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A Question About Time Alignment

I was reading a review of the Wilson Alex V on Stereophile recently. (Published just in time. I’m thinking about picking up a pair. Maybe a couple for the bedroom, too.) And it raised a long-standing question of mine, one that I hope the wiser minds on this site can answer. 
 

Wilson’s big selling point is aligning the different frequencies so they all reach your ear simultaneously. As I understand it, that’s why they have minute adjustments among the various drivers. The woofers put out bass notes that move slowly thanks to their long sound waves while the tweeters are playing faster moving, high frequency notes with short waves. Wilson lets you make adjustments so that they all arrive at the ear at once. 
 

It seems to me, however, that live music isn’t time aligned. Suppose I’m playing the piano and you’re sitting across the room. When I stretch out my left hand to hit the low notes, those notes travel along the same long, slow wavelengths as the notes from Wilson’s woofers. Similarly, the treble notes I play with my right hand move quickly through the short wavelengths. The notes from the piano are naturally out of alignment. If Wilson’s goal is to achieve a lifelike sound, aligning the frequencies doesn’t seem like the way to do it. 
 

Wilson has been selling lots of zillion dollar speakers for lots of years and people continue to gobble ‘em up. Something must be wrong with my line of reasoning. Would someone please point out where I’ve gone wrong? Nicely?

paul6001
erik_squires
16,134 posts
 

So yes, moving the drivers does change the time/phase alignment, BUT!!

It does not alone ensure a perfect impulse response. :D

However, if you align driver's acoustic centers, it means that the crossover works better off axis.

erik_squires
16,134 posts
 

Let me clarify a little.

Each driver has a different distance to it’s acoustic center. Tweeters are shallow, woofers are deep, and we must take this into account in designing the crossover.

Here’s the problem. From the front the tweeter is say 2" closer to your ear than the woofer but at 90 degrees to the side they are the same distance. This means that the phase relationships you take into account in the crossover only hold perfectly true in front of the speaker.

If on the other hand we step the drivers back so that the acoustic centers (usually near the magnets) are exactly aligned, the phase relationship directly in front and at the sides is the same.

Great! this simplifies crossover design. However, if you look at an impulse response in either case, they will still not be perfect. That is more involved. :-)

Another approach here is also to use higher order filters, which D'Appolito recommends for MTM designs.  Steeper filters (also like Joseph Audio's older infinite slope speakers) minimize the phase matching problem off axis in all directions.

deadhead1000's avatar
deadhead1000
714 posts
 

This was a very educational thread. Thanks to all!

urbie
275 posts
 

I don't even think that Wilson's speaker sound that great the monitor audio platinum sound much better.

ghdprentice
7,051 posts
 

Wilson makes some of the most remarkable speakers I have ever heard. I am always impressed… and I am sure they fiddle with them on the basis of time. But it is marketing hype… maybe it is true… but it doesn’t mater, not a reason to buy or not buy their speakers. I never pay any attention to that stuff.

By far, the most amazing audition I have ever had (a couple hours) was with Wilson’s top of the line at its time… carefully set up, simply amazing… 3D images in space. Like holograms in audio. I left with my head spinning and saying that is the best system I have ever heard, I don’t want that, but the most incredible I have heard.

I would decide if they move you and connect emotionally. How they do it is not important. I love Sonus Faber speakers, someone was upset that the cones were made out of paper (a gross oversimplification)… I don’t care… they sound simply splendid to me.

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