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wattage ohms ect

Discussion in 'Amps and Cabs [BG]' started by wotnwhy, Jun 6, 2002.

  1. i've been looking up on amps and heads and there are a few things i'm not quite sure about:

    if an amp head is rated at, say 400 watts should the wattage of the cab(s) be 400 hundred as well


    is it better for the cab(s) to be rated more (say 6/700 watts) or less (say 2/300 watts) than the amp

    and the other thing is ohms, i've seen amps rated mostly at 4 or 8, and some can be changed, but i just don't understand wot thier on about,

    wots best and wot's worst, or are they just defferent, any help would be greatly appreciated


  2. Well, If your amp is rated @ 400W at say 8Ohms, then you could get an 8ohm cab rated for 400W and be ok, but then again, I've been told that using 115% of the power INTO the cab is accepable(called headroom)as long as you don't drive the cab with too much volume.....I'd try to find cabs that are 8 ohms, and a head rated for use of 4 ohms, since the volume can be great....
  3. ok, i think i see,

    so if you have a 400 watt head at 4ohms,

    a 450 watt cab at 8ohms would be the best choice.

    or is that completely wrong? :D


  4. monkeyfinger

    monkeyfinger Moderator Staff Member Supporting Member

    This is not the best choice. If the head produces 400 watts @ 4 ohms, it probably only produces ~260 watts @ 8 ohms. This may be too little gain for you. To make up for the low gain, you would likely try to drive your amp harder. This could put the amp into clipping. Clipping an amp is much more likely blow the speaker than driving to much linear, (not clipped), power to the amp.

    I think you are better off with more amp than speaker. So long as the amp is powerful enough that you would only run it at about 60% max gain under normal circumstances with a solid state amp. With a tube amp, you want to run closer to 80%.
  5. so something like a 400watt head with a 240 watt cab is the best bet (or a 360 watt cab if it's a tube amp)?

    yay or nay?



    p.s. so if an amp is 400 watts at 4 ohms can you change it to 8 ohms and have 260 watts or something, you see i really don't know anything about ohms and stuff, is there an article somewhere on the site (or somewhere else on the web) that explanes about it 'cos i'm sure you don't want to waste your time telling me something thats already been said.
  6. My view would be that you make sure the cab can handle the head's output.

    For example, if the head will deliver 400 Watts RMS into 8 Ohms, then the cab should be able to handle 400 Watts RMS and, of course, be rated at 8 Ohms if the head is to realise it's maximum permitted output should you wish to do that. Likewise, if the head will deliver that output into 4 Ohms then the cab should be rated for the same output, but be rated at 4 Ohms this time.

    There's always a bit of give and take with this - what might be called "headroom" - but a loudspeaker is an electromechanical system that can easily be damaged beyond repair by musicians with a flair for having the Volume pot wound up:eek:

  7. What you need to do IMO is put the speaker wattage issue aside for a moment and first make sure that you have enough *amp* for your playing situation. That is, one that gives you as much volume as you'll need without having to be run flat out (unless for some reason that's what you want). This could be 200 W, 500 W, or 1000 W, depending on your situation. The ratio of the amp output to speaker handling, within reason, isn't really all that important IMO. It's the *ratio of the amp power you have on tap to the power you need in playing your gig* that's more important.

    Once you're sure you have enough amp, then find a speaker that (1) has the sound you like, and (2) can handle *the levels of power that you use*. Since ideally you won't be diming your amp, you don't necessarily have to get a speaker that's rated for the full amp output. That is, you can often use, say, a 250 W speaker with a 400 W amp. This quite often works well. But it's not really *better* to do this, all else being equal. It doesn't protect you from clipping, as is sometimes asserted. You could just as easily use a 600 W or 800 W speaker with a 400 W amp--provided, again, that a 400 W amp is big enough for your needs as described above--and in fact this would give you more protection should you start getting overenthusiastic with the volume knob.

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