Coaxial Differential Dispersion Technology - Martin Audio CDD12-WR 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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