I'm not the OP and not a native speaker either, but am better-than-average at pinpointing sources of misunderstanding:
- @Martelino doesn't know that it is the impedance of the driver that determines how much power is delivered to it by the amplifier; the amp section of the combo doesn't "feed 4 ohms" to the woofer. 4 ohms is only the lowest safe total impedance load that the amp can be hooked to, not something inherent to the amp itself.
Examples: amp+two 4-ohm drivers? Amp shuts down or gets damaged; amp+one 4-ohm driver? It delivers 300W to the driver, which hopefully can take them (if not, driver gets damaged); amp+two 8-ohm drivers? Same as the above, but drivers need only be rated 150W each, for them not to get damaged; amp+one 8-ohm driver? Because the amp "sees" 8 ohms, which is double the minimum safe impedance (4-ohms, at which its 300W rating is valid), it delivers half its maximum power (it's usually a little more than half, for...amp reasons) to the driver, that is to say 150W (again, it is usually a little more than half). With the vast majority of solid-state amplifiers there is no problem whatsoever with the final scenario (again, provided that the single 8-ohm driver can take 150W). As a final example, you could even hook a single 32-ohm woofer to the amp, and the amp would simply feed the woofer about 40W max, precisely because the impedance of the driver is 32 ohms.
- @agedhorse, the Ibanez Promethean p3110 is a combo and, if I remember correctly, its fancy driver has both a coaxial tweeter and also a double voice coil.
Martelino: the "external speaker out", when a jack is inserted to it, disconnects one of the coils of the driver, bringing up the impedance from 8-and-8 ohms (that is 4 ohms, in parallel) to just 8 ohms, which allows another cabinet (which must be 8 ohms or more) to be hooked up to the combo. The amp delivers 300W to the internal double-coil driver, only 150W to one coil if a speaker cable jack is inserted in the speaker out, and again 300W if the cable is connected to an external 8-ohm cab. Why would you want an external cab, since the combo puts out 300W with or without it? Because, more often than not, more speaker area = more volume.
The tweeter doesn't factor in the equation, because it operates at higher frequencies than the woofer coil(s) impedance minima. Or something like that.
So, unless you find the original, double-coil speaker, you can only:
-put in a 4-ohm speaker, and forever give up the possibility to add an external cab;
-put in a single-voicecoil 8-ohm driver, and know that it will only receive 150W, but if the new driver is more efficient then the original it may be just as loud, or more. You will retain the ability to add a cab when needed.
-the mounting of the tweeter (coaxial) is an additional complication. If the new driver is something like the Eminence Beta 10CX, you can mount (in fact you should, whether you use it or not) a screw-on tweeter to it. Not sure if the original tweeter will fit. Alternatively, you could put a tweeter in one corner of the cab, if there's enough room.
I hope I've made sense...
