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Old 10th February 2013, 10:37 PM   #31
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Quote:
Originally Posted by tvrgeek View Post
Wolf,
I doubt the tweeters Fs was the issue. Welcome to the club of us who found this is to an easy driver to use well; but if so, very good indeed. The trick is keeping the the XT25 above 3K. It just plain won't stop flopping in the breeze below that. Look at it's CSD plot. Second order electrical at 4K makes it much happier.
You see I built those Xenums with the SC50 (previous version of SC90) back in 2008. I also had the same issue with the XT25TG30 in my Scandivifias in late 2007, as both are non-FF and have a high Zmax at Fs to compensate. 4th at 3k won't need a notch or comp on the TG30. In both cases, suppressing the Fs magnitude at least a little gets rid of the buzzing issue.

Later,
Wolf
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Old 10th February 2013, 10:50 PM   #32
tvrgeek is offline tvrgeek  United States
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Hmmm. Just used ARTA to measure the response of an XT-25 with and without a 10 Ohm shunt resistor. Solid state amp. Other than the tiny difference in amplitude, the MLS plot 1/24 octave un-smoothed is identical. By identical. printed and held to the light. Identical within the width of the plot line.

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Old 10th February 2013, 10:59 PM   #33
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If you had no series component, the FR will not change, only the impedance will reflect a difference. There has to be a voltage divider.

Are you doing a full-sweep? The Fs is where the problem would be heard.

Quick-Check: Play James Taylor stuff on it in a system, with and without comp.
Later,
Wolf
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Old 11th February 2013, 12:58 AM   #34
ODougbo is offline ODougbo  United States
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Just remembered - there a 33ohm on the Vifa/SF project that I've been working on.

James Taylor...don't have that in CD, but can't wait to let TVR listen to a Chris Isaak CD; very nice, outstanding baritone.
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Old 11th February 2013, 01:05 AM   #35
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Wolf,
Actually my questions were for the OP (post # 7), but I appreciate your explanation of when a resistor in parallel with a tweeter is useful.

From all of the discussion so far, it's obvious the OP, if he expects to get help, has to be specific rather than general about 1st order series crossover networks and a resistor in parallel with the tweeter. The tweeter he intends to use should be named and what his proposed cross-over frequency is.

Regards,
Pete
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Old 11th February 2013, 09:55 PM   #36
tvrgeek is offline tvrgeek  United States
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Sweet Baby James? Any tips on track or what to listen for? I usually rely on Joni Mitchel and Joan Baez as their voices seem to be really tough. Then Julian Bream's guitar, Harry James horn, Dave Grusin for "tightness" in the bass, etc.

I used the DCX for a fourth order at 1K for my test. This puppy needs to be used above 3K, so any problem in a sweep at 450 where the Fs is is just not going to tell me much. Right or wrong?
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Old 12th February 2013, 08:20 AM   #37
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TVR-
It mostly has to do with his lower range than the higher stuff. "On the Roof" is a good example. "Carolina in my Mind" would also likely work.

Since you knocked down the resonance issue for your test before the measurements were taken, you won't experience their issues. I xover'd at 2.6kHz, and was fine, BW3 acoustic- as long as the resistor (or LCR) was present. It does not have to be used above 3kHz only, but it gets easier if you do.

The increase towards Fs is rather gradual, and peaks really high, and is why it should be dealt with. The SC90/50 can take a 2.5kHz xover point, and the TG30 can take a 2.1-2.2kHz xover point.

Granted, I'm using passive filters for this, so YMMV...
Wolf
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Old 14th February 2013, 07:03 PM   #38
Philfr is offline Philfr  France
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Hi all,
I try a 33 Ohm with 6db serial xover..
Nothing change in impedance curve or response curve.
But how calculate this value ?
Thank's.
Phil.
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Old 14th February 2013, 08:20 PM   #39
tvrgeek is offline tvrgeek  United States
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I guess the key term there is "easier." With that we would agree. I try to pick drivers to use in their easy zone. Spend more on a tweeter and less on notch filters is my preference. We are nit-picking a $35 tweeter after all.

Thinking back on the crossover topology and the use of a parallel resistor. I just can't see a technical reason putting a 33 Ohm resistor in parallel with 4 Ohm VC is going to do much of anything useful unless it has significant inductance. Ever measure some of those "Low L audio quality" resistors? I have to think about this some more as I only see negatives.
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Old 14th February 2013, 08:38 PM   #40
tvrgeek is offline tvrgeek  United States
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Quote:
Originally Posted by ODougbo View Post
Just remembered - there a 33ohm on the Vifa/SF project that I've been working on.

James Taylor...don't have that in CD, but can't wait to let TVR listen to a Chris Isaak CD; very nice, outstanding baritone.
And if you remember, that was not the MS recommended solution but "advice" in a crossover that had several other odd things that did not work.
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