Dumb question re: 8ohm for 4ohm speakers.

Discussion in 'Speakers' started by MarZutra, Sep 12, 2017.

  1. MarZutra

    MarZutra Super Member

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    Hi all, a really dumb question for those that know....
    I have a line on a pair of vintage Epi 602 speakers that run 2 8" 4ohm drivers in each. Basically the boxes and crossovers. I have the tweets but sadly these 4ohm drivers are extremely rare to find single on the used and sourcing four would be neigh impossible.
    Further, new matching 8" 4 ohm drivers are available however the cost of purchasing 4 and having them shipped to Canada would kill any and all deals for the speakers themselves and their 'restoration'.
    My question is that I have 4 refurbed Epi 8" 8ohm drivers that look exactly like their 4ohm drivers. What would happen if I substituted the 4 original Epi 8" 4ohm drivers with original Epi 8" 8ohm drivers?
    Or is there any way to 'change' a 8ohm to 4ohm?!?! Living where I do - and 'free trade - has killed so many potential deals/projects...
    Thanks...
     
  2. StimpyWan

    StimpyWan Super Member

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    Is this the speaker? If so, there are 2 8" woofers and a 6" front midwoofer. Plus, they use 3 tweeters per cabinet. That wouldn't be cheap to rebuild.

    As to the 8 Ohm / 4 Ohm question, I'm not sure. It looks like the original design used 2 4 Ohm speakers in series, for an 8 Ohm load. No crossover, as they basically ran full range, with a designed in roll off at the top. So, in theory, you could try your 8 Ohm woofers in parallel*, for a 4 Ohm load. And while it would work, the balance between the rear woofers, and front drivers would be off. You could add l-pads to the 6" and tweeters, in order to re-balance the speaker, if you don't mind the mod work. Or sell your woofers, and try to find the correct drivers?

    Good luck!



    * (Edited for reasons unknown) :rolleyes:
     
    Last edited: Sep 12, 2017
  3. bowtie427ss

    bowtie427ss arigato gozaimashita Subscriber

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    I think he means parallel.


    I might also consider a ".5" mod by introducing a choke(inductor) in series with one of the tandem woofers such that the woofers only provide a parallel load below whatever knee point the inductor creates.
     
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  4. StimpyWan

    StimpyWan Super Member

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    I said (thought) parallel...!!! :p:D Thanks! :thumbsup:
     
  5. StimpyWan

    StimpyWan Super Member

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    I borrowed this image from CSP (Thanks larrybody). It shows a L-pad added to a speaker, that uses a single cap as a crossover. It looks easy to do, if you want to add some adjustment capability to your EPI's?

    [​IMG]
     
  6. MarZutra

    MarZutra Super Member

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    Hey Stimpy, thanks for weighing in. Yes those are them. I am asking the question because the cost of the speakers plus shipping to NS makes a limited budget for the rest of the restoration of them. I checked with Huw the last time this subject came up and it works out to about $100.00CDN/driver. This happened to me once before when a seller of a pair of Epi M400 in Toronto wouldn't ship. Next I know, I saw just his cabinets and crossovers on the used - as he parted out the speakers. .... I was PISSED to say the least because I contacted HUW about attaining the drivers would have been 8 drivers at $53US/driver plus all the tweets....

    This is why I was asking about using original 8" 8ohm Epi in place of the 8" 4ohm Epi...
     
  7. StimpyWan

    StimpyWan Super Member

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    With the simplicity of the crossover, I'd give it a try. It's not like the impedance differences will shift crossover frequencies, since the woofers have no electrical components to affect. Plus, you may find that you like the slight bass increase the 4 Ohm load should provide. And if you have a big enough room, you could partially mitigate that (if needed), by playing with room placement. Further into the room, and the bass reinforcement from boundary effects would be lessened.
     
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  8. MarZutra

    MarZutra Super Member

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    Thanks... Greatly appreciated Stimpy.
     
  9. saabracer23

    saabracer23 AK Subscriber Subscriber

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    Since there really is nothing in the crossover you can make this work. Generally you would need to change each component in the woofers circuit. I don't remember of the top of my head but it's either multiply or divide the value of the certain component by 2. Example would be the 12uf cap would go to 24uf and the 1.5 mH inductor would go to .75 mH, etc. but keeping the circuit layout the same.

    So you'll be going from two 4 ohm woofers wired in series to two 8 ohm woofers wires in parallel to end with a 4 ohm load instead of 8. You may find the woofer may draw more current and will need to adjust the tweeter level with the l pad. Otherwise perfectly fine.

    Dan
     
  10. gdmoore28

    gdmoore28 Super Member

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    I agree with StimpyWan - just install the two 8 ohm woofs wired in parallel for a 4 ohm load. It's the only direction that makes financial sense, and you won't need to concern yourself with the crossover at all.

    Let us know how it works out for you.

    GeeDeeEmm
     
  11. MarZutra

    MarZutra Super Member

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    Thanks guys. Fingers crossed. Surely will. Cheers from up North.
     
  12. MarZutra

    MarZutra Super Member

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    Ok guys, I've found a copy of the crossovers, now if I'm going to re-cap them anyway, what would I have to do to the crossovers to make them run 8ohm drivers (or switch from the 4ohm to 8ohm for the drivers)?
    [​IMG]
     
  13. saabracer23

    saabracer23 AK Subscriber Subscriber

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    If you're just replacing the two rear woofers then keep all of the components in the crossover the same value. The woofers are run wide open. So just switch out the 10 uF cap with another 10. Same with the resistors if you choose to do so.

    Dan
     
  14. MarZutra

    MarZutra Super Member

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    Oh, Ok Dan. Was thinking that I'd have to change them with different half, or double, values for uF. Thanks very much.. Greatly appreciated.
     
  15. saabracer23

    saabracer23 AK Subscriber Subscriber

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    Only if you're changing the drivers in that circuit, so since that capacitor in no way effects the woofer frequency response you're good!

    Dan
     
  16. bowtie427ss

    bowtie427ss arigato gozaimashita Subscriber

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    If you wire 8 ohm woofers in series where the system was engineered for 4 ohm woofers, their output is going to be attenuated a few db relative to the original woofer load while the rest of the speaker system remains the same.

    If you wire 8 ohm woofers in parallel where the system was engineered for 4 ohm woofers in series, their output is going to be increased a few db relative to the originals, and rest of the speaker system as well as increasing the load on your amplifier.

    This is why i suggested using an inductor on one of the woofers to roll off it's response as well as it's impedance fairly low to smooth both the overall system response and load.
     
  17. MarZutra

    MarZutra Super Member

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    Thanks. I think what I'll do is when/if this project materializes, I will get everything out on the table and post pics and get step 1, 2, 3 etc. as to what/how and if I need to purchase anything else. I'll have to do this on the cheap due to the cost of purchasing 4 replacement 4ohm drivers will kill the project entirely.
    Best again and thanks.
     
  18. onplane

    onplane What! No Wake???

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    To save $'s the clear answer is to use the 8" 8 ohm drivers you already have. You would naturally want to wire these in parallel (resulting in a 4 ohm load), but this means your other drivers would be way behind the woofers in SPL. That is, the parallel woofers would simply over power all of the other drivers.

    Another option no one has mentioned is bi-amping! That is dedicating an amp to power the woofers and a separate amp (could be a lower power unit) to power the high frequency drivers. You would bring everything into balance simply using the volume controls on the two amps.

    Now, this means you'd need another amp and I am a strong proponent of recycling old mid power units currently collecting dust. Using these units to power just high frequency drivers makes all the sense in the world.

    It would mean that you'd have to bring out two additional terminals, but that's not a big deal and would not be very expensive.

    Hope this helps...
    Regards,
    Jerry
     
    Last edited: Sep 15, 2017
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  19. MarZutra

    MarZutra Super Member

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    Thanks onplane. Never thought of that. Thanks very much. I'll keep you all posted. Greatly appreciated...
     

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