?

    instead of listening to us internet hoes, why don't you look at your amp manufacturers notes? According to my Mesa's notes, double is better than half the impedance.

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    Toneologist CaughtLikeFire's Avatar
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    Default Re: 16 Ohm Speaker in a 8 Ohm Amp?

    Quote Originally Posted by supernosher View Post
    According to my Mesa's notes, double is better than half the impedance.
    I never planned to mismatch impedances with my Stiletto so I never noticed that statement in the manual . . . interesting

    Thermionik's conclusion seems more logical to me though
    Quote Originally Posted by Ayrton View Post
    most of what I hear sounds like a great riff trapped in a terrible song

  13. #13
    supernosher
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    Default Re: 16 Ohm Speaker in a 8 Ohm Amp?

    Quote Originally Posted by CaughtLikeFire View Post
    Thermionik's conclusion seems more logical to me though
    logic is not all it's cracked up to be.
    Last edited by supernosher; 05-19-2009 at 12:28 AM.

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    Tone Member Thermionik's Avatar
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    Default Re: 16 Ohm Speaker in a 8 Ohm Amp?

    OK supernosher - before you call me out..... I am a Bassman player (6G6-A), and:

    I don't listen to 'internet hoes'.
    I DO look at my amp manufacturer's notes.

    Fender amps use shorting jacks on the main speaker output. This means that if you plug a cabinet into the extension jack with nothing in the main jack the output transformer will be shorted. Fender say this short circuit is better than no load connected, but warn that it may fool you into turning the volume up all the way and driving the amp hard into a short, which is not good for any length of time.

    So my point, and Fender's point too, is that running a 4ohm or 8ohm OT into a short (0ohm) is better than running it into 16ohm, because to the OT, the 16ohm speaker is almost as bad as running with no speaker. My bad for using the word nearer to imply 'almost as bad as'.

    I don't write the rules, it ain't my conclusion, it ain't my logic.
    I think the 'Laws of Physics' come in to play,
    so take it up with Fender.....
    or the universe
    or something.

    Just trying to help a fellow picker. Fried OT's ain't cheap.
    Last edited by Thermionik; 05-19-2009 at 11:05 AM.
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    John Mayer's Mankini ImmortalSix's Avatar
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    Default Re: 16 Ohm Speaker in a 8 Ohm Amp?

    Quote Originally Posted by kevlar3000 View Post
    I have been running my 8 ohm heads into 16 ohm cabs for nearly 7 yrs now, never had an issue.
    If Kev can get away with it, I bet you can. I know he really cranks his amps up.

    That being said, he don't run no junk...

  16. #16
    supernosher
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    Default Re: 16 Ohm Speaker in a 8 Ohm Amp?

    I'm glad we are discussing this and our intentions are one.

    Quote Originally Posted by Thermionik View Post
    OK supernosher - before you call me out.....
    I wasn't calling you out as much as making the point that not all circuits are the same, and so there is no single rule that works for all amp circuits.

    Quote Originally Posted by Thermionik View Post
    running a 4ohm or 8ohm OT into a short (0ohm) is better than running it into 16ohm, because to the OT, the 16ohm speaker is almost as bad as running with no speaker. My bad for using the word nearer to imply 'almost as bad as'.
    This makes no sense at all. You say "0 ohms is better than 16 ohms", and then say "to the OT, 16 ohms is almost as bad as no speaker".

    The only thing that makes sense to me is choosing to fry the power tubes rather than the OT, because they're easier and possibly cheaper to replace, but I haven't heard of 16 ohms on a 8 ohm tap frying the OT.

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    Default Re: 16 Ohm Speaker in a 8 Ohm Amp?

    Check out this Q &A with Jeff Bober from Buddha Amps: Premier Guitar

    In his response, Jeff clearly states that if you do run an impedance mismatch, you do NOT want the speaker load to have a greater load (or "lower number") than the output impedance of the amp:

    When the speaker load is greater (has a lower number) than the output impedance of the amp, the load placed on the output tubes increases and can cause premature failure of the tubes. Tube failure can sometimes cause other component failure in the amp as well – screen grid resistors and hum balance resistors are typical casualties of shorted output tubes.

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    Human powerplant Vasshu the humanoid typhoon's Avatar
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    Default Re: 16 Ohm Speaker in a 8 Ohm Amp?

    With tubeamps.....comes straight from a guy who has build these things for more than 4 decades....keep the impedance matched....tubeamps do not like mismatch very much.
    Not gonna miss you know!
    Information is not knowledge.

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    Tone Member Thermionik's Avatar
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    Default Re: 16 Ohm Speaker in a 8 Ohm Amp?

    OK, I am the messenger, that's all. Don't shoot me..... take it up with Fender.

    Received wisdom trio:

    [1] Never run the amp with no speaker plugged in. This can cause major damage to the OT.

    [2] It's OK to add another speaker into the external speaker jack because a mismatched speaker load won't kill the amp, whereas an open circuit (disconnected speakers) may do so.

    [3] It's also all right to overdrive the amp. Tubes are very tolerant to massive overdriving, unlike solid state amps, which definately are not. As long as the tubes don't overheat or stay overdriven for long periods, it's rarely fatal.

    Transformers work on ratios, and the output impedance (say 8 ohm) is reflected back to the tubes by that ratio (say 500 times) to load the tubes at (say 8x500 = 4000 ohms). Raising the speaker to 16 ohm raises the impedance 'seen' by the tubes to 16x500 = 8000 ohms, lowering the speaker to 4 ohm lowers the impedance 'seen' by the tubes to 4x500 = 2000 ohms.

    The output tubes power output depends on impedance matching. They have a 'sweet-spot' load that they work best on, giving the most power out (widely available in charts posted all over the internet - the design load impedance of power output tubes). Other loads will get less power because the tube itself limits how much power it will transfer out. There are two 'sweet-spots', highest power or lowest distortion, and they vary from tube to tube.

    From zero ohms load up to some ohms higher than the optimum power load, power tubes do not destroy themselves, they merely change how much is transfered to the load. A tube amp with a tap for 8 ohms will give the nominal power of the amp only with a "matched" 8 ohm speaker load.

    If you connct a 16 ohms speaker, the power tubes 'see' the higher ohms on their plates, and can only put out about half the nominal power. Likewise a 4 ohm speaker on the 8 ohm tap means the tubes 'see' roughly half of the matched load, and again will put out only about half of the nominal power.

    So - lets consider the open circuit scenario, or running your amp with no speaker.

    If you open-circuit the output, the energy that gets stored in the OT magnetic core has nowhere to go if there is a sudden change in the drive voltage (like you hit a chord), and acts like a discharging inductor, much like the old coils in auto ignition circuits.

    This can generate voltage spikes sufficient to flash through the OT's insulation and short the windings. I personally would not risk double the rated load on any tap, and NEVER let open-circuit happen - it can fry the transformer. Why?

    Well - when you have too LOW an impedance connected, the power tubes can't give all that much more current, so fatal overheating is fairly unlikely. But if you apply too HIGH a load, the power tubes still limit what they put out, but something else kicks in.....

    That voltage spike that broke down the insulation on the chord played earlier and the burning residues it left inside the transformer make breakdown easier at the same point on the next cycle of that chord, and quickly break down insulation to make a conductive path between layers giving a permanent short, or a burnt through wire giving you an open-circuit OT, but either way a dead transformer.

    Now tubes can be rotated out and new replacements pushed in to replace them.
    OT's are, erm, a little more long-winded to replace.
    Just like this answer.
    Long winded.

    And, for the record, I have fried OT's in the past by running heads without the cabinet plugged in, hearing nothing, turning volumes up and hitting chords to see if I could hear anything.....

    I tend not to fall for it these days.

    But you have your own lessons to learn the hard way, and all the help I can give amounts to nothing compared to the first (and hopefully last) time YOU see YOUR OT fry.....
    Last edited by Thermionik; 05-20-2009 at 12:30 AM. Reason: to correct typo - thanks supernosher
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  20. #20
    supernosher
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    Default Re: 16 Ohm Speaker in a 8 Ohm Amp?

    wow, Thermionik must be right because he typed more! Check your math Thermionik... 8x400 != 4000. You meant to type 8x500.

    Jeff Bober quote - I think that was a typo on his part (clearly my ass!). The next paragraph says what I said:

    (the guy is plugging into an 8 ohm cab)
    Generally, an impedance mismatch is chosen so that the output power, due to the mismatch, is reduced, causing the output stage to break up or distort earlier, providing the warm, overdriven, tube-like tone that we all know and love at a lower volume level. If you’d like to employ a mismatch for this reason, the safer method would be to set the output impedance to 4 ohms instead of 16.
    So, he would have his 8 ohm speaker cab plugged into a 4 ohm tap.

    ALSO, remember that speakers are not one linear impedance. The impedance varies across the frequency spectrum.
    Last edited by supernosher; 05-19-2009 at 05:39 PM.

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