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In Reply to: Re: Holism and Reductionism - Fourier Series posted by tomservo on September 8, 2003 at 06:17:15:
Tom -Are you kidding me? Remember that I am skeptical of claims of perfect acoustic phase by loudspeaker manufacturers. I'm agreeing with Dawson's assertion that the perfect quadrature is non-realizable, at least in the approximated form you've likened it to as a direct radiator.
The mass/spring system forms a filter that changes phase with frequency. Reactive components used in the circuit also form filters that modify phase. The phase of the current through the circuit is relatively easy to find with reactive formulas, and it is non-zero over much of the audio bandwidth for every speaker motor and/or crossover discussed here. For that matter, it is also not a constant quadrature at 90 o .
Beyond this, the speaker's diaphragm is not a point source, but rather a planar source. It approximates a point source at frequencies where wavelength is large compared to diaphragm size and acts as a radiating plane above that. This creates a filter system too. And finally, we have cone flex to consider, which also creates a filter that isn't minimum phase.
Horn's are not exempt either - They suffer from all the same causes of phase shift as direct radiators, and they have some additional ones as well, such as path length, diffraction and other dispersion modifiers and additional resonances such as those caused by panel vibrations and those from 1/4 wave peaking. Sure you can limit those, and that's the hope of every designer. And sure a "perfect load" would be perfectly resistive, having no phase shift. But we're not talking about hypothetical perfect loads here, and to design with such an assumption is absolutely foolish.
So there's good reason to question claims of perfect acoustic phase from a design based on components using these technologies. Then again, there are a lot of good design choices and solutions that will work well. Dawson has given you some examples of those he has found. But academically speaking, there are complications that prevent optimizations of all criteria simultaneously. If this weren't so, we'd probably not be building such a variety of machines.
Wayne
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Follow Ups
- Re: Holism and Reductionism - Fourier Series - Wayne Parham 09/9/0302:31:42 09/9/03 (2)
- Re: Holism and Reductionism - Fourier Series - tomservo 06:05:24 09/9/03 (1)
- Re: Holism and Reductionism - Fourier Series - Wayne Parham 14:18:38 09/9/03 (0)
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