take a look at my fr plots and tell me what you think about that null - Page 2

pjpoes · 18th July 2008, 02:23 AM

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.

jupiterjune · 18th July 2008, 11:23 PM

Quote:

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

Salas · 19th July 2008, 12:39 AM

Miscalculated acoustic centres during crossover modeling, the most likely cause for curious null. Or lack of any modeling at all...

R-Carpenter · 19th July 2008, 01:48 AM

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.

pjpoes · 19th July 2008, 02:44 AM

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.

19th July 2008, 01:48 AM	#14
R-Carpenter diyAudio Member Join Date: Oct 2007 Location: Brooklyn Navy Yard	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. __________________ http://www.diy-ny.com/

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18th July 2008, 02:23 AM	#11
pjpoes diyAudio Member Join Date: Jan 2005 Location: New York	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.

19th July 2008, 12:39 AM	#13
Salas diyAudio Chief Moderator Join Date: Oct 2002 Location: Athens-Greece	Miscalculated acoustic centres during crossover modeling, the most likely cause for curious null. Or lack of any modeling at all...

19th July 2008, 02:44 AM	#15
pjpoes diyAudio Member Join Date: Jan 2005 Location: New York	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.