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Ahhh, I Am So Confused!?!?

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  • Ahhh, I Am So Confused!?!?

    I am trying to design a center speaker, nothing special, for my college apartment. I removed some drivers from another system, and wanted to re-box and re-cross them. However, I am freaking out with how to determine the appropriate inductors and capacitors in relation to the impedance of "everything." As a side note, if someone could explain the principles of impedance (ohms) in an understandable, as possible, manor, it would be much appreciated. For example, ohms of a receiver, speaker, and how they relate together and with filters. Back to the speaker, the center I am trying to design, remember nothing special, will be two way with 6 ohm drivers. The receiver will be 8 ohm. I want to high pass the tweeters at 4000 and band pass the mid with the tweeters and 150. I also want it to be second order so there will be a 12db role off. If anyone could provide, and/or explain how I would determine, the inductors and capacitors to be used, I would be very thankful.

    Thank you,
    Tony Williams

  • #2
    Re: Ahhh, I Am So Confused!?!?

    Originally posted by floppygoat View Post
    I am trying to design a center speaker, nothing special, for my college apartment. I removed some drivers from another system, and wanted to re-box and re-cross them. However, I am freaking out with how to determine the appropriate inductors and capacitors in relation to the impedance of "everything." As a side note, if someone could explain the principles of impedance (ohms) in an understandable, as possible, manor, it would be much appreciated. For example, ohms of a receiver, speaker, and how they relate together and with filters. Back to the speaker, the center I am trying to design, remember nothing special, will be two way with 6 ohm drivers. The receiver will be 8 ohm. I want to high pass the tweeters at 4000 and band pass the mid with the tweeters and 150. I also want it to be second order so there will be a 12db role off. If anyone could provide, and/or explain how I would determine, the inductors and capacitors to be used, I would be very thankful.

    Thank you,
    Tony Williams
    Wow. You basically just said, "Tell me how to design loudspeakers. K Thx." :rolleyes:

    Here's the gist of it. Impedance is resistance. It just happens to be resistance to an AC signal instead of DC. The kicker is that the impedance of a driver is totally variable. It will be high in some places, low in others, and then high again somewhere else. Totally variable.

    Resistance, of course, is the measure of how much the electrical components inhibit the flow of electricity. You say your receiver is 8ohm, but that's not entirely correct. It means your receiver shouldn't be used with speakers below 8ohm because they let electricity flow more easily. Keeping them supplied with the extra current places some additional strain on your receiver, much in the same way it'd be awkward running a 3-legged race with Usain Bolt as your partner. Now on to crossovers.

    Electricity takes the path of least resistance. That's not entirely true for crossover design, but just roll with it. Think of electricity taking the path of least resistance through your crossover.

    Capacitors become more resistive as the frequency drops. Inductors become more resistive as the frequency rises. The most simple crossover would be a cap in front of the tweeter and a coil in front of woofer. In this arrangement, the impedance of the coil would be very high at high frequencies, so, taking the path of least resistance, the electricity would flow elsewhere and tweeter would reproduce the high frequencies instead of the woofer. For low frequencies, it's the same situation (just the other way around). 2nd order crossovers (12dB/oct) work the same way, but they increase the impedance at TWICE the rate, so the sound gets cut off twice as fast. Don't ask me exactly how that parallel element does its job, I only sort of know, myself. :p

    Keep in mind that, most likely, if you are starting with 6 ohm drivers your speaker will end up being 6ohm when you're done. That's because in my examples above, for any given frequency, it is being played by just one driver.

    As to picking the proper crossover element values, for that, you need to know the impedance of the driver AT the frequency in question (because impedance is variable and all). That's why you see a lot of us guys with measurement rigs. Because it's hard to get decent results with guesses.

    If you don't have the impedance, you can just go with 6ohm since that's the best you know. You can plug those numbers into what are known as "the textbook formulas". I don't know where they are on the web, but I know where to find them in the Loudspeaker Design Cookbook on my shelf... I guess you could google for "textbook crossover 2nd order". Should turn up the info you would need.

    Personally, I'd build a new box, but use the same crossover as before. Then read a bunch, then try and improve on the existing one.

    Comment


    • #3
      Re: Ahhh, I Am So Confused!?!?

      I was going to use the previous crossover, but in only comes with the tweeters. They have two 4.7 uf caps in parallel. The mid was given a full range signal with no filter. This makes it sound like crap. To correct this, I was going to filter it as well. The problem comes with determining what the cutoff frequency is of the tweeters filter. The best I could guess, in relation to the speaker ohms, the "cookbook," and basic knowledge of cone tweeters, it probably crosses right around 4000, or a little lower. But, in an effort to match the cutoffs more precisely, rather then guessing the cutoff for the mid, I was going to recap the tweeters to 4000 and match the mid. However, I was going to use a band pass for the mid to remove some low end distortion. Again, nothing fancy, just something to fill a missing component of a 5.1 and decent vocals until I can either buy one or replace it.

      Back to the filters:
      Since the charts from the "cookbook" I was able to view does not have suggestion for 6 ohm speakers, I am unable to determine which caps/inductors to use in order to create a 4000 high pass crossover. If I am able to determine this, the whole thing can come together.

      Thanks,
      Tony Williams

      Comment


      • #4
        Re: Ahhh, I Am So Confused!?!?

        Originally posted by floppygoat View Post
        Since the charts from the "cookbook" I was able to view does not have suggestion for 6 ohm speakers, I am unable to determine which caps/inductors to use in order to create a 4000 high pass crossover. If I am able to determine this, the whole thing can come together.
        It will literally be halfway between the 4ohm and 8 ohm values.

        Also, look into adding a zobel to the midrange.

        Comment


        • #5
          Re: Ahhh, I Am So Confused!?!?

          Since you'll just be using textbook formula filters, HERE is a good calculator that will work for any impedance:

          http://www.mh-audio.nl/CrossoverNetw...udspeakers.asp

          If you don't have any specs for the mids, coming up with a zobel to level the impedance (so the lowpass inductor works properly) will be pure guesswork. Start with R = the nominal impedance of the driver, and C = around 10uf. Then add small value capacitors in parallel until it sounds right -- you'll probably have to evaluate the results by ear.

          You might also want to get Ray Alden's book and study up on the basic theory.

          Comment


          • #6
            Re: Ahhh, I Am So Confused!?!?

            Originally posted by brianp View Post
            If you don't have any specs for the mids, coming up with a zobel to level the impedance (so the lowpass inductor works properly) will be pure guesswork. You might also want to get Ray Alden's book and study up on the basic theory.
            I figured any zobel was better than no zobel, ESPECIALLY if the rest of the network is guesswork.

            I 2nd the "Speakerbuilding 201".

            Comment


            • #7
              Re: Ahhh, I Am So Confused!?!?

              It'd help to know what brand the previous speakers were, as well as the size of the motor on the mids. The motor is the entire magnet/voice coil assembly. I guess it's basically helpful to know if the speaker is hefty. I'm doubting so.

              The reason I ask is this: the impedance rise in a speaker (the reason you need a zobel, or impedance correction filter) is essentially caused by the reactance (mostly inductance) of the voice coil assembly. This is listed in most speaker specs. With a small, simple motor, you're probably looking at .2-.4mH, and with a 6 Ohm nominal impedance ...

              Well, find a zobel calculator and plug in .3 and 6 Ohms and see what you get ;p
              I am trolling you.

              Comment


              • #8
                Re: Ahhh, I Am So Confused!?!?

                The motor is surprisingly very hefty. Not sure of brand or exact weight though. And the tweeters only have caps in parallel. What does that do? Everything I see suggests a cap and inductor, not two of one? Using a calculator, 2000 is the cutoff, I assume, with a 6 ohm speaker and two 4.7 uf caps?

                I will look into the zobel.

                Thank you,
                Tony Williams

                Comment


                • #9
                  Re: Ahhh, I Am So Confused!?!?

                  Placing caps in parallel simply adds the values together. Two 4.7 uF caps would therefore become 9.4uF - which is not very much protection for a tweeter. You'll probably want to decrease this value to 7 or 8 uF to add some power handling and lower distortion. 4.7uF is a very common value for capacitors (for reasons I, admittedly, do not know - it seems entirely arbitrary) and it is likely the designers needed something "near" a value for a cheap price.

                  That being said, here's a bit of basic theory for you - capacitors and inductors are essentially opposites in the audio world, though their method of action is not exactly related. In this way, series and parallel behaviors are reversed - capacitors in series will reduce value, while inductors will add, and so forth.

                  Capacitors work by storing energy and releasing it rapidly. Inductors are harder to explain, but they utilize magnetism and resonance and other delightful terms that have entire books to themselves.

                  For starters on your new crossovers, do some simple by-ear tests with a tone generator on your computer hooked to your raw drivers individually. Listen at important, easily recognizable frequencies like 1Khz, 2Khz, and so forth, and see which sound louder or softer, or which ring like a bell on the midrange. This will give you an (extremely) rough idea of how your drivers behave.

                  For a physical demonstration of how capacitors work, try listening to the tweeters full-range (at a low level! this is important) then with both capacitors hooked up, and finally with only one. You can turn it up with the one capacitor in series with the driver - you'll have the most protection with this setup.
                  I am trolling you.

                  Comment


                  • #10
                    Re: Ahhh, I Am So Confused!?!?

                    Whoah boy!

                    I remember when I was in college, I undertook a very similar journey into speaker building with a friend of mine (this was a decade before I found the DIY community). Long story short, the end result sounded really bad. I couldn't figure out what was what, aside from plugging in a few "rough" values into a table. Confused, I went to the library, got some books on the subject, which were full of math! I tried to understand it, but after a few weeks, I pretty much gave up and assumed I'd never understand.

                    But that was then, this is now and we have a really active Internet community. I also highly recommend Alden's book to get you going. Then, apply what you read to proven designs to see how parts do what they do. Run them through simulations. Honestly, I don't know how else to answer this mass of questions you have than to recommend you do some woodshedding, because I know that once you are able to grapple one thing, you're going to have a huge library of new questions.
                    Isn't it about time we started answering rhetorical questions?

                    Paul Carmody's DIY Audio Projects
                    Twitter: @undefinition1

                    Comment


                    • #11
                      Re: Ahhh, I Am So Confused!?!?

                      Boy, Paul hit it...go to the link in his post and read the MFAQ's he has there before you go any further. Even a textbook calculator using just the impedance of the drivers will be woefully inadequate. Like Paul, I dinked with DIY and algebra-formula/textbook XO's for years and never achieved even a marginally acceptable result. I built a pair of Speakerlab S2's in 1977 from a parts kit and cabinet plans. Knocked the c-r-a-p outta most anything friends/family had. What I didn't understand was the complexities involved with the XO design. I thought I could just trust the "math" to come up with a good XO. Man, was I wrong. When I found this forum over 9 years ago, my eyes were opened and I understood why all those calculator/textbook XO's always sounded like poo. Get Ray Alden's book, well written and easy for beginner-types (which in some ways, I still am) to grasp. Here's one of the simple calculators that has a little more choices...still inadequate, though.

                      http://www.pvconsultants.com/audio/targetgen/pcdc.htm

                      And this one:

                      http://www.pvconsultants.com/audio/c...r/xoversim.htm

                      The xoversim is much better, as it uses more data. Just plugging in the driver's impedance and XO frequency isn't enough.

                      John A.
                      "Children play with b-a-l-l-s and sticks, men race, and real men race motorcycles"-John Surtees
                      Emotiva UPA-2, USP-1, ERC-1 CD
                      Yamaha KX-390 HX-Pro
                      Pioneer TX-9500 II
                      Yamaha YP-211 w/Grado GF3E+
                      Statement Monitors
                      Vintage system: Yamaha CR-420, Technics SL-PG100, Pioneer CT-F8282, Akai X-1800, Morel(T)/Vifa(W) DIY 2-way in .5 ft3
                      Photos: http://custom.smugmug.com/Electronic...#4114714_cGTBx
                      Blogs: http://techtalk.parts-express.com/blog.php?u=2003

                      Comment


                      • #12
                        Re: Ahhh, I Am So Confused!?!?

                        Heh, better you start with something cheap/torn apart anyway. The first pair of speakers I constructed used Vifa PL line drivers and the DX25 tweeter - and I'll be damned if I didn't think I was awesome. In retrospect, it probably wasn't the finest idea to spend that much money on my first project and not know what I was doing at all. At least I knew expensive drivers were probably better. Durr.

                        I got my start at Basic Car Audio Electronics - a fantastic place to learn the basics of speaker theory.

                        Messing with the tools at The FRD Consortium might also prove valuable (I'm posting the main link cause no one else has!)
                        I am trolling you.

                        Comment


                        • #13
                          Re: Ahhh, I Am So Confused!?!?

                          Just a big
                          "Thank You" to MSaturn for the http://www.bcae1.com/
                          site, Wow, it explained things in a way that this old brain can understand. I am less confused now.

                          Thanks for this place and people
                          cuggie
                          "What's Time To A Pig?"

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