Speaker Ohm Ratings?

Discussion in 'Amps/Cabs Tech Corner: Amplifier, Cab & Speakers' started by Weener, Aug 5, 2006.

  1. Weener

    Weener Member

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    What is the difference between different amp speakers being different Ohm rating? Do they sound different? I need some answers!

    Thanks

    Weener
     
  2. donnyjaguar

    donnyjaguar Member

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    The impedance of the speaker shouldn't have any bearing on the sound. The impedance is chosen to match the amplifier that is powering it. Therefore if you run your tube amp off the 8 ohm tap into an 8 ohm speaker, it should sound the same if you run it from the 4 ohm tap into the same model of speaker with a 4 ohm impedance.

    Generally speaking 8 ohm speakers are more versatile as many amplifiers are specifically designed for this impedance. The 4 ohm speakers became more popular for car audio because you could in theory double the output power. This is because car audio systems used the 12Vdc of the vehicle for the power amplifier and could net about 4Watts into 8 ohms but would deliver about 8Watts into 4 ohms.

    Nowadays with BTL outputs and on-board switchmode power supplies its no longer an issue. But in 1970 it sure was. It was never really an issue in home consumer products because you'd simply chose a power transformer with whatever output voltage you needed.

    In a tube amplifier, if you double up the number of output tubes you can create twice the power. But...you need to half the output impedance to take advantage of it. If you parallel 2x 8 ohm speakers (which results in 4 ohms) you can achieve this.

    Hope this helps!

    DJ
     
  3. billyguitar

    billyguitar Member

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    Not in a tube amp. A mismatch in a tube amp will always cut the power a bit because a mismatch is not as efficient but not by half or conversely not doubled into 1/2 the load. Only a few watts difference either way. Don't run a tube amp at a lower impedance than it's made for, it'll wear out your expensive tubes faster. You can go up, say an 8 ohm amp into a 16 ohm cab but it won't sound as good so why bother? You'll only lose a few watts.
     
  4. rockon1

    rockon1 Member

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    Not sure his question has been answered. Ive often wondered if an 8 ohm version or 16 ohm version of the same speaker sounds exactly the same. How do they make the resistance different? More windings or something? Wouldn't whatever they did to change impedance affect the tone even minimally? Old Tele man ,...ummm... ya lost me on that explanation!
     
  5. donnyjaguar

    donnyjaguar Member

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    Thinner wire has a higher resistance and also more wire has a higher resistance. I'm not a loudspeaker designer but I'd guess that speaker manuf's would use a combination of both to bring a 4 ohm speaker to 8 ohms. With more windings comes more inductance and also more capacitance across the windings. In fact I gather some manuf's use this extra inductance to limit the high-frequency response of woofers in home hi-fi systems as it can be used to eliminate the inductor normally placed in-line with the speaker to limit high freq response. This reduces costs. Musical instrument speakers are a different beast though. That said, an 8 ohm speaker will probably sound a little different than a 4 ohm one, all else being equal. What probably has more effect is the output tranny of the tube amp. An 8 ohm winding has, well, more wire so the coupling efficiency is probably going to be better. Also the currents on the leads to the speaker will be lower resulting in less copper losses due to heat. In 50Watts guitar amplifiers this really isn't going to make a big difference but at 1kW levels it would be more apparent.

    DJ
     
  6. Junior

    Junior Member

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    OTm does tend to expound, rather than explain, but he's just saying what Billy said, with the math. ;)

    Any description of the differences in sound between a 4 ohm speaker and a 16 ohm speaker would be an exaggeration. I think if you were to try to compare two otherwise identical speakers, you'd be more likely to hear differences in the tranny windings. I haven't actually tried this, though.

    At any rate, the voice coil is one of the more precise elements of a loudspeaker - the paper cones are the result of averaging randomization, the dope on the surround is notoriously unequal, magnet material is another toss of the dice, then it's charged.... and finally, we have to hope the coil is centered in the gap. This is why audiophiles rave in rapture about "imaging" - to get a sound to appear to come from dead center between two speakers, both speakers need to produce identical excursions at all frequencies. More money, more precision, better imaging. Or, a little money and a lot of luck. Again, I digress.

    In theory, you can get better damping - a more controlled bass resonance - with the higher ohmage, but in practice, for all the above reasons, it's not a rule of thumb. And, if you did find two speakers where this was true, a quick spray on the surround of one could reverse things.


    Edit: Tee hee, Donny and I were posting at the same time. I didn't realise I was largely repeating what he said.
     
  7. bettiefan

    bettiefan Member

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    Matt Bruck has mentioned in his Guitar World column that different impedance speakers do sound different. I think he preferred 16-ohm speakers, but I can't remember what he said the difference was. I think a bit less mids in the 16-ohm compared to the 8.
     
  8. Weener

    Weener Member

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    I read an article after I posted the question and the gentleman who wrote it said that the difference impedances aren't what makes the speaker sound different but the kind of load that it makes on the amp. For example an amp that's setup for an 8 ohm speaker is modified with a 4 ohm speaker that is otherwise identical to the 8 ohm. Because it's less resistance, the reacts differently to the mis-matched load, either working harder for great6er impedances or less on more.

    Thanks,

    Weener
     
  9. Junior

    Junior Member

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    :jo

    Seems we're going over people's heads here.

    As EVH's toady, I'm sure Mr. Bruck is an expert on setting up guitars, but an expert on speakers, he is not. And, as I can't find anything by him that's not associated with advertising, it seems his opinions are available to the highest bidder. In all humility, I have to say the posters in this thread are much better equiped to answer this sort of question.

    Weener, the article you reference is talking about a mis-match, we have been discussing the possibilty a sonic difference based just on the coil impedance and assuming a connection to a properly matched transformer.

    Consider this: given how picky both audiophiles and musicians are about their equipment, if there was an audible, meaningful difference, then it would be widely known and highly touted after all this time.

    If your original question was about a mis-match, well, that's a whole different story, and we'll have to switch gears. :messedup
     
  10. impactblue

    impactblue Member

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    Quick question...


    Can i plug the Fender Champ 600 (4ohm minimum) into an Epiphone Valve Jr Extension Cab (16ohm). Apart from loss of volume, there wont be any damage will there???
     
  11. Groovey Records

    Groovey Records Member

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    Welcome To TGP Weener

    The answer maybe if all other variables are equal no but "IF" certain other variables are different in value other results and effect may be achived. Clear as mud uh ?

    Is that OK, Ol Tele Man:) Your the bomb!

    Wenner BTW
    KABONG


    [​IMG]
     
  12. Monroe

    Monroe Guest

    ...and leaving the math alone for a second, lets say we have an amp with three taps: 4, 8, and 16-ohms. And, lets say we also have three of the same model speaker, but for different nominal impedance ratings (also, 4, 8, and 16-ohms)

    Hooking only one speaker up at a time to it's properly matched output tap, you are probably more likely to hear differences based on the OT winding and to which tap the NFB is wired than any differences in the speakers themselves.

    But, that isn't to say the speakers would not have subtle differences. One manufacture may take these possible differences into account more so than another during the design phase. And we haven't even gotten to multi-speaker cabs with options for wiring in parallel, series, or even series/parallel, etc, all of which impart subtle changes in the resonse of the system. I think we would all like to able to claim to hear such subtle differences, which partly fuels the boutique gear industry.
     

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