Recomendations for using 2 4ohm woofers in a 3way.

Is it wise to use 2 4 ohm 10" woofers in a three way design? Impedence/Ohm issues?
Series might be preferrable to parrallel at 2 ohms or less.
Yes. It happens in commercial designs ALL the time.

Would I do it? No. Dropping the impedance to approx 1.5 ohms or lower in the midbass - where most music energy is - invites current dumping from the amp and generally overtaxes the amp. Yes, watts today are cheap (and speaker manufacturers are counting on that fact) but regardless, the quality suffers due to poor damping (control) from the amp. Of course, it depends how you are designing the box - ported or closed box. Either way, quality suffers unless you have a truly heroic (and generally very expensive) amp.

Better to stick with the parallel hookup, even though your overall sensitivity remains the same as a single driver. The reason for going with two is a sharp reduction in overall distortion since for a given sound level, two woofers are working less hard than a single one.

Steve Rothermel

OOPS. Meant to state series hookup instead of parallel (for preferred method).

Steve Rothermel
If not using series maybe it's best to use 8 ohm woofers instead of 4 ohm. Also should the sensitivity match the mid and tweeter or can they be off a couple db?
If anything, you would want to use mids and tweeters that are more efficient, as it is easier / more cost effective to "pad" or "attenuate" higher frequencies than it is lower frequencies.

Starting off with two 8 ohm woofers would be advantageous in more ways than one. Sean