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Tech Design.....
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An Discussion of Stored Energy/Linear Distortion, Part I.
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John Kreskovsky Music and Design © November 2005 |
Figure 1. Driver having poor burst response. Figure 2. Driver having good burst response.
The base frequency response of these
two drivers can be observed at the T=0
axis (back plane of the plots). As can
be seen,the drivers have very different
raw frequency response and the CDS
plots give an indication of how the
irregularities in the frequency response
translate into linear distortion. A perfect
driver with flat response form 0 Hz to
infinity would show a flat 0dB line at
T=0 and nothing for T>0.
Figure 3 shows thew CSD plot for an
electrical filter with a 4nd order
bandpass response which represents
the desired acoustic target for a
midrange response in a hypothetical
speaker system. Note that it is far from
perfect and suffers its own linear
distortion and stored energy compared
to a perfectly flat response. However,
depending on how well the crossover
filter is designed, we would expect the
CSD plot for either driver to have the
same characteristics when connected
to its filter. Any deviation from this
behavior indicates some residual linear
distortion relative to the true bandpass
response.
Figures 4 and 5 then show the CSD
results for drivers 1 and 2,
respectively, in combination with their
respective crossover filters. Both plots
show some deviation from that
presented in Figure 3, thus we can
conclude that neither crossover filter
represents the perfect linear correction
to transform the raw driver response
into the targeted bandpass response.
This is a result of both some error in
the digital transfer functions indicating
a residual level of linear distortion, and
possible nonlinear components in the
driver response (nonlinear distortion).
However, it is also clear that with their
respective filters in place both system
perform very closely to the ideal and
will have similar characteristics with
regard to linear distortion and stored
energy.
The conclusions to be drawn here are:
that linear distortion tests on a raw
driver are not necessarily
representative of the behavior of the
driver when connected to a carefully
designed crossover network; linear
distortion is just that, a linear effect,
and can be corrected by application of
linear networks to shape the response
to the desired target; different system
which have similar impulse, frequency
or CSD plots will have similar burst and
stored energy characteristics.
two drivers can be observed at the T=0
axis (back plane of the plots). As can
be seen,the drivers have very different
raw frequency response and the CDS
plots give an indication of how the
irregularities in the frequency response
translate into linear distortion. A perfect
driver with flat response form 0 Hz to
infinity would show a flat 0dB line at
T=0 and nothing for T>0.
Figure 3 shows thew CSD plot for an
electrical filter with a 4nd order
bandpass response which represents
the desired acoustic target for a
midrange response in a hypothetical
speaker system. Note that it is far from
perfect and suffers its own linear
distortion and stored energy compared
to a perfectly flat response. However,
depending on how well the crossover
filter is designed, we would expect the
CSD plot for either driver to have the
same characteristics when connected
to its filter. Any deviation from this
behavior indicates some residual linear
distortion relative to the true bandpass
response.
Figures 4 and 5 then show the CSD
results for drivers 1 and 2,
respectively, in combination with their
respective crossover filters. Both plots
show some deviation from that
presented in Figure 3, thus we can
conclude that neither crossover filter
represents the perfect linear correction
to transform the raw driver response
into the targeted bandpass response.
This is a result of both some error in
the digital transfer functions indicating
a residual level of linear distortion, and
possible nonlinear components in the
driver response (nonlinear distortion).
However, it is also clear that with their
respective filters in place both system
perform very closely to the ideal and
will have similar characteristics with
regard to linear distortion and stored
energy.
The conclusions to be drawn here are:
that linear distortion tests on a raw
driver are not necessarily
representative of the behavior of the
driver when connected to a carefully
designed crossover network; linear
distortion is just that, a linear effect,
and can be corrected by application of
linear networks to shape the response
to the desired target; different system
which have similar impulse, frequency
or CSD plots will have similar burst and
stored energy characteristics.
Figure 1. Driver 1 frequency response and CSD.
Figure 2. Driver 2 frequency response and CSD.
Figure 3. Frequency and CSD plot of 2nd order band pass filter.
Figure 4. Frequency and CSD plot of Drive 1/filter combination
Figure 5. Frequency and CSD plot of Drive 2/filter combination
