Quote Originally Posted by topspeed
I've always wondered this and with the influx of more and more coax designs hitting the market (i.e. TAD Model 1) my curiousity is getting the best of me. When a driver moves, is the majority of the sound coming from the center, the edge, or the whole surface of the cone? For example, my B&W woofers have an enormous dust cover (for lack of a better term) thereby leaving very little of the driver cone exposed yet the mid's are your typical driver design.

I've also seen lots of soft dome tweeters that actually have a protective cap over the center of the dome thereby only exposing the outer edges of the dome. I'd always thought that would in some way muffle the sound but obviously I'm wrong. Fostex full range drivers have a bizarre wave guide(?) attached to the dust cover so what does that do? Questions, Questons, Questions!

Chances are I'm overanalyzing this. Just curious I suppose.

Any takers?
Yeah, I'm in the mood to overanalyze things.
WARNING: this contains high school geometry

Imagine a 6" speaker cone. Let's simplify things and make it a flat disc, instead of a cone, that has a 6" diameter or a 3" radius. The amount of air moved by such a speaker is directly proportional to its surface area, pi × r² = 28.27 in².

Let's divide this speaker into three concentric circles like a target, with each circle an additional inch larger in radius. The inner circle (Circle 1) has a 1" radius, the next circle (Circle 2) has a 2" radius, and the outer circle (Circle 3) has a 3" radius. Their areas are:

Area 1 = pi × 1 = 3.14 in²
Area 2 = pi × 4 = 12.57 in²
Area 3 = pi × 9 = 28.27 in²

What are the additional areas are contributed by each additional ring, where Ring 1 is the same as Area 1, Ring 2 is Area 2 - Area 1, and Ring 3 is Area 3 - Area 2?

Ring 1 = 3.14 in² = 11.1% of the total area
Ring 2 = 9.42 in² = 33.3% of the total area
Ring 3 = 15.71 in² = 55.6% of the total area

The outer 1" of radius contains over half the total surface area. So the outer part of this speaker should move most of the air and produce most of the sound. With bigger speakers the outer rings have an even greater proportion of the total surface area.