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How do Ohms work

Discussion in 'Amps and Cabs [BG]' started by warwickbass, Jan 1, 2002.


  1. warwickbass

    warwickbass

    Dec 8, 2001
    Minnesota
    Im lookingat buying a PLX3402 Power Amp, and teaming it up with a Eden Navigator, my problem is the cabniets, 2, 4, 8, Ohms? what does this all mean to me can i mix and match, do they all have to be the same, whats your advice and what do you use?
     
  2. Hategear

    Hategear Workin' hard at hardly workin'.

    Apr 6, 2001
    Appleton, Swissconsin
  3. warwickbass

    warwickbass

    Dec 8, 2001
    Minnesota
    I have done a search and came across the same page you did, I can do the formulas :p but I guess I need a better description on the variables and what not. :confused: My problem is ive had no prior intros into this. :eek:
     
  4. warwickbass

    warwickbass

    Dec 8, 2001
    Minnesota
    Ok it seems like ive got the formula wrked out! the amp I intend to buy puts out 2, 4, 8ohms, stereo 2ohms having the highest wattage, and 4, 8, and 16 ohms, bridged mono, 4 having the highest wattage. my question now is as posted on the previous thread 2.67 ohms can an amp run at an off number or does it have to be 2 4 8 or 16 on the dot?
     
  5. Hategear

    Hategear Workin' hard at hardly workin'.

    Apr 6, 2001
    Appleton, Swissconsin
    I would imagine that if your amp gives you ratings down to 2-ohms, that you should be able to run at 2.67-ohms with no problem. I personally don't feel comfortable when dealing with those "weird" numbers. My thoughts on running two seperate cabs (right or wrong) are to match one cab with another -- a 4-ohm cab goes with another 4-ohm cab, a 2-ohm goes with a 2-ohm and an 8 with an 8.

    I wouldn't feel right if I was running one 8-ohm and one 4-ohm, but that's just me.
     
  6. geshel

    geshel

    Oct 2, 2001
    Seattle
    2.67 ohms is just as fine as any whole number. It's just a rough measurement of an electrical property.

    If the amp can handle 2 ohms, then it can handle 2.67 fine. Note, however, that the specs you listed only go down to 4 ohms bridged mono. So, to run at 2.67 ohms you'd have to run only one side of the amp into the cabinets. This won't hurt the amp but is kind of silly.

    The main problem mixing a 4 ohm and 8 ohm cab is that the 4 ohm one will get more power. If it is a bigger cab (4x10 v. 2x10), this may work out great. But remember that ohms are a measure of resistance, and since the resistance in the 4ohm cab is lower, more of the power will flow through it.

    Here's how I think of volts/amps/ohms: Take a really tall column of water. Poke a hole in the side, and water comes out.

    volts -> height of the water in the column (above where you punch the hole)

    amps -> amount of water (ie gallons per minute) coming through the hole

    resistance -> inverse to the size of the hole

    power -> the velocity of the water coming out of the hole (proportional to the height of the column, volts) times the amount of water coming out (amps, depends on the volts and the resistance)

    So, punch a bigger hole (lower resistance), more water comes out. Punch two, one half the size of the other one, and more water will go through the bigger one.

    It's a rough metaphor, some things don't work the same between the two things, but for me that helped get a handle on the terms involved.
     
  7. Bob Lee (QSC)

    Bob Lee (QSC) In case you missed it, I work for QSC Audio! Gold Supporting Member Commercial User

    Jul 3, 2001
    Costa Mesa, Calif.
    Technical Communications Developer, QSC Audio
    What cabinet(s) do you have or plan to get?

    Your cabinets don't all need to be the same unless you want them to sound identical.

    My rig contains a PLX 1602 in bridged mono driving an 8-ohm EV 1150 stage bass system (2-way: 15" + an 8").
     
  8. warwickbass

    warwickbass

    Dec 8, 2001
    Minnesota
    im trying to base what cabs i will get off of what i learn here, so heres what ive got... i can run 4 8ohm cabs at 2 ohms i can run 2 4ohm cabs at 2ohms and i can run 1 2ohm cab at 2ohms, but not 2 2ohm cabs at 2ohms because 2 2ohm cabs run at 1ohm using the formula in the other thread 1/( 1/2+1/2) correct? im just trying to figure out what cabs at wich ohms i should buy. and heres another question can i run a 4 ohm cab at 8ohms, and can i run a 8 ohm cab at 4? this all gets more and more confusing as i go on, the way i understand it running a 4 ohm cab at 8 ohms is underpowering it (if you cn do that) and runing a 8 ohm cab at 4 ohms is over powering it... i think .... sounds right?
    anyway i thank you for your help so far ... hope i dont sound too ignorant.. and damn thats a lot of ohms isnt it?
     
  9. geshel

    geshel

    Oct 2, 2001
    Seattle
    i can run 4 8ohm cabs at 2 ohms i can run 2 4ohm cabs at 2ohms and i can run 1 2ohm cab at 2ohms, but not 2 2ohm cabs at 2ohms because 2 2ohm cabs run at 1ohm using the formula in the other thread 1/( 1/2+1/2) correct?

    Yes.

    and heres another question can i run a 4 ohm cab at 8ohms, and can i run a 8 ohm cab at 4? this all gets more and more confusing as i go on, the way i understand it running a 4 ohm cab at 8 ohms is underpowering it (if you cn do that) and runing a 8 ohm cab at 4 ohms is over powering it... i think .... sounds right?

    I don't know what you mean by "run a 4ohm cab at 8 ohms". I think the answer is "no". The ohms measurement of a cab is a fixed propery. (some 4-driver cabs can be switched internally between 4 and 16 ohms, however).
     
  10. warwickbass

    warwickbass

    Dec 8, 2001
    Minnesota
    thanks fellaz my brain is now saturated and my questions answered :cool: ... for now :rolleyes:
     
  11. JimM

    JimM

    Jan 13, 2000
    Northern California
    Just a note:as long as the output stage is solid state you'll have no problems down to two ohms.if you ever use a tube amp(or valve amp),you should know that they want a precise speaker impedence.some have a switch so you can choose between different ohm loads.

    I learned that from TalkBass.
     
  12. Munjibunga

    Munjibunga Total Hyper-Elite Member Gold Supporting Member

    May 6, 2000
    San Diego (when not at Groom Lake)
    Independent Contractor to Bass San Diego
    Ohms work fine, when properly adjusted.
     
  13. Forgetting bridging, look at the highest power/impedence that the amp can put out. For example, 1400w @ 2ohms.

    This means that the amp can handle a total load of 2ohms - which means 1 x 2ohm cabinet, 2 x 4ohm'ers, or 4 x 8ohm'ers (or combinations thereof, using the formula, to arrive at a total impedence of no less than 2ohms).

    You can plug any bass cabinet in that is equal to or higher in impedence than the amp. For example, an 8ohm cabinet will run quite nicely with an amp that can handle 2ohms - it's just that (as said before) the higher the impedence, the lower the power that the amp can produce (obviously affecting volume).

    A stereo-bridgable amp is nice in that you can either run both sides of the amp, or bridge it (which combines the power of both sides into a higher impedence) - which gives you flexibility as power requirements increase.

    Obviously the lowest impedence cabinet will draw the most from the amp, but settling for a single 2ohm cabinet (if there was one) would mean that you're unable to add further speakers (as they would again lower the impedence past the safe level). Watch out for 2ohm loads as well, amps do run quite hot with a load like this and some aren't too stable.
     
  14. Williebee

    Williebee

    May 4, 2001
    Lots of interesting ohm comments, some of which are backwards. Most of the wrong info has been corrected with previous threads, but, ohm=resistance. The lower the number (ie 2 ohms, the more you tax the amplifier, the more heat it generates, the faster it wears out, which of course depends on the amp. Here is a decent analogy: if you are driving a car with a 400hp motor at 1/2 throttle and you want to pass, usually no problem. Lets call this engine headroom. If you run that same car wide open and want to pass, you have no more power to draw from the motor to pass with. If you have an amp that is rated at 400 watts into 4 ohms of resistance, and run it into 4 ohms, your amp will be giving those speakers all it has at nominal volumes. Then if your playing style requires any sort of dynamic range, you have no where to go. If you run that amp into an 8 ohm cab, plenty of headroom. One other note, ohms change when speakers heat up. That 8 ohm cab, which may read @ 6.7 ohms cold, may draw considerably more when heated up. This is important because when you run out of headroom with your amp and start clipping your signal, you're pounding the heck out of your speakers and could damage them and the amp. My simple rule, 4 ohm amp rating, 8 ohm cabinet, 2 ohm amp rating, 4 ohm cab (or 2-8ohm cabs. This is why stereo power amps are best if you play loud. More speakers, less resistance = clean healthy running bass rig. I hope this helps, Good Luck!
     
  15. Richard Lindsey

    Richard Lindsey

    Mar 25, 2000
    Metro NYC
    AFAIK this is incorrect. You don't have more headroom in the situation you describe--you have *less*, because the amp can't generate as much power into a higher-ohm load. Generally it's true that running an amp at its minimum rated load puts more stress on it; but the reason people try to do this at all is that you get more power. If you run an amp with a rated minimum of 4 ohms into an 8 ohm cab, you'll be putting less stress on it, but you'll also get less power and thus less headroom, and that's the tradeoff.
     
  16. basslax

    basslax

    Apr 20, 2000
    Washington, DC
    ok im really stupid. anyone wanna do the really dumbed down one for me??

    :confused:
     
  17. OUCH! No, no...if a solid-state amp can only handle a 4ohm load and you run with a 2ohm load, the power amp WILL die after a while (depending on how hard you push the amp). At low levels you can get away with it though.

    Correct. If an amp can produce 400w @ 4ohms, it'll only deliver ~240w @ 8ohms - less headroom.
     
  18. Williebee

    Williebee

    May 4, 2001
    Here's a suggestion, why not call 3 bass amp manufacturers that build amps you like. Ask for technical assistance and see if you can get a consisis, then let us all know the facts.
     
  19. All the information is in all the above posts (and plenty of other threads on TB).

    Think of it like a performance exhaust on a bike or car - it will draw more power from the vehicle (amp) than the standard exhaust, regardless of the engine's output.
    Therefore the standard exhaust would be the "8ohm cabinet", the performance being the "4ohm cabinet".

    Hope this made sense! :D
     
  20. JimM

    JimM

    Jan 13, 2000
    Northern California
    I thought he said his amp will do down to Two ohms.I didn't mean that all amps can do two.My main point was that there's a difference between SS and tube amps.
    I guess I can't speak conversationally on this board,but will have to pretend I'm writing a book.

    I can't win

    I got 'ouched' here once before for saying that I thought going down to two wasn't a great idea even on amps that were rated for it.That's because during my 25+ years as an appliance tech I've seen circuits fail due to heat that wouldn't have failed if they had been running a lighter load.You can't lower the current in a microwave oven,for example, but you can keep the strain on an amp down by using speakers with higher ohm loads.But what I'm describing could be called "babying" the amp.

    I wish there could be a page or two about this in the FAQs page.I think if it had pictures that would help mucho.