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ok amp people, tell me why this won't work...

Discussion in 'Amps and Cabs [BG]' started by superbassman2000, Dec 17, 2004.

  1. ok, i haven't actually tried it yet, because i am almost certain it won't work. but i am just thinking in thoery...so here it goes...last night i was thinking about ohms and all that good stuff, and i was wondering...what if you took a 4 ohm resistor like this one and put a 1/4" plug on each side and plug it in between a 8 ohm amp and a 4 ohm amp. from what i remember in my science class, the resistor and the cab would be running in series at a total load of 8 ohms right?
    so would this work? or do i have no idea what i am talking about? :D

    so basically it would be a little box that i could run in between an amp and a cab that will allow for a cab of fewer ohms run safely with an amp of higher ohms...

    so...explain to me why this won't work!
  2. thinking that resistance and impendance are two different things both measured by ohms! and you're getting them confused.
  3. TrooperFarva


    Nov 25, 2004
    New City, NY
    Well, the resistor is rated for 10W. So if you have a 10W amp, in theory, that'd work. But since you want to drive 2 cabinets, i doubt its a 10W amp, because that wouldn't work anyway. I think if you tried it, the resistor would bust. I think, in theory, that if you found a resistor that could handle the wattage of your amp, it would work. But from my experience, resistors don't go anywhere even close to that range of power. Thats just my thinking on it, I could be completely wrong.
  4. TrooperFarva


    Nov 25, 2004
    New City, NY
    Impedance, I think, is the overall measure of resistance, capacitance, and inductance in a circuit. So adding a resistor in series will increase the Impedance the same amount. I think. Again, I could be wrong.

  5. Yes, this would provide you with a 4 Ohm load, BUT (there's always a 'but' ;)) you'd need a resistor that could safely dissipate at least half the amp's power at 8 Ohms. Such resistors do exist ( I have a couple of 225W ones) but they're big, expensive and they get hot. I'm not sure it's really a feasible thing to do.
  6. billfitzmaurice

    billfitzmaurice Commercial User

    Sep 15, 2004
    New Hampshire
    Owner, Bill Fitzmaurice Loudspeaker Design
    Assuming that the resisitor didn't instantly melt down (which this one would) one half of the power being produced by your amp would be dissipated by the resistor as pure heat, so your amp would have to produce twice the power to achieve the same output from the speakers as without the resistor.

    Tom Scholz produced a device called the Power Soak to do just this with a guitar amp, the intent being to allow the amp to go into high distortion overdrive mode while limiting the power to the speakers (Marshall also made somthing similar). I doubt if you want to do that on bass.
  7. ok, thanks guys,
    i knew it couldn't be that simple, because otherwise it would have been invented already!
  8. BillyB_from_LZ

    BillyB_from_LZ Supporting Member

    Sep 7, 2000
    You really just need to get an 8 ohm woofer for that Peavey cabinet of yours... :D
  9. Toasted


    May 26, 2003
    Leeds, UK
    That'd be a good idea. Could you run two 4 ohm resistors in series, so they made a combination of 4ohms, but could handle 550 watts?

    I dunno, ust throwing ideas about.
  10. Tim__x


    Aug 13, 2002
    Alberta, Canada
    That would then be 8 ohms, resistances in series add.
    If you put let's say 500, 2 watt 2.2k ohm resitors in parallel you would get a 1000 watt 4.4 ohm resistor that would be suitable for this fruitless endevouer.
  11. JOME77

    JOME77 Supporting Member

    Aug 18, 2002
    Even if you got a resistor that was rated at the required wattage it wouldn't accomplish what you're after. Half of the wattage would be disipated across the resistor and your speaker would only see 1/2 the wattage (assuming an 8 ohm speaker and 8 ohm resistor). Think in terms of how a power soak works. It allows you to basically convert a 100 Watt amp top a 25 or 50 Watt amp (in terms of volume) by "soaking" a certain percentage of the power via the high wattage resistors.
  12. asmith


    Nov 19, 2004
    The previous posts are right - the short of it is that if you got something that would make the "ohm count" what you're looking for, it wouldn't produce the same sound because other things go away also. The fun part would be seeing the resistor or whatever melt or explode. :) The idea of getting an 8 ohm cab (posted above) is a good solution IMO.
  13. NJL


    Apr 12, 2002
    San Antonio
    hmmm, i wonder if this is how accugrove does it.....
  14. Hounddog

    Hounddog Supporting Member

    Dec 2, 2004
    Southern, Illinois
    Sadowsky Featured Artist
    Matt and Trooperfarva are right Impedance is a total measurement of Resistance, Inductive reactance and capacitive reactance.

    While Ohm's Law applies directly to resistors in DC or in AC circuits, the form of the current-voltage relationship in AC circuits in general is modified to the form:

    where I and V are the rms or "effective" values. The quantity Z is called impedance. For a pure resistor, Z = R. Because the phase affects the impedance and because the contributions of capacitors and inductors differ in phase from resistive components by 90 degrees, a process like vector addition (phasors) is used to develop expressions for impedance. More general is the complex impedance method.

    Using complex impedance is an important technique for handling multi-component AC circuits. If a complex plane is used with resistance along the real axis then the reactances of the capacitor and inductor are treated as imaginary numbers. For series combinations of components such as RL and RC combinations, the component values are added as if they were components of a vector. Shown here is the cartesian form of the complex impedance. They can also be written in polar form. Impedances in this form can be used as building blocks for calculating the impedances of combination circuits like the RLC parallel circuit.

    Source: A Hyperphysics Website
  15. so what about the 2 10" speakers?
    or are you saying just replace the 18" with a new 8 ohm 18" and it'll be a 8 ohm cab, and i'll be happy? :)
  16. BillyB_from_LZ

    BillyB_from_LZ Supporting Member

    Sep 7, 2000
    Take a look at what I wrote about this in the other thread...

    I basically said that at frequencies above the crossover frequency, the impedance of the 10s might (emphasis on might as I don't know for sure) be well above 8 ohms as most speakers exhibit their minimum impedance at the low end. At any rate, if used with a passive crossover, the 10s will always have a capacitor in series with them and it has a reactance of at least 4 ohms at the crossover frequency (assuming that the 2x10 section is 4 ohms and the crossover is 6 dB/octave).
  17. geez billyB you are really smart! you should come up to wisconsin to teach me in the art of amp! anyhow, i will start looking for a replacement 18, and i will see if i can find out about those 2 10s, and what impedence they run at...thanks for all the help guys!