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ohms etc.

Discussion in 'Amps, Mics & Pickups [DB]' started by klem.gote, Apr 4, 2009.


  1. klem.gote

    klem.gote

    Jan 18, 2009
    New England
    Bass Player
    Hello all,

    I just spent time reading through the newbie threads on ohms, watts etc., (till my mind went numb). Too much math and electronics for me to handle. Can anyone explain it, in simpler terms? Why are there different ohm ratings for different speakers, is higher or lower better, can I plug a bass head into speakers with different ohms? Any info at all would be greatly appreciated!!!

    Thanks
     
  2. johnz

    johnz

    Apr 26, 2008
    Ashland, OR
    I'll take a crack at it - but no guarantees as to simplicity!

    "Why are there different ohm ratings for different speakers?"
    There are a number of reasons for having a variety of speaker impedances ("ohms" for normal people). I suspect that the most important reason is that it gives the folks that put the speakers in cabinets more options, hence, speaker manufactures can sell more speakers. I'd be happy to elaborate, but it would require some math...

    "is higher or lower better?"
    With modern amps (transistor amps as opposed to your old SVT tube behemoth) lower is better to a point. Transistor amps generally put out more power as you reduce the speaker impedance (ohms). It's not a linear relationship. As I recall a GK MB150 puts out 100 watts using its single, internal speaker. If you plug in their extension cabinet (in this case, cutting the speaker impedance by half) the output of the MB150 goes up to 150 watts. The "to a point" part I mentioned earlier has to do with the maximum rating of the amp. Amplifiers generally have a "minimum impedance" rating. Most amp's minimum load impedance is between 2 and 4 ohms. If you lower the speaker ohms below this level, the amplifier releases its magic smoke, requiring a trip to the amp repair shop for a refill ;). One simple piece of math will keep you out of trouble here. Assuming that all of your speaker's have the same ohms, and assuming that you're "paralleling" the speakers (which is what we generally do), simply divide the ohms of one speaker by the number of speakers to find the resulting ohms. You have two 8 ohm speakers in parallel, it results in a 4 ohm load to the amp. You have eight 8 ohm speakers in parallel, it results in a 1 ohm load to the amp (which is generally way too low!).

    "can I plug a bass head into speakers with different ohms?"
    Yes, you can. But, it's not generally something you want to do because it's inefficient. The current and, hence, the power, through the speakers divides in proportion to the ohms. Say your amp is putting out 100 watts and that you have paralleled two speakers, one rated at 4 ohms and the other at 8 ohms. The 4 ohm speaker will be taking 66.4 watts of the amp's output while the 8 ohm speaker is (relatively) loafing along, only handling only 33.6 watts. Does that sound fair to you?! I'd be happy to elaborate, but again, it would require some math.

    The bottom line (no pun intended): Different speakers have different ohm ratings so they can sell more speakers (not "just" to confuse you!). Lower ohms get you more power - but don't go too low! Don't use mixed speakers unless it's an emergency.

    I hope that helped (and sorry to be so long winded) <- JZ
     
  3. Bob Gollihur

    Bob Gollihur GollihurMusic.com

    Mar 22, 2000
    Cape of New Jersey
    Big Cheese Emeritus: Gollihur Music (retired)
    I've written FAQs on ohms and impedance from both the input and output persectives, see http://www.gollihurmusic.com/faq.cfm

    Hope they simplify the matters for your.
     
  4. klem.gote

    klem.gote

    Jan 18, 2009
    New England
    Bass Player
    Hi guys,

    Thank you!! Both of you were of help to me, I think I'm starting to get a basic grasp on it, which is all I wanted. I've always been a combo guy so I never really had to worry about this stuff, but I'm now thinking about separate components. I think I confused you with the "different speakers" question. What I meant was, could I use one head with a 4 ohm speaker and then use the same head into an 8 ohm speaker, but I think I've got that straight now. Thanks again for your input (sorry!!).
     
  5. jsbarber

    jsbarber

    Jun 7, 2005
    San Diego
    Klem - here's an analogy that may be helpful, or not...

    Say you have a 10 speed bike, (if you're under 30 we'll call it a 20 speed bike), and you're riding along in 8th gear. You're able to sustain 20 mph, (this is a 4 ohm cabinet), then you switch to 10th gear. It's hard to peddle this sucker. Even though you can peddle slower, it takes a lot of power to peddle that bike and you can't sustain 20 mph in this gear (8 ohm cabinet), your power output is lower.

    Now suppose you were to shift down to 6th gear. This is easy to push, but man you're legs are burning out spinning along at a very high cadence at 20 mph and you're getting tired just pushing your legs that fast. (This is the 2 ohm cabinet.) Mayber a really light weight rider can ride at this cadence but most riders can't. So in 6th gear you can't maintain the pace, even though each peddle stroke is easy.

    Amps that can drive the two ohm cabinet can push out high power into a low load. Every amp has a miniumu load, where it will burn out if you push it hard into a smaller load.

    Hope this helps, if not - well I tried...

    Jim
     
  6. klem.gote

    klem.gote

    Jan 18, 2009
    New England
    Bass Player
    Hi Jim,

    Interesting analogy, thanks!! Every perspective helps. Now I just need to get the visual out of my mind of trying to play a bass on a bike. Especially going uphill. I have been in one or two rhythm sections that felt like I was pushing a truck up a very steep hill. A hill with no end, no top to reach, just endless, pointless pushing.
     
  7. etoncrow

    etoncrow (aka Greg Harman, the curmudgeon with a conundrum)


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