adjustable xover

I would like to build a crossover for my sub that is adjustable between 60-100Hz at least. I am also interested in a phase adjustment. I know most people would recommend just getting a plate amp, but I prefer my sub as passive being driven by a Leach amp for the time being and a Leach SuperAmp in the future. I have searched the site but sub xovers are not so common. I can settle for a passive filter if I have to but I would like to see a success story before I go that route. I have a 142.5L vented shiva to the exact specifications listed on the Adire site. Thanks for your help,

Austin
 
Adjustable xovr

you can make an adjustable passive crossover, but I would suggest, to make it simple, using breakpoints at 1/3 octave points, something like 50,64,80,100,120 Hz. The simplest method would be to use these frequencies to calculate the value of the inductors at the break points and switch in more inductance in series. You can either buy the inductors from Parts Express or Madisound, or be more creative and wind your own, tapping the inductor at the appropriate break points. Note, you can also buy one big inductor from one of the above suppliers and "unwind" it and insert taps. Note well, the impedance function of a loudspeaker is not remotely "resistive". So using the standard formula for 6db crossover is only going to be an approximation. Get's a little harrier if you want to go to 12db/8vo.

One of the cheapest and most useful tools for designing passive crossovers is a Heathkit LRC bridge, these go for ten to twenty bucks on EBay.
 
DIY inductors

One thing you should remember if winding your own inductors, or unwinding and rewinding a manufactured one, is that the tighter they're wound, the more inductance they posess. If you go unwinding a manufactured one, you may be messing with the rated value of inductance.

Also, for air-cored inductors, a handy way to keep your inductor windings tightly together when you take them off your core is to glue them using Britfix Aircraft Model Cement. This glue does not interfere with the other values of your inductor (eg. it doesn't make your inductor into a capacitor).

If you walk into a shop and ask for Britfix, you might get some strange looks - this glue is a favourite among glue sniffers :)
 
adjustable passive xover website?

Does anyone know of a website discussing adjustable passive crossovers?

I did have a conversation with the gentleman at sound.westhost.com and he was very helpful. Has anyone used the circuit he has listed on his site for my application? It seems like exactly what I need. I am kinda hesitant to use opamp circuits though in fear that it will degrade the sound. Perhaps I should just go with the passive. Well, I just checked the site and it appears he took down the project today. So, if you know which one I am talking about and have experience with the circuit could you comment on it please (It was a variable crossover, phase and other options specifically for subs). Thanks,

Austin