Regarding Cyburg Needles - What Is A Notch Filter? - diyAudio
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Old 25th March 2008, 03:28 AM   #1
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Default Regarding Cyburg Needles - What Is A Notch Filter?

I have a couple of FR projects burning in my brain. Before I choose one over the other I want to get a feel for the work and complexity involved.

I am now considering the Cyburg Needles using Tangband W3-871S as my first FR project. The reason is that is seems to be within my skill level, seems inexpensive and big bang for the buck.

I have a realy dumb question. What is a notch filter and how do I build one? When explaining please keep in my I am rather dumb and have minimal understanding of electronics. I can almost find myself around a schematic.

In all humbleness....Jim
HiFi - Jazz - Wine
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Old 25th March 2008, 03:47 AM   #2
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I can tell ya what it does, but don't have a clue how to make one. A notch filter is a filter that removes a band of sound centered around a certain frequency or, in other words, makes a 'notch' in the sound. It's the opposite of a band pass filter (I don't know if that helps at all) and is therefor sometimes called a band stop filter. If you look at the front of a graphic equalizer each slider or fader is nothing more than a notch filter (as long as you are using it to attenuate, or "turn down" whatever frequency it is set too) Hope that helps.

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Old 25th March 2008, 03:59 AM   #3
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Someone else will probably come along and say this better that I, but this should get you started.

A notch filter in this context is designed to reduce annoying peaks in the spectrum of a small diameter speaker that's being called on to do full-range duty. Different drivers have different peaks, and so need different filters to give an even frequency response.

The filter does much what a crossover does--in fact, sometimes people call them crossovers, even though they cross nothing over from one speaker to another. They use a combination of capacitors, inductors (coils) and resistors to manipulate the frequency response. A notch filter reduces a specific, usually narrow, frequency band.

Capacitors pass high frequencies; the larger the value, the lower the frequency. Inductors act the opposite way, and pass low frequencies, the higher the value, the lower the frequency. The frequencies at which they pass signals depends on the impedance. The untechnical way of saying this, is that with a lot of voltage and current flowing, it takes higher-value capacitors and inductors to pass/block a given frequency than it would for a much small flow of signal. It is possible to implement a notch filter at line level, but the components would be a few orders of magnitude lower for the same effect (and, BTW, inductors are not usually used for line-level filtering).

Resistors are pretty obvious in that they reduce the amount of signal flowing through them and are used to adjust the amount of filtering effect the notch filter is allowed to have.

Here's a link to a speaker design using that TB driver:

You can see that the filter consists of a capacitor an inductor and a resistor in parallel. The capacitor blocks everything below a certain frequency (high-pass); the inductor blocks everything above (low-pass). The resistor is there to determine how powerful the effect of the filter is. Make the value of the resistor lower and more signal bypasses the filter and goes directly to the speaker. Raise it, and you force more of the signal o pass through the filter. When you build the thing, buy some resistors of other, close values and try swapping them out to see how much of the filtering effect you want for your design, taste, music, room, etc.

Of course, it can get a lot more complicated than that, with things like slope, order, phase and more. But that's enough to get a grip on the basics.

You can build it just like a crossover, on a thin piece of plywood, plastic, bare circuit get the idea.

Have fun!

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Old 25th March 2008, 12:44 PM   #4
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Originally posted by Buckapound
Here's a link to a speaker design using that TB driver:

Have fun!


Thanks for the link. The schematic, the photo, the explaination and the parts list in your link of the notch filter clarified it quite well for me.

I think I can build that sucker.

Thanks again.....jim
HiFi - Jazz - Wine
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Old 25th March 2008, 10:06 PM   #5
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If I could, you can

You don't even need any mounting plate for the notch. I just twisted the component leads like I was making a caramel wrapping. Meant to do it properly it later, but it never happened.

On notch failure, the worst thing that can happen is that your sound cuts out. It's as simple as can be. Looking forward to hearing what you think of the speakers.
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Old 27th March 2008, 11:44 AM   #6
Bluto is offline Bluto  United States
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Default On Wisconsin!

Don't feel bad Jim -

We're from Wisconsin , we know our Cheese!!

I'm in that boat with Ya Bud!

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