Wiring three 8 Ohm Speakers to get 5 .33 ohms

Discussion in 'Amp Tech Center' started by drob, Nov 1, 2016.

  1. drob

    drob Tele-Holic

    Posts:
    525
    Joined:
    Jan 6, 2011
    Location:
    Toronto
    So I spent too much time today trying to figure this one out. I have a couple of old PA speakers with three 8 ohm drivers. I pulled the back off of them because one was buzzing. I saw that they were wired differently from each other so pulled all the wire and thought I'd start fresh. That was a mistake. I found the bad driver and replaced it in the cabinet but am now trying to rewire it. I have wired two speakers (B&C) in series for 16 ohm's. I then fed that pair by connecting the + to the + on speaker A and took a run from that to feed the + on Speaker B. I took the - from speaker C and connected to the - on A which is also connected to the - speaker wire. So I have the B&C pair in series connected to the A in parallel. Does that sound about right? If of course you can understand what I wrote.
     
  2. waparker4

    waparker4 Doctor of Teleocity Ad Free Member

    Posts:
    18,996
    Joined:
    Nov 9, 2011
    Location:
    Philadelphia, PA
    Why?

    Unless you wire them all parallel or all series, the speakers are not going to produce even levels.
     
  3. drob

    drob Tele-Holic

    Posts:
    525
    Joined:
    Jan 6, 2011
    Location:
    Toronto
    My powered pa can run 4 or 8 ohms. This is the only way to get a resistance acceptable. The speakers were wired this way, but on one the tweeter was wired in parallel while the other was in series. They're pretty pathetic but it's for my sons band to practice with.
     
  4. waparker4

    waparker4 Doctor of Teleocity Ad Free Member

    Posts:
    18,996
    Joined:
    Nov 9, 2011
    Location:
    Philadelphia, PA
    You can unhook one speaker for 4 ohms, or if it is a solid state PA, it should be able to drive more than 8 ohms (i.e. series) you will have less power but it should not cause a problem.
     
  5. telemnemonics

    telemnemonics Doctor of Teleocity Ad Free Member

    Age:
    60
    Posts:
    17,378
    Joined:
    Mar 2, 2010
    Location:
    Maine
    I suspect that you need to get info on the wiring of your (old) PA cab, since tweeters may have required a crossover network to prevent high power low frequency signal from reaching them.
    Old time series parallel PA wiring would have included the fact that different drivers had different power ratings.
    If you wired the PA to the tweeter, and the tweeter to the series woofers, you might just blow the tweeter right away and have a 16 ohm load.
    It's also possible you have a 30w horn and two 20w woofers, in a PA cab rated for 60w.
    This is not really the same as guitar cab wiring.
    Any info on cab or drivers?
     
    waparker4 likes this.
  6. robt57

    robt57 Telefied Ad Free Member

    Posts:
    23,713
    Joined:
    Feb 29, 2004
    Location:
    Portland, OR
    You can get 5.33 with series/parallel wiring. But the one off the series side of the circuit is going to take 2/3 of the power and the other two split 1/3 of the power. It could work if you are using two lesser speakers with one robust driver off the series side of the circuit. I doubt you will hear the two on the series side spitting the 1/3 power if at all.

    Get this spread sheet:

    http://www.duncanamps.com/technical/impedance.html

    If you do not have Micro$oft Office for 'Excel' to open the spread sheet, you can get Open Office here: http://www.openoffice.org/download/
     
    Last edited: Nov 1, 2016
  7. waparker4

    waparker4 Doctor of Teleocity Ad Free Member

    Posts:
    18,996
    Joined:
    Nov 9, 2011
    Location:
    Philadelphia, PA
    My comments are assuming the three drivers are the same. (To clarify)
     
  8. robt57

    robt57 Telefied Ad Free Member

    Posts:
    23,713
    Joined:
    Feb 29, 2004
    Location:
    Portland, OR
    The circuit doesn't give a sheit FWIW. The math will show where the power is going to go and which drivers in the circuit will be doing what work. More watts more work, right?
     
    asnarski likes this.
  9. robrob

    robrob Poster Extraordinaire Ad Free Member

    Posts:
    7,551
    Joined:
    Dec 29, 2012
    Location:
    United States
    I agree with waparker4, just unplug one of the speakers and run the other two in parallel.
     
    asnarski likes this.
  10. robt57

    robt57 Telefied Ad Free Member

    Posts:
    23,713
    Joined:
    Feb 29, 2004
    Location:
    Portland, OR
    Will the two cover the power requirements?
     
    waparker4 likes this.
  11. telemnemonics

    telemnemonics Doctor of Teleocity Ad Free Member

    Age:
    60
    Posts:
    17,378
    Joined:
    Mar 2, 2010
    Location:
    Maine
    Sounds like the OP assumes the same thing.
    IDK!
     
  12. drob

    drob Tele-Holic

    Posts:
    525
    Joined:
    Jan 6, 2011
    Location:
    Toronto
    The original speaker has 2 of the same drivers and one with an enclosed basket that I assume handles the highs. On one speaker, the closed basket had a capacitor wired to it, I assume to filter out some lows. It did not have the third speaker wired correctly so it wasnt ever connected. The other speaker was wired with the cap on one of the regular drivers with no cap on the closed basket. It had one of the pair if identical drivers with rot on the paper cone. It was coming away from the basket gasket causing the buzzing sound. I have replaced it with a speaker from an old Vox pathfinder. I now have the cap as the second speaker in series so it's last in the chain.
     
  13. dsutton24

    dsutton24 Doctor of Teleocity Ad Free Member

    Posts:
    10,199
    Joined:
    Dec 29, 2010
    Location:
    Illinois
    What a weird thread...

    Take two speakers, wire them in series. Hang the third one across the series pair. It's really no more difficult than that.
     
  14. drob

    drob Tele-Holic

    Posts:
    525
    Joined:
    Jan 6, 2011
    Location:
    Toronto
    i think I've done the opposite. I wired to the third with the two in series hanging of it. Does it make a difference?
     
  15. robrob

    robrob Poster Extraordinaire Ad Free Member

    Posts:
    7,551
    Joined:
    Dec 29, 2012
    Location:
    United States
    Two wired in parallel will provide the correct load to the amp and the two speakers will equally share the load at 50/50. With all 3 wired up one will be hit with 66% of the power so two speakers will have more power handling than three.
     
IMPORTANT: Treat everyone here with respect, no matter how difficult!
No sex, drug, political, religion or hate discussion permitted here.


  1. This site uses cookies to help personalise content, tailor your experience and to keep you logged in if you register.
    By continuing to use this site, you are consenting to our use of cookies.