Cab/Speaker Wiring Help

Discussion in 'Amps/Cabs Tech Corner: Amplifier, Cab & Speakers' started by granite, Dec 31, 2005.


  1. granite

    granite Member

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    If I have a 8-ohm mono 2x12 cab with two 16-ohm speakers wired in parallel, is it possible to remove one of the speakers and somehow use an 8-ohm speaker in its place? If possible what would I have to do...rewiring, etc...

    My initial thought is that this is not possible or safe.
     
  2. bob-i

    bob-i Member

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    Not really. If you do that the 8 ohm speaker will take 75% of the load. Also the 16 ohms speaker will appear much quieter. It'll work in a pinch but it's just not a good idea to mix impedances.
     
  3. granite

    granite Member

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  4. John Phillips

    John Phillips Member

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    Actually the 8-ohm speaker will take 66.6% (2/3) of the power - power divides in reverse proportion to impedance in parallel, so the 8-ohm speaker will take twice as much power as the 16. (In series it's the other way round.)

    This can be useful to even out power handling and/or sensitivity differences, and it won't make the 16-ohm speaker that much quieter than the 8 - only 3dB if they're the same sensitivity. People often mix speakers of the same impedance but 3dB difference in sensitivity (eg a G12M-25 and a G12H-30), which gives the same apparent difference in volume.

    A 16 and an 8 will also give a 5.33 ohm load to the amp, which is OK from either an 8 or 4-ohm setting, but will reduce the power a bit either way.

    I would agree with Bob that it isn't ideal unless you've got a good reason to do it, but sometimes it can be very useful... eg a 16-ohm Celestion Blue and an 8-ohm G12H-30 in parallel. This gives a true 45W pair and allows both speakers to be driven fully and safely from an amp of that power. If both were the same impedance you're limited to 30W and can't drive the G12H-30 fully without risking blowing the Blue.
     
  5. granite

    granite Member

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    Hmmm...interesting stuff. My soon to be delivered cab will have a 16 ohm Emi Red Fang & a 16 Ohm Emi Wizard. I wanted to try mixing in an Emi Tonespotter but it only comes in 8 ohms. Plan to use the cab with a Hayseed 30 head. Since the RF is suppose to be sonically similar to the Blue and the Wiz similar to the G12H30, might it be OK to experiment? Especially if I want the amp to be a little quieter.
     

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