Driver matching...

If you had a woofer that was 4 Ohm with 99dB sensitivity, what options besides a 4 Ohm / 99dB tweeter could you use? What would be the match with an 8 Ohm tweeter?

(I know this is a simple way to look at it).

Thanks.

Impedance of tweeter is irrelevant for the most part, as long as the amp can handle that nominal impedance. Usually, xover and attenuation will alter the impedance curve anyway.

Hypothetically, if you have 99dB woofer, after full BSC this number will drop -6dB. This means a tweeter at 2.83V of 93dB will be appropriate, impedance notwithstanding.

The other end of the exercise is that to work in a reasonable box, that this woofer will not play very low, and is likely better as a midrange. This is of course unless you want to take a loss and plan for better extension by further reduction of the mids in the xover. This means a less sensitive tweeter could be used.

Later,
Wolf
 
Tweeters are usually more sensitive than woofers. At least the ones I would buy.
One puts resistors in series with the tweeter to lower the output level. This makes impedance 12 ohms or 16 ohms or whatever.
One puts crossover components in front of both tweeter & woofer to keep sound of frequency they can't reproduce out of them. This makes the impedance of the out of range sound higher than the impedance of the in range sound.