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SB1000e out-of-band EQ
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<blockquote data-quote="Bennett Prescott" data-source="post: 16906" data-attributes="member: 4"><p>Re: SB1000e out-of-band EQ</p><p></p><p></p><p></p><p>Helge,</p><p></p><p></p><p></p><p>The reason your subs need a big cut at 200 is because of your incorrect crossover settings.</p><p></p><p></p><p></p><p>Out of band EQ can be a handy tool (for reasons Art has elucidated), but what is really happening is that you ''like'' the overlap around 100Hz, but by the time it gets to 200Hz you've stopped liking the extra contribution from the subs and want their response to be gone. That's not to say you don't also need some out of band EQ, although that has not been my experience when aligning EAW systems run on the UX8800, but the real problem is your crossover selection.</p><p></p><p></p><p></p><p>Here is the problem: Your tops roll off somewhere in the 80Hz range (let's just say). Maybe they die a little higher or a little lower, but the point is that regardless they are rolling off near where you would set their high pass filter for system integration anyway. That means that when you apply your high pass it combines with their existing acoustic rolloff and produces additional rolloff and phase shift. With a 4th order filter, you may be seeing an 8th order acoustic response.</p><p></p><p></p><p></p><p>Your subwoofers on the other hand, if not effectively low passed, will go to 1kHz or so before they start to roll off. This is octaves away from where you would set your low pass. That means that, if they are equalized flat or are flat of their own accord, when you apply your 4th order L-R filter you are getting almost an ''electrical'' response. If you set it at 100Hz then your filter is down 6dB at 100 and falls 24dB/octave beyond that, with the expected phase response to match.</p><p></p><p></p><p></p><p>So while your tops are gone just below your crossover point, your subs are rolling off at half the rate and with half the phase shift. This means that while you can match phase at crossover, it won't stay matched for long. Furthermore, when you boost your sub level 10dB or so your sub response extends for half an octave or more before it equals your top response, and still contributes for another half an octave beyond that... this is where your 200Hz overlap comes from.</p><p></p><p></p><p></p><p>An ugly solution is to use an 8th order L-R filter for your sub low pass, that will at least make the slopes equal and make your phase alignment a lot easier. I don't like using high order filters, though, so I avoid this.</p><p></p><p></p><p></p><p>The best solution is to drop your sub low pass to 60-70Hz. This will account for the crossover overlap, and with a little care you can usually get the phase alignment to play nice. Sometimes I'll increase the order of the low pass filter just to make the phase slopes line up, but once you're playing with 4th order filters already you start to get into nasty sounding filters when you go much beyond that (or it could be argued that it sounds nasty already, and you would ideally use a lower order filter for your top HPF...)</p><p></p><p></p><p></p><p>I suspect the reason you don't like doing this is because of time. Your tops are incurring the phase shift of a 4th order filter at 100Hz. When you have the sub filter there as well it incurs the same phase shift, so they remain time aligned if they were to begin with. Now that you've shifted the LPF for your subwoofers almost an octave lower, however, they incur almost twice the phase shift, or almost twice the delay. What you need to do is add delay to your tops to make their delay at the crossover point equivalent to the subs... 2-4ms is what I find to be normal, probably on the high side of that for such steep filters.</p><p></p><p></p><p></p><p>Hopefully that is useful, I've had too much coffee and so I'm a little stream-of-consciousness.</p></blockquote><p></p>
[QUOTE="Bennett Prescott, post: 16906, member: 4"] Re: SB1000e out-of-band EQ Helge, The reason your subs need a big cut at 200 is because of your incorrect crossover settings. Out of band EQ can be a handy tool (for reasons Art has elucidated), but what is really happening is that you ''like'' the overlap around 100Hz, but by the time it gets to 200Hz you've stopped liking the extra contribution from the subs and want their response to be gone. That's not to say you don't also need some out of band EQ, although that has not been my experience when aligning EAW systems run on the UX8800, but the real problem is your crossover selection. Here is the problem: Your tops roll off somewhere in the 80Hz range (let's just say). Maybe they die a little higher or a little lower, but the point is that regardless they are rolling off near where you would set their high pass filter for system integration anyway. That means that when you apply your high pass it combines with their existing acoustic rolloff and produces additional rolloff and phase shift. With a 4th order filter, you may be seeing an 8th order acoustic response. Your subwoofers on the other hand, if not effectively low passed, will go to 1kHz or so before they start to roll off. This is octaves away from where you would set your low pass. That means that, if they are equalized flat or are flat of their own accord, when you apply your 4th order L-R filter you are getting almost an ''electrical'' response. If you set it at 100Hz then your filter is down 6dB at 100 and falls 24dB/octave beyond that, with the expected phase response to match. So while your tops are gone just below your crossover point, your subs are rolling off at half the rate and with half the phase shift. This means that while you can match phase at crossover, it won't stay matched for long. Furthermore, when you boost your sub level 10dB or so your sub response extends for half an octave or more before it equals your top response, and still contributes for another half an octave beyond that... this is where your 200Hz overlap comes from. An ugly solution is to use an 8th order L-R filter for your sub low pass, that will at least make the slopes equal and make your phase alignment a lot easier. I don't like using high order filters, though, so I avoid this. The best solution is to drop your sub low pass to 60-70Hz. This will account for the crossover overlap, and with a little care you can usually get the phase alignment to play nice. Sometimes I'll increase the order of the low pass filter just to make the phase slopes line up, but once you're playing with 4th order filters already you start to get into nasty sounding filters when you go much beyond that (or it could be argued that it sounds nasty already, and you would ideally use a lower order filter for your top HPF...) I suspect the reason you don't like doing this is because of time. Your tops are incurring the phase shift of a 4th order filter at 100Hz. When you have the sub filter there as well it incurs the same phase shift, so they remain time aligned if they were to begin with. Now that you've shifted the LPF for your subwoofers almost an octave lower, however, they incur almost twice the phase shift, or almost twice the delay. What you need to do is add delay to your tops to make their delay at the crossover point equivalent to the subs... 2-4ms is what I find to be normal, probably on the high side of that for such steep filters. Hopefully that is useful, I've had too much coffee and so I'm a little stream-of-consciousness. [/QUOTE]
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