HK Audio CDR 210 F - Manual (Page 7)

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2 Development Objectives
2.1 High Frequency Range
The tweeter should radiate coherent waves through-
out its frequency range. In addition, the phase posi-
tion should be fine-tuned and tweaked to harmonize
with the midrange woofer to afford the highest
possible fidelity and natural response. In order to
ensure uniform dispersion of sound, the driver should
channel into a constant directivity horn that is
free of undesirable diffractive effects and does not
adulterate the sonic image.
2.2 Middle Frequency Range
Midrange frequencies should be projected in short,
dry bursts. Homogenous dynamic response approp-
riate to the tweeter is also desirable. Like the
tweeter's time-aligned frequencies, the midrange
woofer should be time-aligned for all frequencies
that it transmits. To fulfill a line array system's
handling potential, its mid/high unit should satisfy
the requirements of full-range voice applications.
2.3 Low Frequency Range
Low frequency energy should be dispersed into the
air faster and with the greatest possible dynamic
precision. A bass array with a large near field is
desirable. Subwoofers should be designed for versa-
tility, affording greatest flexibility in setup options.
3 Emphasized Radiation
Technology™
So how does one go about developing a next
generation line array? Emphasis is a familiar concept
in analog technology. What this means is that those
signal components that will later be dampened are
emphasized first. To apply this concept to wave
fronts, the fringes that are later smoothed must
be emphasized first. In this case, emphasis means
simply that the edge areas are projected earlier in
time, forming a slightly inward curving wave front
whose sound vectors face slightly inwards
(see Figure 3 a).
When applied to a continuous line source, this
creates a waveform as shown Fig. 3 b. Because
large line arrays typically consist of several identical
segments, a dedicated speaker would be required
for each segment. Apart from the fact that such a
continuous line source would be hard to implement,
practical applications also mandate great flexibility,
rendering such a concept in-feasible.
For these reasons, every element is curved slightly.
(Fig. 3 c). Due to the gaps between the elements,
which as stated above are inevitable anyway, both
ends of every element's wave fronts are reshaped in
the same way. A line source forms again at a certain
distance (Fig. 3.1). Emphasized Radiation technolo-
gy is thus able to sustain the even wave for a longer
period, thereby significantly extending the line
array's near field in the high frequency range!
To clarify the influence of the gap, the following ex-
amines the directivity of an ideal line array without
gaps and of a line array with evenly and unevenly
distributed gaps. Basically, it can be said that every
line source is always accompanied by undesirable
side lobes. Like interference, these side lobes are
clearly audible artifacts and therefore extremely un-
desirable. Unfortunately, they cannot be avoided al-
together, so it is important to minimize their level.
Figure 5 shows that an unevenly distributed gap
(pink) causes more irregular and more pronounced
side lobes. Without a gap (red) present, the array's
first side lobe occurs at a level of -13.58 dB. When
distributed across four elements of the same size
(blue) with the gap accounting for 18 percent of
the surface area, the level increases to -12.83 dB.
If these gaps are distributed unevenly, the level of
the first side lobe rises to -11.93 dB. This is nearly 1
dB higher than the level attained with the unevenly
distributed gap alone!
It is very important that the gap is distributed as
uniformly as possible across the full breadth of the
radiator. COHEDRA
® achieves this by using two
different housing shapes for the mid/high array,
affording the greatest possible uniformity in gap
size for all typical configurations. This also ensures
minimum variation in gap size for the J array, a
configuration that today is used almost exclusively.
Figure 3 a-c: Emphasized radiation in a line array
Figure 3.1: Extended line Array near-field
Figure 4: Effect without gap (red), with evenly distributed
gap (blue), and with unevenly distributed gap (pink)
Figure 5: Typical J shape
COHEDRA ® Technology