WD25TEX - raising value of tweeter coil resistor ??

[VantheMan]

In "The Next Step" re the WD25TEx , Peter invites users to experiment with the value of the resistor in series with the tweeter coil, stating that going up from 2R2 by as little an a0.5R increment would give a slightly warmer sound.
Has anyone tried this ?

[Richard]

" I have shown before that the best acoustic performance is given where there is a mild 1 or 2dB depression through the crossover region for the on-axis response. This doesn’t necessarily translate to a loss of acoustic power in this area, however, due to the wider dispersion, and therefore greater radiating power, of the treble unit.

The level of this depression is set by the resistor in series with the 0.42mH coil. Increase this resistor and you flatten the transfer curve of the treble crossover, decrease the resistance value and you sharpen the transfer curve as the crossover turns over. Feel free to play with this value; reducing it produces a slightly brighter performance, increasing it produces a warmer performance. You only need a change of, say, 0.5 Ohm to appreciate the difference.

You can see the overall response of the system in Fig. 1. together with the crossover slopes overlaid. Following the typical Linkwitz-Riley responses the crossover point is -6dB at 2kHz. The larger 0.42mH coil chosen, with its series resistance, gives a small shelf in the treble response below crossover, but this is the compromise chosen on the basis of listening tests!

The phase coherence of the drive units and crossover is easily indicated just by reversing the phase of one of the units. If the acoustic crossover is phase perfect then there would be just a sharp notch at 2kHz. I’m very satisfied by this result (Fig. 2) which marries up with the listening result where it’s not easy to discern the individual drive units and the stereo image is rock solid at all frequencies."


Hi Van, I read the complete article (small part above) as a description of how Peter arrived at the finished design. He includes notes about the effect of some changes but overall it reads as “fait accompli” to me. That said, it would be an easy change to try so let us know if you give it a go.

[VantheMan]

Hi Richard,
I guess I’m a bit wary of the word warm. I think what I’m really after is more bass presence but I don’t want to lose definition. My speakers are right up against the back wall and on some disks bass is deffo lacking and I find myselfhaving to up the volume. I sUppose it’s as much certain recording/pressing’s fault too.One is never satisfied and if ever you are, it doesn’t last long.

[Richard]

Hi Van, I like a warm sound, immersive and detailed, nothing obvious, and lower volumes these days so I might not be the one to advise! Try adding/moving soft furnishings around. Speaker/room combinations often have quite a narrow volume range they work happily at and sometimes the only way is to change the speakers or room. Moving things around and absorbing some hf reflections might help by letting you play it a little louder.

[Brian]

Originally Posted by VantheMan

Hi Richard,
I guess I’m a bit wary of the word warm. I think what I’m really after is more bass presence but I don’t want to lose definition. My speakers are right up against the back wall and on some disks bass is deffo lacking and I find myselfhaving to up the volume. I sUppose it’s as much certain recording/pressing’s fault too.One is never satisfied and if ever you are, it doesn’t last long.

I don’t think there is much to be done about it. Granted, I’ve owned only the standmount WD25A’s, but I’ve heard the WD25T’s and both are a bit lightweight in the bass imo.

Why not change the resistor and see how it works out?

[VantheMan]

Hi Brian,
I aim to try a 3R resistor but I haven´t yet mastered the art of sticking them with chewing gum ! So I am dependent on a mate who right now is rushed off his feet but it shall be done and I will return with my gut feeling.

Richard,
I agree that it is Peter´s "fait accompli" but he does say "feel free to experiment" so who knows what warm means for him and for me. I like warm too but not suffocated. Let´s see.
Chris

[bob orbell]

I think 3R will kill the HF, keep posting. Bob

[VantheMan]

Thanks Bob,
Peter says 0.5R increase is noticeable so maybe better 2.7R then.
Chris