ok elementary question

Discussion in 'Amps and Cabs [BG]' started by softscrubmonkey, Nov 25, 2004.

  1. softscrubmonkey


    Nov 19, 2004
    St. Louis
    ok youve probably gotten this question alot, but im still a bit fuzzy on the whole ohms thing. can any explain it to me...in the kings english?
  2. ardorx


    Sep 23, 2004
    Sugar Land, TX
    ohms is how much resistance is going through a "circuit"
    the cab+head being the circuit. I don't know. I'm probably missing alot...but i do know the ohms symbol is the omega sign. I'm in electronic systems at school. :)
  3. Yossarian


    Jun 24, 2004
    and when you're combining ohms, you use crazy-math. Yes, that's the scientific term. What I'm saying is:

    8 ohm cab + 8 ohm cab = 4 ohm resistance.
    4 ohms + 4 ohms = 2 ohms.
    8 ohms + 4 ohms = 2.666 ohms or something like that.
  4. ohms are a measure of resistace.

    If you connect your amp to one speaker, the ohms rating is equal to that speaker's ohms rating. An 8 ohms speaker would have a rating of 8 ohms.

    if you connect speakers in series mode then you add the ohm ratings together to get total resistance.

    Speaker A + Speaker B = Total Ohms Rating
    8 Ohms + 8 Ohms = 16 Ohms

    Two 8 Ohms speakers wired in series will have a total rating of 16 ohms

    if you connect speakers in paralell mode then you end up reducing the resistance. this is usually the case when you "daisy chain" cabs to gether.

    Resistance = (Speaker A x Speaker B) / (Speaker A + Speaker B)
    Resistance = (8 Ohms x 8 Ohms) / (8 Ohms + 8 Ohms)
    Resistance = 64 / 16
    Resistance = 4 Ohms
  5. Take away the electricity, and it might be easier.

    If you have a hose pipe, and you pump water through it, the more powerful the pump, the more water you get. The pump 'head' is equivalent to the voltage, which drives the current (water) through the system.

    The hose has some resistance to the flow of water. Thinner pipe - less water, bigger pipe - more water. Also, longer pipe - less water, shorter pipe - more water. The resistance of the pipe is equivalent to the electrical resistance, which is measured in ohms.

    If you put two pipes in series, the pipe is longer, so the resistance goes up, so you get less flow. If you put two pipes in parallel, you have two paths for the water, so you get more flow, in other words, your resistance has gone down.

    When you match speakers to your amplifier, what you are doing is equivalent to selecting hozes to maximise the flow from the pump, without overloading it.

    Moving on to the 'crazy maths', when you put speakers in series, the resistance gets bigger, so you add the ohms (A+B).
    When you put speakers in parallel, the resistance goes down, and the calculation is 1/((1/A)+(1/B)). In other words, for two 8 ohm speakers: invert them [1/8+1/8] add them [1/4], and un-invert them [4] ohms.
    (8 ohms & 4 ohms -> [1/8+1/4] ->[3/8] -> [8/3] ->2.66 ohms)
  6. softscrubmonkey


    Nov 19, 2004
    St. Louis
    ok so ive got a SVT head that powers 4ohms and 8ohms but ive got a 4ohms cab. what happens when i add another 4ohms cab? or can i even do that?
  7. Jack


    Sep 6, 2003
    Newcastle, UK
    You cant, if your head will only go down to 4ohms, anything less will cause dangerous overheating and possible damage to amp/cab/you. :)
  8. ok i haver a question...if you have a head that can do 300 watts at 8ohms would it be louder or softer going through a 4 ohm speaker?

    Basically do you want lower ohms (4) or a higher amount (8)?

    Details are always appreciated :)
  9. csholtmeier


    Feb 8, 2004
    omaha, ne
    Less ohms (lower impedance) means your power amp is going to produce more power. My power amp produces 600 watts bridged at 8 ohms, 830 watts bridged at 4 ohms. Running bridged to 4 ohms also means that the amp runs hotter and therefor is more susceptible to thermal shutdown.
  10. IvanMike

    IvanMike Player Characters fear me... Staff Member Supporting Member

    Nov 10, 2002
    Middletown CT, USA