Coaxial Differential Dispersion Technology - Martin Audio CDD Series User Manual

CDD USER GUIDE

COAXIAL DIFFERENTIAL DISPERSION TECHNOLOGY

All CDD Series full-range models feature Martin Audio's unique, patent-pending Coaxial Differential Dispersion™ technology. CDD
systems augment the 'point-source' benefits of coaxial drivers with the consistency of coverage which Differential Dispersion
technology can deliver.
Non-coaxial systems can suffer from uneven frequency response in the crossover region because of interference between the
LF and HF sections; depending on the listening position, this causes off-axis variations, particularly close to the loudspeaker. In
contrast, coaxial systems aim to sum LF and HF contributions at all positions off-axis, even close-up.
A disadvantage of conventional coaxial devices can be HF beaming, where the HF dispersion reduces at higher frequencies. This
is primarily because the HF energy emerges through a narrow tube in the pole-piece of the magnet system. CDD Series coaxial
devices overcome this by the use of a static waveguide that merges seamlessly with the unique cone shape — maintaining the
dispersion pattern even at very high frequencies.
A Differential Dispersion horn has a trapezoidal dispersion pattern in both vertical and horizontal planes which covers the target
area more evenly than a system with a conventional, fixed dispersion type horn. With a conventional horn, the speaker is usually
placed above head height and aimed towards the centre of the audience. This produces an imperfect coverage pattern which
misses out some areas — particularly side areas close to the loudspeaker.
In contrast, a CDD Coaxial Differential Dispersion system produces a rectangular coverage pattern extending to all corners of the
audience area, while wide horizontal coverage is achieved very close to the loudspeaker. The consistency of frequency response
and SPL thus achieved throughout the audience area is exceptional. The improved coverage close to the source also means that
CDD speakers can often be spaced further apart, reducing overall speaker count.
The two EASE plots shown above illustrate the coverage obtained from four CDD speakers (on the left of the plot) as compared
with that obtained from four equivalent Martin Audio AQ Series speakers (on the right). The plots are taken at 4 kHz (left) and 8
kHz (right), with all other measurement parameters remaining constant. It can be seen that the CDD coverage is significantly
more even across the width of the audience area at these important mid-range frequencies.
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