16 ohm vs. 4 ohm sound difference in a Marshall cab?

Discussion in 'Amps/Cabs Tech Corner: Amplifier, Cab & Speakers' started by kwk13, Mar 7, 2006.


  1. kwk13

    kwk13 Supporting Member

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    I have a Marshall cab with the 4/8(st)/16 ohm selector on the back. I have always used it in the 16 ohm setting with my Reinhardt 18 watt head set at 16 ohms. For kicks the other day I switched both the head and cab to 4 ohms and noticed a definite tone difference. In the 4 ohm setting, it sounded like it had a lot more low end punch to it, more meat. Am I just imagining things? I thought the tone would basically be the same and that the head compensated for the load setting? If I'm not crazy, why do most guys I hear of use the 16 ohm setting over the 4 with a Marshall head?

    Thanks for any info!
     
  2. Shea

    Shea Member

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    I think that low end punch might be the result of what they call better damping. And I believe damping refers to the amp's ability to maintain control over the movement of the speaker cone. That can make a big difference down around the resonant frequency of the speaker, if I understand this stuff correctly.

    The 4 ohm setting puts all 4 speakers in parallel, whereas the 16-ohm wiring is a combination of series and parallel connections. Parallel connections generally allow better damping than serial ones.

    I believe ultralinear operation would permit even more "low end punch" and "meat," but I've never tried an ultralinear amp.

    Shea
     
  3. John Phillips

    John Phillips Member

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    No, you are not imagining things. 4-ohm sounds fuller, smoother and deeper than 16-ohm, all else being equal. The reasons are the damping factor as Shea said, and the different ratio of inductances between the amp's transformer and the speakers, which shifts the frequency balance slightly more to the low end.

    16-ohm sounds more present, peakier and brighter. 16 is traditional for Marshalls (the old cabs were always wired for that, with no other options) and gives more of that classic bright crunch - 4 ohms gives a more modern, heavier sound.

    There's also the myth that using 16 ohms is better "because it uses all the windings in the transformer". Actually whether it uses all the windings or not is irrelevant, the unused part dosn't carry any current and the amp does not 'know' it's there - it's exactly the same as using a transformer with only a 4-ohm winding, which then would equally be the whole winding.

    What sounds best to you, is best. Some people like different setups for different tones.
     
  4. Shea

    Shea Member

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    That's what I was inclined to believe. But a thread on another forum made me reconsider the "whole winding" theory. If the output transformer is interleaved, and the different impedance taps are simply taps on one continuous secondary winding, then using one of the lower impedance settings will probably cut out some of the interleaving and, I think, result in poorer coupling between the primary and secondary. But I assume the difference would mostly be in the high end.

    Shea
     
  5. Jon Silberman

    Jon Silberman 10Q Jerry & Dickey Gold Supporting Member

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    Wow. I guess I was one of the prior myth believers. Thanks for setting the record straight, John.
     
  6. kwk13

    kwk13 Supporting Member

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    This is why this place is great! A bunch of smart guys all willing to share their knowledge. Thanks a million guys. I thought I was crazy for a while.

    Thanks Again,

    Keith
     
  7. markdurham

    markdurham Member

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    I don't want to get into if using the full secondary winding affects the amp's tone. A vintage Fender that only has a 4 ohm secondary is using the full secondary winding simply by design.
    But it's no myth that on an OT with multiple taps, the 16 ohm winding has more voltage driving the speaker cabinet than the 4 ohm winding does. That's easy enough for anyone to measure.
    An OT transforms more than just impedance. It transforms current and voltage also. The higher voltage and lower current at the primary is transformed to a lower voltage and higher current at the secondary. The turns ratio from the primary to secondary is lower at the 16 ohm tap than at the 4 ohm tap and therefore the voltage on the secondary is higher at the 16 ohm tap than the 4 ohm tap. And the current is higher at the 4 ohm tap than it is at the 16 ohm tap. Notice how those old Marshall 16 ohm cabs have much smaller speaker wire than Fender combos with only a 4 ohm output even though the wire from the OT to the speakers is much longer? With more voltage to drive them they didn't need larger wire. This may be the reason some people prefer the "full secondary winding", when using vintage Marshalls, without being able to put their finger on exactly why.
    As mentioned, the better low end with the speakers in parallel is all about the damping inherent with that configuration. That has nothing to do with which tap you connect the speakers to. If you had 4-64 ohm speakers(OK, I know they don't exist) connected in parallel to the 16 ohm tap, you would hear the same tighter low end.
    That being said, I do prefer the sound of speakers wired in parallel. My apoligies to those who love the tone of their vintage AC30's with the speakers wired in series. With a 4x12 wired series/parallel you get a bit of both.
    markd
     
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