What study shows preference for linear phase speakers as opposed to allpass? I would like to read this, I didn't think people were doing listening tests of such a thing.
Normally I'd assume that creating a speaker with two different filters having the same directivity/magnitude but different phase characteristics would be impossible but I guess it's possible now.
I seem to recall that during the development (and later) of the now legendary Klein+Hummel O500C 3-way DSP monitor blind tests were conducted to asses the properties of the three switchable modes of phase linearisation (none = minphase filters, linphase tweeter-to-mid only, full = linphase tweeter-to-mid and linphase mid-to-woofer), but can't dig up a reference atm.
Phase linearisation of any given speaker is well outlined, conceptually, these days:
You just need to obtain, with a DRC software package, the acoustic
allpass phase (excess phase) of the speaker, preferably converted to clean analytical form (with the help of curve-fitters, when required).
The
time inverse of the impuse response of this allpass then is directly the
phase-compensation convolution kernel for a convolver (FIR "filter"), placed on the overall input signal.
Practical examples of this approach are Grimm LS1, for example.
We now can A/B this when switching between the phase-correction kernel and dummy kernel with a "1" at the at final peak sample position in the phase-compensator.
On top of that, we can introduce regular allpass kernels (not time-inversed) to the phase-correction speaker and by this we can asses the effect of arbitrary excess phase / group delay in full isolation, comparable to headphones but with the special properties of real speaker setups.
With a good non linear-phase speaker as the foundation of such experiments, say a Neumann or Genelec, I'm really quite convinced almost anybody will a) be able to detect the (admittedly usually subtle) differences to linear-phase and b) develop a preference for the linear-phase version. It takes some training and obviously some passion for the topic in general, with a lot of evenings quickly adding up...