'Now I want to make speakers which have flat response from 80Hz-20kHz (THX crossover point is 80Hz)' [STEFAN]'...if you are referring to "THX Approved" speakers, I think that any quality speaker is going to play music or home theater just fine...'
[member in a HT forum]
Speakers complete list of THX testing categories (from www.thx.com Product Test):
Axial Frequency Response Analysis
Directional Characteristics
Sensitivity
Impedance
Harmonic Distortion
Low Frequency Cut Off
Phase Angle
Stray Magnetic Flux
Maximum Output Level
Acoustic Noise Level
Polarity