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8 ohm cab vs 4ohm cab

Discussion in 'Amps [BG]' started by dwm74, Jun 17, 2010.

  1. dwm74

    dwm74

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    I'm currently on the lookout for my first head/cab setup, and like many of us, am a little confused when it comes to ohms and compatibility. (And yes, I have already read the sticky at the top of this section.)

    I ran across a used Genz Benz 4 x 10 cabinet, but it's an 8 ohm cab. Which means any amp I use will be running at the lower wattage 8 ohm setting. Based on what I've learned so far, I would want a 4 ohm cab to get the maximum wattage output from my amp, as most amps list their max wattage for 4 ohms, right?

    Or is there away to change the cab from 8 to 4 ohms?

    Thanks in advance for any helpful advice!
  2. poorbassist15

    poorbassist15

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    From what I understand, 8 ohms is less power if you're running a 4 ohm head.
  3. BassmanPaul

    BassmanPaul Gold Supporting Member

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    There is no way of changing an 8Ω cabinet to 4Ω. You don't necessarily need to get the maximum out of your amp. I think you'll find the GB cabinet will be loud enough for you. If you want more add a second identical cabinet.

    Paul
  4. devilock76

    devilock76

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    I am going to say a comment that will probably insight flaming and what not.

    Unless you are buying a full stack cabinet, read that as 8x10 or 6x10 or any type of massive cabinet that would rarely ever need to be partnered with another cab, buy an 8 ohm.

    Let me explain, I used to have tons of 4 ohm cabs, I mean tons, and always had 2 ohm capable or bi-amped rigs. I was never satisifed with tone or power. I am much happier with my 8 ohm cabs I have now and a 4 ohm capable head. Now granted my more current gear is a step up but let me explain some things that have been my experience.

    1. 8 ohm cabs feel louder than the similar 4 ohm cab against the same head. Don't ask me to quantify it, because I can't, it makes no sense to me, it is counter to all logic to me in how these things should work, but hands down I have found 8 ohm cabs just have more punch and kick than 4ohm cabs. A gross generalization and I am sure others will flame this, just my experience.

    Now for more logical all could agree with points.

    2. 8 ohm cabs have more options. Why, because there are way more heads out there that are 4 ohm capable than 2 ohm capable or bi-amapable (even a word) at all levels of price point. Also far more combos that take extension speakers can do so with an 8 ohm vs a 4 ohm. With 8 ohm cabs you just seem to have more options with your setup.

    3. No matter how capable a head may be, and stated that it can run 2 ohms, at 2 ohms these heads just seem to run out of juice quick, have MAJOR power draw from the circuit, get way hotter, etc etc. I don't like running at 2 ohm any more, period. I don't think it is a good idea. Again personal experience. And here is another one. All of the 2 ohm capable heads I have played, owned, and demod, seemed to have less punch at 4 ohms than heads that were only 4 ohm capable at the same or better wattage for the 2 ohm head.

    Now if you are sure you are only going to have one cabinet ever then get a 4 ohm cabinet, and never pair it period. But if you think you might pair it then go ahead and get 8 ohm cabinets. Heck even if you think 4x10 is all you will ever get instead of getting 1 4 ohm 4 x10 get two 8 ohm 2x10's. FIrst of all they will be easier to carrier, you can stack vertically if you like, and it is highly unlikely both will crap out on you at the same time, so if one craps out you still have the other 2x10 running just in case.

    Anyway these are my opinions from personal experience. I have owned and demo'd Peavey's, GK's, Carvin's, Ampeg's, SWR's and power amp systems with Yorkille and Crown power amps, Warwick, Genz Benz, Avatar, Peavey, Epifani, SWR, GK, Ampeg. despite brand and in fact even within the same brand I have found 8 ohm cabs and the only 4 ohm capable heads to be all around better. Just my experience.

    One minor exception, SWR, SWR's despite a typically lower power rating than other heads/combos I have mentioned are 2 ohm capable and sound great. The Super Redhead I find to be an awesome example of this. Yeah I know makes no sense. This exact thought has been on my mind for a bit now, especially having recently dumped all my 4 ohm cabs and setting up my new mini rig of doom which TOASTS all past rigs I have had.

    Anyway I hope I don't get people's hackles up too much with some of my statements.

    Ken

    P.S. - oh and to the question, the only way to change an 8 ohm cabinet to 4 ohm is to change the speakers.
  5. Bardley

    Bardley

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    First, you cannot change the impedance of a cab without completely changing the components (speakers, crossover, etc), though someone will ask at least twice a week if you can. ;) You are better off buying a new cab if you need a different impedance.

    If you ever plan on using more than one cab, you should get an 8ohm cab. That way when you use two 8ohm cabs (in parallel) you get a 4ohm load on the amp.
    Don't stress about trying to get the max wattage from your amp. More watts does not equal more sound. I have used a single 8ohm cab for years and get plenty of volume out of my shuttle 6.
    If you never plan on using another cab with your head, you are fine buying a 4 ohm cab.
  6. devilock76

    devilock76

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    To add to the wattage, the best increase in wattage you would get between an 8 ohm and 4 ohm cab is half, best case, but typically less. That will only translate to a 3db increase in volume which typically most can't hear.

    Worry about cabinet efficiency more and frequency curve.

    Incidentally I really like GB cabs and find them pretty efficient. Although a very different cab I have a GB Neo-x 1x12 and I find this to be a micro monster.

    Ken
  7. Jaco who?

    Jaco who?

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    Age old much repeated question. Answer will always be: it depends. If you have a modest amount of power from a 4Ω minimum head, say 300 or less watts, love it, never plan on replacing it, don't play or plan on ever needing ear bleeding volume, you'll probably be fine with even a 4Ω 2x12.

    If you have a more powerful head, you'll reach the displacement limit of the cabinet way way under it's bogus 1000 watt (example) thermally rated limit anyway, so you'll be much louder and less likely to make farty noises with more speakers, so a pair of 8 ohm cabs will make more sense.
  8. BurningSkies

    BurningSkies

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    The extra wattage you gain from your amp at 4ohm isn't really worth much in terms of extra volume.

    But if you get a nice 8ohm cab and you decide that you DO need to be louder, you can still add a second cabinet, something you couldn't do if you bought a 4ohm cabinet (assuming your head won't take a load below 4ohms). You'll end up getting much more volume out of a second cab than you do with one cab and a 'handful' of extra "watts".
  9. dwm74

    dwm74

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    Wow! Thanks for all the quick responses, and sorry if I asked questions that have been asked before.

    Having said that, I'll ask another one... can I run this 8ohm cab with a 4 ohm solid state amp and be safe? IIRC, solid state amps automatically adjust the impedance, and the cab is 'under' the limit. (The reason I ask this is because I'm looking at several heads that only list 4 ohms as their impedance, whereas other list 4 & 8.)

    Thanks again.
  10. BurningSkies

    BurningSkies

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    If the head is safe to 4 ohms, it means you can use any cab (or combination) that has an impedance above 4 ohms.

    You can use a single 8ohm, or 2x 8ohms (a 4ohm total) or a single 4ohm cab.

    If you try to combine a 4 and an 8ohm cab, you'll end up with a total load of 2.67 and that will be below the rating for your head and you risk failure.
  11. Toolmybass

    Toolmybass Supporting Member

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    I have 3 heads that i use with ONE 4x12 Mesa Cab. (obviously not at the same time)

    1.Ampeg SVT-VR 300 watts with a 4Ω or a 2Ω setting
    2.GK 1001 RBII 700 watts with a 8Ω or 4Ω draw (no switch)
    3.Mesa MPulse 360 watts 4Ω draw (2Ω min)

    I specifically special ordered my 4x12 at 4Ω's so that i could safely use it with all 3. There would be alot of others that you could use this cabinet with. I may be wrong but i was told (when ordering my cab),that the exact same speakers would be in my 4x12 as the 8Ω ...BUT that it would be wired differently (series/parallel) to make it 4Ω instead of 8Ω

    If you dont request the 4 it comes in at 8Ω's If you going to just use one cabinet i would def get one in 4Ω's. I was just trying out 2 channels in this pic with a 4x10 Mesa. But do not use the 4x10. Just the 4x12

    TMB
    [​IMG]
  12. devilock76

    devilock76

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    That just doesn't sound right. Ignoring the horn for a second and assuming all speakers are the same, if you had 4 x 8 ohm speakers in there you could basically wire them a couple of ways:

    1 - all series - total ohms = 32
    2 - all parallel - total ohms = 2
    3 - series parallel - total ohms = 8*

    The last one typically being each set of two is in series and then the sets are wired parallel (although you could do the inverse), ok you could wire 3 in parralel and 1 in series to that creating a 10.67 ohm load. Quite frankly the only way I can get my head around going from 8 ohms to 4 with the EXACT same speakers would be an added resistor which basically means the speakers get the same wattage in either configuration so nothing gained. So say the are all in parallel and a 4 ohm resister is wires in series to that parallel circuit. That is the best I can come up with.

    Ken
  13. agedhorse

    agedhorse Development Engineer-Mesa, Product Support-Genz Supporting Member

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    You are correct.
  14. RickenBoogie

    RickenBoogie

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    +1 to most of these replies, the ones that say get an 8 ohm cab. Squeezing all the wattage out of an amp will not get you any more volume. Volume is achieved with speakers, more speakers equals more volume. Get the 8 ohm cab, and add anther one if you need to, later. Have fun with your new rig.
  15. jeffgnr90

    jeffgnr90

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    so if i were to run my 2ohm 600w head into 2 2 svt210av's and an acoustic b115neo, I would be running at 2.67 ohms right? Would all my speakers be putting forth the same volume? And how could I get this potential rig down to 2ohms??
  16. Vince Klortho

    Vince Klortho

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    Yes, 2.67 ohms is right but they probably would not be putting out the same volume unless the speakers all had the right properties of excursion, cone area, and cabinet design (volume and porting.) The only way to get down to 2 ohms is to add another 8 ohm cabinet. Four of them in parallel would have a total impedence of 2 ohms.

    When the speakers are all in parallel and are of the same impedence they will each get the same power. Whether they put out the same volume is practically irrelevant I think. What really matters is can they handle the power they are getting and do they all sound good together.
  17. Downunderwonder

    Downunderwonder

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    The other thread you bumped is going to give you what you need.
  18. Shardik

    Shardik

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    I am thinking in those terms, too, given an amp rated for minimum load impedance of 4 ohms. The flexibility of 2x 8 ohm cabs is much better than 2x 4ohm cabs.

    Let me explain:

    If you want to travel light and don't need the full power of both cabs, a single 8ohm cabinet will not work harder than it does when working in pairs. And you do not need the full power from that amp when driving only one cab.

    On the other hand, when you are driving two cabs, you will need all the power you can get from that amp (if you have hauled two cabs, you want to be loud), and two 8 ohm cabs in parallel will utilize that power, making the load 4 ohm, seen from the amp.

    BUT (yeah, you may disagree):
    The maximum amp effect does not matter that much. What is most influencial on that loudness from the cabs, and how much air they are able to move. That means the area of the speaker cones and how much that magnet-and-coil motor is able to move it.

    Even if a speaker has a rated power handling, that does not mean its movement increases linearly throughout the range from 0 to (power handling limit). The speaker motor has real limits to linear excursion, and rarely do you need (power handling limit) watts to get there. When that maximum linear excursion is reached, you will get less movement in that speaker for the effect increase. In practical use, that means that even if you increase your amp power from 250w to 500w, and have a 210 cab rated at 500W (which means each element can handle 250W), it is not uncommon that the same element reaches its linear excursion limit at 25-50W, and that linearity collapses after that. It will still be louder, but not THAT much louder. Bottom line is that the increase in loudness from 250W to 500W is even less because you reach the limits of air movement at a power lower than that max power rating.
    Adding to the confusion is the sensitivity of the cabinet. Usually specified in SPL (dB) at 1W, 1m from the cabinet.
    Choosing a higher sensitivity cabinet can completely negate the need for more amp power.

    My bottom line for playing loud:
    Focus on how much air those cabinet elements can move. Then focus on how much amp you need to drive them properly. That is usually less than the max power rating of the cabinets.
  19. Downunderwonder

    Downunderwonder

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