Ohms laws for dummies

Discussion in 'Audio & Electronics' started by Forklift, Jul 6, 2004.

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  1. Forklift

    Forklift Wanna B Jack o all Trades

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    I help people out with this alot, and I thought this might make a good sticky in here, so think about it. People never know what an ohm is or why its needed in selecting speakers, so Ill try my best to explain.To get multiple subs to an amp thats bridged sometimes requires some thought and most people skip this step and need either new subs, a new amp, or both . If this is you , stop reading, I make my hours off you and therefore my living. if you are the type of person that slaps stuff together without knowing a thing about it , never checks into it , never asks question and thinks you know it all, we love/hate you and keep it up to keep us fed.
    All amps put out their most power at a certain ohm load(except some ones with the regulated power supplies that are pricey and arent around much). Most all amps are rated at 4 ohms per channel at a certain distortion ratio, say 100 watts per channel, 4 ohms driven at .8%THD ( Total Harmonic Distortion). This means that a static ohm load ( a resistor not a speaker on the amp) it will produce 100 watts. Now once a speaker is on the amp it will of course move and change the ohm load, but we wont get into that right now.
    Now if we change the ohms, say from 4 to 2, most amps will double the power to 200 per channel, but your distortion will double or even quadriple from .8 to 1.6 or maybe 3.2. This is why the cleanest sounding systems always have high wattage amps even on the highs and even the subs are run in stereo or one sub per amp(but thats mainly to reduce "crosstalk" and difference in subs , plus the ultra high dollar amps to run multiple subs get $$$). Now most of us cant hear that level of distortion, some people say they can so we also wont worry about that.
    Now another fact to consider in this , is that the amp will "see" a different ohm load once its bridged. An amp thats 4 ohm stable bridged is also 2 ohm stable stereo. This is because an amp that has a 4 ohm load on it bridged "sees" 2 ohms per channel, I dont know why, it just does so live with it. This makes it easy to see why people like to bridge their amps, because they put out more power. If our theoritical 100 wpc amp does 200 wpc at 2 ohms and you add the 2 channels, you get 400 watts into one channel. This will make you now have twice the amp you bought , it doesnt matter if its all going into one sub or 4.
    When wiring multiple subs theres 3 ways to do it, series, parellel( I never know if Im spelling that right) and series/parellel. Series means that the subs share one terminal like Christmas tree lighting. When you do this, its a wire from one + to the next subs - and the left over + and - go to the amp. Parellel means they share 2 terminals like plugging in multiple pieces into a wall socket. When you series subs, their combined ohm load doubles everytime you double the subs and when you parellel them their combined ohm loads are cut in half everytime you double the # of subs.
    Some subs also fall into the dual voice coil category and some even into the quad voice coil category (and if you need help wiring those up mail them to me in at least pairs and Ill try to maybe get them back to you as they are usually nice pricey subs I would like to own). DVCs need to be treated like 2 speakers per sub and 4 subs per every 2 subs. The amp doesnt care if you only have 2 subs cuz it sees 4. If you saw the paragraph before this is where the series/parellel wiring comes into play. If you have 2 DVC subs that are 4 ohm per coil and you have a 4 ohm stable amp, youll need this. What you do is run a wire from the + on one side of the sub, to the - on the other side. Do this to the other sub and now the subs are seried out to make each sub 8ohms. After this you run each subs left over + to the amp and each - to the amp.
    I hope this little think I did helps some people out.
    (# of subs)ohm of each sub , type of connection = combined ohm load
    (2)4s par = 2 , (2)8s par = 4
    (2)2s par = 1 , (2)1s par = 1/2
    (4)4s par = 1 , (4)8s par = 2
    (4)2s par = 1/2 , (4)1s par = 1/4

    (2)4s ser = 8 , (2)8s ser = 16
    (2)2s ser = 4 , (2)1s ser = 2
    (4)4s ser = 16 , (4)8s ser = 32
    (4)2s ser = 8 , (4)1s ser = 4

    its easy to see the way it works like this and these will do probably every possible type of speaker install you will ever need including house speakers. The only 2 other installs that some people do are 3 8ohms on a 4 ohm stable amp (2.66 ohms) and 3 4ohms on a 2 ohm stable amp( 1.33 ohms). If you need more help on this , let me know and I hope I can answer it

    Scott Spiehler Jr

    One sub:
    1SVC_2-ohm_mono.jpg
    1SVC_4-ohm_mono.jpg
    1SVC_8-ohm_mono.jpg
    1DVC_2-ohm_mono.jpg
    1DVC_4-ohm_mono.jpg

    2 subs:
    2SVC_2-ohm_mono.jpg
    2SVC_4-ohm_mono.jpg
    2SVC_8-ohm_mono.jpg
    2DVC_2-ohm_mono.jpg
    2DVC_4-ohm_mono.jpg

    3 subs:
    3SVC_8-ohm_mono.jpg
    3DVC_2-ohm_mono.jpg
    3DVC_4-ohm_mono.jpg
     
    Last edited: Oct 18, 2009
  2. Ryan

    Ryan GMFS Member

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    I think this will help alot of ppl out....including me.
     
  3. x6369x

    x6369x eBay-aholic

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  4. Forklift

    Forklift Wanna B Jack o all Trades

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    thats a good add-on to this. If you dont mind Ill add it to my other threads I copied my paragraph to

    and 4 sub setups:
    4SVC_2-ohm_mono.jpg
    4SVC_4-ohm_mono.jpg
    4SVC_8-ohm_mono.jpg
    4DVC_4-ohm_mono.jpg
     
    Last edited: Oct 18, 2009
  5. Forklift

    Forklift Wanna B Jack o all Trades

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    my first sticky! Im going to Hawaii yeah!
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    Last edited: Oct 12, 2006
  6. sierraon22s

    sierraon22s GMFS Member

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    very usefull info. Thanx for clearing it up for us dummies. :D
     
  7. Nicholas

    Nicholas GMFS slowest truck :read:

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    Good job on it...if you had gotten it out a day or 2 earlier, you woulda saved your self a lil time with helpin me...thanks for helpin all the dummies like me out there with this sorta stuff.
     
  8. Forklift

    Forklift Wanna B Jack o all Trades

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    well you put the thought in my head and you were the straw that broke the camels back on that one single question i seem to get all the time. More so Im tired of the people that dont even know what an ohm is and just say they know what they are doing and to give them any ohm sub we have. Thats like having a corvette and pulling it into Exxon for a fill up and just saying " whatever", your running risks
     
  9. Nicholas

    Nicholas GMFS slowest truck :read:

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    Yeah, im sure you do get that question a lot. I wish i knew more about this sorta stuff, but im tryin to learn.
     
  10. carterbeauford

    carterbeauford GMFS founding member

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    quick direct link
     
  11. Kal

    Kal GMFS Senior OG Member

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    Nice write up!! There is a shit load of stuff I didn't know about. :worship:
     
  12. RandomHero

    RandomHero GMFS Senior Member

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    Im not sure that info covered my situation. I want to wire two 12" type r subs down to 2 ohms. should I buy 4ohm subs or 2 ohm subs?
    by the way if this matters, I am going to run them off of a mtx 1501d amp.
    Like I said they have dual voice coils so I think that might change things, but if anyone can do a little research and help me out, im not very knowledgeable of this sort of thing
     
  13. x6369x

    x6369x eBay-aholic

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    You need (2) 2 ohm DVC subs, and wire em like this:
    [​IMG]
     
  14. RandomHero

    RandomHero GMFS Senior Member

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    :stupidme: I should have just read the post, it completely slipped my mind that dvc mean dual voic coil. Thanks for the quick help
     
  15. nu2chevy

    nu2chevy GMFS Member

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    by the way.the ohm value is the impedance(resistance to a.c.) of the voice coil and not the actual value if measured with an ohm meter.don't attempt to figure speaker load by measuring across speaker terminals with a meter.
    it's spelled parallel.
    series---rt(resistance total)=r1+r2+r3....
    parallel----1/r1+1/r2+1/r3....= 1/rt
    in parallel if all loads are the same value then rt = value of load/number of loads
    i'm not an electrical engineer or anything;just like to help!!
     
  16. pbuilder

    pbuilder New Member

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    forklift
    To answer the ? about WHY when bridge the amp sees 2ohms is false. I tstill sees 4 ohms but now you have 2 channels. A amp that has 2 pos. temnals that come from the transistors will not bridge. If you look at a bridgeable amp , one of the outputs says + but it is a ground and the other channel ground is a -. What is going on is one channel is + and the other is - signal which you will need for it to work. We are working with DC so this will make a full path for the signal when it is bridged. The reason the power doubles and the distortion is because you have 2 channels to one output. Channel a is 100 watts and channel B is 100 watts then you have 200 watts when you connect them to one speaker or a set of speakers. What makes more watts in a channel is current at a set voltage, say 35 volts. Each transistor can handle so much wattage so they add more transistors.

    Hope that helps someone.
     
  17. Forklift

    Forklift Wanna B Jack o all Trades

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    I dont know where all the links went, but I just fixed all the pics of the wiring diagrams and all is well again in here
    pbuilder, no that didnt help, but Im about to start studying for my master so maybe that will help me to understand it
    and Nu2chevy, I just didnt wanna get these guys all confused with math. Just heres a picture and do it like this or you will be having another "I think I blew my amp" thread
     
  18. 02sittin22s

    02sittin22s GMFS Member

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    Awesome write up man thanks a lot, this will help me a ton on pickin out my new speakers here in the next month thanks!!
     
  19. Forklift

    Forklift Wanna B Jack o all Trades

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    welcome, Im about to write another one
     
  20. matthimself

    matthimself GMFS Senior Member

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