Amps: wattage and handling.

Discussion in 'Amps and Cabs [BG]' started by projectBdaddy8, Oct 19, 2003.

  1. Hey guys,

    I know i already asked a while back about mixing brands, but now i have a somewhat technical question. If i wanted a rig with a 1x15" and a 2x10", what kind of head would i need to power them. In other words, how does the wattage and handling match up with multiple cabs. If the handling is seperate for both cabs, do i get twice the power than with one. Also, why are their ratings for seperate measures of resistance (aka: ohms). As you can see i am thouroughly confused and desperately need your help.

  2. IvanMike

    IvanMike Player Characters fear me... Staff Member Supporting Member

    Nov 10, 2002
    Middletown CT, USA
    okie dokie
    1st most amps will drive loads down to 4 ohms
    in the real bass world that mean that you can connect 1 4 ohm speaker to them, 0r two 8 ohm speakers to them for a final load of 4 ohms (8 ohms + 8 ohms = 4 ohms when wired in parallel which is how its done with amps with 2 speaker outs or by "daisy chaining" speakers together)
    you could also just plug one 8 ohm speaker in to that amp and just be running a load of 8 ohms
    in theory an amp will put twice the watts into an 4 ohm load than it will into a 8 ohm load but....generally the amp will put a little less than twice the watts into this 4 ohm load due to other limiting factors in the amp
    so ya gotta know the wattage that each speaker you are considering will take, and how many ohms it is, as well as the wattage the amp you are considering will put into 8 ohms and 4 ohms, (and if it can go as low as 2 ohms)
    if life is good maybe you'll find an amp that puts say 400 watts into 4 ohms, and both a 2x10 and a 1x15 that are 8 ohms each, and can handle at least 200 watts each
    did i lose you yet?

    generally speaking like i said before, this theoritical 400 watt head will probably put more than 200 watts into 8 ohms (let's pretend 250)
    this means that if you want to use one of your 200 watt 8 ohm speakers with it, you'll have to be carfull not to run it flat out or you might damage that speaker. OF course, you could always run the amp with 8 ohm speakes that can handle more than 200 watts each - nuthin wrong with that

    say you have a head that can handle 2 ohms, you want to avoid using a 4 ohm cab and an 8 ohm cab with it as the 4 ohm cab will get twice the power and ya probably wont hear much outta the 8 ohm cab
    you could however use 1, 2, 3, or 4 8 ohm cabs with the 2 ohm head or 1 or 2 4ohm cabs with it
    if you use a stereo head, just treat each side independently when figuring out what to use with it
    ok ya must be confused by now.....:D
  3. Nominal Impedance: 8 ohms
    Program Handling: 400 Watts
    RMS Handling: 200 Watts

    What does this mean? And at what resistence is the RMS Handling?
  4. IvanMike

    IvanMike Player Characters fear me... Staff Member Supporting Member

    Nov 10, 2002
    Middletown CT, USA
    nominal impedance is really the impedance of the cab so you should read it as such - the impedance of a cab can very widley depending what frequency is being thrown at it
    RMS watts are what you are looking for when figuring out how many watts it can really handle
    program handling and peak handling are always more, but you should look at the RMS watts when figuring out what it will take (especially from a bass)
    RMS means root mean square; it's not the average power handling but generally close to it
  5. Stephen Soto

    Stephen Soto

    Oct 12, 2003
    Yeah, I hear that cabs can handle more than or double their RMS though continuously.
  6. Mcrelly


    Jun 16, 2003
    Minnesota, USA
    Also I think its safe to say, correct me if I'm wrong, that two different kinds of cabs (15 + 210 for example) will probably have different efficiencies. one cab may sound louder than the other when plugged into a mono amp together. either get two of the same cab, try before you buy or use a stereo amp so you can adjust the volume of each cab separately.
  7. IvanMike

    IvanMike Player Characters fear me... Staff Member Supporting Member

    Nov 10, 2002
    Middletown CT, USA
    dont belive that a speaker can handle double the rms continously unless you want to recone the speakers
    and generaly, cabs of different efficiancies will sound ok together (this is based on real world experience - not specs)
  8. notanaggie

    notanaggie Guest

    Sep 30, 2003
    Anymore, you need to pay attention to power ratings.

    The various manufacturers started rating at the max they thought they could stretch to and then added a little. That's because we tended to believe them and so bought one over another partly based on that spec.

    Ok, so YOU and I bought on tone, but somebody did buy based on power, so the power got to be a key spec.

    Anyway, these days I would be doubtful of even the power rating, let alone double. And that isn't just on the Peaveys, Fenders and Crates, its everybody's specs.
  9. nonsqtr

    nonsqtr The emperor has no clothes!

    Aug 29, 2003
    Burbank CA USA
    Well, here's my 2c. If you're using a big cab and a small cab, you might want to think about bi-amping. How this works is, the low frequencies go through the big speaker (15), and the high frequencies go through the little ones (10's). This will require two power amps (unless you're using a passive crossover, which isn't likely if you're operating above a hundred watts), but the one that powers the small speakers can be a lot smaller than the low frequency amp. For instance, a GK 800RB uses 300/100 watts. Also note that your 2x10 is probably a 4 ohm cabinet, while your 1x15 is probably 8 ohms. Putting them in parallel will result in a 2.6 ohm load, which may be too low for many solid state amps. My recommendation would be, head over to your local GC and play around with a few of the biamps and see if you can get the sound you want. You can also use a preamp/poweramp combination to accomplish a biamp, I powered my practice rig that way for a few years, using an SWR Studio 220 for the high end, and a kilowatt Carvin power amp for the low end. If you end up having to put your two cabs in parallel, you'll need a power amp that can handle a 2 ohm load.
  10. thanks for the response so far..keep it coming.

    im trying to avoid anything complicated like biamping. most 15s and 2x10s ive seen have similar and comparible power handling. but it looks like ill probably go with a 4x10 anyway. anybody have any suggestions on bang for buck....especially as far as a 300 or so watt head...maybe less
  11. alexclaber

    alexclaber Commercial User

    Jun 19, 2001
    Brighton, UK
    Director - Barefaced Ltd
    But bass is never continuous. Even if you played overdriven sludgy eigth notes continuously the dynamic range of the signal would be at least 3dB and therefore an amp capable of producing 200W RMS would be at most delivering a continous equivalent RMS power of 100W. Hence if you drive a 350W cab with a 900W head (like my QSC/Acme rig) you'll struggle to burn out the drivers without running into amp clipping. Over-excursion is a different matter, but that's not solely related to amp power - the most important factor is the amount of power being delivered below the tuning frequency of the cabinet.

    Depends how different the efficiencies are.

  12. rumblethump

    rumblethump Supporting Member

    Mar 25, 2000
    Pioneer CA. 95666
    Ivanmike, I agree with your advice but would like to add:

    "say you have a head that can handle 2 ohms, you want to avoid using a 4 ohm cab and an 8 ohm cab with it as the 4 ohm cab will get twice the power and ya probably wont hear much outta the 8 ohm cab"

    In the case of a 2x10 4 ohm cab. Usually this means it has 2 8ohm 10s. When paired with a 1x15 8 ohm cab, each individual speaker receives the same amount of power. Combined impedence seen by the amp 2.67 ohms which is fine for a 2 ohm amp. I use this exact setup and don't find the 15 to have any less volume. I also like the option of being able to use either cab separately or together depending on the situation.
  13. mobax

    mobax Supporting Member

    Dec 31, 2002
    New Baltimore, MI
    Musician's Friend is advertising a GK700RB for $399.99. I think shipping is free.
  14. if i got a head that provides 350W of power at 4 ohms, and a 4x10 that could handle 400W at 8 ohms. would the head provide half the power, or would it overpower the cab?
  15. the head would probably put out something like 240 watts at 8 ohms
  16. well, if the speaker can handle 400W @ 8 ohms, how much would it handle at 4 ohms?
  17. The amplifier will "see" an 8 ohm load if that's all that is connected to it, in effect producing approximately half of its 4 ohm rating. If you wanted the amplifier to "see" a 4 ohm load you would need two 8 ohm cabs or one 4 ohm cab. The amplifier will not "care" unless you go under the 4 ohm rating.:D
  18. the speaker is 8 ohms no matter what, so it handles 400watts no matter what.
  19. nonsqtr

    nonsqtr The emperor has no clothes!

    Aug 29, 2003
    Burbank CA USA
    Well, the "power rating" can be based on many things, and different manufacturers rate (and test) their speakers differently.
    Some ratings are limited by the speaker voice coil, others are limited by the average heat dissipation over time, others are limited by maximum excursion, etc etc.
    So the particular power that a speaker will handle is definitely dependent on what's feeding it. For instance if there is a significant impedance mismatch in a solid state amp, it may not matter all that much as long as the speaker impedance is higher than the amp's minimum rated impedance. On the other hand, a significant impedance mismatch in a tube amp could be disastrous for both the amp and the speaker.
    To really answer the question, it's helpful to get to the specifics, about "which" speaker, and "which" amp, and so on. At some point it becomes confusing and inaccurate to think in generic terms.