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I have a 3 way speaker, all the drivers are 4 ohm. The tweeters are defective. If I replace them with 8 ohm tweeters what kind of problems will this create? Any simple things I could do to the crossovers to make this work?
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Not only will you have to change resistors to get the balance correct. you will have to change the capacitors and inductors to keep the same transfer function of the crossover because the values of the caps and inductors depend on the impedance of the driver that will be changed by changing the voice coil. you are literally redesigning half the speaker.
Yep. For a 1st order crossover f=1/(2*pi*C*Z) so the frequency and impedance are related. For a 2nd order crossover f= 1/(2*pi*sqrt(L*C)) and so the frequency is independent of the impedance. However the Q of a 2nd order filter is dependent on the impedance (Q = Z*sqrt(C/L) ).
Therefore if you have 1st order HP you will need to halve the capacitor and if it is a 2nd order the sqrt(C/L) needs to be halved (C/L is 1/4). Halve the cap value and double the L value (the product L*C will remain the same). Of course this assumes that that real impedance of your 8 ohm speaker is actually twice the real impedance of the 4 ohm speaker - and that is unlikely.
Edits: 03/02/15 03/02/15
A simple 8Ω~10Ω resistor in parallel will make the crossover point the same, but you will need to use a more efficient tweeter to replace the original.
More info (make/model/photos, etc.) would help to recommend a replacement driver.
It is a KEF uni-q NT25 tweeter (SP1240). 1 inch 4 ohm VC. I want to try to rebuild them. I can find 8 ohm VC that look like they might work but no 4 ohm.
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thanks for the link, I also found some on Ebay that may work so that may be my solution if I can't find a 4 ohm voice coil that will work.
thanks for the link, I also found some on Ebay that may work so that may be my solution if I can't find a 4 ohm voice coil that will work.
You really have no choice but to use the KEF part (unless you want to mount a tweeter in a pod on top and re-design everything).
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