WD25TEX Millennium Crossover R5 Resistor Value

[westers]

Hi

I'm rebuilding my WD25T's with the standard tweeter and instead putting the Millennium tweeter in it (the T25CF002 version).

I found the Hi-Fi World article that Peter wrote and wanted to know if the value for R5 in the crossover diagram are the values shown, or does the value shown assume that's the total combined resistance of both the inductor and resistor. For example, is R5 actually 2.2 ohm, or is it actually 1.3 ohm with the inductor L2 adding 0.9 ohm to give a total value of 2.2 ohm?

Anyone who built these with the millennium tweeter know the answer? In Peter's V2 article of the standard tweeter (from the WD articles CD), he does call out that the value of R5 should be calculated by deducting the resistance of L2 from the figure shown, thus giving the actual value of the resistor. I would assume he's used the same logic for the earlier crossover design for the Millenium tweeter, but didn't call this out.

Link to the Millenium tweeter article https://www.hi-fiworld.co.uk/index.p...next-step.html

[VantheMan]

Interesting, I built mine with 2.2 resistors but it’s a fact that he says he had to up the value of the coil to suit the Millennium but doesn’ t mention if that implies lowering the value of the resistor. Also I have no idea of the resistor value for the previous tweeter - was it in fact also 2R2 ? If so, wouldn’t that be a rather large coincidence ? Why should 2 different tweeters need the same total value?
What, in theory, would be the effect of too high a value for this resistor in this sort of crossover? Is the difference negligible ? For that matter , given my utter technical ignorance, what do micro henries have to do with ohms ?

Oh dear………please don’t try and enlighten me, I won’t get it. Just tell me if the resistance will lower the high frequency roll off point. I have always thought the Millennium was good atcontrolling treble splash but at the same time, the treble was not particularly extended if that makes sense.

[Riggers]

Hi Westers and Van

I must admit when I was building my crossovers I did consider this same issue. My feelings were that how much difference could <1ohm make to the overall sound that would not be impacted elsewhere by factors such as speaker position, influence of furnishings etc. I am very happy with the balance of my wd25T’s and am not convinced enough to bother pulling the crossovers out to fiddle with some resistor values.

This may change if one day get the urge and insert some Mills wire wounds or the like

Phil.

[Greg.]

I’ve checked the files for WD25T EX and can confirm that the correct value of R5 is 2R2, being a Welwyn wire wound 3 Watt +/-5% W21-2R2JI, RS part number 139-3390.

[A Stuart]

Originally Posted by VantheMan

... what do micro henries have to do with ohms ?
Oh dear………please don’t try and enlighten me....

Oh dear! Enlightenment is upon you! There is no escaping your destiny !
Henries are measures of inductance, same idea as Farads are measures of capacitance.

Inductance fights against the rate of change of current , ie stops higher frequencies more. This is in a similar but somewhat opposite way to capacitors passing higher frequencies readily while stopping lower frequencies and DC.
This ability to deter (I am avoiding the word "resist" to keep that word separate) rapid change of current means that for every given frequency of signal, a certain number of volts is required to drive each amp through. This stopping-strength is the "Reactance" of the inductor at the given frequency. The value of the reactance happens to be 2*PI*frequency(in Hertz)*Inductance(in Henries), and as it is a volts per amp value, reactance is stated in Ohms.

Real life inductors are never pure inductors. They have a combination of their own inductance (Henries) and resistance of their wire, as you are already aware. Inductive ohms and resistive ohms do not add up by normal arithmetic, but can be considered since you are now brimming with enthusiasm as being at right angles to each other along different sides of a rectangle.
If you swapped to a different make of inductor whose wire gave it a different internal resistance then if you wanted to keep the overall electrical behaviour the same you would need to alter any related external resistor as per your query, but internal characteristics of a component would not typically be referred to on a circuit diagram. So unless you changed to a different brand of inductor then simply fit the resistor shown on the original diagram.

Alastair

[VantheMan]

Thanks Riggers, Greg and A. Stuart for putting me out of my misery, although It appears I should have owned up to having fitted Mills 12w wire wounds instead of theWelwyn’s but I’m pretty sure I liked their effect. Maybe the Millenniums are so good that they have lulled me into a false sense of insecurity regarding their roll off point or maybe it’s just my duff lugs.

[westers]

Thanks all for confirming. Having thought about it some more I had come to the conclusion that it would be the 2R2 value as Peter hadn't called it out to be anything other than that.

As for Micro Henries, he's Sherlock Ohmes very small, imaginary friend