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Old 28th April 2005, 12:44 PM   #11
float is offline float  England
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Jeeeeesus Vuki, thats some crossover How long did it take you to come up with that!!??
My experiences tally with yours exactly regarding first orders and so on.
My low pass actually consists of a 1.8mH with a 9.4parallel cap( second order electrical) and a zobel of a 3.9 cap and 8.2ohm resistor. I altered the zobel from the values for flat impedance to shape the top end response a bit.
Measurements with a radioshack spl meter show a good third order acoustic rolloff, but l have a slight loss of level between say 1.25khz and 2khz. It looks from your FR plot that you may have the same thing?

Bob, I can generously offer a free storage facility for any excess quality amp channels you have
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Old 28th April 2005, 04:40 PM   #12
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Quote:
Originally posted by BobEllis
If you want to get really fussy, you might try a notch filter on the tweeter to tame that small peak in response at around 3-4K. I plan to try it on my next version of the crossover. Not that I hear a need, but the Moxlite boards have eq in the tweeter section so why not?
I'm not sure about the original TC120tdx (if that is what you have float), but the tdx2 like mine does not have this peak (at all), it's quite a different beast to the newer TD5. Its response is smoother and is about 3dB more efficient in the usable range, however it starts rolling off a lot sooner at the low-end and has a higher Fs. A 2.4kHz crossover would barely be 1 octave above resonance for the tdx2 but the it does have a far smaller resonance peak than the TD5, its impedance is almost flat across the board, so it might sound just fine. Only one way to find out!

Quote:
Originally posted by vuki
And, of course, you can't use Andromeda crossover because it's intended for a 3-way so you would have very bright sounding speaker without help of the bass driver.
Apologies! I hadn't realised Mr Gee had tweaked them that much, the Andromeda used to be a pure 2-way with sub.

I never finished my speakers with the TC120tdx2, but I think I'll try some tweaking as well, sadly via the arduous non-active route. One more thing to add to the list of future projects!

Just done a quick search for the parameters of the TC120tdx and its Fs is even lower than the TD5, just under 700Hz. Couldn't find any response plots though, but it seems it may be as different again as the tdx2 and TD5 are from each other. You'll just have to play around float, but a low cross-over point is definitely back on the cards and will flatter the woofer too.
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Old 28th April 2005, 07:41 PM   #13
vuki is offline vuki  Croatia
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Here is the fr measurement of ss18w8545 at 1m in his box. One can see a large and broad peak from ca. 600-1100Hz. It's this driver's feature and you can see it in almost every commercial speaker using it. It ads to some of midrange "warmth and presence" unique to that driver. To get rid of it (that's - if you want to) you have to use more complex filters than simple textbook crossover filters. Otherwise (to get rid of it) you either have to use larger inductor and than have sudden drop after 1,1kHz ( float ) or use smaller inductor and live with it and have somewhat agressive midrange/highs.
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Old 28th April 2005, 10:09 PM   #14
float is offline float  England
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Quote:
Originally posted by Noksukau



Just done a quick search for the parameters of the TC120tdx and its Fs is even lower than the TD5, just under 700Hz. Couldn't find any response plots though, but it seems it may be as different again as the tdx2 and TD5 are from each other. You'll just have to play around float, but a low cross-over point is definitely back on the cards and will flatter the woofer too.

Resonance on the tc120tdx is quoted as 694hz with a Zmax of 25 ohms. I wonder if anyone considers the successive tc120 models to be improved? It seems that the parameters have changed for the worse from tdx - tdx2 - td5.

I have used a simple second order of 4.7uF cap and 720mH coil (and L-pad of 5.6ohm series, 4.1ohm parallel) and this gets -6db down at 2500hz and 34db down at tweeter resonance; the shape of the rolloff isn't textbook-perfect, but it's not that far off.

The aspect of the sound that troubles me most is a slight lack of solidity in voices - e.g. Norah and Diana Krall sound great, but theres a hint of wispiness or phasiness that prevents you believing that they're in the room with you.
Its that rock-solid image that I want.
Maybe I'm expecting too much of the system- cd63 ki-sig and audiolab 8000s power with a shunt-passive pre.
Or is the lack of energy (maybe 3db) from 1250hz to 2000hz a likely culprit?
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Old 4th May 2005, 02:11 AM   #15
Aghead is offline Aghead  Canada
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higher crossover pt?

this might sound crazy, but i think the 2-3 khz area is better done by woofers than tweeters, no matter how expensive tha latter. i've got the scanspeak 8" 8554 kevlar and 2905/9700 crossed over somewhere between 3 and 4k witha simple 2nd order and it's better this way than lower, but this is just preference.

carbon is way more critical here.

i would be most concerned about the 3k peak on this woofer - look at the time delay graph if you can find it but if it's not too nasty give this suggestion a try.
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Old 4th May 2005, 03:30 AM   #16
tktran is offline tktran  Australia
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the 9700 is one of the very best tweeters, but measurements show that suffers from higher distortion below 2Khz, particularly horrible at 1.5Khz:

http://206.13.113.199/ncdiyaudio/mar...0_and_9700.htm

This seems consistent with your observations.
The 9700 may measure flat down to 800Hz, but will sound best crossed steeply (eg. acoustic LR4 @ 2+Khz) or higher if using shallow slopes.
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