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Loudspeaker Impedance



Combining Speakers of The Same Impedance



In a Parallel connection both positive terminals are wired together and both negative terminals are wired together.

One wire goes from one of the positive terminals (doesn't matter which) to the tip (hot) of the speaker cabinet jack or cable. Another wire goes from one of the negative terminals to the sleeve (ground) of the speaker cabinet jack or cable, and so on for all the others.

The total impedance (Z) of a parallel connection is the individual impedance divided by the number of speakers that you are using.

  • 2 of 8 ohms = 8/2 = 4 ohms (Twin, Vibrolux, Pro, Bassman, Bandmaster)
  • 2 of 16 ohms = 16/2 = 8 ohms (Marshall Bluesbreaker)
  • 4 of 8 ohms = 8/4 = 2 ohms (Super reverb)
  • 8 of 32 ohms = 32/4 = 4 ohms (Ampeg SVT)
  • 3 of 8 ohms = 8/3 = 2.7 ohms (old Bandmaster)


In a Series, the positive terminal of one speaker is connected to the negative terminal of the other (doesn't matter which). This leaves a free positive terminal which is connected to the tip (hot) of the cabinet jack or cable and a free negative terminal (on the other speaker) which is connected to the sleeve (ground) of the cabinet jack or cable.

To find the total impedance (Z) of a series connection mutiply by the number of speakers:

  • 2 of 8 ohms = 8 x 3 = 16 ohms ('Red knob' Fender Twin)
  • 2 of 16 ohms = 16 x 2 = 32 ohms
  • 3 of 4 ohms = 4 x 3 = 12 ohms


Multiple speakers are generally hooked up in a Series-Parallel connection.

In order to figure out the total Zwe now combine both of the above formulas:

  • 4 of 4 ohms = (4 x 2)/2 = 4 ohms
  • 4 of 8 ohms = (8 x 2)/2 = 8 ohms
  • 4 of 16 ohms = (16 x 2)/2 = 16 ohms

Series Parallel Wiring

Typical 4 x 12 Marshall Style Cabinet



 




Number of Drivers Series Parallel Series+Parallel
2 x 4 ohm 8 2 n/a
2 x 8 ohm 16 4 n/a
2 x 16 ohm 32 8 n/a
3 x 4 ohm 12 1.334 6 or 2.667
3 x 8 ohm 24 2.667 12 or 5.337
3 x 16 ohm 36 5.334 24 or 10.667
4 x 4 ohm 16 1 4
4 x 8 ohm 32 2 8
4 x 16 ohm 32 4 16


Combined Speaker Impedance Chart

 

Important!! Please note from the above chart that it is Impossible to get 8 ohms when connecting four 16 ohm speakers together in any possible manner!!



Combining Speakers of Different Impedance


When 2 speakers of different impedance are connected together, either in series or in parallel, it is impossible to deliver the same power to both speakers! If one is 4 ohms and the other is 16 ohms, for example, the 4 ohm speaker will be receiving 4 times the power of the 16 ohm unit when they are connected in parallel! Definitely not recommended!

Series connection is no better for the opposite situation occurs and the 16 ohm unit is now handling 4 times the power.

The formula for parallel Z is:

  • Zt = 1 / ((1/Z1)+(1/Z2)+(1/Z3))

Using one 4 ohm and two 8 ohm units this gives:

  • Zt = 1 / ((1/4)+(1/4)+(1/8))

  • Zt = 1 / (5/8)

  • Zt = 8/5

  • Zt = 1.6 ohms

For series connection just add everything up:

  • Zt = Z1 + Z2 + Z3

  • Zt = 4 + 4 + 8

  • Zt = 16 ohms









ImpedanceMatching :: Impedance

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