Hi yes I will go through a crossover the problem I have is the original tweeter they no longer produce parts for but I have found a voice coil that will fit from the same manufacture
Thanks
a 4-ohm resistor is required to match the impedance for crossover values to remain the same, although, the efficiency of the new tweeter should be a consideration, since adding the 4 0hm resistor will drop the output by 3 dB.
you would put it in series with the speaker, BUT, this will dissipate half the wattage so it will get hot..... I would find a sufficiently rated resistor for that, but I really would not recommend doing it this way, you can always add another 4 ohm tweeter in series with it, or get a different crossover that can handle driving the 4 ohm tweeter.
It is a non-standard value, I doubt you will find one off the shelf > Yellow, black, gold
You forgot to post the crossover circuit. Sometimes it is just one simple capacitor in series with the tweeter to block bass sounds. Replace the capacitor designed for 4 ohms with a capacitor having half its value for 8 ohms.
If the new tweeter is not loud enough then simply turn up the treble tone control.