A Question About Time Alignment

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.

Hello Paul6001.  All the sound waves move at the same speed. The wavelengths vary with frequency, but not the speed of their travel. We are trying to reproduce music that arrived sometime in the past on the diaphragm of a microphone. We do not want to add any more time "smear" when we listen to that recrded music. The microphone(s) "hear" what you would hear sitting in the same place as the microphone(s). We want to produce the same sonic patterns in our room that the microphones picked up. So we don't want parts of that recorded sound to reach our ears earlier or later than other parts. Don't mess up the puzzle! If it gets messed up, we won't be able to reassemble in our brains the sound pattern that hit the sensitive parts of the "mikes." If we distort that pattern, we will not be able to successfully reconstruct the performance captured on the recording. The feeling of "being there" depends on an accurate reconstruction of the sound patterns in the recording. Woofers are generally larger than tweeters. If we mount them on the same panel, the voice coils that vibrate to reproduce sound are at different distances from the panel (this is why flat panel speakers have an advantage in accurate sound reproduction - all the sound leaves from the same place). So the sound from the woofer arrives a bit later than the sound from the tweeter. That's the problem some speaker builders try to solve by either moving the tweeters backwards or moving the woofers forward. That leads to some odd loking boxes, but, if perfect reproduction is the goal, it's worth it. Ideally, all the sound producing parts of the speaker system are at equal distance from your ears. Happy listening.