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Speaker Load Options - Will Resistors Work?

Discussion in 'Amps and Cabs [BG]' started by xray, May 3, 2010.

  1. xray


    Feb 15, 2009
    Kona, HI
    First, can you use a speaker jack, wire and an 8 ohm resistor as a load on a speaker to make it 1/2 of what the cab is rated?

    If yes, do they sell shunts you can plug into speaker cabs to get this effect?

    It may be a stupid question, but it's never been asked - I checked!:confused:
  2. Sorry, wont work.
    You will lower the cabs impedance, but the extra energy this extracts from the amp will only heat up the resistor. So nothing to be gained here. In fact, since amps rarely deliver twice the power if you halve the impedance, it will probably be a net loss.
  3. xray


    Feb 15, 2009
    Kona, HI
    So there's no way to emulate a speaker load - bummer - I appreciate it though 'cause I know very little about trons.
  4. The question is why? Do you want to turn your cab into a space heater? Half the power of a 400 watt cab is 200 watts of resistor and then the speakers are limited to 200 watts for the 400 watt total.
  5. johnk_10

    johnk_10 vintage bass nut Supporting Member Commercial User

    Feb 16, 2008
    Thousand Oaks, CA
    John K Custom Basses
    even if you could emulate one, if it doesn't make any sound, its useless (and harder on your amp).
    IMO, the best, and simplest way to emulate a speaker is with another speaker.
  6. Speakers are a lot more than resistors to emulate with an audio signal. Resistors can't emulate the INDUCTANCE or IMPEDANCE of a speaker.
  7. Bassamatic

    Bassamatic keepin' the beat since the 60's Supporting Member

    If you just want to drop 1/2 the power you can do this, but you would need a HUGE power resistor! It would cost more than another cab. And WHY?
  8. ehque


    Jan 8, 2006
    The OP needs to answer this question first.
  9. xray


    Feb 15, 2009
    Kona, HI
    Not trying to reduce amps power!!! Trying to match a cab to an amps impedance, but based on the feedback this won't work. That's why the analogy of using resistors to explain how ohms law work when you're placing cabs in parallel or series is not totally true. Obviously, based on your comments, a speaker cabinet represents more than is a resistive load. So based on what you've said; you need to compensate for the resistance, impedance and inductance which only a speaker can provide. Thanks
  10. ZolkoW


    May 8, 2006
    Hungary, EU
    are you using an all-tube amp?
    if not, why trying to match the impedances?

    if the first is true, I think, a big-watt (we need a couple of hundred watts!!! and it's gonna be hot!) resistor will work, as the speakers behave at lower frequencies (where most of the energy occurs) quite like the resistor.
    Once I did a load test on my amp, I used a 24V truck bulb, which was about 8 ohms... played some notes to my looper, then let the rig alone with the flashing lightbulb for an hour :)

  11. He could always use a carbon pile.


    A 200 or 300 Watt resistor is, like you say: "HUGE".

    Think of a 200/300 Watt light bulb. Bright and hot comes immediately to mind. And big.
  12. David1234


    Jun 1, 2004
    Sydney, Australia
    Endorsing Artist: SWR Amplifiers
    The law remains true (ohms law, and combining resistances), but you don't benefit from it since the resistors you add will consume all those extra watts you're asking your amp to make. You'll get hot resistors and no extra sound.
  13. It can be done, but not with a resistor. You need an output transformer just like those on tube amps. Glockenklang used to make one for this purpose ( maybe they still do ).
  14. To what would to transformer output legs go? A transformer if it's not actually working at doing something is just a slight parasitic load and unless it's sending power somewhere - it's just idling. Right? Once it builds a field it is saturated and needs "relief".

    If you are saying they use an output transformer, it would likely have to be reversed (input to secondary windings) and still there's the problem of dumping the (now primary) load somewhere.

    Was that Glockenklang transformer just being used as a a dummy load or what? Maybe it ran a hotplate for heating their Schnitzel for a dinner break.

    This sounds real close to perpetual motion to me. But at this point I will keep an open mind. I'm not too old to learn something new.
  15. What are these cabs your trying to match anyway? From a scientific standpoint all this might not be worth the hassle because the two cabs together might well cause so much phasing that there won't be a decent increase in volume and/or you'll get a really unbalanced sound. Either way it could potentially sound like a big bag of arse, what are you working with?
  16. I think of it this way ::: he asked a question (silly or not) and if we can actually see and tell what we know - we are all learning something by this exercise - even if it's futile and won't work.

    The fun is the challenge to find a cohesive answer. I think that's happening and we are all better for it.

    I am, anyway. I certainly would not shoot someone in the foot for asking a question like this.

    You are, of course - very right here - it isn't likely a good idea to mix/match things like this - but hey - it's fun to see if it sticks to the old cave wall!
  17. ehque


    Jan 8, 2006
    Basically you use a 2:1 winding transformer connected between your amp and your cabinet. The impedance of the cab (that the head sees) can now be doubled or halved depending on the way the transformer is plugged in. You'll need quite a big transformer.

    If the OP has a 500W/4ohm, 300W/8ohm head (for example) and is trying to erk out the last bit of power, resistors won't work (changing the impedance to 4 ohms for the 200W extra power will result in half the power going to the resistor, which DECREASES sound output, not to mention will require a stonking big resistor).
  18. OK - that makes sense. I thought he was stating to use the extra transformer as a load instead of another speaker or cab, but I see it is being used as an inverter for a virtual Ohms decrease to fool the amp.

    Still - there's gonna be a hotplate running somewhere from all the heat (from hysteresis?) radiation.
  19. James Judson

    James Judson

    Jul 16, 2009
    Yes you can do that and it will work. Finding an 8 ohm resister with a rating of 100's of watts will not be easy. The question thats already been asked is "why"? You could just turn the volume down half way.

    gui****s with that big ass tube amp frequently do this all the time. The device they use is call a "power brake". It allows them to crank that amp up so they get their "tone" but limit the noise output to the speaker. It allows for impedance matching so amps and speakers are all happy.

    For those of you that like to use big words like impedance, inductance, ohmage etc. Let me give some definitions.

    Resistance is constant. It reacts the same to AC or DC. Measured in "ohms".

    Inductive reactance (coil of wire or inductor) acts like resistance but changes with frequency. It is measured in "henrys" but the ohms go up as the frequency goes up.

    Capacitive reactance (capacitor) acts like resistance but changes with frequency. It is measured in "farads" but the ohms go down when as the frequency goes up.

    Impedance is a combination of resistance, capacitive reactance and inductive reactance. It is measured in "ohms".

    Ohms law is basically simple but takes a lot of study to understand.

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