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2.67 ohms?!?!

Discussion in 'Amps and Cabs [BG]' started by Wxp4759cb, Apr 21, 2001.


  1. Wxp4759cb

    Wxp4759cb

    Nov 23, 2000
    Kansas City, MO
    Is it dangerous to run my amp at 2.67 ohms. I have a 700 watt Peavey Firebass700 head. I'm running a 4 ohm 4x10, and a 4 ohm 1x15. Does this damage anything? Also are both cabs the same loudness? It seems to me that the 4x10 is louder, but it is hard to tell, because which ever one you are at ear level with sounds louder.
     
  2. Reid

    Reid

    Aug 25, 2000
    Oakville, Ontario
    Those two 4 ohm cabs make a load of 2 ohms, if you want to know if your amp can run it, RTFM or check on their website. Too see which is louder (assuming it is safe to run them both) place them on the ground a few feet apart, then it should be easier to tell which is louder.
     
  3. embellisher

    embellisher Holy Ghost filled Bass Player Staff Member Supporting Member

    The Firebass is rated at 700 watts @ 2 ohms, so should handle a 2 ohm load. I have heard stories about them going into protect mode(shutting off) when run at 2 ohms at very high volume for extended periods of time.

    If the 4x10 cab is truly louder than the 1x15, it is probably 6db(or more) more efficient than the 1x15. It is not uncommon for a 4x10 to be this much more efficient than a 1x15. Good 4x10s run between 101 & 110 db efficiency, but only the very best 1x15s get as high as 103 - 105 db.
     
  4. Wxp4759cb

    Wxp4759cb

    Nov 23, 2000
    Kansas City, MO
    I ment to say a 8 ohm 1x15. sorry.
     
  5. embellisher

    embellisher Holy Ghost filled Bass Player Staff Member Supporting Member

    If it is an 8 ohm 1x15 the 4x10 will definitely sound louder.

    1st, the 4x10 is probably more efficient.

    2nd, the 4x10 is pushing more air due to the increased driver area.

    3rd, the 4 ohms of the 4x10 have the capability of drawing twice as much power from the amp as the 8 ohms of the 1x15.
     
  6. Wxp4759cb

    Wxp4759cb

    Nov 23, 2000
    Kansas City, MO
    Dangit. Is it worth trading it in for a 4 ohm one? I didn't buy it someone bought it for me, and they didn't know there was any difference.
     
  7. Wxp4759cb

    Wxp4759cb

    Nov 23, 2000
    Kansas City, MO
    Also someone at a music store told me he could change it into a 4 ohm, by putting in a different resistor or something like that. Is that possible? Would that void the warranty?
     
  8. BassmasterG,

    The only ways you can modify the 15 to be 4 ohms is to change the driver or have the coil rewound. Putting a resistor in line works in theory, but it would have to be big enough to dissipate the power of the amp. That's a big resistor! And it would get hot. Real hot. Dissapating all that power through a resistor wouldn't give you any more volume anyway, because the extra power developed by the amp will just be dissipated by the resistor. This would DEFINATELY void your warranty. It probably won't make much difference in overall level if you get a 4 ohm 15, because it takes a lot of power to make a noticeable difference in volume. 410s tend to sound louder than 15's of even equal efficiency because they are better at reproducing mid frequencies than 15s are, and humans hear mids better than lows.
     
  9. what would the load be with a 8 ohm and a 4 ohm cab ???..
     
  10. Wxp4759cb

    Wxp4759cb

    Nov 23, 2000
    Kansas City, MO
    2.67
     
  11. Wxp4759cb

    Wxp4759cb

    Nov 23, 2000
    Kansas City, MO
    so what would be the volume difference if I got a 4 ohm to replace the 15. Also is my amp run in parallel? Each cab plugs into a seperate power outlet on the back. Wouldn't they draw the same wattage? I though they only differ if you daisy chain them.
     
  12. embellisher

    embellisher Holy Ghost filled Bass Player Staff Member Supporting Member

    They only differ in the amount of power that they draw if they are different impedance.

    It doesn't matter if you use the 2 outputs on the back of the head or if you daisy chain them, if they are both 4 ohms and your amp puts out 700 watts at 2 ohms, each speaker will get 350 watts.
     
  13. Wxp4759cb

    Wxp4759cb

    Nov 23, 2000
    Kansas City, MO
    How does the head know to send more power to one than the other?
     
  14. Hello BassMasterG.

    The head doesn't 'know' anything at all. It doesn't work like that.

    I'll try very hard not to get bogged down with electronics theory. So here goes.

    The impedance of the cab or cabs is what determines everything, taking into consideration the power in Watts that the head can develop across a load of given impedance (power = the voltage the head can develop across the cab or cabs multiplied by the current it can supply. Watts = Volts x Amps is a mathematical way of saying the same thing). It's all a question of what's known in the trade as Ohm's Law.

    Embelisher says the head will run 700 Watts across 2 Ohms. OK, say we have two, 4 Ohm cabs connected in parallel: the total load presented by the cabs to the head thus = 2 ohms.

    The head will deliver the same (RMS) voltage across both cabs. (That RMS voltage is the signal from your bass, amplified by the head by whatever amount.) That means, because the cabs are 4 Ohms each, the same electrical current will flow through each one: the total current from the head is shared equally between the two cabs because they are the same impedance each. The important thing here is that it is the impedance of the cab that determines what current flows from the head (and so the quantity of Watts developed), the head does not determine the current.

    Conversly, if the cab impedances are unequal, the head will deliver different currents into each cab. And, because the head delivers the same RMS voltage across each cab, the quantity of Watts given out by each cab will be different. Again, the impedance of the cab determines what current flows, not the head.

    The end result with cabs of different impedances is a different amount of Watts being developed by each, and more Watts being given out than either cab could deliver as an individual.

    To conclude - hoping that it all made some sense to you - is that the head does nothing more than deliver Watts as the product of voltage and current to the cab or cabs. The cabs determine the total impedance load so they determine the maximum amout of Watts the whole system can generate.

    Hope that makes some sense.

    John
     
  15. Nikehawk

    Nikehawk Guest

    Jul 29, 2001
    Yorkville, IL, USA
    Ok, I got the Firebass and the 4 ohm 410, I want to get the 8ohm 115 as well...and I understand this will produce 2.67 ohms, which is fine with me...but is it fine with my amp? Ive heard conflicting stories about if this is good...The firebass has parallel jacks on the back...so if I get the 15 and produce the 2.67 ohm load will my amp go haywire soon because of the decimal numbered load?
     
  16. Luis Fabara

    Luis Fabara

    Aug 13, 2000
    Ecuador (South America)
    Audio Pro - Ecuador
    Dont worry Nikehawk.
    The Decimal thing is almost meaningless.

    Why?
    Here is the answer:

    1) Impedance such as 4 or 8 Ohms is just Nominal impedance, actually the resistance of a speaker varies depending the frequency it reproduces, so the amp actually is never seeing a flat 4 or 8 Ohms.

    2) The 2 Ohms Load in the Amp is the MINIMUM Load it can handle before it fries itself because of the ammount of current that is being pulled by the speakers/drivers. So you can virtually use anything above 2 Ohms Nominal Load.

    3) 2.67 Is Fine as long as the Head says 2 Ohm Minimum. (This is the short answer)
     
  17. Munjibunga

    Munjibunga Total Hyper-Elite Member Gold Supporting Member

    May 6, 2000
    San Diego (when not at Groom Lake)
    Independent Contractor to Bass San Diego
    I just want to stick my nose in here and congratulate all you folks in this thread for your persistence in being helpful. Good info. No, I'm not being sarcastic, but just this once.
     
  18. It is OK to run the 4 ohm 4x10 and the 8 ohm 1x15. If you had a hard time telling if one was louder than the other, then they are balanced well enough. Besides, if you turn the bass EQ up a little they will probably sound equally loud becuase low frequencies will be handled by the 15 better than the 4 10s (probably - it depends on the cabinet specs). So the relative volumes of the cabinets will vary according to the frequency of the note you are playing. Sometimes the 4x10s will seem louder (on the higher notes). Sometimes the 15 will seem louder (on the lower notes).

    All of the info given by others in this post is accurate, but you need not get bogged down in the numbers. If it sounds OK to you, then it's OK. I wouldn't start re-coiling drivers or replacing them unless a could hear that there is a problem.
     
  19. Steve S

    Steve S

    Jul 26, 2000
    Luis,

    I have the Acoustic Clarus amp which can handle 2 ohms. Does this mean that I can hook up 8 ohm and 4 ohm cabinets and not worry about my amp frying?