To much high

Fix your room. Add some absorbtive elements until you get the sound you're listening for.

-rw-

You can also experiment with spkr. positioning, the most radical being a severe toe in to give you nearfield listening to eliminate most of the room. This should help identify how much the room affects the sound or if it's the gear.

Then again, you can use cables as tone controls.

Ditto to the above. You are wasting your time trying different speaker cables. Try moving the speakers, especially toeing them in. I actually have mine crossfiring about two feet in front of me. Adding room treatment can help too. You said nothing of what your room is like and that is the biggest culprit. Speaker position tweaking costs nothing so is certainly worth a try. Treatment will help more than just the highs.

Assuming you ruled out the source material, if its the speakers, accept it and be more selective in future. If the room is too bright, then first treat the direct reflections: side wall, floor, ceiling.

This is done by placing a mirror on a side wall until an imgage of the speakers appears in the mirror from the listeing position. That is the spot to place an acoustic device (of 2' sq should suffice since the location is so accurate). Try a pillow on a table first, or garment on a hanger, whatever to experiment.

A throw rug on the floor similarly located if the room is not carpeted.

Then try the wall behind the speakers. BTW the greater the reflected distance (path of the sound energy), the less significant its reflection is. When it reaches and exceeds several feet in distance over the direct speaker to listener path, it is no longer an issue.

This can be a useful practice anyway, especially with box speakers, being carful to not over-damp, or deaden the room. Or perhaps it will add enough absorbtion if the room is too bright.

And if I may suggest, rather than prefer some 'sound' quality over another, which is masking the info on the source material, aspiring to 'true to the original' in playback. That is, the best you can do with any system is accurately reproduce whatever in on the recorded material.

With transparent speakers, appropriate setup, and a distortion free amp to power them, you will hear and can then discern the good, the bad, and the ugly, in available recordings.

If however you mask the source with perferred distortion in any component in the sysem, you are also masking any well produced and engineered sonic excellence that may otherwise be available to enjoy as 'live' like realism, which is all the more involving.

The system is a means to an end, is it not. Rather than an end in itself: where you would sit and listen to how 'good' your system 'sounds', and using the music only as means to enjoy the system.

Would not anyone rather than point out to friend how their system sounds, instead not have to point out how real the music sounds: as though it were happening in the room?

"To much high"

Is that different than 'From much high'?

I think you meant 'too'. :-)
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I would have to say that the statement of 'wasting time switching cables' is a little off the mark, as cables can greatly impact the overall sound. (Van den Hul vs. Kimber, in general, have totally contrasting characteristics - Van den Hul being warmer/slower vs. Kimber being lively and quick). Having said that, I believe a combination of what was stated in the previous responses can help to finely tune / tone down the 'brightness'. Try placing a large area rug on the floor in front of your speakers. Also, putting some form of sound absorption material on the wall behind this system will greatly help, whether it be a wall-hanging decorative rug or sound absorption material specifically designed for that purpose. Side walls (first reflection point) and wall behind the listening area should be similarly tamed. Some or all of these changes can help to tame the beast and won't break the bank in doing so.

I definitely agree with NOT using errors in other components to fix errors in another.

Try to fix your room as much as possible. After that, add a resistor to the tweeter circuit. (This resistor must be added BEFORE the tweeter's filter cap or you'll change the crossover point. This may be easy or difficult depending on the complexity of the crossover.)
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I agree that treating the room is definitely the best approach. I will not repeat any of the excellent advice already given.

However, if that is impossible, for either room constraints or spouse constraints (Boy, I know the later!), than rather than switching speaker cables, perhaps you could try something less expensive like switching out the interconnect between your source and preamp, or between your preamp and amp.
You might want to try a Cardas Golden Cross cable. It might just take the edge off the brightness. (A friend of mine used to use these cables to take the edge off his CD player.) You should easily be able to find a used pair on Audiogon (or Ebay) and give it a shot. If it does not work, you can easily get most of your money back. (You might want to ask any friends who are audiophiles to lend you some of their cables, so you can experiment. I have lent out cables for that purpose before.)

Just a thought. Good Luck!

Definitely treat the room. And, as has been suggested, going to a different IC can often help with the shrill highs. Although I prefer silver cables with our tube-based system, I found the Audience AU24 IC and the Analysis Plus Crystal Oval both took some of the high end edge out that is present with the silver IC's. There are many excellent options out there.
Hope this helps.

Guys, thanx for the advice, I will experiment with placement and some absorbing materials. And Didactically, being an ex-radio engineer, I know how original sounds, and I know these speakers are a bit bright. But because I fell in love with their potential I'll try to squeeze out every last drop that's in them.
Jeffreybehr, if I would use a resistor to reduce tweeter output (say, 1 ohm - 5 watts), wouldn't the best place be in the '+'-cable between cross-over and tweeter? I don't know, that just seemed the most logical place, but I might be wrong here, so any advice would be appreciated. And then: is it possible to get to high? :) But you're right, I probably meant 'too much high', but since I'm from Holland I tend to mess up things like that......

Satch:
Chiming in: the room (some expense). Placement (no expense).
What lead you to silver speaker cables? Depending on implementation some silver cables can vary the highs quality... Might you have any old speakers cable to swap for a test (no expense), a friend that could lend a hand here ( you will know your next expense, if they work you don't return them one less freind though!!)?

Hah! Friends only cost money, dropping by at random, emptying the fridge, so losing one is only a good thing :). Seriously, I chose the cable since it went well with my old speakers, and I do have some old pieces lying around, so that's one experiment that's on my list....