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Another 'which cab?' post!!!!!!

Discussion in 'Amps and Cabs [BG]' started by Vipa, Sep 10, 2005.

  1. Vipa


    Aug 11, 2005
    Ok.... I have the Ohm thing nailed and know where I'm going along those lines. What I can't find is any clear guidence on power output v power handling.....

    SWR Power 750 power amp arriving next week to go with my Bass Pod XT Pro as a pre (no discussion necessary, I love my BP and am a huge fan of modeling) and now I need a cab or two to go with it.... but... I'm getting confused and want to get it right!

    Was originally going GK but then decided to go down the pre-power route.

    My thoughts were... get a 4x10 then later add a 1x15 for larger venues but want to stick with SWR and am getting confused with the numbers... please help...

    Power 750 = 750w @ 4 ohm
    450w @ 8 ohm

    The Goliath III (which would be 1st choice) is 700w handling and available in either 4 or 8 ohms.

    Following my original line of thought I would be looking at an 8ohm cab to be followed by a son of bertha 1x15 8 ohm cab at a later date BUT.....

    that means for the majority of time I'm gonna be running the 700w cab with a mere 450w amp... is this ok? Will it cause any issues?

    The obvious option is to go for the 4 ohm Goliath as then I would be running the 700w cab with 750w from amp but this then causes other issues if I come to add a son of bertha 1 x 15 later.....

    the amp would handle the combined load of 2.67ohms but due to the different impedances the amp would again be underpowering the cabs...

    Help.... I'm getting really confused with this.... :help:

  2. There's no such thing as underpowering cabs unless clipping comes into play. Go with the 8 ohm Goliath. The 450watts into it should be enough for your typical smaller gigs.
  3. Vipa


    Aug 11, 2005
    This is the bit i don't understand....

    I always thought of it a bit like cars and engines..... i.e. the power handling of the cab is sort of like the weight of the vehicle and the output of the amp like the power output of the engine...

    a 100BHP engine in a 5 ton car is gonna struggle like hell to get the thing moving very well whereas a 500bhp engine would get things going with ease with power to spare and therefore have more control rather than having to run flat out just to make things work?

    Will a 100w amp struggle to work a 1000w cab?

    Using the above analogy surely I'm best going for the 4ohm version then the amp will be running far more efficiently and somewhere down the line this has to filter through to sound quality.... or am I missing the point here?

    But then.... what problems or issues am I going to encounter (if any) by combining a 4ohm goliath (700w) and an 8ohm son of bertha (350w)

  4. Lowtonejoe

    Lowtonejoe Supporting Member

    Jul 3, 2004
    Richland, WA
    No. If you want to think of it in car terms power is the gas pedal and the speakers are the engine.

    The more gas, the faster the engine revs.

    Now lets say your motor built up to consistantly turn 10,000 rpms.

    Stepping on the pedal enough to turn the motor at 1,000 rpm wont hurt anything. That's the 100w amp into a 1,000w cab.

    Turning it at 1,000 rpm won't hurt it but if you want, you can step on the gas until you reach 10,000 rpm (1,000w rms). That's what happens when you get a bigger amp.

    Now...if your motor was only designed to go up to 4,000 rpm (400w rms) and you take it up to 10,000 rpm (1,000w rms) you will blow something, if not immediately, very quickly. You CAN get away with overrevving a motor once in a while. Same thing with a speaker. That is known as the 'peak wattage'.

    Running an amp at 4 or 8 ohm has no effect on the sound quality as long as the amp CAN run a 4 or 8 ohms! Most do. Also, if an amp is rated to run at 4 or 8 ohms running it all day at 8 ohms won't hurt it. It's about if you NEED the power.

    Are you sure you only want to be able to use one cab with the amp? That's why it is much more common to get 2 - 8ohm cabs. If you need the power, you have the cabs to get it. If you don't need it, you can just use one cab.

    You will NEED to be sure that your amp can run at a 2.67 ohm load.