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benefit provided is that the lowest resonance is at 2 KHz, two octaves above the crossover
frequency. Below 2 KHz there are no resonances to store energy and cause ringing. An
additional benefit is that the aluminum's much higher compressive strength results in almost
all the energy of a transient attack being transferred to sonic output rather than being absorbed
in compression of the diaphragm material.
Even though the diaphragm resonance at 2 KHz is two octaves above the crossover, it's
ringing would cause a slight sonic effect if not corrected. We have therefore incorporated into
the electrical network a notch filter which complements and cancels the resonance. To our
knowledge, this is the first application of a metal woofer with resonance compensation.
Figure 7 shows the time response of the woofer with its crossover network but without
resonance compensation. The peak with its consequent ringing at 2 KHz can be clearly
identified. Figure 8 shows the time response with resonance compensation. Although some
trace of the resonance is still discernible, it has been drastically reduced to a minor level.
Diffraction
Diffraction causes frequency response and time response errors and therefore a reduction
in tonal, spatial, and transient fidelity. Diffraction occurs when some of the energy radiated by
the drivers is re-radiated from the cabinet edges at a later time. For musical signals that
remain constant for a few milli-seconds, diffraction causes, by constructive and destructive
interference, an excess of energy to the listener at some frequencies and a deficient amount of
energy to the listener at other frequencies. Diffraction also causes all transient signals to be
radiated to the listener a second (and possibly a third) time, smearing transient impact and
Cabinet-edge diffraction
tweeter
Figure 9 Response of tweeter in square-edged cabinet
90 dB
80 dB
200
300 400 500
1k
2k
3k
4k 5k
Figure 10 Response of tweeter in CS3.6 cabinet
90 dB
80 dB
200
300 400 500
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2k
3k
4k 5k
3
distorting spatial cues.
To greatly reduce diffraction the CS3.6
employs a front baffle that is curved at the edges so energy radiated along the baffle can
continue into the room without encountering abrupt cabinet edges. Figures 9 and 10 illustrate
the beneficial effects of the CS3.6's curved baffle on the response of the tweeter.
Results
The end result of greatly reducing
diffraction and diaphragm resonances is
a speaker with very accurate tonal
characteristics. Figure 11 shows the
on-axis frequency response of the
CS3.6. It is uniform within 1.5 dB
from 28 Hz to 20 KHz. Typically, it is
within 1 dB from 30 Hz to 10 KHz.
Subjectively even more important is the
octave-averaged frequency response.
Figure 12 shows this response to be
within 0.5 dB from 36 Hz to 20 KHz
showing extremely accurate overall
tonal balance. Furthermore, as a result
of gradual crossover slopes and
relatively low crossover points made
practical by the use of high output
driver design, the off-axis frequency
response of the speaker system is
almost as smooth as its on-axis
response. This unusual performance is
important for producing a uniform
amount of ambient energy at all
frequencies, necessary for natural
10k
20k
spatial reproduction. Figure 13 shows
this octave-averaged, 30 off-axis
response to be almost within 1 dB
from 33 Hz to 17 KHz, showing
extremely uniform dispersion of energy
at all frequencies.
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20k
Figure 7 Time response of woofer without compensation
Figure 8 Time response of woofer with compensation
Figure 11 On-axis frequency response
90
80
70
20
100
1K
Frequency
Figure 12 Octave-averaged on-axis frequency response
90
80
70
20
100
1K
Frequency
Figure 13 Octave-averaged 30 off-axis frequency response
90
80
70
20
100
1K
Frequency
10K
20K
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20K
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20K
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