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In Reply to: Re: Example please? posted by Ben P on February 26, 2007 at 00:30:05:
No, it doesn't make sense because it's not true. Whether or not the driver can be "corrected" has nothing to do with whether or not it's minimum-phase. Actually, being minimum-phase is precisely why it _could_ be corrected.The only reason a hard coned driver "can't" be corrected with filters is because the breakup peaks/dips are of very high Q and flattening the FR passively or even actively non-DSP can't be done easily due to the magnitude of the values needed and the number. High Q's may not be fully correctable due to insertion losses (coil resistances primarily), but that's a limitation of the real components, not a limitation induced to the physics. That is the one and only limitation to smoothing the response completely in the non-DSP world.
Think about it. Any and ALL areas in any and ALL raw driver responses are due to some form of resonance, or energy storage. Even the most gradual, minimal peak/dip of very low Q and low magnitude is a resonance. It's absolute no different than the high Q peaks at breakup. The only difference is that low Q resonances allow for components of reasonable magnitude to correct them.
It's also possible now to use DSP to completely linearize every last peak/dip of any Q/magnitude. It's a simple matter with the right software, I do it in SoundEasy. The only thing that is occurring in this instance is that there is essentially an unlimited amount of DSP-generated "filtering" going on that is limited in the analog domain whereas there is essential no limitation in DSP. I can take the worst hard-coned driver and make the breakup linear.
This works only on-axis, of course, since off-axis all drivers differ from their on-axis response. That part is no different than a driver that has decreasing dispersion at higher frequencies. You just have to take it all into account.
And again, as an example, I have many times used CALSOD (a DOS tool from the 80's into 90's no less) to create a driver model that perfectly matched the resonances in FR, as I said. The phase is then generated from this FR model. This generated phase perfectly matched the measured phase.
How does the software create the model you might ask? You start with an ideal, perfect 2nd order bandpass. Then you iteratively add minimum-phase elements (MPE) to the model. These are nothing more than a Q and magnitude at a selected Fc. This simply adds a resonance. I've gone up to as many as about 40, maybe more, to detail minutely up to the limits of the measurement, 22K. The generated phase matched the measured phase perfectly. Were either the measured breakup or the modeled breakup not minimum-phase, then the model would break down, the FR would not match and the phase would not match. It all does match, perfectly.
The most common method for using hard-coned drivers is simply to cross them lower. There is one aspect to breakup that can't be controlled through the crossover and that's harmonic distortion. High Q resonances will magnify any distortion components whose harmonics coincide. The best way to prevent this is to cross low enough to keep the fundamental down so that only higher harmonics may coincide, since in general as the harmonic increases, the magnitude decreases. This is true of all drivers, though, it's just that hard-coned drivers have breakup with higher magnitude, thus they "amplify" the distortion harmonics more. But all of that has nothing to do with whether or not the breakup is minimum-phase.
dlr
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Follow Ups
- Re: Example please? - dlr 02/26/0715:11:07 02/26/07 (1)
- Re: Example please? - Ben P 03:27:01 02/27/07 (0)
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