Ferrite Core Inductors for Crossovers

[r_s_dhar]

1. Could someone suggest a nomogram for designing a DIY ferrite cored inductor to be used in passive Xover?

2. The ferrite rod found in older AM radio sets -- can we use this as a core? A friend of mine tells me that these rods are unsuitable as they get easily saturated at audio frequencies.?????

[kelticwizard]

I think the way it works is that ferrite core inductors get saturated at high frequencies, not low. Anything suitable for radio work will easily be OK for audio frequencies.

The major purpose of adding ferrite is to cut down on the number of turns required for air-core inductors. The more turns, the higher the DC resistance. The higher the DC resistance, the less desirable the inductor. However, ferrite adds undesirable distortion effects, so it is a balancing act. Air core inductors give superior performance, assuming that you can get one with a low enough DC resistance.

The basic approach is to use air core inductors unless the DC resistance simply gets too high, then switch to ferrite core.

[r_s_dhar]

Thanks Mr. kelticwizard for that piece of information

[Lisandro_P]

My speakers use a passive LCR filter to feed the tweeter, and the inductors use a ferrite core. They're SMALL, and i haven't messed with those yet (they look handmade and somehow fragile, the coils are very tidy and covered with shrink tubing), but these speakers sound to me, and everyone else, amazing. It's a compromise; i'd love to switch the inductors to air cored ones, and perhaps there'd be an audible diference, but for me it's just not worth it.

[Thatch_Ear]

Lisandro,
Inductors limit the highs. If you have small ones in the section with your tweeter it is simply to limit how high it will go. It could be your tweeters need to operate under a certain level to avoid dammage. If that is the purpose I can see little advantage to changing them out as where they are cutting the frequency off is more than likely above the range of human hearing. Just a guess.

[Lisandro_P]

Exactly. I tried to not to mess too much with the crosover (only replaced a bipolar electrolytic with a polyester cap), because it has quite an impact in the sound and it's suposedly optimized for the drivers and the enclosure.

[planet10]

Originally posted by Thatch_Ear
Inductors limit the highs. If you have small ones in the section with your tweeter it is simply to limit how high it will go.

Are the LCR in series or is the L shunting the tweeter?

dave

[planet10]

Originally posted by kelticwizard
The major purpose of adding ferrite is to cut down on the number of turns required for air-core inductors. The more turns, the higher the DC resistance. The higher the DC resistance, the less desirable the inductor. However, ferrite adds undesirable distortion effects, so it is a balancing act. Air core inductors give superior performance, assuming that you can get one with a low enough DC resistance.

A middle ground is to use a gapped inductor -- similar to what is done in SE Output transformers.

Some paper wrapped around the core before you start laying on the windings would probably do the trick (Note: i've never actually done this myself)

dave

[Lisandro_P]

The R & C is in series with the tweeter and the L is conected to the C-tweeter node and ground.

[planet10]

Originally posted by Lisandro_P
The R & C is in series with the tweeter and the L is conected to the C-tweeter node and ground.

That makes it a 2nd order filter (with a bit of padding -- the R).

You can ignore what Dave Thatch_Ear said about the L rolling off the top.

dave