Tech Design.....

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An Discussion of Stored Energy/Linear Distortion, Part I.

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An Discussion of Stored Energy/Linear Distortion, Part I.

The base frequency response of these

two drivers (figures 1 and 2) 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. (Such a

response can typically be obtained

from a wide bandwidth amplifier or

preamplifier.)

Figure 3 shows thew CSD plot for an

electrical filter with a 4nd order

bandpass response (2nd order HP and

2nd order LP) 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. (See Part 2 for a discussion

of stored energy in crossovers.)

Figures 4 and 5 then show the CSD

results for drivers 1 and 2,

respectively, in combination with their

respective digital crossover filters

constructed to yield the targeted band

pass response. 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. The

advantage of using drivers which have

smoother raw response is that the

crossover filters and response shaping

required to obtain the desired acoustic

targets can be much simpler.

two drivers (figures 1 and 2) 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. (Such a

response can typically be obtained

from a wide bandwidth amplifier or

preamplifier.)

Figure 3 shows thew CSD plot for an

electrical filter with a 4nd order

bandpass response (2nd order HP and

2nd order LP) 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. (See Part 2 for a discussion

of stored energy in crossovers.)

Figures 4 and 5 then show the CSD

results for drivers 1 and 2,

respectively, in combination with their

respective digital crossover filters

constructed to yield the targeted band

pass response. 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. The

advantage of using drivers which have

smoother raw response is that the

crossover filters and response shaping

required to obtain the desired acoustic

targets can be much simpler.