Phase Shift in Audio Amplifier
Unfortunately unless you have expensive linear-phase, planar-speakers or similar high quality speakers, the group delay distortion is quite significant in that it distorts the triangulation of the sound source on a stage.

But lets assume you have an anechoic room with perfect speakers.

The phase response is only shifted 50% at the half power point and the pass band must be 2 decades higher if phase shift is critical but by that point the amplitude is now 20 dB attentuated per order of the filter per decade. So our perception tends to ignore that.


  My Rule of Thumb for phase response is 1.5 decades of bandwidth above useable bandwidth with less than 10 degree phase shift.  For 1 degree such as TV baseband color video, you need at least 2 decades more bandwidth.


The ideal LPF response is a flat group delay found in this filter normalized at @1kHz.


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