Hey all,
I'm delving into crossover design and I am not experienced in it at all. I have also forgotten a lot from my circuits classes at university but I will do my best to understand whatever comes here and brush up on those concepts.
I have a general design for my crossover and I'm considering wrapping my own air coils. My main question comes in when using different values for coil height, diameter, and wraps I can get the inductance value with different dimension of the coil.
Something I can not seem to find any information on is possible design constraints for the air core diameter. Other than space, are there reasons to keep the air gap smaller or larger? Does going too large have potential for picking up RF? Or is there a change in latency of the field forming that can affect the performance based on the size?
I guess another way to put it would be is there any reason that I cant wrap a coil with a 2 inch diameter as opposed to half an inch? They can calculate out to have the same inductance but I imagine it can't be that simple.
I don't know what is worth considering or what is even an issue. Hopefully someone might know more about inductor properties here and can explain something.
Thank you guys for any help.
I'm delving into crossover design and I am not experienced in it at all. I have also forgotten a lot from my circuits classes at university but I will do my best to understand whatever comes here and brush up on those concepts.
I have a general design for my crossover and I'm considering wrapping my own air coils. My main question comes in when using different values for coil height, diameter, and wraps I can get the inductance value with different dimension of the coil.
Something I can not seem to find any information on is possible design constraints for the air core diameter. Other than space, are there reasons to keep the air gap smaller or larger? Does going too large have potential for picking up RF? Or is there a change in latency of the field forming that can affect the performance based on the size?
I guess another way to put it would be is there any reason that I cant wrap a coil with a 2 inch diameter as opposed to half an inch? They can calculate out to have the same inductance but I imagine it can't be that simple.
I don't know what is worth considering or what is even an issue. Hopefully someone might know more about inductor properties here and can explain something.
Thank you guys for any help.
The main constraint is wire diameter. The greater the diameter the lower the resistance of the inductor, but the coil dimensions become unreasonably large.
There are some useful pointers re bobbin size here: Article, How to build a loudspeaker crossover inductor
There are some useful pointers re bobbin size here: Article, How to build a loudspeaker crossover inductor
Hey Galu, thanks for the reply.
I actually skimmed that article earlier today. Wire diameter and other dimensions all make sense. The thing I was curious about was if I could make the former diameter bigger as it would make wrapping the coil a little easier. I have plenty of room in the cabinets I built so that's not a consideration.
But even though the equation for L will spit out a coil with a 3, 4, 5 inch diameter and so on, there has to be a limit to how big that former can go before the inductor doesn't act like an inductor anymore and is just a long wire or something. That's more of what was interesting me, if that makes sense.
Appreciate the reply.
I actually skimmed that article earlier today. Wire diameter and other dimensions all make sense. The thing I was curious about was if I could make the former diameter bigger as it would make wrapping the coil a little easier. I have plenty of room in the cabinets I built so that's not a consideration.
But even though the equation for L will spit out a coil with a 3, 4, 5 inch diameter and so on, there has to be a limit to how big that former can go before the inductor doesn't act like an inductor anymore and is just a long wire or something. That's more of what was interesting me, if that makes sense.
Appreciate the reply.
I once was the technical rep for a large arcade game. it was 12 feet on a side, surrounded by windows, and inside were a few radio controlled Army tanks. You drove them around and shot at targets with LEDs. The way we controlled them was we ran a loop of wire around the perimeter. The connection to the tanks was inductive from that field.
But you were concerned about RF. Well think about it. RF is everywhere but the levels are so very low, and so are the impedances in a speaker, so any picked up RF would be tiny and swamped by that low impedance. it would be like working in a steel mill and worrying if the crickets make too much noise.
But you were concerned about RF. Well think about it. RF is everywhere but the levels are so very low, and so are the impedances in a speaker, so any picked up RF would be tiny and swamped by that low impedance. it would be like working in a steel mill and worrying if the crickets make too much noise.
Looking at the physics, this would appear to be a non-issue in terms of crossover inductors.
An externally hosted image should be here but it was not working when we last tested it.
Your former would have to physically fit the loudspeaker enclosure, and I see no reason why an inductor of that scale would not retain its property of self-induction.
You have flexibility there, all reasonable designs will work, you pick one or the other based on practical/construction/availability/space reasons.
Don´t worry about RF in a crossover which will feed a "brute force" passive device.
Help yourself, if same inductance and DCR both will work the same when connected to your speakers,
Air-core coils do not have an air gap.
The size should not approach a wavelength; for audio, much less than a mile.
Tesla made some large-diameter coils which apparently worked OK:
https://public-media.si-cdn.com/filer/15/97/15972379-a704-4c12-8848-196d954896dc/42-55992923.jpg
(This is known to be a double-exposure)
History of the Tesla Coil and its Geometries | Waveguide
(Off-topic but an interesting excursion into hi-voltage coil shape)
The two main parameters for loudspeaker (2 to 20 Ohm) audio filters are inductance and resistance. Sometimes a system needs loss and the coil resistance can be part of this, for a savings in money. Often we want "very low loss". We optimize the proportions and increase the size until the budget is busted.
Optimum proportion is *about* 1:1:1.... final coil is say 1" wide, 3" overall diameter, with a 1" center. However significant deviation is insignificantly less optimum, so we usually start with any convenient broomstick or spool and work it out.
Perfect opportunity to go straight to active crossovers! It's the latest rage. Get rid of those big coils! Amps love pushing a driver with no inductors!
And it gives you chance to build different amps.
Nelson Pass designed active xo kit in diyaudio store:
DIY Biamp 6-24 Crossover – diyAudio Store