"Maximum Modal Suppression" Redefining the Performance of Compression Drivers

Celestion's research department created a unique way of improving the performance of a compression driver, leading to a patented new design for phase plugs. We call it Maximum Modal Suppression.

September 16, 2011

CDX14-3050 - the first product to incorporate the new phase plug design
Many of Celestion's latest compression driver products now feature a unique design of phase plug, developed using patent-applied-for design methodology that greatly reduces the occurrence of "cavity resonances".

Used in tandem with this new phase plug is a "deep-drawn" titanium diaphragm to increase the overall stiffness of the membrane.

Together, these innovative new features result in  more accurate sounding compression drivers that exhibit much lower distortion than many typical large format devices currently available.

This technology has been deployed in the CDX14-3050, CDX14-3060, CDX20-3000 and CDX20-3075 compression drivers.

A New Landmark in Compression Driver Design

In 1953, Bob Smith recognised the limitations of the "Equal Path Length" method for calculating the width and position of annular phase plug slots. He developed a set of criteria for determining these dimensions which more effectively suppressed modal excitation to achieve lower distortion. Smith's methodology has now been the established technique for annular phase plug design for over 50 years.


Compression Driver Timeline

With Smith's work as their start point, Celestion engineers Mark Dodd and Jack Oclee-Brown looked further into modal decomposition as applied to a curved diaphragm. Possibly the most significant development in annular phase plug design in over 50 years, their new design criteria re-define the ratios used to calculate slot width and position, resulting in greater modal suppression and reduced air non-linearity.


Innovative New Phase Plug Design for Improved Modal Suppression

Applied to the development of the phase plug for the CDX14-3050 and CDX20-3000 compression drivers, this new design methodology re-calculates slot width and slot positioning ratios. The result is improved modal suppression within the phase plug, and hence lower distortion. The photographs below demonstrate the variation of slot width ratios, compared to that of a typical phase plug design, which is the principal characteristic of the new Celestion design.*


Comparing the new Celestion phase plug slots to a typical compression driver's design

Deep-Drawn Diaphragm for Increased Stiffness

 The deep-drawn diaphragm exhibits first modal break up around 15kHz. In comparison, a typical large format compression driver diaphragm starts to break up in the 8-10kHz range. The higher threshold frequency of the diaphragm avoids the break-up (distortion) within the critical mid-range listening band of 2-10kHz associated with lower profile diaphragms.

Illustrating the deep drawn Celestion diaphragm, compared to a typical (shallower) compression driver

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