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Riddle Me This - What Makes One Speaker 8 Ohms And Another 16?

Discussion in 'Amps/Cabs Tech Corner: Amplifier, Cab & Speakers T' started by frankie5fingers, Aug 25, 2011.

  1. frankie5fingers

    frankie5fingers Supporting Member

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    OH... no
    I'm curious. What, exactly, are the differences between a speaker of one ohm rating and another? I understand the reasons why we use different resistance(s), but I'm wondering how we create one vs the other. What actually "makes" the difference, wire, windings, what?
    Thanks
     
    Last edited: Aug 25, 2011
  2. CharlyG

    CharlyG Play It Forward Gold Supporting Member

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    The thickness,the type of wire, the length and number of windings affect the resistance, which affect the impedance.
     
  3. frankie5fingers

    frankie5fingers Supporting Member

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    OH... no
    I've been traveling, thanks for the responses.
    Am I correct that according to this equation, I can determine the resistance rating of a speaker as well as the hypotenus of a right triangle?
    Now the next question. Beyond the concept of amp design, i.e. designed with the idea a certain resistance coresponds to a given sonic signature, can we also imply something like- lesser resistance results in greater longevity? More power? Greater resistance requires more power, thus greater headroom? Again, just moving down the trail for curiosity's sake. Thanks.
     
    Last edited: Aug 28, 2011
  4. schmidlin

    schmidlin Member

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    your rule of thumb is approximate, but ???....this ain't geometry. It's electro-mechanics.
     
  5. Sweetfinger

    Sweetfinger Member

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    "the idea a certain resistance coresponds to a given sonic signature" doesn't make any sense. You're also confusing DC resistance with AC impedance. A 100 watt amp will deliver 100 watts into a 64 ohm load. The same amp will deliver 100 watts into a 4 ohm load provided the transformer has the correct taps. The delivered voltage and current are what changes. The output transformer matches the tubes output to the speaker input.
    http://www.ohmslawcalculator.com/ohms_law_calculator.php

    Input 100 watts into an 8 ohm load. This tells you the voltage and current the amp is delivering. Now deliver 100 watts into essentially an open circuit- 10 million ohms. That's what happens when you don't plug in your speaker cab. See what happens to the voltage? You've created a much higher voltage than your transformer is rated for, so the signal arcs and your transformer is blown. But notice that at the higher voltage, you have a lower current. It all has to add up.
     
  6. Thad

    Thad Member

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    Its greek to me. For one thing the label is different!
     
  7. frankie5fingers

    frankie5fingers Supporting Member

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    OH... no
    Traveling again - sorry for the delay.
    OK, now I understand there are differences in wire, number of winds, etc. (thanks Charley). I can also see why that above formula doesn't work on a right triangle and finally, I don't mean to confuse DC resistance with AC impedance. I totally understand that there are matrices, laws, formulae and principles behind the science of it. I'm not trying to short-cut the study of Acoustic Engineering or its disciples, but the engineering doesn't answer my question. I'm talking sound, not science, and I should have been clearer. Maybe a better way to ask: Were I designing an amp and wanting a certain characteristic, say more headroom. Would I design it to use a 16 ohm speaker load? For earlier breakup, a 4 ohm load? How about if I want to mod an amp for more breakup? I see why multiple speakers will require one thing or a very high powered amp something else (possibly). What I'm trying to learn is whether or not I can achieve, repeatedly, some sonic characteristic (all other materials and configurations being equal) by altering the design for a 4, 8, or 16 ohm load, and what that difference would be. For example - taking a 50 watt JCM 800 switched for 16 ohm load into one Celestion Lead 80 16(15) Ohm. Same amp, switched to 8 Ohm load into one Celestion Lead 80 8 Ohm. Is there a repeatable, discernable difference?
     
  8. chervokas

    chervokas Member

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    The nominal impedance of the speaker has pretty much zero bearing on how the speaker sounds. Impedance matching between tube amp and speaker will have an impact on how the whole system sounds. When the output impedance of the amp matches the impedance of the speaker you will have maximum power transfer from amp to speaker and the most clean headroom. If there's a mismatch in either direction you will limit the amount of power the amp delivers to the speaker resulting in lower headroom from the amp and lower output from the system. But there are other problems that can result from mismatching loads -- flyback voltages in certain circumstances, a build up of heat in the OT, for example -- that make mismatching less than ideal in most circumstances and potentially dangerous to the OT in others.

    Theoretically there might be a slight, very slight difference in tone with a multitap transformer when you're using, say, its 16 ohm tap to drive a 16 ohm load vs its 4 ohm tap to drive a 4 ohm load by virtue of your having engaged more or fewer of the transformer's wiring at the different tap points. But the differences will be vanishingly small.

    But, remember impedance actually varies with frequency. We talk about 4 ohm speakers and 4 ohm output transformers, but that's nominal impedance. As you play the impedance of each changes and impedance curves and resonant frequencies do play a role in the characteristic tone of components.
     
  9. frankie5fingers

    frankie5fingers Supporting Member

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    OH... no
    OK. I won't pretend to fully understand a given resonant frequency and the resulting sonic curve, but that's where I'm heading. Why then, excepting certain situations whereby a certain speaker configuration would require a specific architecture, do we have speakers with different loads? Again, not counting a unique requirement, why the differentiation among amps with only one or two speakers? Is it as simple as "that's what we had in the shop the day we built the prototype"? Thanks.
     
  10. CharlyG

    CharlyG Play It Forward Gold Supporting Member

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    It mostly has to do with cabs with multiple speakers. If the speakers in a 4x12 were 4 ohm the cab would show a 1 ohm load! 16 ohm spkrs would show 4 ohms and 32 ohm spkrs, 8.
     
  11. frankie5fingers

    frankie5fingers Supporting Member

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    OH... no
    I see. Sorry for being obtuse but hey, I went to public school. I get it though. It's really more a matter of having a minimum number of serviceable ratings to accommodate the various speaker configurations. Beyond that, it seems more a matter of preference. Thanks for the patience OTM, Charley, chervokas and Sweetfinger, and for the schooling. That is exactly what I was wondering.
    Thanks, Frank
     
  12. chervokas

    chervokas Member

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    Well, there are ways to wire a 4 speaker cab -- a combo of parallel and series wiring -- to get several different impedances. But yeah, this is correct.
     
  13. CharlyG

    CharlyG Play It Forward Gold Supporting Member

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    I didn't want to go too far on one post, and figured it would be brought up sooner or later.:beer
     
  14. guitarcapo

    guitarcapo Senior Member

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    As you see these equations are frequency dependent...So really if you plug in different frequencies...you will get different impedance values.
    Since speakers are made to transmit many different frequencies over a wide range and not just one, it's really not accurate to say that a speaker has a given single impedance....and why you can probably use different impedance rated speakers with an amp and not be that damaging to things. The speaker might just not be as efficient at the frequencies you are trying to hear. I have a Champ that sounds a bit brighter with a 3.2 ohm Weber speaker compared to it's 4 ohm counterpart. I like the sound. Doesn't hurt the OT at all.
     
  15. bennybeatts

    bennybeatts Member

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    Leo Fender used 4,8,16 ohm speakers because that's what he had available and it worked

    then everybody else copied and we all still use the same basic design

    (sorry for the thread revival...!)
     
  16. Scumback Speakers

    Scumback Speakers Gold Supporting Member

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    The voice coil determines the ohm rating of a speaker. They are wound with different wire gauges to achieve the ohm reading. Typically a 16 ohm speaker uses a 13.4 ohm voice coil, and an 8 ohm speaker has a 7.2 ohm voice coil. This can vary slightly resulting in readings plus or minus 10-15%.

    I've measured 16 ohm speakers with a multimeter and the range has been 14.2 - 12.9. For an 8 ohm speaker, the range is usually 7.4 - 6.9.

    The cone, surround, doping, and dust cap do not set the ohm rating.

    Hope that answers your questions.
     
  17. frankie5fingers

    frankie5fingers Supporting Member

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    OH... no
    It does...thanks. I was curious about the physical characteristics. I guessed the VC windings were key but wasn't sure if anything else was spec'd for a given resistance.
    Thanks again, Frank
     
  18. Scumback Speakers

    Scumback Speakers Gold Supporting Member

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    You're welcome, sir. While the voice coils can have different former materials (paper, kraft paper, nomex paper, kapton, etc) that will allow higher temperatures to be sent to them (i.e. more power produces more heat) without melting/failure, that doesn't change the ohm rating. They can have an effect on tone with the different former materials.

    But basically when using a given wire gauge, and winding it X number of times, you get a particular ohm rating.
     
  19. jamison162

    jamison162 Supporting Member

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    Which is typically NOT how speakers are wired in a 4x12. Don't confuse people. Most of the time they are wired in parallel/series pairs. 4 x 16 ohm speakers = 16 ohm cab; and the only way to wire an 8 ohm 4x12 cab is to use 4 x 8 ohm speakers...noone makes 32 ohm speakers that I know of. :huh
     
  20. Sweetfinger

    Sweetfinger Member

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    Actually not as uncommon as you might think.
    http://www.fliptops.net/catalog/product_info.php?products_id=325
    The Jensen P-12Q is also available in 32 Ohms. Doing a Google search for "Eminence 32 ohm" kicks up a big list of Eminence speakers in 32 ohm, so they are out there. IIRC the speakers in a Fender Bassman Ten combo are 32 ohms.
     

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