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In practice the proper execution of a first order system requires very high quality, wide
bandwidth drivers and that the impedance and response variations of the drivers and the
cabinet be compensated across a wide range of frequencies. This task is complex since the
acoustic outputs of the drivers must roll off at 6 dB/octave and not simply for the networks
themselves to roll off at 6 dB/octave. For example, if a typical tweeter with a low frequency
roll-off of 12 dB/octave is combined with a 6 dB/octave network, the resulting acoustical
output will roll off at 18 dB/octave.
Figure 16 is a plot of the absolute phase response of the CS3.6. It shows that the phase
response is within 20 above 200 Hz and within 10 from 400 Hz to 15 KHz. However, in
our opinion, what is most important is the phase deviation from the mathematical "minimum"
phase response of an ideal transducer with the same frequency response. This deviation is
called the excess phase and is plotted for the CS3.6 in Figure 17. This graph shows the excess
phase to be less than 5 to beyond 10 KHz.
The result of phase coherence (in conjunction with time coherence) is that all waveforms
will be reproduced without major alterations. The speaker's reproduction of a step waveform
best demonstrates this fact. Like musical waveforms, a step is made up of many frequencies
which have precise amplitude and phase relationships. For a step signal to be accurately
reproduced, phase, time and amplitude response must all be accurate. Because this waveform
is so valuable, it is commonly used to evaluate the performance of electronic components. It is
not typically used for speaker evaluation because most speakers are not able to reproduce it
recognizably. Figure 18 shows the CS3.6's response to a step. That the step is reproduced so
recognizably is the result of accurate phase, time and amplitude response.
ENERGY STORAGE
Any part of the speaker that absorbs energy will re-radiate it later in time in a highly distorted manner. Although not loud enough to be
consciously heard, stored energy causes significant detrimental effects. The music's subtle detail is obscured, causing both a reduction in
clarity and loss of spatiality as well as noticeable colorations of voice and other midrange sounds. The main storage mechanisms are the
driver diaphragms and cabinet walls, especially the baffle.
The lack of cabinet wall vibrations is one advantage of membrane speakers and why they have an "unboxy" sound. However the
problem of cabinet vibrations in dynamic loudspeakers is not inherent but rather can be reduced as much as is affordable.
One method of attempting to reduce the problem of stored energy is to apply damping to the offending component. The idea is to damp
motion with a viscous material so that the stored energy can be dissipated as heat instead of mechanical vibration which produces unwanted
sound. This method has limited benefit for two reasons. First, energy can only be dissipated as heat after there is unwanted mechanical
vibration to convert. Secondly, even though some of the absorbed energy is transformed into heat, it is still absorbed from the desired sonic
output and therefore the distortion mechanism still exists. A much better approach, in our opinion, is to reduce the energy absorbed.
The primary cabinet problem is baffle vibration because movement of the drivers can directly excite the baffle and the resulting
extraneous energy it is radiated directly toward the listener. The CS3.6 employs a 3" thick baffle in order to reduce unwanted vibration.
Figure 19
5
0
-5
-10
-15
-20
-25
-30
-35
0.5
1.0
1.5
2.0
Time – msec
first 150 microseconds, a result of very good time coherence. It also shows that the speaker's output has already decayed to -20 dB after
only 200 microseconds and has fallen to -40 dB after only 900 microseconds. This rapid decay provides very clean reproduction with very
good inter-transient silence.
DISTORTION
The primary sources of distortion are the drivers' magnetic motor systems and the electrical components of the crossover network. We
have taken unusual steps in the design of the CS3.6 to greatly reduce these sources.
Crossover Components
The usual type of capacitor for speakers is electrolytic. This type has the advantage of very low cost but also causes audible distortion
due to dielectric absorption and other mechanisms. There are only three electrolytics used in the CS3.6 and none of these is in the signal
path. All are used in zobel networks to correct the drivers' impedance and are bypassed with high quality polystyrene types to provide
performance closer to the polystyrene type than the electrolytic. The polystyrene capacitors are custom–made to our specifications and
employ tin foil rather than aluminum. The use of tin allows the copper lead wires to be soldered, rather than welded, to the conductor
resulting in purer sound. The tweeter feed capacitors are pure polystyrene and all other capacitors, including a very large 200 fd mid-range
feed, are polypropylene bypassed with polystyrene.
All the CS3.6 inductors are air-core, which completely eliminates distortions caused by magnetic saturation, and hysteresis and are
wound of high purity, low oxygen copper. Also, the speaker's internal wiring uses custom–made solid conductor, high purity copper with
polypropylene insulation.
5
The walls of the CS3.6 enclosure are constructed of 1" thick fiberboard, and extensive internal
bracing further increases wall stiffness.
To increase the mechanical rigidity and therefore reduce unwanted vibration, all CS3.6
drivers incorporate chassis of cast magnesium rather than stamped steel or plastic.
As previously discussed, much attention has been given to the reduction of diaphragm
vibrations to reduce the amount of energy absorbed through resonances.
2.5
Figure 19 is the Energy-Time curve of the CS3.6. It shows how the output energy of the
speaker is distributed in time. First, it shows that all of the primary energy is focused in the
Figure 16 CS3.6 phase response
Transfer Function Phase - deg
100
80
60
40
20
0
-20
-40
-60
-80
-100
1
Frequency - KHz
Figure 17 CS3.6 excess phase
Transfer Function Excess Phase - deg
100
80
60
40
20
0
-20
-40
-60
-80
-100
0.1
1
Frequency - KHz
Figure 18 CS3.6 step response
0.5
1.0
1.5
Time – msec
10
10
2.0
2.5
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