need help with passive notch filter design - Page 2

jimbones · 8th October 2012, 11:11 PM

OK so it is 400hz and 1 khz and a 4db peak

tvrgeek · 9th October 2012, 09:22 AM

You need to measure the center of the peak and the -3dB points to either side of it. It is helpful to know the impedance in that region too.

Per chance, are you sure this is not an artifact of misaligned BSC and crossover? We need a lot more data to help.

jimbones · 9th October 2012, 12:10 PM

Quote:

Originally Posted by tvrgeek

You need to measure the center of the peak and the -3dB points to either side of it. It is helpful to know the impedance in that region too.

Per chance, are you sure this is not an artifact of misaligned BSC and crossover? We need a lot more data to help.

OK I will get the -3db pts. As far as impeadance you don't mean the "published" driver impeadance at that frequency do you?

True, I am not sure if this is an artifact of BSC/crossover. i do not have any BSC.

jimbones · 9th October 2012, 01:21 PM

Hmm, I was looking at 2 software tools Edge and PCD. Edge looks like it is easier to use.

Pano · 9th October 2012, 04:26 PM

Edge is very simple and easy to use, PCD has a different usage. If you have good frequency and impedance measurements you can use PCD to figure your notch filter. Knowing the cause of the peaks is important, there may be a better way to fix it than the notch filter.
As Jay points out, 1150Hz is going to be tough. You'll hear every little thing you do there, so you might want to make the notch broader and shallower than the FR indicates.

Listen, try, listen.

tvrgeek · 9th October 2012, 04:30 PM

Edge is very helpful. Great place to start, but the real world is never quite what you model. Build and measure. Think. Build and measure again. Look at the simulations and see if they can explain what you measure. They are a tool, not an answer.

Ignore the published nominal impedance. You should measure it in the range where the filter will be working. If you use a Zobel, that should be in place.

The reason I bring up BSC, is depending on baffle size, the 1K region is not atypical to be getting a big edge induced boost. Lowering the first pole may do a better job than adding a notch. Sometimes you can just increase the size of the first inductor in the crossover for the same basic effect.

Pano · 9th October 2012, 04:32 PM

Agreed. Open baffle low pass means big inductors. It really works.

jimbones · 9th October 2012, 04:56 PM

Wow. Ok I have lots I want to communicate but in writing it is a bit much. Let me start with this. Someone on the PE forum offered to Sim my XO. The LP (on dayton rs270) is a 4th order. I questioned the 10mh L1. He said it was needed even though calculated values showed it to be 4.7mh. I changed it to 4.7 and the speaker sounds much better but, with the bump. Now i guess that is why it was such a large inductor. For those that are interested in the background info on the speaker and how it came about with all the gory details a link is provided. i hope this gives perspective.

Lambda Speaker Thread

Pano · 9th October 2012, 07:11 PM

Most people don't understand Open Baffle crossovers. (I say this having heard a lot of bad ones). Not surprising as OB and box are not the same. Most of what you read and learn about crossovers is for box speakers.

tvrgeek · 9th October 2012, 08:27 PM

Linkawitz does a pretty good discussion of them.

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8th October 2012, 11:11 PM	#11
jimbones diyAudio Member Join Date: Nov 2004 Location: ny	OK so it is 400hz and 1 khz and a 4db peak

9th October 2012, 09:22 AM	#12
tvrgeek diyAudio Member Join Date: Dec 2009 Location: Md	You need to measure the center of the peak and the -3dB points to either side of it. It is helpful to know the impedance in that region too. Per chance, are you sure this is not an artifact of misaligned BSC and crossover? We need a lot more data to help.

9th October 2012, 01:21 PM	#14
jimbones diyAudio Member Join Date: Nov 2004 Location: ny	Hmm, I was looking at 2 software tools Edge and PCD. Edge looks like it is easier to use.

9th October 2012, 04:26 PM	#15
Pano diyAudio Moderator Join Date: Oct 2004 Location: North Carolina Blog Entries: 4	Edge is very simple and easy to use, PCD has a different usage. If you have good frequency and impedance measurements you can use PCD to figure your notch filter. Knowing the cause of the peaks is important, there may be a better way to fix it than the notch filter. As Jay points out, 1150Hz is going to be tough. You'll hear every little thing you do there, so you might want to make the notch broader and shallower than the FR indicates. Listen, try, listen.

9th October 2012, 04:30 PM	#16
tvrgeek diyAudio Member Join Date: Dec 2009 Location: Md	Edge is very helpful. Great place to start, but the real world is never quite what you model. Build and measure. Think. Build and measure again. Look at the simulations and see if they can explain what you measure. They are a tool, not an answer. Ignore the published nominal impedance. You should measure it in the range where the filter will be working. If you use a Zobel, that should be in place. The reason I bring up BSC, is depending on baffle size, the 1K region is not atypical to be getting a big edge induced boost. Lowering the first pole may do a better job than adding a notch. Sometimes you can just increase the size of the first inductor in the crossover for the same basic effect.

9th October 2012, 04:32 PM	#17
Pano diyAudio Moderator Join Date: Oct 2004 Location: North Carolina Blog Entries: 4	Agreed. Open baffle low pass means big inductors. It really works.

9th October 2012, 04:56 PM	#18
jimbones diyAudio Member Join Date: Nov 2004 Location: ny	Wow. Ok I have lots I want to communicate but in writing it is a bit much. Let me start with this. Someone on the PE forum offered to Sim my XO. The LP (on dayton rs270) is a 4th order. I questioned the 10mh L1. He said it was needed even though calculated values showed it to be 4.7mh. I changed it to 4.7 and the speaker sounds much better but, with the bump. Now i guess that is why it was such a large inductor. For those that are interested in the background info on the speaker and how it came about with all the gory details a link is provided. i hope this gives perspective. Lambda Speaker Thread

9th October 2012, 07:11 PM	#19
Pano diyAudio Moderator Join Date: Oct 2004 Location: North Carolina Blog Entries: 4	Most people don't understand Open Baffle crossovers. (I say this having heard a lot of bad ones). Not surprising as OB and box are not the same. Most of what you read and learn about crossovers is for box speakers.

9th October 2012, 08:27 PM	#20
tvrgeek diyAudio Member Join Date: Dec 2009 Location: Md	Linkawitz does a pretty good discussion of them.