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  • How do I make a low pass filter?

    It's for a tiny 4 1/2" 8ohm Woofer (299-001) I got on closeout and I want to make a tiny sub with one or two of them using a Dayton TA2024 (300-385). I figured I could make two low pass filters, and hook up two of these little guys and use both channels: one for left and one for right.

    I tried to follow a schematic I got online:



    from http://www.electronics-tutorials.ws/.../filter_2.html

    I used a 20W 8ohm resistor and four 25V capacitors (2 100uF, 2 47uF), working off the formula :

    R * C = 2 * Pie * Fc

    I was trying to get the Fc to be around 375Hz.

    Sounds like it's trying to cut out high frequencies, but it's also WAY quieter. Cranked with the little dayton is just above audible.

    I see the low pass filters for sale here and they are noting like the circuit I made. They have solid core inductors and a capacitor. If that's the way to make one- how do I do it? How to I determine the mH and gauge and capacitor strength ifI have all the amp and driver info?


    The "bible" has two broken links in the four crossover page links so I have been all over the internet. I am overloaded now- and I think if I just knew what the right parts in the right order were... I'm trying here.
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    I bet you never heard the my favorite on band. Push this (1, 2, 3) through your new project. Radio DJs can't help telling you what to listen to. Please don't mistake it for rudeness or that we think we're superior to you. We are not. At all.
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  • #2
    Re: How do I make a low pass filter?

    Generally, if you are trying to cut out the high frequencies, an inductor and cap will do it, but it may not do it with good results. Is there any FRD available for the driver you are using? You could use it in PCD to cut out anything above 300-400hz by simming a filter.

    Edit: I just simmed two 4.5" drivers I had the FRD, and was able to get a nice clean, step roll off at 400hz using a 4.0mH inductor and a 50uF cap. Iron core coil and NPE cap should work fine for your purposes. It would be best if you could get measurements of your drivers in the enclosures before designing a filter though.

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    • #3
      Re: How do I make a low pass filter?

      Originally posted by dustinbagby View Post
      Generally, if you are trying to cut out the high frequencies, an inductor and cap will do it, but it may not do it with good results. Is there any FRD available for the driver you are using? You could use it in PCD to cut out anything above 300-400hz by simming a filter.

      Edit: I just simmed two 4.5" drivers I had the FRD, and was able to get a nice clean, step roll off at 400hz using a 4.0mH inductor and a 50uF cap. Iron core coil and NPE cap should work fine for your purposes. It would be best if you could get measurements of your drivers in the enclosures before designing a filter though.
      Nothing included with driver. The brand is listed as "Factory Buyout" and the only marking on it is "Made in Taiwan." I asked in the Q&A section if there is one available.

      But I'll try your suggestion and see what happens.
      A/V Obesessed Amateur and really, really green.
      I bet you never heard the my favorite on band. Push this (1, 2, 3) through your new project. Radio DJs can't help telling you what to listen to. Please don't mistake it for rudeness or that we think we're superior to you. We are not. At all.
      about.me/spaker
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      • #4
        Re: How do I make a low pass filter?

        Hey-

        Do any of you guys wind your own inductors? What about solid core? I tried looking for solid core iron plain cores and it was impossible unless I wanted 5000 from China.

        I don't suppose an air core would work here?
        A/V Obesessed Amateur and really, really green.
        I bet you never heard the my favorite on band. Push this (1, 2, 3) through your new project. Radio DJs can't help telling you what to listen to. Please don't mistake it for rudeness or that we think we're superior to you. We are not. At all.
        about.me/spaker
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        • #5
          Re: How do I make a low pass filter?

          Air core would work, just more bucks and higher DCR. Iron core 18ga. 4.0mH is $11.23, air core 18 ga. 4.0mH is $18.81.

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          • #6
            Re: How do I make a low pass filter?

            Spaker,

            I believe that the diagrams and formulas you discovered there are intended for use in circuits with a high impedance load, or "signal level" applications where the attenuation caused by the series resistor is inconsequential, or the series resistor represents the output impedance of the source (not sure on this).
            Pro/Fi Cinema Speaker project: "From the Ashes"

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            • #7
              Re: How do I make a low pass filter?

              http://www.diyaudioandvideo.com/Calculator/XOver/

              Use the smallest gauge available.
              Currently resigned to living in balmy Zephyrhills, FL with the snow birds.
              Howard H

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              • #8
                Re: How do I make a low pass filter?

                Can those drivers even make any bass?

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                • #9
                  Re: How do I make a low pass filter?

                  Originally posted by zhillsguy View Post
                  http://www.diyaudioandvideo.com/Calculator/XOver/

                  Use the smallest gauge available.
                  This... is AMAZING. Thanks for that link!

                  I ordered some 18 and 20 gauge last night. A few hundred feet of each. Why not be brave and try to wind one (two) myself?

                  This is a goofy project made mostly out of spare parts. The woofer is just part of it and it stumped me. Because I am dumb and new at this, no matter how much I read... I just have to "do it" or see something done to know it. Thanks for all the assistance. Even though this project is meaningless, I have learned a lot stumbling through it: info I will use when it matters.
                  A/V Obesessed Amateur and really, really green.
                  I bet you never heard the my favorite on band. Push this (1, 2, 3) through your new project. Radio DJs can't help telling you what to listen to. Please don't mistake it for rudeness or that we think we're superior to you. We are not. At all.
                  about.me/spaker
                  Facebook

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                  • #10
                    Re: How do I make a low pass filter?

                    OK. So I am back on this... in a way. I have been messing with that link zhillsguy posted trying to figure out a crossover for a different project. Then I wondered... can this thing (the link) calculate a low pass filter if I tell it 8ohm tweet (imaginary), 8ohm woof (real) and lets say a crossover at 400Hz, and it gives me a simple design with a cap and inductor wired to a tweet and woof.... what would happen if I made it and didn't include the tweeter? Would it act as a low pass? Obviously, to complete a circuit, omitting the tweet means a straight connection between where the tweeter + is in the diagram to where the - is. So just a wire and not a tweeter.

                    I have a feeling this is no good... I have a feeling it needs the impedance of the tweet to make the crossover work. But It was just a thought... because I am still trying to figure this out and learn more about XO in general.
                    A/V Obesessed Amateur and really, really green.
                    I bet you never heard the my favorite on band. Push this (1, 2, 3) through your new project. Radio DJs can't help telling you what to listen to. Please don't mistake it for rudeness or that we think we're superior to you. We are not. At all.
                    about.me/spaker
                    Facebook

                    Comment


                    • #11
                      Re: How do I make a low pass filter?

                      I am going to suggest that you read the stickies at the top and get a better understanding of what a crossover does and how it does it. There is more to this than assuming a driver has a nominal load so requires x crossover for y crossover point. The crossover freq is a function of the impedance profile, the transfer function, etc, etc, etc.....
                      https://www.facebook.com/Mosaic-Audi...7373763888294/

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                      • #12
                        Re: How do I make a low pass filter?

                        Originally posted by Spaker View Post
                        OK. So I am back on this... in a way. I have been messing with that link zhillsguy posted trying to figure out a crossover for a different project. Then I wondered... can this thing (the link) calculate a low pass filter if I tell it 8ohm tweet (imaginary), 8ohm woof (real) and lets say a crossover at 400Hz, and it gives me a simple design with a cap and inductor wired to a tweet and woof.... what would happen if I made it and didn't include the tweeter? Would it act as a low pass? Obviously, to complete a circuit, omitting the tweet means a straight connection between where the tweeter + is in the diagram to where the - is. So just a wire and not a tweeter.

                        I have a feeling this is no good... I have a feeling it needs the impedance of the tweet to make the crossover work. But It was just a thought... because I am still trying to figure this out and learn more about XO in general.
                        You cannot replace a tweeter with a straight piece of wire. What you are suggesting is a direct short for high frequencies.

                        Learn to use WinISD alpha. It is free and simple to use once you get to know it. Lots of people here use it for uncomplicated sub builds. It has simple x-over calculators also. JohnnyRichards has a tutorial on it.

                        Also, as suggested, start educating yourself following the stickies at the top.
                        Don't worry, if your parachute fails, you have the rest of your life to fix it.

                        If we all did the things we are capable of doing, we would literally ASTOUND ourselves - Thomas A. Edison

                        Some people collect stamps, Imelda Marcos collected shoes. I collect speakers.:D

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                        • #13
                          Re: How do I make a low pass filter?

                          Oh I have. Several of the crossover links in the stickies are broken links. Aaaand I hate to pull this card out, but I am severe ADHD / learning disabled. I can read pages and pages and pages and retain nothing. I have to "do it" to get it. It's not like I am trying to shortcut the due diligence. I am trying best I can... and have been day in and day out and sometimes all night long for almost a year. It takes me much longer than most. However, once I do something right, it's in there and in there forever. I know, it's hard for people to understand this and most probably think- what the hell are you doing this for, then? Because I love it. And because, like I said, once I do something, I can do it forever.

                          I'll look into the WinISD (software?) And I love JohnnyRichards stuff; I'll look for the tutorial. I wish his DIY designs still had available drivers! Love the inexpensive way!
                          A/V Obesessed Amateur and really, really green.
                          I bet you never heard the my favorite on band. Push this (1, 2, 3) through your new project. Radio DJs can't help telling you what to listen to. Please don't mistake it for rudeness or that we think we're superior to you. We are not. At all.
                          about.me/spaker
                          Facebook

                          Comment


                          • #14
                            Re: How do I make a low pass filter?

                            I would also say to download Jeff Bagby's software. In particular PCD. Playing around in there will show you how "textbook" values do not work. A driver whether it is a woofer, mid, or tweet has an impedance that changes with frequency. The nominal values give us an indication of the driver but are basically useless when finding out how the driver will behave with different slopes and crossover points.

                            I really do understand about ADHD. I was not diagnosed with it as a kid as I probably should have been and I now have 3 kids that do have various degrees of it.


                            Oh and JRs stuff is great. I have built a couple of his designs and heard others. Building one if his designs (say cabrinis) will give you some experience in how crossovers work and part of the design progress. Simple build with a minimal crossover.
                            https://www.facebook.com/Mosaic-Audi...7373763888294/

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                            • #15
                              Re: How do I make a low pass filter?

                              What range of "bass" are you expecting (hoping?) to get out of these drivers (in Hz)?

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