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May 23, 2021 / consort3

Precision cost-effective crossover.

I built one of Bill Waslo’s IMP loudspeaker measuring devices back in the day and it helped  my understanding of Speakers. I then bought a Behringer DCX2496 DSP crossover with a companion A500 amplifier to match the XLR differential output of the DCX. The A500 has the QSC type floating ground output which damaged the IMP, but I was able to fix that. Beware of the A500 if connecting test equipment to it.

One thing I noticed with this setup was that LR4 crossovers typically needed a frequency offset to get the best null with a reversed tweeter. I assume drive unit phase and relative positioning cause this. Offset is when the HP and LP filters are at different frequencies.  Anyway I would chase the null down varying one of the frequencies until the null started going up at which point i knew the the system was  180 degrees out of phase. Flipping the phase 180 on the DCX I would check for a flat response. If it was not flat I would pick another crossover frequency. This technique required precision frequency adjustment of the DCX each step being about 2%.

I got involved with single op-amp 4h order filters when I found Conrad Hoffman’s  applet on the EEVblog. However I was not 100% happy with my attempt to make a 4th order LR filter with it. Recently I found a circuit which inspired me to try again to get a LR4 type and this time I felt it is worth reporting. See my page Single op-amp 4th order LP/HP filters for details. So you tweak the DCX or equivalent to get the frequencies and then use the nearest E96 table values. Precision at a reasonable price.

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