Your first paragraph is like an abstract for an MIT white paper. Check out MIT's web site under "technology".
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Judith, please don't make the mistake of interchanging phase issues in ELECTRICAL paths (wires)with those of MECHANICAL/ACOUSTIC transducers in AIR!
I'm getting a bit above MY depth here, too, but some wire manufacturers would have you believe that their constructions somehow are as important or effective as getting lowest phase (and group delay) in speaker/room loading. Watch out! Copper is NOT air!
It's good that you are asking the question in an engineering context. As stated, your question is too broad for a simple answer, but I suggest that you pose a similar question on one or more of the specialty forums at Audio Asylum (speakers, cables, amps), where it should generate more in depth technical discussion.
Beg to differ. Phase and time coherence is not a priority for the vast majority of speaker manufacturers. Of the hundreds out there only a handfull design for these parameters. The jury seems to be out on the importance of these characteristics and the tradeoffs, at least in loudspeakers, generally involve having the drivers contributing significant energy outside of their optimal bandwidth. Sometimes the medicine kills you while knocking out the cold. That said, compared to loudspeakers, most electronics are significantly more phase coherent, as are most cables.
Judit, Quads like any fullrange electrostat or any fullrange single-driver cone speaker, are inherently time aligned. The phase alignment has to do directly with the phase shift that may occur in the single drive element. The advantages of these types of speakers goes beyond the time and phase characteristics, and into speed and coherence. Disadvantages may include narrow dispersion and intermod distortions, and possibly limited low frequency extension.
Multi-driver systems may use different techniques to create time and phase alignments, but are inherently hampered by the multiple drivers themselves. They try to simulate point source sound, but never really achieve it. In addition, the crossovers and additional drivers create as many or more problems than they solve. Advantages may include wide frequency extension, lower intermod distortion, and possibly higher power handling and SPL. Disadvantages would include crossover distortion, driver matching and overlap problems, and lack of the point source radiation pattern that they seek to simulate.
Much depends upon the system and goals you wish to achieve, and your particular sensitivity to these various disadvantages of each type. Picking the faults that you can live with is as important as picking the strong points. Nothing is perfect, and compromise is going to happen with all designs. The sound is the final arbiter, and designs are simply ways to get there. You must pick your poison.
As far as electronics matching up with these speakers, unfortunately, there is a hodge-podge approach to this in audio today. Components are designed to work with a wide range of other components, and cannot take individual speaker characteristics into account. This leads to the inevitable "synergy" discussions about what amp is best for what speaker. Some basic guidelines can help, but auditioning is really the only solution.
With the present situation, all distortions in the system will add together to give a total system distortion, as well as the same result in total system phase linearity. Some work is being done in distortion cancelling "synergy", but this is very strictly limited to certain amps and speakers that are not "mainstream" products. At least, not yet.
I must be in a disagreeable way today. All single element and single driver systems are not inherently time aligned. In fact, when a cone driver is used above the frequency that it maintains pistonic motion it is operating in breakup mode wherein one part of the cone is moving outward while another is moving in. Interestingly, many very fine systems operate their mid/bass or full range drivers this way. Flat frequency response can be maintained as well as excellent dispersion, however time response is, necessarily, compromised. Virtually all single cone systems with 5" or 6" drivers are in breakup as early as the top of the midrange. The Lowther and several others such as the Phillips even add a whizzer cone to tailor the breakup of the cone. There will not be any passing of square waves on these systems. Not with the integrity of Judit's beloved Thiels and Vandys and certainly not like the Quad 63 which actually uses annular rings and a delay line to yeild both phase coherance and point source dispersion.
All speakers will benefit from a more perfect signal. Phase and time correct speakers are no different. Feed them a good signal through good electronics and wire and you will be justly rewarded.
For a good read, visit the Audio Perfectionist Journal. Richard Hardesty believes in this design. Also, read watchdog #13 at the same sight. Fried discusses time and phase coherent speakers. I agree with what he says. I've been using this type of design and found it to be a very good thing. I have been ultimately disappointed by other designs. They start off well but then you begin to miss something.
Time and phase speakers I feel are misunderstood. One, we are talking acoustical phase which affects time(and visa versa) Two, they are very hard to design properly. Three, they have complex crossovers to achieve the design goals contrary to what some would have you believe is a single cap. Four, they are MORE costly to build. Five, they DO require a more complex setup. This is the most important aspect really. It makes or breaks the speaker.
Most dealers don't have a clue to how to set them up or don't want to take the time. You can't just slap them in any old spot like a lot of other speakers and expect decent sound. It want happen.
Once I was exposed to this design, I want being going back. They will perform adequately without the best electronics but will reward you if you can afford the best. Just make sure they are set up properly.
Marty...most speakers...operating as such in the time domain...are poor instruments...but then again...not every time and phase correct speaker has "blown my hair back"...Vandersteen,Meadowlark,etc are good speakers...but to me..their shortcomings have more to do with LF extension(or lack of it)...and in this regard...at their prospective price point...they are no different than many other designs...