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Old 21st July 2007, 10:57 PM   #1
omni is offline omni  United States
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Default notch filter help

I am trying to notch out the nasty spikes in the woofer response curve which start in the 1500-1700 Hz range..........Does anyone have any experience they can share with me, please............Respectfully.........Omni
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Old 22nd July 2007, 11:42 AM   #2
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Hi omni,
can you describe...
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Old 22nd July 2007, 01:03 PM   #3
MarkMcK is offline MarkMcK  United States
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I assume that a passive crossover was used when you did the testing you include with your post. If so, then I suggest using a series notch filter, wired in parallel, added after the crossover network. This places the notch filter between the crossover and the woofer.

Tune the notch filter for 2 kHz. Since you are already down about 35 dB, I don't believe that you will have to worry much about the series resistor value in the notch filter. You can tweak it if you want, but it should have little audible impact.

I should say, however, that I do not trust the accuracy of your published graphs. Looks too good. I have to assume that actual performance is far worse than what you show here. That is too bad. It makes it very difficult for anyone else to help you when you provide bad data.

Best of luck to you with your project.

Mark
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Old 22nd July 2007, 02:26 PM   #4
omni is offline omni  United States
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Mark, Thank you for your input. What you describe is perhaps the circuit I may use, and somewhere I read about tuning notches to 2kHz..........However, I don't have any frame of reference as to how to determine the component parts.....I have read Dickasons writing on notches but when I applyed his math in my simulator, there was no change on the resultant curve.............So, would you possibly share with me how I may determine component parts values accurately?.........In reference to my graphs: I used Jeff Bagbys' Crossover Designer 5.1 along with the FRD tools found at rjbaudio.com ..............I will take your statement that my graph Looks too good, as a compliment..........Thank You.........As far as the actual performance of the speaker goes: You would be shocked to say the least..........They perform very nicely. A great deal of time went into the design, using the tools I mentioned, along with the help from some friends I have made on this forum............They do suffer, however, from a slight soundstage imbalance, which I believe can be remedied. The notch I seek to install is just the first of a few tweaks I am gonna perform.........So by trusting my data, and my ears, I seek the experience of people like you, who have the knowledge and skills, in the hope that I may accomplish this.............Respectfully........Omni
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Old 22nd July 2007, 05:47 PM   #5
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I too have had success with series notches.

We need to know the frequency extremes of the notch, the impedance of the driver(s) at the upper and lower ends and how much attenuation you need.
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Old 22nd July 2007, 05:59 PM   #6
omni is offline omni  United States
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OK Cal, I will get back to my simulation here shortly, and provide the specs you mentioned. Thank You very much for your post.............Omni
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Old 22nd July 2007, 07:48 PM   #7
omni is offline omni  United States
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Cal.........Here are the specifics: Rise begins at 1500 Hz.....up to 1882 Hz............So frequency extremes of notch would be 1500-1882 or somewhere 2000?..................Impedance of driver at 1500Hz is 17ohms...........Impedance at 1882 Hz is 19.7 ohms.........attenuation in the neighborhood of 8 db............I hope this information is adequate for our purposes............If not, please let me know.............Respectfully.............Omni
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Old 22nd July 2007, 09:20 PM   #8
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8 dB attenuation? OMG. We may have to consider a parallel notch. I think trying to do that with a series notch will drop the impedance too low at that point. Let me think about this.
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Old 22nd July 2007, 09:45 PM   #9
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Do you happen to have some extra coils and caps? I was wondering what you might get if you use a 4 ohm resistor, a 30 mfd cap and a .3 mH coil in a series notch. I see around a 6 dB drop there.
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Old 22nd July 2007, 10:02 PM   #10
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I'm having a bit of trouble with the parallel. I don't have a lot of experience with them and this is what comes up.

18 mfd, .4 mH and 18 ohm resistor.
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