Re: FIR filters
I don’t have a background in signal processing … so this thread has made my head hurt trying to remember all my university mathematics … Hilbert transforms and all that stuff … but on the plus side it’s given me a few new ideas regarding processing the DIY's ... so thanks everyone for a great thread; can’t wait to see what Michael and Frank finally come up with.
Just to add a bit more to Arts post …. If you look at how a FIR filter is implemented using a bunch of delay taps, intuitively a crossover (FIR) will require a delay of more than the period of the crossover frequency. If you want the slope of the filter to be steep, you will require even more time.
I assume your question is to some extent relating to the DIY's you have built / processing. What I have done is use a short FIR time of 2.5ms in the Lake. This allow FIR linear phase crossovers as low as 500 Hz for the low/ mid and mid/hi.
A FIR crossover for the subs required too much time so I have used a standard IIR LR crossover. I processed the subs separately and it’s important to remember the high-pass filter protecting the excursion limit of the bass drivers as well as the crossover slope and frequency will affect the time alignment. I also used some all-pass filters to match the phase response shape / slope of the sub to the phase of the DIY at the crossover. By doing that you will get the correct LR summation at, and either side of the crossover.
