I agree with this. A proper 3 way in this size has to use a small sealed mid driver (some kind of 2-2.5" class), there just isn't the space for a separate woofer to have enough cabinet volume.That's probably because it isn't. I could imagine Edifier engineers making this speaker, reusing parts from the MR3 like the tweeter, woofer and waveguide, as a low-cost response to studio monitors with 5-6.5 inch bass drivers.
"Our MR3 is alright with improved bass response compared to MR4, but 65Hz @ -6dB is still insufficient. And people don't want to buy/have a large unwieldy subwoofer. How bout we enlarge the enclosure and jam a 5-inch woofer inside" sorta thing