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Maybe a silly impedance question . . .

Discussion in 'Amps and Cabs [BG]' started by i_got_a_mohawk, Jan 4, 2006.


  1. This is just a silly question . . . move to misc or off topic if need be

    Anyway, i was wondering, ive been looking at guitar amps with my guitarist, cus all he knows about guitar amps is you plug in and they should make a noise

    And i have been wondering for the past couple days, how come guitar amp speaker cabs are 16 ohm, you would never see a 16 ohm (well, rarely) bass cab

    I can understand its probably something to do with bass amps requiring more power to a lower impedance would make sense, but, why do guitar amps seem to run into higher impedances?

    maybe a silly question :eyebrow: , but, if anyone knows, cheers
     
  2. I believe you are noticing the huge difference between how a tube amp reacts to different impedance vs. a solid state amp. Most guitar amps are tube, and are meant to be exactly matched to cabinet impedance. I'm not realy a tube guy, but understand that higher impedance is 'better' for a tube amp... however, a tube amp will deliver the same power into different loads, and usually has a switch that allow you to change the output of the amp to match for different cabinet ohms (4, 8, 16, etc.).

    For tube bass amps, it's the same thing. However, most bass amps are solid state (even if they have a tube preamp, the power sections are typically solid state). In that case, the lower the impedance of the cabinet, the more power the amp will put out... up until you reach the lowest safe operating impedance (usually 4ohms, sometimes 2ohms).

    That's a 'layman's' explanation, but I believe it to be correct.
     
  3. Lower impedance is better for tube amps if i remember right :p (Outwith the proper tolerences of the specific amp)

    However, what your saying makes sense, its just so bass cabs can be used with both tube and ss amps . . . however . . . you do get alot of SS guitar amps, so, im back to square one on that one
     
  4. theshadow2001

    theshadow2001

    Jun 17, 2004
    Ireland
    I've been wondering this as well It seemed quite strange why my guitarist has a 16 ohm cab. does this mean that his peavey ultra which has a min operating load of 4 ohms could power 4 of these cabinets??
    and I thought a half stack was too much
     
  5. ras1983

    ras1983

    Dec 28, 2004
    Sydney, Australia
    power issue is a big one.

    bass frequencies require much more power, typically more than 300-400 watts to compete with a guitar amp. since most cabinets are 4 or 8 ohm, it would be very expensive to build a bass amp that can put out 300-400 watts at 16 ohm aswell as high wattage at the lower impedances.

    its cheaper to stick with tradition and build amps that can cater for the vast majority of bass cabs that are 4 and 8 ohm.

    so my guess is its probably more of a traditional-'this is the way it has always been' thing.

    another reason could be sound clarity, many reference monitors are 16 ohm and up because it is believed that higher impedance gives a higher sound clarity. with bass, clarity isn't as big a problem because of the low and boomy nature of the low frequencies. on the other hand, guitars have much higher frequecies that have very strong overtones and harmonics, and may actually sound clearer with 16 ohm cabs.
     
  6. It's simple.The earilest guitar speakers were industrial PA speakers. In their application, you didn't want a significant amount of power for hi-fi, just maximum voltage at the speaker's frequency fresponse. Since heavy-cored and interleaf wound output transformers, which would be required for large low-end and low impedances and high end respectively, were expensive to make and made their parent amp more expensive, most PA amps were made cheap and they used higher impedance speakers in order to have smaller output transformers and thus, be cheaper. 16, 32, 40, and even 50 ohm speakers were common among the first amps, with the larger values dying off as larger amps became more economical.

    The first guitar amps and cabs were made with common, cheap, off-the-shelf components, among them 16 ohm speakers. Correctly wound, there is NO difference in sound between two speakers of the same model and differing impedances, but guitar players are superstitious, and have to have 16 ohm output to get their "sound" even though their new 16 ohm cabs are now made in China with ceramic magnets. :rolleyes: Bass players, OTOH, usually just want to be heard and sound good. We don't care what Jimi Ray Johnson Page Santana played or if their old Marshalls and Fenders had a 16 ohm output.

    You've got it dangerously backwards! LOWER is safer; matched is better!
     
  7. I was talking about matching. From what I understand, it should always be matched, and that 'matched at 16ohms' is the optimum for a tube amp versus matched at 8 ohms or 4ohms.... however, from your post above, it sounds that might just be a myth.

    Some posters above still don't seem to realize that when a tube amp's impedence is matched to a cabinet's impedence, the amp puts out full power regardless of the absolute impedence, so it really doesn't matter that much. However, with a SS bass amp, it's a totally different thing... which was the original question.
     
  8. jokerjkny

    jokerjkny

    Jan 19, 2002
    NY / NJ / PA
    ...dusts off and puts on superstitious guitar player hat...

    a few peeps say that higher impedence ratings make more use of a tube guitar amp's transformer's windings, which makes for a brighter, more open and textured sound.

    ...puts away superstitious guitar player hat...

    *shrug*
     
  9. Technically speaking, the higher output transformer secondary impedance you have, the closer you are to the actual output impedance of the tubes themselves. Also it is easier to induce a high voltage than it is a high current through a higher resistance, so even if it's less than a watt or so, a 16 ohm tap MIGHT have slightly more power than an 8 ohm tap, which MAY have more than a 4 ohm tap, etc. In practice, it means nothing in terms of tonal difference for guitar speakers. For bass, lower impedance is desired for easier current transfer for low frequencies.


    I don't understand what you mean by "absolute impedance" versus "matched impedance." Please explain that.

    Huh? No it wasn't. Mohawk's question was why do guitar players usually have 16 ohm cabs, which are a holdover from early tube days. Where do you get ss bass amp?

    Actually, higher impedances use FEWER windings, but I have heard that same argument before. If guitars had a significant amount of signal at above 10 kHz, that MIGHT hold water, but most top out at 6-7 kHz for single coils and 5 kHz for humbuckers and even that is basically just fret noise.
     
  10. Cheers PBG, so, basically its just because guitar players are superstitious ;)

    What your saying makes sense, much appreciated, thats goes for everyone else who replied to this thread too :)