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4 vs 8 ohm cabinets - why it matters?

Discussion in 'Amps and Cabs [BG]' started by Funkateer, Aug 16, 2005.


  1. Funkateer

    Funkateer

    Jul 5, 2002
    Los Gatos, CA
    A lot of cabs are offered in both flavors. Why would I choose one over the other?
     
  2. cheezewiz

    cheezewiz

    Mar 27, 2002
    Ohio
    To get the most possible wattage out of your head.
     
  3. Funkateer

    Funkateer

    Jul 5, 2002
    Los Gatos, CA
    If less ohms == more watts (and there are no side effects), why are 8 ohm cabs offered at all?
     
  4. billbern

    billbern

    Sep 11, 2004
    Daytona Beach, Fl
    Endorsing: Inearz In-ear Monitors
    Because two 4 ohms cabs are a 2 ohm load, lower than many bridged power amps can handle.
    Bill
     
  5. Blueszilla

    Blueszilla Bassist ordinaire

    Apr 2, 2003
    The Duke City
    I've heard that some 8 ohm versions of cabs are a bit smoother sounding than their 4 ohm counterparts. They won't get as loud, but they might have a larger range of application, say at a smaller venue. With both 4 and 8 ohm offerings, you can mix/match, use one by itself or two if you need more volume, or take advantage of amps that support 2 ohm loads.
     
  6. There's lot's of info on this if you do a search. However, quickly, it's best to optimally match the ohmage of your cab with the minimum ohmage that your amp will run. The lower the ohms of a cab means the less resistance, hence more power getting to the speakers. Most transistor amps like SWR, most of the Eden models, Thunderfunk, etc. run 'optimally' at 4ohms... so you should try to match your total speaker ohmage to that target (some amps run 'safely' down to 2ohms, but this is a whole other issue!). Tube amps like the original SVT's are also another different story, and have impedence matching switches.

    So, if you are like me (a freelance, jobbing musician who plays a lot of one nighters) I NEVER want to carry along two cabinets. Therefore, I get the best sounding cab that I can find and purchase a 4ohm version, so that the maximum safe output of the amp gets to the cab. If, on the other hand, you prefer two cabs (for example, two 210 cabs... so that you can use one for smaller gigs and combine both for larger gigs), then you would typically want two 8ohm cabs, since combining two 8ohm cabs in the typical way results in the amp 'seeing' 4ohms. The added advantage of this solution is that when you are only using one small cab like a 210 at 8ohms, your amp will put out a lower amount of watts, which probably matches up better to the single smaller cab. When you add the other 8ohm cab to get a total 4ohm load, your amp will put out its full power into the two cabs. Cool!

    (of course, if you are running a stereo power amp, this all kind of changes... and you have to decide if you want to run stereo... which probably requires two 4ohm cabs) or mono-bridged, which would typically require two 8ohm cabs... or sometimes only one 8ohm cab based on the minimum bridged ohmage)

    Hope this helps. Do a search also.... some great technical info on the site regarding series/parallel, internal cab wiring to achieve a certain ohmage... amps that will safely run at 2ohms (which is sometimes different than manufacturers claims), etc.
     

  7. I don't think this would be true... all other things being equal.
     
  8. Blueszilla

    Blueszilla Bassist ordinaire

    Apr 2, 2003
    The Duke City
    Why? Please elaborate.

    I heard this from a very reliable cab manufacturer.
     
  9. I have a tube amp so I get 8 ohm cabs..........

    It'll put out full power into 8 or 4 ohm........... :cool:

    So I have the option of one cab or two..........

    I usually just bring one !

    JJ
     
  10. billfitzmaurice

    billfitzmaurice Commercial User

    Sep 15, 2004
    New Hampshire
    Owner, Bill Fitzmaurice Loudspeaker Design
    They aren't. Drivers with different voice coil impedances also have a number of other different specs as a result. Voice coil inductance is the most obvious, but there are more and they all affect the sound. However, while saying that an 8 ohm box will sound different than a 4 ohm box is true, the impedance alone is not an accurate predictor of excatly how they will differ. All those other factors also must be considered. Two otherwise identical 8 ohm boxes can sound different if one has two 16 ohm drivers parallel wired and one has two 4 ohm drivers series wired.
     
  11. Blueszilla

    Blueszilla Bassist ordinaire

    Apr 2, 2003
    The Duke City
    Thanks Bill. Are you any relation to a Greg Fitzmaurice?

    Since it's arguable that two of the same cab could have a bit different sound (however slight) due to these 'component tolerances', it seems reasonable that two of the same cab but with different impedances would have different response curves that could translate to tonal differences to the listener. How MUCH of a difference is probably subjective, YMMV, etc...
     
  12. Blueszilla

    Blueszilla Bassist ordinaire

    Apr 2, 2003
    The Duke City
    Jorg Schroeder, when discussing which mini 12 to buy. I trust him enough to go with his word. He most likely has much more experience testing both so it was easy to take his advice.
     
  13. I guess the 'all other things being equal' is the difficulty. However, within a given manufacturer, I would imagine that the difference in a 4ohm versus 8ohm version of the cab with identical inputs (which is difficult, since you would have to find two versions of the same amp that put out identical power, one at 8ohms and one at 4ohms) would be impossible to hear in any sort of real world setting. So, you would be much better served to focus on matching your power amp's optimal output versus focusing on a possible, subtle difference in inherent sound based on the wiring of the cab, etc. (e.g., I would imagine pumping 1200 watts into a 4ohm cab would result in a very noticable difference in head room, openess of the low end, a small but noticable increase in volume, etc. when pushed compared to the same amp generating much less power (600-800 watts) into an 'identical' 8ohm cab).
     
  14. The most valid reason for offering 8 ohm cabs is for those of us that have an amp that uses 4 ohms at it's lowest operating impedance and if we want more air movement we might use two 8 ohm cabs that would allow the amp to operated at it's max rated wattage of 4 ohms.
     
  15. Blueszilla

    Blueszilla Bassist ordinaire

    Apr 2, 2003
    The Duke City
    The inputs, or more accurately, output, of the amp does change. I think we are talking about a real world setting where you are using a single amp for both cabs. Do you agree that the amps output power will change depending on which cab (4 or 8 ohm) you use? If so, the amps output power will be in a different range of its total rated capacity to get the same spl for each cab. I can see, technically at least, where this would affect some tonal qualities of the cab.

    I can also see where a 4 ohm cab would get louder sooner than the 8 ohm version. Maybe this is the source of the 'smoother' comment.

    This is moot for me anyway, as I don't have two identical cabs of different impedances to A/B. I like having two cabs of different impedances for the reasons you stated earlier, more choices/possibilities. And I am like you somewhat, as I gig regularly with 2 different groups and freelance 4 to 6 times a month. I need a small good sounding rig. Two cabs for me is no problem, when I need it.
     
  16. My entire point is that the output power of the amp will change... with the 4ohm cab allowing the full, safe power of most transistor heads to be used by the cab. That's the point! As long as you are not driving the amp to clip, most of us would rather have an amp putting out its maximum power. Of course, if you aren't really pushing the limits of the amp, this all doesn't matter. :)

    I think we are talking semantics here.... yes, a 4ohm cab will sound different than the same cab in 8ohm version primarily due to pumping more watts into it. If you found a way to pump more watts into the 8ohm (i.e., with a bigger amp), it would sound different also.

    It sounds like you went with the 8ohm version, which to me is the right choice when talking about a small cabinet like the Schroeder mini. It think this is true for the following reasons:

    1) A relatively efficient, small, single speaker cab like the mini will probably be driven pretty well by the reduced output of most transistor amps running at 8ohms.

    2) As you and a number of others point out, it gives you the option to add a second 8ohm cab, thereby increasing volume due to the additional cab and the increased power output of your amp at 4ohms (again, assuming a mono transistor amp).

    In my case, I have a Schroeder 1210 (4ohm) and an EpifaniUL410 (40hm). Both those cabs are capable of handling the high power output of my amps (either the TF550 or the Walter Woods Ultra), and... both are capable of pushing plenty of air for my larger gigs (Epi410) and smaller and moderate sized gigs (Schroeder).

    Rock on :bassist:

    PS Are Jorg's cabs cool or what :hyper:
     
  17. im like that, but with two 4 ohm cabs :D
     
  18. Blueszilla

    Blueszilla Bassist ordinaire

    Apr 2, 2003
    The Duke City
    I'm confused, but in agreement with this line of thinking. Although my settings give me lots of headroom, as I don't use max power, I guess I just haven't had to yet!:smug:

    Agreed.

    Me too!

    That they are, my friend!
     
  19. Jerrold Tiers

    Jerrold Tiers

    Nov 14, 2003
    St Louis
    The option of 8 ohm cabs allows using a particular type of cab (having a certain rating) with a larger power amp... you just use more of them to be louder, as mentioned.


    Sound differences....

    The 4 ohm and 8 ohm versions of a driver will normally sound different. I don't think there is a rule as to which sounds better. I would suspect the 8 ohm versions to generally be a bit nicer, but I don't have a really good reason for that.

    To start with, the weight of wire in the voice coil is almost certain to be somewhat different between the two, due to available wire gauges etc. Right there is a difference that will affect brightness, resonant frequency, etc.

    Then also, the number of turns of wire will not necessarily be proportional to impedance between them, so it is possible for the BL product to be somewhat different.

    Inductance, as mentioned, may not balance out proportionately with nominal impedance, especially when trying to balance the other considerations as well. Another high end difference.

    They are different animals, they may be close, but are very unlikely to sound the same.
     
  20. Interesting!

    How about cabinets with multiple drivers? For example, a 4 ohm 2x10 would have two 8 ohm drivers in parallel. Might it sound better than an 8 ohm version of the same 2x10 that uses two 4 ohm drivers in series?

    On a related note, I've heard that series speaker connections may compromise the sound moreso than parallel. What sort of difference might there be sonically?