X-MAX

A WORD ABOUT LONG THROW IN THE REAL WORLD

Traditional ways of determining X-max [voice coil winding length (-) gap height (÷) 2] does not tell the whole story of speaker excursion. What makes a speaker work? We have an alternating electromagnetic field (the voice coil) interacting with a stationary magnetic field (the magnetic gap). The force of the magnet is concentrated in the magnetic gap; the area between the top plate and the pole piece. The magnetic gap is the only place that the magnetic flux lines flow directly between the top plate to the pole. Electro-magnetic fields, like voice coils, are driven perpendicular, (90 degrees), to stationary magnetic fields, like a speaker motors. When the alternating signal is positive, the coil moves up in the field, and when the signal is negative, it moves down in the field.

As the coil moves up and down in the gap, it moves the cone back and forth, which creates the pressure waves in the air we call sound. The voice coil is driven by the interaction with the magnetic field in the gap.

This interaction generates a force and is converted into sound waves. What we are interested in, is the force. The force is energy over time. This is not to be confused with how far a speaker cone is moving. Generating acoustic wave force is a function of the speaker's interaction with enclosure, and the environmental loading from which they are playing in.

The xmax spec thrown about by today's marketing companies plays a minor fraction in the elements that make your car or home audio system sound good. It is not analogous to torque, horsepower or any other fundamental measurement of power.

How far the coil CAN move in a motor system does not describe HOW it moves as power is delivered. Xmax cannot describe how fast the coil can stop its motion, and go back the other directio. It cannot describe what happens when the force goes up 10 times, how the coil deals with the increased inertia.
A high Xmax spec can be easily designed into a speaker, especially one where the Xmax spec is measured by a system in which the speaker isn't driving itself. But these aren't real world applications, the real world isn't summed up by these simple formulas, Dumbass graphs, or a speaker's Dumbass rating.

REAL WORLD COIL MOTIONS

We care about what happens to a coil when 1000 watts of kickdrum come crashing into the speaker. How does it handle that? We R&D around how to make coils react better, faster and stronger. We strive for more coil control, not theoretical travel as the cone is pushed by air pressure while plotting suspension resistance.
What is more important than the Xmax number, is what percentage of coil is in the gap at any particular time. The magnet gap acts like a linear clamp, forcing the coil into linear motion as it passes through. The more coil wire passing through the field, the more linear the travel will be. The stronger the field, the more control you get over the coil. This makes the speaker sound better when you actually have current flowing through it.