A Question About Time Alignment

I am glad I am a speaker designer and Not a Physicist like some here. Sound is altered not only by distance. Especially when yo consider that the speed of sound is relatively SLOW. Sound is altered and affected by Temperature, Humidity, Barometric pressure... So once again, when it comes to speaker design, I am so glad I don't know anything about sound propagation. One of the first things I worked with 40+ years ago was where I placed my drivers, front to rear. In an effort to find the best placement and the least sound cancelation. If this placement wasn't a factor then room treatments would also be meaningless.

I mentioned just a couple of days ago how I was tweaking the Cant/Tilt to my speakers experimenting on how it changes the WHOLE soundstage. Just by a few degrees. and what it the main thing that is being modified, the forward position of the individual cones by just a few centimeters at a time. This is a simple inexpensive experiment that ANYONE can do on their own at home. You must also realize though that if you are using something like Diraclive this will change how your system is tuned by Dl.

Also, though Diraclive does wonders on manipulating reflective signals and how they interact with each other, it is minimal AT BEST when looking at Frequency.

Thanks to bdp24 for a patient, thorough explanation. I would add a couple of related points (For the record, I have a pair of Thiel CS6 speakers that were designed to be time and phase coherent).

At the PNW Audio Fest I attended a talk by Andrew Jones on speaker design. The subject of time alignment and phase coherence came up. With his witty sense of humor he made a very good case that this is not a major reason why one speaker sounds better than another. It sounds good in theory but in practice it is not a major factor in good speaker sound.

I've heard large Wilsons at three audio shows. At one of the rooms I waited until a slow time when I could sit in the sweet spot and I heard the holographic effect that people were raving about. It was impressive but there were other characteristics of the sound that I didn't like. In another room, however, I heard the same holographic effect - perhaps to an even greater degree. These were Acapella horn speakers that make no claims of time alignment. The sound was so enveloping and the location of the instruments so defined that it was spooky. I thought my Thiels imaged well but this was another level. Due to this experience I'm not sure that time alignment is the key if your major criteria is holographic imaging.

And lastly, the audio industry is becoming very good at selling their products with a story. In marketing is is called a Unique Selling Proposition (USP). Most of the ultra high end products have an elaborate story about a certain characteristic of their product that explains why it is different from its competitors (and worth more money). The audio cable companies are the champions in this category. It ain't easy justifying $10,000 for a pair of wires. Wilson has settled on Time Alignment along with it's cabinet materials. If you read Stereophile or TAS I'll bet that if I named off 5 other high end speaker companies you could tell me their USP off the top of your head.

Bottom line is that how a speaker sounds is the most important factor regardless of it's design parameters and marketing story. You just can't sell a pair of speakers for more than a 2 bedroom house without making the buyer comfortable that he (face it, it's a guy thing) is getting something really cool.

Time alignments are somewhat necessary for good sound but most loudspeakers are only time aligned at one listening position unless concentric or full range. Still, it's best to get proper alignments or you have a frequency imbalance, not just a time issue. If tweeters are too close output is higher if farther away it's lower other transducers are also similarly affected.

To those suggesting that phase coherence doesn‘t matter: listen to a recording in- and out of polarity (i.e. reverting phase) and pay attention particularly to the leading edge of instuments. If you can‘t hear the difference either buy a better system or have your ears checked.

Regarding time allignment: the wider the diaphragms are appart, the harder it is to achieve since 1st and subsequent reflections will be affected by the distance between diaphragms. This particularly affects higher frequencies with their more bundled dispersion characteristics.