4 ohms. The amp is 50 watts (so they say) and the Eminence is a 200 watter. The tech at Crate said it should work.
Test the speaker with your PA amplifier (disconnect the Taxi amp) or normal bass amp to determine if it sounds OK in the Taxi enclosure. The only reason it would distort badly with 50 watts of clean power is if the voice coil is rubbing, possible if the magnet shifted from a bad drop in shipping, though usually that causes the coil to become locked and the speaker would just make a low level midrange when played.
The Taxi amp is rated 50 watts at 10% distortion (not clean, but not terrible) with 13.6
volts, about what you get from a car battery when the engine is on and the alternator keeps voltage up. A small lead acid battery as used in the Taxi can only provide about 12.6 volts when fully charged and used at low levels, if you try to pull 50 watts from it as needed for the low notes in a tiny enclosure, the voltage drops and the amp will distort at a lot less power output (probably less than half), the new speaker probably reproduces the low frequency amp clipping more accurately (sounds worse) than the original.
If we figure the amp really can only deliver around 25 watts of low bass when battery powered, the low "E" (40 Hz) would only be about 88 dB at one meter with a 10" in the Taxi enclosure. My voice with no amplification can hit that level easily, but it would only take around 70 dB in the midrange to sound as loud as 88 dB at 40 Hz.
So unless your new speaker is shot, the only recourse for getting more clean bass is better batteries (like Lithium Ion Iron Phosphate, LiFePO4) which are far more expensive, (but lighter) and can deliver near full power till they run out of juice (which can ruin them) or a larger, more efficient (and heavier) cabinet.