take a look at my fr plots and tell me what you think about that null - Page 2 - diyAudio
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Old 18th July 2008, 02:23 AM   #11
pjpoes is offline pjpoes  United States
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Bah, me stop fiddling, that will never happen. It's my crossover design, it wouldn't be hard to go back to what it was.

Jupiterjune, you seemed to have missed where I said that null wasn't being caused by driver phase issues. reversing the tweeter causes a small null at the crossover point, which is much lower than that null.

I think its the tweeter attenuation, I just need to get some more resistors and try stuff out. I may remove the shunt resistor and see. I actually want to increase the padding resistor a little if I can, to tilt down the response.

I'm not going to get into a debate over cone materials here, I think thats a pretty well beaten horse. The drivers are Focal utopia Midbass drivers and TC120tdx tweeters.
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Old 18th July 2008, 11:23 PM   #12
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Jupiterjune, you seemed to have missed where I said that null wasn't being caused by driver phase issues. reversing the tweeter causes a small null at the crossover point, which is much lower than that null.
I was actually more interested in what happens to the response at around 3kHz with the tweeter inverted. But yeah, I did miss that post about the crossover null.

The audible distortion you describe really sounds like cone breakup of the woofer. But at a 1.8 kHz crossover point, this would seem a bit unlikely unless you have a low order crossover or really, really nasty cone breakup.

JJ
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Old 19th July 2008, 12:39 AM   #13
Salas is offline Salas  Greece
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Miscalculated acoustic centres during crossover modeling, the most likely cause for curious null. Or lack of any modeling at all...
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Old 19th July 2008, 01:48 AM   #14
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It could be a bad cone brake up of the woofer in the crossover region. Have you or do you have an ability to measure woofer distortions in a free air?
Also, I find analog sweeps very helpful is sorting out simple bugs. Try to run tweeter by itself (with the crossover, and woofer (also with the crossover in the enclosure).
As for the null, remodel the x-over and change a couple of capacitors.
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Old 19th July 2008, 02:44 AM   #15
pjpoes is offline pjpoes  United States
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The distortion is in the tweeter, I have measured them separately. It's not the offsets, again, I covered then when I said I modeled and even tried a ladder delay network. I did finally figure out what the problem was. I measured all these focal drivers I have a while back and threw them in my system. The tweeters I threw into this speaker were the TC120td5's, but I accidentally threw the Tdx version into the model. The problem is the tweeters level, it has a sort of general upward slope, so I need to increase the padding and shunt values, possibly even just remove the shunt resistor all together. Then I think the next step is the conjugate filter for the distortion.
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