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In Reply to: RE: what is a 1st or 2nd or 4th order speaker crossover design? posted by cloudwalker on July 25, 2016 at 20:33:15
the 'order' of a speaker crossover refers to the rate at which the crossover attenuates the 'unwanted' signal, (this is also called: slope) for example -6dB/octave is 1st order, -12dB/octave is second order, -18dB/octave is 3rd order-
But it is not just the attenuation- there is also a Phase shift (180 degrees in even order crossovers.
Mixed slope crossovers are sometimes employed to address other aspects (difficulties) with the speaker design - time and phase issues being chief...
Happy Listening
Follow Ups:
" there is also a Phase shift (180 degrees in even order crossovers."
For a 2nd order there is 180 degrees phase shift, 3rd or has 270 and 4th has 360 degrees phase shift.
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
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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thank you for the correction-
Happy Listening
First order is 90 degrees too right?
ET
"If at first you don't succeed, keep on sucking till you do suck seed" - Curly Howard 1936
It would be logically except that the upper and lower bands being only 90 degrees apart, sum together without phase shift so they are an exception to the 90 degrees per order rule that applies to the familiar "named" crossover types.
Edits: 07/26/16
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