DIY Inductors: Any Advice?

Anyone have any tips or advice for making inductors? I'm planning on building a pair of speakers soon that will require crossovers. Inductors are expensive, however, and I was hoping to save money by building my own.

 

My advice is don't! Unless you have an inductance bridge or meter, you'll never know what inductance you're winding, and trying to get two to match won't be easy either. Winding air-cored inductors really needs a winding machine, and cored inductors will be limited in power handling.

Apart from that, yes you can calculate how many turns on what diameter and length to get the right inductance, but al, calculations assume a careful, layer winding, and that's really difficult without a coil winding machine.

If you're making your own 'speakers, why bother with a passive crossover at all? There's every benefit to going active, whether with a DIY 'conventional' active filter using opamps, or better a DSP-based crossover as I use. DSP is definitely the better way, as it allows totally repeatable filters and adjustable on the fly, with EQ usually built in for free. It's likely to cost little more than a good quality passive crossover if you buy good quality inductors.

S

 

Thanks for your reply. I guess I should have mentioned that I do have an inductance meter. In this project, I was actually thinking about building a passive crossover, testing it, and then doing another configuration with an active crossover (from op-amps) for comparison.

 

Ah, that puts a different light on it. With an inductance meter you'll be able to make the necessary measurements.

As to hints or suggestions, get or make a coil winder. Many years ago, I made one out of an old wheel-brace and a mechanical counter to count the number of turns. Take it slowly, and make sure the turns are even and the wires, of whatever gauge you calculate, are laid in neat layers. Pile winding works OK if you're just trying for a certain inductance, but the amount of wire used will vary, so the resistance of coil, and hence its Q will vary, so making an identical pair will be more difficult. How much this matters, given that no two drive units are identical, is moot however, and pile winding is a lot easier, if messier.

I wound coils back in the days when making filters, but found very early on that for audio I could simulate inductance using opamp gyrators so except for RF coils, didn't bother. As for loudspeaker crossovers, I only ever made high power inductors for valve amplifier power supplies, and all my DIY loudspeakers were active, so never made any.

S

 

Thanks! That's helpful.