A Question About Time Alignment

@carlsbad (edit: and @erik_squires) has/have it exactly correct: all frequencies travel at the same speed---the well-known "speed of sound".

As to time alignment of the drivers, a major objective in a multi-driver loudspeaker is to get the different drivers to be in phase with one another, especially at the crossover "point" (read on). At that crossover point (not a single frequency, but the frequency range withing which driver outputs overlap), if two involved drivers are in phase, their combined outputs will "fill in" the declining slopes of both drivers, thus producing a flat freqency response (for instance, the falling output of the low end of the tweeters output and the falling output of the high end of the midrange drivers output. Those declining outputs are the consequence of the two drivers raw responses combined with the crossover filter slopes). If the two drivers are not 100% in phase at the crossover frequency, that won’t occur "completely", and there will be a "dip" in response. It’s complicated, but drivers are referred to as having certain "degrees of phase rotation", a subject far too technical to explain in this post. The information is available in the literature.

But there is another consideration. "Time aligned" drivers are aligned at a given listening position, that position in relation to the drivers. In his excellent YouTube videos, Danny Richie of GR Research demonstrates how moving a measuring microphone (which is a substitute for ears) effects the phase relationship between drivers. Two drivers in phase at a listening position equidistant between two drivers can become somewhat or even significantly out-of-phase when the mic is moved above or below that equidistant position.

"Time aligned" has become a marketing buzz word, but it is an over-simplification of the complex relationship between drivers in all multi-driver loudspeakers with crossovers. Just buy a Sound Labs or Sanders full-range ESL, a planar-magnetic dipole (Eminent Technology or Magnepan), or a loudspeaker designed by Danny Richie ;-) . The latter are available only as DIY kits, but you can do it!

PS - Looking at the step response (Figure 5) this is not a time-aligned speaker.  If it were there would be a single rising impulse followed by a long decay.  The two peaks are indicators that these speakers are phase aligned. 

A reason why you want time aligned drivers in a multi-driver loudspeaker is that you want the fundamental frequency to arrive at your ear at the same time the overtones arrive.  There are multiple ways to achieve time-alignment in a loudspeaker including the placement of the drivers.  As mentioned above by others, some people think it's important and others don't.

My Sonner Legato Unum are time aligned and sound fantastic in my system. 

As are the entire Sonner line.  Simply a wonderful speaker no matter what amplifier I use. Much of this is due the the driver time alignment. 

The Legato Series was engineered in a way that they can be driven by a small or large vacuum tube or solid state amplifier and easy placement or set up in a room. Sophisticated cabinet design utilizing one piece molded curve cabinet, state of the speaker drivers, and high quality crossover components work in harmony with our Symmetrical Panoramic design crossover network to deliver a natural sound, effortless micro and macro dynamics, huge soundstage with a sense of air around the musician and instrument while maintaining music emotion.

This series was created to deliver musical expression, huge soundstage and vivid imaging on a small foot print with a more attainable price point.

TECHNOLOGY

At Sonner Audio, our focus is on providing you sound quality that is authentic and emotionally rich. Our Creative Development Team finely tunes each speaker beyond computer modeling and simulation, with extensive human listening tests to bring a completely unique, realistic and dynamic experience to fellow music enthusiasts like you.

 Sonner Audio Legato Unum Loudspeaker | REVIEW - Part-Time Audiophile (parttimeaudiophile.com)

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Physical time alignment of drivers is accomplished by building them into the cabinets so that the magnets/voice coils are vertically aligned so they are radiating the same info in temporal alignment, reaching the listeners ear at the same time.

What is audio time alignment?

In other words, the high frequencies and low frequencies much reach the listener's ear at the same time. A system which meets this criterion is said to be “time aligned.” One way to accomplish this is to place the tweeter further away from the listener than the woofer, and this is done in many speaker systems.

ASR answer to the question: