Does Time alignment and Phase coherency make for a better loudspeaker?

@tomic601 , An engineer does not need ears to develop a phase coherent loudspeaker, just a measurement microphone.

In order to be accurate (I did not say sound good) a speaker has to start with a flat frequency response and be time coherent which as unsounds relates assures phase coherence. Unfortunatly, for speaker designers this has to include the room the speakers are set up in. For state of the art accuracy one has to be able to adjust frequency response so that the speakers are flat from 20 Hz to 20 kHz. This also assures that both channels have exactly the same frequency response which is very important for imaging. If a subwoofer is added one has to make sure they are time coherent with the main speakers. The only way all of this can be done is with digital signal processing. Afterwards the frequency response can be adjusted so the system sounds good to the owner. I like mine up 5 or 6 dB at 20 Hz and down 6 dB at 20 kHz. Done this way the difference between speakers is based on the way they radiate into the room and what kind of source they are point vs line.

Generally, speakers with controlled radiation patterns sound better because they cause less room interaction. Horns, dipoles and line arrays come to mind. Omnidirectional speakers require much more room treatment and produce a smaller soundstage like sitting at the back of the hall. This can sound quite natural depending on the recording. 

@mijostyn ^that^ is all well put.

a few points

flat frequency response is easily obtainable in front of speakers but if the idea is to make a loudspeaker sound good, truly flat frequency response is the wrong goal (google ’bbc dip’)

time coherence is only meaningful if delivered at the listener’s ears, which is not so easy in a domestic listening environment

phase response/inversion has rarely made a major difference in the sound in my own experience (many hifi units allow for remote switching of phase, so it can be very easy to test for oneself)

lots of the things about speakers and what makes them sound good are hard to measure, so as in many things in hifi audio, measurement based criteria are necessary but insufficient conditions for a pleasing result

@jjss49 , flat is always the best place to start. It is a reference point from which adjustments can be made to suit. You can tell me you like your bass boosted 3 dB. 3dB from where? Frequency response and group delays can be easily measured with a $300 microphone and computer program. What can not be measured is the speaker's radiation pattern but this can be determined exactly from the design of the speaker. It is important to remember that the room, the speaker and where the speaker is in the room have to be considered as a unit. Frequency response curves can change dramatically just by moving the speaker a few feet. Identical speakers will have different frequency response curve depending on where they are in the room. Even in what appears to be a symmetrical room they will measure differently. It seems that only people who have no experience measuring loudspeakers in rooms think good sound is hard to measure. Once you know what type of      soundstage you like and choose the appropriate type of speaker, assuming the speaker is well designed you optimize the system in your room by measurement. You can not get to the most accurate sound without it. You start with accuracy then tune it to sound good to you.  If you have a shrill recording and have to ability to punch in a Grundy Curve (BBC curve), wonderful. I have one on a preset if I need it.

It's harder than not so easy to have time coherence at the listener ears in a home environment unless your room is an anechoic chamber. It impossible because of reflections and the inconvenience of having two ears.