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Speaker impedance: another 'old-wives-tale'?

Discussion in 'Amps and Cabs [BG]' started by Rockin John, Nov 5, 2001.


  1. The guitarist went looking for some replacement 16 ohm speakers. Ignoring the technical side of impedances for the sake of this point, the guy at the music store told him that he would expect better fidelity from 16 ohm units over 4 ohm units.

    Whilst it might be possible to show some differences with sophisticated test gear, I suspect that in the real world of rock music the impedance of a drive unit makes no difference to quality of sound it delivers.

    Comments please.
     
  2. mchildree

    mchildree Supporting Member

    Sep 4, 2000
    AL/GA
    I'd say "Think Again!"....

    Impedance of speaker/speakers has a direct effect on the output of the amplifier and how hard the amp is working. In the case of guitar amps, especially, it's a well-known phenomenon that most tube amps sound best when they're being pushed near their limits. Therefore, you'd want a total load that allows the amplifier to acheive output in watts for the full power rating. Every SVT I've had worked the same way.

    Now if the total load is the same, as in comparing 1- 4 ohm speaker against 4-16 ohmers against 2- 8 ohmers, that's all a matter of taste. "High Fidelity" is a highly subjective term.
     
  3. But what about 4 16s wired series/ parallel to give 16 ohms and 4 4s wired just series to give 16 ohms. Any difference there?
     
  4. Richard Lindsey

    Richard Lindsey

    Mar 25, 2000
    Metro NYC
    Question: not to be a jerk about it, but what does "fidelity" have to do with guitar amps and speakers anyway?

    The amps most guitarists prefer (and I have a some idea of this, being a guitarist as well as a bassist) cannot by any stretch of the imagination be considered high-fidelity devices. Especially when you crank up the amp a bit (disortion, by definition, equates to loss of fidelity). Guitar amps are not accurate reproducers of sound but co-participants in *creating* tone. The whole reason the classic amps and speakers sound "good" to guitarists is that they *fail* to reproduce the input accurately--but that this failure happens to yield a musically euphonious result.

    So my opinion, FWIW, is that "fidelity" is really a meaningless concern in this context. The issue is really gonna be, do they sound different, and which one do you prefer?
     
  5. OK.

    What I'm trying to get at, is the store guy's comments seem to have no basis in fact.

    In other words, however one defines 'fidelity', I hold the view that it's simply untrue to say that 4 ohm speakers produce a worse sound than do 16 ohm units.

    The guy's statement is IMHO about as useful as saying, what?, yellow is a nicer colour than blue. Yet if spoken with authority to anyone who knows no better, or is a bit unsure, the notion the 4 ohm speakers sound rubbish could easily form part of rock music folk-law. Just like 'series wired bass cabs sound rubbish'.

    Is 16 better than 4: is yellow nicer than blue?;)

    Just a few thoughts....

    John
     
  6. mchildree

    mchildree Supporting Member

    Sep 4, 2000
    AL/GA
    Well, maybe he just needs to clarify. For a particular amp, it could be very true that a single 15" speaker at 4 ohms doesn't sound as good as 4 16-ohm ten inchers, but that would be a function of speaker size and the resultant tonality in regards to a particular instrument...not so much the actual impedance of the speakers.
     
  7. Bob Lee (QSC)

    Bob Lee (QSC) In case you missed it, I work for QSC Audio! Gold Supporting Member Commercial User

    Jul 3, 2001
    Costa Mesa, Calif.
    Technical Communications Developer, QSC Audio
    You're right, John, there's nothing inherently better about the sound quality of a 16-ohm driver versus an 8- or 4-ohm one.
     
  8. The damping factor is 4x higher with a 16-ohm load than a 4-ohm load.

    :D
     
  9. Bob Lee (QSC)

    Bob Lee (QSC) In case you missed it, I work for QSC Audio! Gold Supporting Member Commercial User

    Jul 3, 2001
    Costa Mesa, Calif.
    Technical Communications Developer, QSC Audio
    Aww … wise guy!! ;)

    I said driver, not load!
     
  10. Similar speakers with different impedences will behave a bit different though, no? As bgavin said, the damping factor is different. The frequency vs impedence curve would also be different, what about the other parameters? I've always wondered about that. I realize that, say, a 16 ohm driver isn't inherently better sounding than an 8 or 4, but is any impedence more desireable to an amplifier (above it's minimum impedence)? Apart from the differences in output power. For example does, say, an MX3000 prefer any particular impedence? I'm guessing no.....but...
     
  11. I figured ya needed a poke, jusso you know everybody still loves ya...

    :D

    Besides, I think of ALL those JBLs that were produced for years and year, all in 16 ohm loads. They had pretty good fidelity, for sure.
     
  12. Bob Lee (QSC)

    Bob Lee (QSC) In case you missed it, I work for QSC Audio! Gold Supporting Member Commercial User

    Jul 3, 2001
    Costa Mesa, Calif.
    Technical Communications Developer, QSC Audio
    Only in that a lower impedance will pass more current for a given voltage than a higher impedance will. And current is what produces the voice coil's magnetic field, which reacts with the magnet to move the cone. All else being equal, a 4-ohm driver will have about 4× the acoustic output of a 16-ohm driver with the same voltage applied across it. Whether it's better or more accurate or sounds nicer depends on factors other than impedance.



    If the net damping factor is high enough, the difference will be inaudible. Let's say you have a damping factor of 600 with a 16-ohm speaker load and 150 with a 4-ohm load. For one thing, you would have to double the voltage on the 16-ohm speaker to match the power delivered to the 4-ohm speaker. But the difference between the damping factors is negligible.

    We know that the impedance curve would be higher on the Z axis. But if the drivers were of otherwise identical design, the shape of the curve could well be the same. For example, let's say a driver's voice coil is in two separate 8-ohm segments. In series, it's a 16-ohm speaker; in parallel, it's 4 ohms. If you did separate Z vs. f sweeps, you'd probably find that the 16-ohm curve is about the same as the 4-ohm curve, with the same bumps and dips, except that it's four times further out on the Z axis.

    Unless you have a tube amp with separate taps for different speaker impedances, no, a well-designed amp won't "prefer" any particular impedance, as long as it's high enough that the amp doesn't overheat or otherwise adversely react to sourcing a lot of current.

    Hey, SG, I've always wonder about St. John's—do people frequently confuse it with Saint John, NB? I can imagine a Flames vs. Leafs game … :)
     
  13. MikeyD

    MikeyD

    Sep 9, 2000
    If one is talking about only the loudspeakers, and the frequency (phase and amplitude) response is identical, then it doesn't matter what the nominal impedance is. However, when you look at driving the "load" (speaker) with a "driver" (amplifier), it becomes a system issue, because the two interact. The impedance of the speaker can have important influences on how the amplifier behaves, but as Bob says, the difference between how typical load variants affect some amplifiers is probably inaudible.
    - Mike
     
  14. Thanks Bob and Mike, you've confirmed my suspicions. I figured that was the case but I wasn't entirely sure. Good discussion, I love this stuff! Bob, there's a good bit of confusion between the two cities. UPS, Fedex and others tend to have a bit of difficulty with it. I've had lots of stuff sent to Saint John (or Saint Toilet as the locals call it). I think the AHL thing is a bit of a tongue twister for the announcers. St John's doesn't smell as bad :D but the weather is horrendous.:p