This is what happens with a uniQ driver if they are driven fullrange .
Kef Q100
www.erinsaudiocorner.com
View attachment 238928
At +-3mm movement of the cone, you get a 8 dB difference at 7,5 KHz in frequency response. This happens if you play real music containing deep bass . The cause is the cone acting as a variable waveguide for the tweeter when its moving .
This can not be seen with a sine sweep.
To solve this problem , a uniQ driver or any other coaxial driver has to be HP filtered at about 300 Hz . This is done in Kef reference 1.
So the ls50M is compromised because of this , the problem gets smaller if they are HP filtered at 80 Hz .