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Bass Head and Cab Question

Discussion in 'Amps and Cabs [BG]' started by ckdhaven, Jul 24, 2012.

  1. ckdhaven


    Jul 19, 2012
    Cedar Rapids IA
    Is there a "rull of thumb" bass players use when picking a speaker cab for the amplifier head????

    My biggest experience comes for live sound reinforcement and we make sure the amps are 25% to 35% (at least) rated at more wattage than the speaker cabs at the same Ohm rating...

    Is this true for bass amps and cabs too?
  2. Hactar


    Sep 25, 2011
    Boulder, CO
    Well, here on TB, seems like this is the sort of topic that starts stuff, sometimes bad stuff... :)

    If you are smart with your volume knob, and you know when to stop pushing a cab, having a bit more wattage on hand can give a nice amount of headroom and such.
  3. barryaudio


    Feb 9, 2012
    Authorized Builder: fEARful bass, greenboy designs, Bill Fitzmaurice
    At high power, a lot of the same rules for SR apply to bass amps. I agree that amp headroom is important for bass. So is high pass filtering. If you are buying a bass amp, most of them have filtering built in. If you are going the preamp-poweramp route, look into a model poweramp that has DSP built in. You may also be able to put a limiter on the amount of power going to your cabs, like in SR work. What sort of setup/application are you thinking of?
  4. ckdhaven


    Jul 19, 2012
    Cedar Rapids IA
    I am looking at a variety of heads from Ampeg to Markbass to GK>>>

    I'm thinking 500w + "Short Stack" .... I already have a Radial Bassbone DI... so a DI on the amp isn't 100% needed.

    We are not a huge band and we are good at keeping stage volume down to reasonable levels. However my little Ampeg BA115 just isn't "cutting it" anymore.
  5. Just be aware too that the wattage ratings of cabs is only the thermal rating, and really is of no use in bass amplification.

    You need to be more concerned about low end displacement limits of the speakers which can be half that of the thermal ratings.
  6. ckdhaven


    Jul 19, 2012
    Cedar Rapids IA

    If it's not too much trouble.. Can you explain this?

    Or would it be simpler to make a recommendation for a cab for these heads... I like the idea of a 4x10 cab...

    Markbass Little Mark 800
    Ampeg SVT-7Pro
    GK MB fusion...
  7. For my tastes I would totally rock a 7-pro and a fEARful 15/6. The combo sounds great, and the cab isnt going to go "pop" with that head even at stupid volumes.

  8. I am far from a speaker guru, but I'll try.

    Speakers make sound by moving air like a piston (displacement). Low frequency output is limited to the speakers ability to move. When you go past that, you can cause mechanical damage to the speakers cone (over excursion) or to the voice coil and former itself by it slamming against the backplate.

    In most commercially available speaker cabinets, that can happen at half it's thermal rating depending on how much low end content you use.

    So basically having tons of headroom in your amp may be a waste (ie: 500 watt cab powered by a 1500 watt amp would be overkill because most likely the cab will start sounding bad at around 250-300 watts).
  9. +1
  10. barryaudio


    Feb 9, 2012
    Authorized Builder: fEARful bass, greenboy designs, Bill Fitzmaurice
    Maybe not a guru, but well put!

    As stated, most commercial bass cabs mechanical limits will come into play before thermal. If you are using higher end/custom gear it may be the other way around. Certainly using a 1500W amp in a 500W cab is absurd, but you were only suggesting 25% over, not 200% over. Probably a better way to state headroom is to use an amp that will only be used up to 75% of its max rather than tying it to a speaker cab spec.

    When your speakers will reach their mechanical limits depends on a lot of factors in addition to power, i.e. use of high pass filtering, EQ, playing style, and effects.

    Amp headroom is good to think about. So is being under your thermal and mechanical limits of your speakers. If possible, it is first good to identify how loud you need to be, then choose amp+speaker combination that will get you there. I think you have some good ideas for amps that will probably all be perfect fits for your situation. You need to now find a cab that will work well with those. I would suggest you start with a single 8 Ohm cab and scale up from there id necessary. Of course, I like CL400Peavey's suggestion of a 15/6. :)
  11. bw79072


    Nov 11, 2010
    I see 'displacement limited to xxx watts or thermal limit of xxx watts on most of Eminence's cab designs...is there a way to figure that factor? If so, could someone please explain?
  12. JimmyM


    Apr 11, 2005
    Apopka, FL
    Endorsing: Ampeg Amps, EMG Pickups
    Having more power than your cabs can handle is for people who know what they're doing. So many bass players have proved themselves to have zero control of themselves and will turn up and up and up till they blow their cabs if given the opportunity, especially newbs.
  13. Korladis

    Korladis Banned Supporting Member

    No. The general rule is to use your ears, because cab power ratings are typically not very reliable.

    Personally, I prefer to use cabs that can handle more power than my head puts out. Preferably way more. My amp puts out 180 watts, and my cab probably handles about 400. In the not too distant future, I'll be using that same head with two cabs, which combined would probably handle about 800 watts.

    While I could also easily blow up the speakers in my cab by using way too much low end, the risks of speaker damage due to regular playing are still considerably less than they would be if my head put out more power.

    In short, I don't want how loud I can turn up my amp to be extremely limited by how much power my cabs can take. So I prefer hardier cabs with a less powerful head, especially since I tend to have an overdriven sound, which can make it harder to hear when speakers are reaching their limits.

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