Sloped baffle

I'm a fan of time-and-phase coherent speakers (and a GMA owner). Just want to throw that out there...

One correction to the conversation - single-driver speakers are NOT time-and-phase coherent. They would be if the speaker operates as a perfect-piston over the entire frequency range, but this is not reality. At certain frequencies, the driver can't respond as quickly as a perfect-piston, and the phase starts to lag.

BTW, I never thought about drivers not being time-coherent. What does that mean? I thought time misalignment was between/among drivers.

Let's look at just 2 of the physical components of a driver (imagine a midrange driver): the cone and the suspension (the surround and the spider).

The cone itself has mass, and because of the kinetic energy of a cone moving outward, it sometimes just can't reverse direction as quickly as the signal is asking. Sure it responds, but with a very slight delay. This delay is one source of phase distortion.

The suspension not only centers the coil in the gap, but defines the resting position of the coil within the gap. Don't believe me? Gently push in on a mid-woofer, and let go. The speaker pushes back out to the resting position as defined by the suspension.

Now, small movements around the "resting point" all experience the same (minute) amount of resistance from the suspension. This is by design and is where the driver operates with minimal effective phase distortion.

Now, midrange drivers require larger strokes to produce lower frequencies, and the suspension applies more (nonlinear) resistance against the movement of the driver as the driver approaches X-max, imparting another set of phase distortions.

This is an oversimplification of the subject. But shows that (good) time-and-phase aligned speakers require more than just a sloped baffle and first-order crossovers.