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Whats an Ohm?

Discussion in 'Amps and Cabs [BG]' started by ii7-V7, Dec 13, 2005.

  1. ii7-V7


    Aug 4, 2002
    Baltimore, MD
    .....And how do I learn about all this stuff? Is there a book?

    And yes, I did a search!

  2. its a value of resistance and an electronic concept known as ohm's law. How deep do you want to go into this subject? If you are asking about loudspeakers you are in the right place.
    if you want a basic concept for general electronics check out (Benard Grobes Basic Electronics)
  3. ii7-V7


    Aug 4, 2002
    Baltimore, MD
    thanks for linking to that thread. I'm reading it...but not really absorbing it yet.

    I treid searching for Benard Grobes Basic Electronics but got no results on yahoo. I'll keep looking.
  4. spectorbass83


    Jun 6, 2005
    There have been many posts about Ohms/Impendence etc..it may sound cliche, but do a search through the amps forum. You will surely find some info. It worked for me many times :cool: best of luck!
  5. ii7-V7


    Aug 4, 2002
    Baltimore, MD
    If I run a search...which I have done....I will get 500 post with the word Ohm in them...but what are the chances that I'm going to read 500 threads? If I type into the search engine, "what is an ohm" I get no matches.

    I understand the frustration of seeing endless, "Whats the best amp," threads, but the search button is not a perfect tool. For some questions I've had good sucess, for others none at all.



    Jan 25, 2005
    Des Moines, IA
  7. jsbarber


    Jun 7, 2005
    San Diego
    You can think about it like this, maybe.

    Think of a tobaggan (sled) on a hillside. You want to slide down. The height of the hill is the voltage. If you had a perfectly smooth sheet of ice and a very smooth tobaggan there would be very little resistance and it would slide very well. If you change the surface and make it less smooth, the tobaggan will not slide as easily. The concept that measures the ability of the tobaggan to slide on the smooth surface is like electrical resistance. (In this tobaggan analogy, physical resistance corresponds to the electrical resistance in a circuit. This is not an accident. Both types of resistance generate heat as the toboggan, or electrons, move along over/through the resistive media.) The Ohm is the unit of measurement of electrical resistance. (Just like the mile is a unit of measurement of distance)

    From the standpoint of your amplifier driving your speakers, AC current flowing through the coils causes them to oscillate and that is what generates the sound. If the current (roughly the speed of the toboggans on the hill) is slow then there is less current and less sound. So as you lower the resistance of the speakers, (by going to lower impedance cabinets), you will generate more current. But as you increase the current, you increase the power dissipated through the amplifier's internal resistance. Then the amplifier's internal resistance ends up generating a lot of heat which it may not be able to dissipate, so it gets real hot. This can cause it to fail, either immediately or over a long period of time.

    The real situation is more complicated than this, surprise-surprise. But maybe this helps you think about it.

    Hope this helps,

  8. Keeaumoku


    Dec 29, 2004
    Hey... I still stay confused, li'dat, brah! :meh: So... try this: I get one surfboard, and I stay on top of a 25-footer on Oahu's north shore... preferably Pipeline... so, the height of the wave going be my voltage... right? If the surf is like one mirror that day... you know: 'da waves stay breaking real even... very little white water... that's gonna reduce the resistance... yeah? Hmmm... I think I'm gettin' it now, brah!

    Only kidding, Jim. I appreciated your analogy... :D
  9. ras1983


    Dec 28, 2004
    Sydney, Australia
    its a little elf like creature that dwells in the confines of dark and secluded; densely populated materials. Its main feature is its unwillingness to move, unless someone or something applies a big enough force. Be warned that as the force is applied the elf screams.

    *** The higher the force applied, the louder the elf screams *** It can sometimes be persuaded with potato chips...

  10. ii7-V7


    Aug 4, 2002
    Baltimore, MD


    Jan 25, 2005
    Des Moines, IA

    isn't that gnome, O Wise One??? :smug:
  12. AxtoOx


    Nov 12, 2005
    Duncan, Okla.
    Let's see if this helps.
    Like was said,Ohm's is resistance, the more resistance the less power. That's why a 4 ohm cab will run the amp @ higher watts than and 8 ohm cab. If you run a cab w/ lower ohms than the amp is rated, especially solid state, you will fry the board because too many watts are running through. Make sense?
    You can google Ohm's Law, but it sounds like that's more info than you are looking for.
  13. 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 are the voltage in volts divided by the current in amperes.
  14. ddnidd1

    ddnidd1 Supporting Member

    From a practical, non-techical point of view you will use Ohms to match a cabinet(s) to a particular amp. For cabinets, Ohms is just a number that tells you how much resistance a cabinet has to the electrical signal that goes to the speakers to generate sound. The higher the Ohms number the more resistance the cabinet has to the electrical signal.

    Typically cabinets are rated at either 4 Ohms or 8 Ohms. This rating is also known as the Impedance of the combined speakers in the cabinet.

    Amps are rated at delivering a specified number of watts to a cabinet typically rated at 4 or 8 Ohms. So what you might see on the amp or in it's manual is output at "200 watts@8 Ohms" and perhaps something like "350 watts@4 Ohms. (Sometimes instead of using the 'word' ohms they will substitute the Greek letter Omega. That you'll have to look up on the web.) The main point here is that you DO NOT want to connect a cabinet with a LOWER ohms rating than that of the output rating of the amp. Connecting a cabinet with a higher ohms rating than that of the amp is OK.

    If you want to connect more than one cabinet to your amp you have to CALCULATE the ohms or impedance of the Combined cabinets. There are tons of posts on how to calculate resistance for multiple cabinets.

    I hope this provides some help.
  15. SnoMan

    SnoMan Words Words Words

    Jan 27, 2001
    Charleston, WV
    I would ask you why you want to know.

    If it's purely for your benefit when it comes to bass and amplification. The Ohms FaQ should be able to help a lot.

    If you want to actually know what an ohm is...and not how it relates to amplification...then...well....thats the kinda stuff that hurts my head.

    My brain can't grasp the concept of pulses of energy through pieces of metal and other materials can create sound. For Instruments...I can handle it more feesibly...but recreating a persons voice...my brain does not even begin to comprehend that.

    Lets not talk about video or anything like that...
  16. ii7-V7


    Aug 4, 2002
    Baltimore, MD
    The Ohm FAQ has been helpful, but I'm finding that I have to go back and understand electronics at an even more basic level to really get Ohms.

    As for why I want to understand it.....I want to understand why it is that information can be turned into energy and then transmitted through a medium. Yes, I hope to one day understand it at that level. Though, I'm in no rush.

    I have found, that for me, I have to know things at that theoretical level before the application of it makes much sense to me.