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Difference between ohms?

Discussion in 'Amps and Cabs [BG]' started by smurff77, Jun 30, 2007.

  1. smurff77


    Apr 5, 2007
    As a newbie I am not sure whether I should buy a 4ohm or 8ohm cab. What is the difference regarding an extension cab...?
    And can you explain RMS.
  2. TrooperFarva


    Nov 25, 2004
    New City, NY
  3. smurff77


    Apr 5, 2007
    Hey, go easy on me...I'm new, female and blonde!
    Read the faq but still not sure so I will ask:
    If I buy a 350w 4x10 combo or separates totalling the same, is it an 8ohm or 4ohm speaker cab I add without losing volume?
    Or, have it got it terribly wrong?
  4. lazyone2


    Jul 27, 2006
    new jersey shore
    Hello Smurff,
    What is the OHM rating of the amp you are buying. That will be the deciding factor in the cabs you buy. Two 8 ohm babs will equal 4ohms at the amp. Two 4 ohm cabs will equal 2 ohms. What equipment are you looking to buy?
  5. rockwarnick


    Jul 29, 2006
    Rockville, MD
  6. RWP


    Jul 1, 2006
    Welcome to Talk Bass! If you have 2, 8 ohm cabs in parallel your amp will see a 4 ohm load. Most amps can handle a 4 ohm load easily and actually provide more power than running at 8 ohms. So, if you currently have a 8 ohm cab connected to your amp adding another 8 ohm cab will work fine. If you add a 4 ohm cab the amp will see a load under 4 ohms and may not be happy with that.

    RMS is a way to rate power amplifiers. A 200 watt RMS amplifier can also be rated as a 400 watt 'peak power' amplifier. Any quality amp will be rated in RMS watts.
  7. smurff77


    Apr 5, 2007
    Re: profile....my brother set this up for me, so sorry for any confusion. I will change it once he tells me the damn password!

    Hate to be a pain but everytime I ask for RMS in the shops they look at me like I'm dim!
    Put it this way....it would be a lot easier if you could answer this:
    Guitarists in the band both have 150w combos, what wattage should I aim for? Shop assistant is telling me 450w but not many bassists I've seen in local venues have more than 200w amps.
    I guess it's about clarity of sound....am I right?
    And is it better to have something like a Trace Elliot combo with 1x15 speaker or Hartke combo with 4x10 speakers?
    I am confused....maybe the jewish harp is less hassle!
  8. RWP


    Jul 1, 2006
    Dude, 2, 150 watt guitar amps?!? You're going to need all you can get. :D Oh, and ear plugs. ;)
  9. remo


    Jan 15, 2005
    the three most important questions before you start to worry about ohms, wattage and speakers:

    1. What is your budget?

    2. What style of music are you playing?

    3. What kind of bass sound are you looking for?
  10. sobie18


    May 5, 2002
    Shaw AFB, SC
    Ampeg SVT Classic & 810 cabinet.

    Play it LOUD!
  11. Hi, smurff77.

    Welcome to TB.


    I'd personally say that a ~500W 4 ohm solid state head paired with a 4*10" and 15" 8 ohm cabs will cover most styles with ease. That way You have three rigs to choose from according to the situation.

    I'm using just a SWR ST220 (~200w) with a 4*10 and sometimes 15" also, but that's just for the stage, there's always PA support. And I play only rock ;) .

    The RMS according to Wiki.


    The reason for the weird looks when asking about RMS is usually that the person You asking about it doesn't have a clue about it.

    RMS can be , and usually is, quite misleading way to rate power in an musical amplifier, because there's quite a few ways to make the numbers look more attractive. But that's unfortunately all that we have, so the shop-hand should know how to explain RMS and all the different ways to measure it. And also (s)he should be able to compare different measurements, but that won't happen any time soon.

    +1 also for the profile, it's a lot easier to give advice when there's at least some clues of the location, age and gear.

  12. sobie18


    May 5, 2002
    Shaw AFB, SC
    T-Bird, nice answer. I second the 410 & 115.

    Smurff77, let us know what you get and how you like it.
  13. BassyBill

    BassyBill The smooth moderator... Gold Supporting Member

    Mar 12, 2005
    West Midlands UK
    A 410 and a 115 might be a nice rig, but it could also be overkill size wise and from a budget point of view. We really need the answers to those 3 questions to be able to advise here.
  14. BillMason


    Mar 6, 2007
    If your guitar players both have 150W amps, you will need *much* bigger than that just to be geard a little bit. Higher frequencies take less power to amplify. You should be looking in the 450-600W range. Try Carvin's website, you can order online, shipping is reasonable, and they have some killer combos around 600w at a little less than $1 per watt. You're right, it's about clarity of sound - a 200W bass amp will start farting out trying to catch up to a 150W guitar amp, and you'll break something eventually, but even worse it'll sound like crap.

    You also can't go wrong with a 4x10+1x15 cab set up! There are sometimes some nice heads and cabs on sale in the TB forums.

    EDIT: Correction, the Carvin combo is *800 watts* (!) for $549!!!!

  15. smurff77


    Apr 5, 2007
    Hey, just checked out that Carvin....looks just right for me as I also have to think of the practicality of transporting. At the moment, our drummer will have to cram it in his motor until I trade my bike in for a car.
    I am based in UK so is that shipping costs just for USA and how am I fixed for parts/repair if anything should go wrong.
  16. Altough the Carvin is rated at 800 watts, depending on the speaker in the combo, you will be getting alot less.

    Another thing to think about.............just because the combo can push 800 watts, don't think for a minute that one 12" speaker is going to do anything when trying to keep up with two 100 watt+ guitar amps.
  17. smurff77


    Apr 5, 2007
    Arrrrgh....I' getting confused with people telling me Carvin 800w or Trace Elliot 250w is fine then find out from the next person it's not.
    We are not a particularly loud band, (guitarists usually on vol 3), I need something practical to transport and need to make a decision or I'll never get to play in this band.
    What do i get?
  18. greenboy


    Dec 18, 2000
    remote mountain cabin Montana
    greenboy designs: fEARful, bassic, dually, crazy88 etc
    The advantage is that the B800 amp head willl go up to 800 watts when the right extension cabs are added, and without them still has more than enough headroom when fully driving the internal speaker.
  19. smurff77


    Apr 5, 2007
    I can't transport an extra cab.
  20. Being in the UK, I'd look at Ashdown first. They make plenty of rigs that can more than do the job. Cabinet ohms is an electrical thing that has to do with how the cabinet matches up with the amp. Most amps are designed to output their full power into 4 ohms. When you plug in 1x4 ohm cab the amp will output it’s full power. Problem is, you can’t plug in anymore cabs. If you’re happy with just the 1 cab then there is no problem. But, if you were wanting to power 2 cabs most likely they would have to be 8 ohm cabs. 2x8 ohms cabs = 4 ohms total. What might happen if you try to power 2x4 ohm cabs. The total ohms would then only be 2 ohm and this would probably over heat the amp causing it to shut down. Ohms are really more complicated than what I describe but if you follow what I have outlined you’ll have the basics down. RMS means how much continues clean power the amp can produce. I have been able to gig for 35 years with rather modest equipment. A good 450-watt SS amp and a 4x10 or 2x15 cab is all I ever needed and then some. Another combination that works well is a 400 watt 2x10 combo with a 1x15 extension cab. Use the extension with the combo for bigger venues and use the combo alone for smaller gigs and practice. That's what I'm getting ready to do now. If your guitar player decides to play his 150 w guitar amp at full volume, the sound will be so obnoxiously loud that you’ll start looking for another band anyway.
  21. Primary

    Primary TB Assistant

    Here are some related products that TB members are talking about. Clicking on a product will take you to TB’s partner, Primary, where you can find links to TB discussions about these products.

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