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<blockquote data-quote="Peter Morris" data-source="post: 201759" data-attributes="member: 652"><p>Hi Michael,</p><p></p><p>I don’t think we are in any disagreement on this issue. My comment was - you have to be careful, not that you can’t do that.</p><p></p><p>I will give you an example … I did a lot of work developing the FIR settings for Turbosound's Flex. The IIR settings didn’t sound too good. The Turbosound 10" “Bass Device” or whatever they called it had two peaks in the response of about 10dB, one at 500Hz and another at 800Hz cause by some horn loading and a band-pass resonance. It crossed over at about 575Hz.</p><p></p><p>What they did was match the phase and amplitude at the crossover and then apply a global filter to the input at 500Hz to flatten the peak. The amplitude response was flat but it always sounded honky at 500Hz and 800Hz. If you pulled 500Hz out on the graphic you could fix the honk but then there was something missing</p><p>.</p><p>The solution was to remove both peaks in the pass-band and then apply the crossover and everything sounded and measure great. If the drivers and horn all summed perfectly there would not be an issue, but they don't.</p><p></p><p>The trick to control temporal issues Dave Gunness style is to have the behaviour of the correcting electronic filter being exactly equal and opposite that of the resonance in the mechanical system you are trying to correct.</p><p></p><p>When those issues are out of band it’s not so critical so an IIR filter(s) is usually fine.</p><p></p><p>FWIW my settings for the DIY and the Flex use a combination of FIR and IIR filters to minimize latency. For the Flex I was able to do a linear phase crossover and EQs with only 2.5ms of FIR time.</p></blockquote><p></p>
[QUOTE="Peter Morris, post: 201759, member: 652"] Hi Michael, I don’t think we are in any disagreement on this issue. My comment was - you have to be careful, not that you can’t do that. I will give you an example … I did a lot of work developing the FIR settings for Turbosound's Flex. The IIR settings didn’t sound too good. The Turbosound 10" “Bass Device” or whatever they called it had two peaks in the response of about 10dB, one at 500Hz and another at 800Hz cause by some horn loading and a band-pass resonance. It crossed over at about 575Hz. What they did was match the phase and amplitude at the crossover and then apply a global filter to the input at 500Hz to flatten the peak. The amplitude response was flat but it always sounded honky at 500Hz and 800Hz. If you pulled 500Hz out on the graphic you could fix the honk but then there was something missing . The solution was to remove both peaks in the pass-band and then apply the crossover and everything sounded and measure great. If the drivers and horn all summed perfectly there would not be an issue, but they don't. The trick to control temporal issues Dave Gunness style is to have the behaviour of the correcting electronic filter being exactly equal and opposite that of the resonance in the mechanical system you are trying to correct. When those issues are out of band it’s not so critical so an IIR filter(s) is usually fine. FWIW my settings for the DIY and the Flex use a combination of FIR and IIR filters to minimize latency. For the Flex I was able to do a linear phase crossover and EQs with only 2.5ms of FIR time. [/QUOTE]
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