Intressanta länkar och tack för dem
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Här visar man hur man går ett steg längre än 6:e ordningens basreflex, med hjälp av dsp-teknik. B.la hur man minskar group-delay fel i basreflex med för små lådor och branta avskärningar, genom att kombinera dsp-shelving med 1:a ordningens filter. Det sista var nytt för mig.
Jag antar att delar av denna teknik används i de Genelec 8335 dsp jag hade hemma nyss.
https://audioxpress.com/files/attachment/2721”Things got especially interesting when I began experimenting with miniDSP’s shelf function. Its shelf filters have variable Q, and with a higher gains (8 to 15 dB) and higher Qs (2-5), I was able to achieve very interesting, very useful shelf functions that achieved the steep 30 dB slope I needed just below fb (see Figure
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Note that instead of continuing to roll off, these filters level off. On the surface, this might appear to be a problem. But it’s not. Because in all practicality, if your initial shelf is deep enough, you don’t need much further rolloff at ever-lower frequencies. If the attenuation of the shelf is 15 to 25 dB, that’s good enough. I add a 6 dB/octave high pass for good measure (see Figure 9).
This has a hidden advantage: far less group delay than a traditional steep filter. I found if I combined a Q = 3, gain = 10 dB shelf filter with a simple 6 dB per octave high-pass filter, I got the well-behaved phase of a shallow filter with the protection of a steep one.
This configuration is formally known as an elliptic filter. An elliptic filter is one where, in order to achieve a very steep slope over a narrow range, you accept peaks and dips (ripple) in both the passband and the stopband. DSP crossovers are as superior to standard active crossovers as active crossovers were superior to passive crossovers.
av gopnik » 2020-08-05 22:59