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2 inputs at 8 ohms? or one mono at 4ohms? which is better?

Discussion in 'Amps and Cabs [BG]' started by nickname, Feb 17, 2006.


  1. nickname

    nickname

    Jan 22, 2005
    I finally matched up my Mesa/Boogie roadready cab with a Mesa Boogies Bass 400+. Im just curious as to which would be the best way to send the signal to the cab. split (2 plugs), with a low and a high input at 8 ohms, or mono (1 plug) at 4ohms?

    Thanks guys
     
  2. AxtoOx

    AxtoOx

    Nov 12, 2005
    Duncan, Okla.
    I'm confused. How many ohms is your cab? Normally if the have 2 1/4 inch jacks in the back, it's an in and out so you can run 2 cabs. If it's a 4 ohm cab, use a speakon or it's usually the jack on the top or left if you look at it.
    If I'm wrong, like I said I'm confused.
     
  3. TrooperFarva

    TrooperFarva

    Nov 25, 2004
    New City, NY
    I think he's talking about one of these deals

    I think if you ran into the two 8 ohm connections, the resulting load to the 400+ would be 4 ohms anyway, so save yourself a cable, and just run straight into the 4 ohm jack on the cabinet. the other jacks are more for if you want to use separate power amps for the top and bottom speakers, i think,
     

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  4. nickname

    nickname

    Jan 22, 2005
    well here is what i've found by trying both.


    if i do just the straight 4 ohms into the into input, it does not get as much power as if i were to split the load into the top and bottom cabinets. this road ready i have has a 15 in thelower end, and a 10 and 2 6's. When i do the split, i don't have to turn up the master as much. i can leave it at a bout 4 and its comfortable. but when i just do the one input into 4 ohms, i have to turn the volume to around 7.

    make sense? can sombody clarify this more for me?
     
  5. basspunk2005

    basspunk2005

    Jan 31, 2005
    England UK
    Im no wizard or anything, but maybe its louder because you got it runing less from more places?insted of more from a lesser amount of places?i dont really understand 100% but i think thats what may be happening?dont go on my word though lol
     
  6. Herman

    Herman

    Dec 25, 2005
    Lynchburg, VA
    When you do the split, which outputs are you using on the amp - 4 or 8 ohm?
     
  7. nickname

    nickname

    Jan 22, 2005
    the split is 8, so i run it off the 8ohms output off the 400+. when i run it into the mono 4ohm, i obviously run a 4ohm load into it.
     
  8. Herman

    Herman

    Dec 25, 2005
    Lynchburg, VA
    OK. I think you should be using the 4 ohm jacks when you run two cables, one to each "half" of your cabinet. Unless I'm missing something, you've driving a 4 ohm total load either way - mono or split - so you have to use the 4 ohm outputs on your amp either way.

    The 400+ manual says:
    "But if you use two 8-ohm cabinets, they will be
    operating in parallel and the total load will be 4 ohms. Therefore, plug each cabinet into a
    4-ohm jack."

    In your case (I think) the "two 8-ohm cabinets" are the two halves of your cabinet.
     
  9. seanm

    seanm I'd kill for a Nobel Peace Prize! Supporting Member

    Feb 19, 2004
    Ottawa, Canada
    It makes no sense :confused:

    The cab has been setup to be bi-ampable. This means it can look like two cabs. I would guess that the 15 and the 10 are grouped togeather and the 6 sixes are grouped togeather.

    So if you bi-amp, you run the highs into the 6s and the lows into the 15 + 10. Since the 400+ is not biampable, you should just run into the 4 ohm input.

    Running two plugs into the two 8 ohms inputs gives you 4 ohms. No difference from plugging into the 4 ohm input.

    So it is six of one, half a dozen of the other. You *should* hear no difference.
     
  10. Herman

    Herman

    Dec 25, 2005
    Lynchburg, VA
    I think you're right except that he was using the 8 ohm outputs when he was running split and the 4 ohm output when running mono. Should have been using 4 ohm outputs in both situations. Running from the 8 ohm outputs with a total 4 ohm load risks damaging the amp.

    From the manual:
    "The amp will produce its full power at all of these mpedances, provided that the total impedance of your speaker cabinets is matched to the output(s) used. (Slight mismatches are not a major problem, but they will cause slightly lower output and may shorten tube life.)"
     
  11. seanm

    seanm I'd kill for a Nobel Peace Prize! Supporting Member

    Feb 19, 2004
    Ottawa, Canada
    I am assuming that the two 8 ohms outputs are in parrallel. Every amp I have seen does this. So running two 8 ohm cabs from the two should be ok.

    However, I do not know this for sure! I can't think of any other reason for two 8 ohm speaker connectors though.
     
  12. Herman

    Herman

    Dec 25, 2005
    Lynchburg, VA
    Normally I'd agree with you but the amp's manual says to use the 4 ohm output jacks when driving two 8 ohm cabs in parallel.

    That's a good point - maybe the manual's wrong.
     
  13. seanm

    seanm I'd kill for a Nobel Peace Prize! Supporting Member

    Feb 19, 2004
    Ottawa, Canada
    I looked at the manual. Basically it sucks. For such an expensive amp, you think they could at least write a real manual. It is way too vague.

    I am guessing that they are warning you that if you go from the amp to an 8 ohm cab. Then 8 ohm cab to 8 ohm cab, you need to plug into the 4 ohm output.

    But your guess is as good as mine, since the manual dosen't go into details.
     
  14. Herman

    Herman

    Dec 25, 2005
    Lynchburg, VA
    I was going to say the same thing about the manual - worst one I've ever seen.
     
  15. nickname

    nickname

    Jan 22, 2005
    so just to clarify; the image that someone posted early, is pretty much the same as mine.

    the 15" is connected to the bottom 8ohm input and the 10 and two 6's are connected to the top 8 ohm input.

    and if i got this correct, i should be running 4 ohms into each 8ohm input on the cab?

    and there should be no difference plugging just one jack from the 4 ohm output into the 4 ohm input on the cab.. correct?

    what is the purpose of splitting then? only if i use a bi-ampable amp? i used to own a svt 4 pro, and it has a bi-ampable option, which actual said which was high and which was low.

    so if i am splitting the load, 4 ohms into each, because the 400+ isnt a bi-ampable amp, means splitting the load really isnt doing anything different?

    so i should just stick to the one "mono" 4ohm input on the cab and just run it from the 4 ohm output on the back of the 400+?

    hehe this is fun isnt it.

    thanks guys.
     
  16. seanm

    seanm I'd kill for a Nobel Peace Prize! Supporting Member

    Feb 19, 2004
    Ottawa, Canada
    Yes. This is by far the safest option. You are running mono, you should use the mono input.
     
  17. ricplyrz

    ricplyrz

    Dec 26, 2005
    "I'd kill for a Nobel Peace Prize"......

    Just buy one...their cheap.....
     
  18. Herman

    Herman

    Dec 25, 2005
    Lynchburg, VA
    In your case, there's no reason to use two outputs from your amp.


    Yes or two separate amps.