1. The Rules have been updated regarding posting as a business on TGP. Thread with details here: Thread Here
    Dismiss Notice

Replacing speakers, don't know anything about 'ohms'

Discussion in 'Amps and Cabs' started by benjammin420, Feb 18, 2009.

  1. benjammin420

    benjammin420 Member

    Messages:
    1,565
    Joined:
    Jan 13, 2009
    Location:
    Vancouver, BC
    I'm looking at replacing the speakers of my hot rod deville to celestions. The amp is 4 ohms, so I assume I need/want 4 ohm speakers. But, what would happen with 8 ohm speakers? with 16 ohms?
     
  2. JPenn

    JPenn Member

    Messages:
    1,780
    Joined:
    Jan 4, 2002
    Location:
    Blytheville, AR
    is it the 4x10 or 2x12?
     
  3. benjammin420

    benjammin420 Member

    Messages:
    1,565
    Joined:
    Jan 13, 2009
    Location:
    Vancouver, BC
  4. benjammin420

    benjammin420 Member

    Messages:
    1,565
    Joined:
    Jan 13, 2009
    Location:
    Vancouver, BC
    sorry, the manual says 8 ohms (its 4 when running an extention cab)
     
  5. benjammin420

    benjammin420 Member

    Messages:
    1,565
    Joined:
    Jan 13, 2009
    Location:
    Vancouver, BC
    I was at a studio and I plugged their silverface Fender Bandmaster into a Marshall 412. It sounded great, til the owner came in an flipped out that i was missmatching the ohms. I dont want to kill my gear, but it was soo good, ive never played a Fender or Marshall that i liked since hearing them together like that
     
  6. Austinrocks

    Austinrocks Member

    Messages:
    7,026
    Joined:
    Feb 10, 2007
    right, my hot rod deluxe is the same way, but I was not sure if the 2x12 was different, I had the 4x10 deville for many years,

    for the 4x10 you can get four 8 ohm speakers, and they will give you the 8 ohms the amp wants,
     
  7. joel98z

    joel98z Member

    Messages:
    567
    Joined:
    Dec 7, 2007
    You will need 4x 8 Ohms speakers if you have the 4x10 and the amps has an 8 ohm out.
     
  8. Austinrocks

    Austinrocks Member

    Messages:
    7,026
    Joined:
    Feb 10, 2007

    depending on the marshall 4x12 cabinets, the 1960 series give you 4, 8 or 16 ohms so you can match the ohms for most amps, just make sure the speakers can handle the power, the 8 ohm is a 2x12 so the power handling is reduced by half.
     
  9. benjammin420

    benjammin420 Member

    Messages:
    1,565
    Joined:
    Jan 13, 2009
    Location:
    Vancouver, BC
    16 ohms handles the most power? 4 ohms handles the least?
     
  10. zoooombiex

    zoooombiex Member

    Messages:
    2,548
    Joined:
    Apr 13, 2004
    Location:
    Columbus, OH
    ohms and power handling are separate.

    power handling is the max wattage the speakers can take before they physically break. (Note, though, that there are a lot of liberties taken when measuring power of amps and speakers.) so if your amp is putting out 80 watts, you need your speakers to be able to handle 80 watts.

    if you're just using one speaker this is easy - it must be rated to handle more than your amp's power. if you have multiple speakers (2x12 or 4x12, etc.), you need to make sure your cab as a whole can handle the amp's power.

    So, eg., if you are using a 4x10 with all the same speakers, and each speaker can handle, for example, 30 watts, that means the four speakers together can handle 120 watts (4x30 watts each).

    If you are not using four of the same speakers in your cab, then the total power handling of the cab is limited by the speaker with the lowest power rating. (Assuming the impedances of all the speakers match) each speaker is getting an equal part of the signal, so you need to know that the lowest rated speaker can handle its proportionate share of the signal. So to get the total power handling of the cabinet, you take the speaker with the lowest power rating and multiply that by the total number of speakers. e.g., say you have 2 15 watt speakers and 2 30 watt speakers in your 4x10. that cab can only safely handle 60 watts (4 x 15 watts). if your amp is putting out 80 watts, each speaker is getting 20 watts. the 30 watt speakers will be fine, but this will eventually blow the 15 watt speakers.


    ohms are separate from power handling. ohms are a measure of impedance (think of impedance as the resistance of the audio signal). the signal coming out of your amp has an impedance (if your amp has multiple outputs for different impedances, that means it can generate the signal with those different impedances). speakers also have an imput impedance - they expect to get a signal with a certain impedance. (they can accept signal with a different impedance but it affects their behavior)

    in general you want the impedance of the signal coming out of your amp to be the same as the impedance of what the speakers are expecting to receive. (actually, with tube amps, you can often get away with mismatching the impedance by a factor of 2, but some amps are more sensitive to this than others, so for now I'd stick with matching the impedances).

    so, if your amp has an 8 ohm out, you want the total resistance of your speakers to be 8 ohms. again, if you only have one speaker that's very simple. the speaker's impedance should be match the output impedance of your amp.

    if you connect multiple speakers, you need to make sure the total impedance of all the speakers together is what your amp is putting out. it's not quite as simple as power handling, where you can just add up each speaker's impedance to get the total impedance of all the speakers. there are two different ways of connecting speakers - they can be wired "parallel" or "in series". (You can find wiring diagrams on the web or TGP.) to avoid the math of actually calculating impedances, just know that if you connect two speakers of the same impedance in parallel, the total impedance of the pair is half of each speaker (so two 8 ohm speakers wired in parallel has a total impedance of 4 ohms). if you wire the speakers in series, the total impedance is the sum of the two (so two 8 ohm speakers wired in series has a total impedance of 16 ohms).

    (note: you can wire together two speakers of different impedances, but this gets more complicated because then they are not sharing power evenly, so I'd stick with using all the same impedance speakers in one cab)

    with a 4x10 or 4x12, it's slightly more complicated, but ultimately easier. if all four speakers have the same impedance, then the total impedance of the cab is the same as each individual speaker (a 4x10 cab with four 8 ohm speakers has a total impedance of 8 ohms). that's because cabs are generally wired in either "series-parallel" or "parallel-series" - and either way the impedance of the cab is the same (though some find tonal differences between the two).

    there are diagrams running around for this. you can also draw up a diagram of the speakers in your cab now - just note which colored wires are running to which terminal on the speakers. when you put in the new speakers, recconnect it the same way.
     
  11. benjammin420

    benjammin420 Member

    Messages:
    1,565
    Joined:
    Jan 13, 2009
    Location:
    Vancouver, BC
    So it sounds like the best thing for me to do, is take it to a pro and have him do it up in a standard setup. I was just curious, since if im if replacing the speakers, what kinds of customization are possible, but there seem to many factors for me to want to screw with it.

    What are the noticable differences between a a cab wired parallel vs series?


    also, has anyone put Celestions into their fender? part of me feels this is like sacrilige, but tone is tone
     
  12. rockon1

    rockon1 Member

    Messages:
    11,455
    Joined:
    Aug 12, 2005
    Location:
    Stamford CT
    In your configuration (4x10) you only have one option really and thats 8 ohm speakers with the original wiring. Bob
     
  13. zoooombiex

    zoooombiex Member

    Messages:
    2,548
    Joined:
    Apr 13, 2004
    Location:
    Columbus, OH
    True - I probably gave too much info above, but that was mainly just to help understand the factors at play. For your purposes I'd go with 8 ohm speakers wired the same as yours now. You could technically switch the wiring (from series-parallel to parallel-series, or the other way around) but I'd stick with the way it is originally wired.
     
  14. benjammin420

    benjammin420 Member

    Messages:
    1,565
    Joined:
    Jan 13, 2009
    Location:
    Vancouver, BC
    no, i thank you, my reason for asking is so i can learn about these things. dont wanna be green forever. Im going thru a phase where im questioning how i can tweak all my gear for my personal liking (but more often i than not i find 'if it aint broke dont fix it')
     

Share This Page