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In Reply to: RE: what is a 1st or 2nd or 4th order speaker crossover design? posted by tomservo on July 26, 2016 at 10:18:08
OK, so 4th order has a 360 deg phase shift ... but in fact this means the LP signal is delayed one whole wavelength compared to the HP signal, does it not?? It's not actually 'in phase'??
So if you have, for example, a miniDSP unit, you should really delay the HP signal by one wavelength (which you can't do with an analogue active XO!)?
I would appreciate your input on this.
Thanks,
Andy
Follow Ups:
The good news is that something that is shifted by 1 cycle (or a half-cycle and then inverted) is very hard to perceive because although it has minuscule delay, it interacts with the overall signal just as if it were in-phase. The timing error does show up in transient analysis, however.Speaker design shares some things with the lossy compression debate: Does the signal need to be absolutely correct if it still sounds correct? :)
Edits: 07/27/16
Hi
To be clear, that 360 degree phase shift happens going from well above to well below the crossover point but yes and when the out put sums flat but one has that phase shift, it is what's called an "all pass" phase response, it also means that the shift is a delay in time where the lower frequencies emerge behind the upper portion.
To make that "go away" so that the sum is all at the same time and like one gets from a single driver covering the entire range is not simple unless one uses FIR filters in DSP where one can separate magnitude and phase. You might want to look at the mini-dsp unit and Re-phase program, the latter is like a graphic equalizer except one can eq the phase independently from the magnitude.
It is possible with passive filters too like we do at work with Synergy horns although one must physically displace the lower F driver to the rear of the upper driver and it requires a non-traditional crossover shape.
The "named" varieties like Butterworth, L&R, Bessel and so on all have that all pass delay and these only sum to flat magnitude when the acoustic centers are aligned.
Hope that helps
Tom
You are correct. The question of how important this is still open even though there are proponents of 1st order crossovers who insist it's the ONLY way(my old friend Bud Fried for one). Consider how good a well implemented 4th order Linkwitz/Reilly crossover performs.
Sure - I'm just wondering if a 4th order Linkwitz/Reilly crossover can be made to perform better with a digital active XO than with an analogue active XO, given the digital XO can implement a delay?
Andy
For a complete understanding of analog - Infinite Impulse Response - and Finite Impulse Response filters, you'll find a great article and its companion piece here (linked in the article below). You've probably also seen some info like this on the mini-DSP website.If you want to use FIR filters so that you can have both matched magnitude / flat frequency response and no shifts (linear) in phase response, you'll require a mini-DSP add on for more computational power (Open DRC or miniSHARC kit).
2nd article:
http://www.prosoundweb.com/article/a_useful_tool_creating_applying_fir_filters/P2/
Edits: 07/26/16 07/26/16
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