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The most important question may be...

...is it possible?

I chose Vandersteens because, as Floyd Toole has written, the idea of time-alignment has "considerable engineering appeal." I used them for 4 years (I wrote 3 years in another thread, but I reconsidered; it's actually 4). But I've stopped using them. In the same paragraph, Floyd Toole also wrote that there isn't much evidence to support putting a high priority on time-alignment.

So is it possible? It's possible to get excellent step response, but there are tradeoffs. But there are fundamental problems that I can't think of an answer too.

1. You have to use first-order crossovers because they have a phase shift that doesn't depend on frequency. And first-order crossovers have a low slope

2. Time-alignment is achieved by offsetting the drivers by an amount equal to the phase shift. BUT THIS CAN ONLY BE ACHIEVED AT A SINGLE FREQUENCY.

3. It can also only be achieved at wavelengths (eg, frequencies) where the required offset is of roughly the same dimention as the loudspeaker: 3 inches, yes. 10 feet, no.

* Points 1 and 2 mean that you get interference effects (or, more accurately, incomplete addition, of signals coming from the different drivers, which makes it hard for a speaker to have good frequency response (though it's possible to do a very good job at a fixed distance, and if you look at the Stereophile measurements you'll se that Dunlavy managed to solve this problem, somehow.

That said, some speakers--like Theils, Vandy's, and a few others--come much closer than most other designs. which helps to illustrate an important point: IT'S A MATTER OF DEGREE. No speaker is perfectly time-aligned, but some do it better than others. I've come to believe that the most important thing is to have one driver hand off to the other in a well-ordered way.

One other point:

* First-order crossovers usually mean using drivers outside the range where they are at their best. This can mean distortion and dispersion problems--which mean that it doesn't work as well in a room as it does in an anechoic chamber.

Does it matter? The answer depends on what matters to you. If you trust well-conducted, rigorous subjective listening tests, you MUST conclude that other things matter much more--like (as someone else said) frequency response, dispersion, and distortion. But we're all different, we value different things, and we hear (or think we hear) different things.

Every manufacturer, of anything, requires a niche to sell into. Time-alignment is a very effective marketing niche (though I am NOT suggesting that the companies advocating time-alignment are insincere). It may matter to you, but the evidence suggests that it doesn't matter to most folks.

Best,
Jim Austin

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