The importance of coil resistance

[VantheMan]

I am thinking of fitting new coils in my external crossovers - Yes, I know that a coil is a coil but I have changed the resistors for Mills and the caps for teflons (always of the same values) and quite like the results so why not ? Anyway Peter´s figures for the coils are 0.76mH and 0.2R and as you probably know the kit versions have a ferrite core. I have seen some Jantzen toroidal air cores (apparently for use with woofers) and which won´t break the bank but the DCR is much lower, more like 0.002R. The lower the impedance the better in many apps. and is often considered a positive move but is it a no-no when it comes to crossovers ?

[Phil Y]

Peter will have taken the D.C. resistance of the original inductor into account when designing the speakers. That 0.2 ohm will be part of the design. Moving to an inductor with a lower resistance will be a deviation from that design. Maybe think of it as removing a 0.2 ohm resistor that is in the original design.
Whether it will be audible, and if so, better or worse, there is only one way to find out.
Presumably, these Jantzen ones are a more expensive part so potentially better sounding.
Personally, I have never experimented with speaker inductors so I am unable to offer an opinion on that score.

Phil.

P.S. I for one will be interested to hear of the outcome.

[andrew ivimey]

Interesting ... I'd a thought that air cored inductors will always be bigger than their equivalent ferrite cored because they don't have the ferrite core to help achieve the inductance. If there are then more windings and therefore more physical size the resistance would be higher.

Still, what do I know?

[Phil Y]

I was thinking the same Andrew but the ones in question are on the hifi Collective site. They are toroidal, so a bit unusual.

Phil.

[VantheMan]

Just to confirm that I rechecked the toroidals and they are not air-cored after all. The 0.76mH one also happens to weigh half a kilo so maybe not. I have ordered some Jantzen Wax-Coils after being assured they are indeed better than their air-cores for such a relatively high crossover point and mid-frequency content. I took their word for it. Not cheap but they won´t break the bank either..
That will be in the New year but yes, I will keep the thread posted.

[Riggers]

Just a question Gents,
I have been toying with the idea of building some WD25T's and have discovered after a quick look on the net that I can get hold of inductors of the correct value but will have lower resistance as Van has discovered. Is it just a case of putting a suitable value resistor in series with the new inductor to achieve the same overall resistance value? I noticed in the schematic that one driver's inductor has indeed a resistor in series but the other driver does not. Is it an issue to add a resistor in series next to the inductor to achieve the overall resistance in Peter's design?
Cheers
Phil.

[Phil Y]

Hello Phil,

I am not really an expert on crossover design but I would have thought that would work. My guess would be that it would be best on the 'amp' side of the inductor rather than the 'driver' side.

Phil.

[VantheMan]

I have ordered the Jantzen Wax Coils which in 14awg wire are indeed available with the right values i.e. 0.76mH and 0.22 ohms and they are air cores. Will let you know how I get on but so far I am pleased with the changes the Mills resistors and the teflon caps have brought. The WD25Ts now begin to sound as their size would suggest they should, at least in my system.

[Yellow]

Yes - I agree. An Air-cored inductor would normally have a higher DCR as it is so much bigger. There's a lot more wire to get through!! Are you figures right. What's important is to keep a similat inductance and DCR in series with the driver if you're changing components. However, if you drop or gain 0.2 ohms, the end result won't sound too diffent from the original design in terms of dB levels. Quality may improve dramatically though.

[VantheMan]

Yes, the values for the Jantzen wax coils are 0.76mH and 0.22R, exactly the same as the figures given by Peter for the WD25TEx. Of course they are 3 times bigger than the original wire coils supplied but as I have external crossovers, size does not matter.