OK, here's some of what I remember:
Polk LSiM704C three-way center: Too much upper bass emphasis, combined with a dip in the mid-tweeter crossover region, gave it a dark, almost muddy sound. Somewhat better with ports plugged but now has weak bass.
Energy C-C1 MTM center: A little too much bass emphasis, otherwise decent but not great on axis. Better with one port plugged. Bass gets a bit weak with both ports plugged.
Jamo C 10 MTM center: Too much bass and too much high treble, like a bathtub response with an EQ set to crank up the bass and the treble. Nice build quality though!
Jamo C 80 MTM center: Decent overall, some deviations from neutrality but nothing glaringly bad, but lacking a little spaciousness probably due to MTM layout
NHT Classic Two three-way center: Decent overall, slight tinny, forward in the midrange. A little better spaciousness in the mids than the MTMs.
NHT Classic Three three-way center: Decent overall, very similar to the Classic Two, just a little higher sensitivity (about 2dB louder, but once I compensate for that it sounded very similar, with the same slight tinny, forwardness somewhere in the midrange)
NHT C-LCR Three way center: Current model, probably my favorite out of these budget centers, fixes that tinniness in the midrange but now has a little too much emphasis in the upper treble
Polk LSiM704C three-way center: Too much upper bass emphasis, combined with a dip in the mid-tweeter crossover region, gave it a dark, almost muddy sound. Somewhat better with ports plugged but now has weak bass.
Energy C-C1 MTM center: A little too much bass emphasis, otherwise decent but not great on axis. Better with one port plugged. Bass gets a bit weak with both ports plugged.
Jamo C 10 MTM center: Too much bass and too much high treble, like a bathtub response with an EQ set to crank up the bass and the treble. Nice build quality though!
Jamo C 80 MTM center: Decent overall, some deviations from neutrality but nothing glaringly bad, but lacking a little spaciousness probably due to MTM layout
NHT Classic Two three-way center: Decent overall, slight tinny, forward in the midrange. A little better spaciousness in the mids than the MTMs.
NHT Classic Three three-way center: Decent overall, very similar to the Classic Two, just a little higher sensitivity (about 2dB louder, but once I compensate for that it sounded very similar, with the same slight tinny, forwardness somewhere in the midrange)
NHT C-LCR Three way center: Current model, probably my favorite out of these budget centers, fixes that tinniness in the midrange but now has a little too much emphasis in the upper treble
