BillFitzmaurice.info

A friend dropped off a dead Headrush speaker. Module is toast and the HF driver is blown.

My plan is to turn it into a passive speaker and replace the HF with a spare I have laying around.

Finding specs on what driver is in there is not gonn'a happen. So, I'm going with an ASD1000. I need to build a passive crossover for it. Doesn't need to be fancy, just something I'll use for testing stuff in the garage.

I plan on a 2-2.5k high pass, so I plugged everything into a crossover calculator to get some numbers of components. Of course, I was offered choices of crossover types – BW, L-R, etc.

So, I went down the rabbit hole of trying to reverse engineer one of Bill’s crossovers to see which type he uses. After plugging in a bunch of values in the calculator, I’m still stumped as to which type is in the OT12s.

Anyway, any thoughts on what I should use? 2nd order? 3rd order? 4th if trying to get down to 2k? BW? L-R? Or, would it be easier to just build a simple 2nd order and cross at 2.5k?

I can figure out the values once I have a clue on which type would best fit this little box (8 inch woofer, if that matters).

Ok, geniuses – GO!

The OT12 crossover is 2nd order low pass, 4th order high pass at 2kHz. Never use 2nd order/2nd order, it creates polarity issues.

I used to summarily recommend LR crossovers (passive or active) because they are -6dB at the crossover frequency and "should" sum to zero at the crossover frequency... or so I thought at the time. Since that time, I learned about phase alignment and all that. In a situation where you have little to no control over the phase alignment between two drivers, it may be better to use the other options, which are -3dB at the crossover frequency, providing a +3dB bump there, which could counteract a fair bit of phase misalignment. Even that doesn't account for any mismatch in sensitivity at that frequency either, which is what EQ is for, I guess.

That's all I have to contribute, Bruce. Haven't got the knowledge to offer anything additional. I'm great with active crossovers, absolute dummy in passive. I look forward to watching and learning as this unfolds.

Bill Fitzmaurice wrote: ↑Fri Apr 03, 2026 4:32 pm The OT12 crossover is 2nd order low pass, 4th order high pass at 2kHz. Never use 2nd order/2nd order, it creates polarity issues.

yep, I saw the 2nd order and 4th order in the plans, but what type of crossover is it? Or, is it your own brew?

Seth wrote: ↑Fri Apr 03, 2026 4:49 pm I used to summarily recommend LR crossovers (passive or active) because they are -6dB at the crossover frequency and "should" sum to zero at the crossover frequency... or so I thought at the time. Since that time, I learned about phase alignment and all that. In a situation where you have little to no control over the phase alignment between two drivers, it may be better to use the other options, which are -3dB at the crossover frequency, providing a +3dB bump there, which could counteract a fair bit of phase misalignment. Even that doesn't account for any mismatch in sensitivity at that frequency either, which is what EQ is for, I guess.

That's all I have to contribute, Bruce. Haven't got the knowledge to offer anything additional. I'm great with active crossovers, absolute dummy in passive. I look forward to watching and learning as this unfolds.

I appreciate it. This is not critical at all. Just gonna be a noisemaker for testing stuff.

And in case anyone is wondering.......the Headrush speakers are exactly the same as Alto.