Announcement

Collapse
No announcement yet.

3.5 Way project.....need crossover help

Collapse
X
 
  • Filter
  • Time
  • Show
Clear All
new posts

  • 3.5 Way project.....need crossover help

    Hello,

    I am new to this forum, so please forgive me if I ask some dumb questions. I am also new to speaker building as I have only completed about 3 projects to date, and I have much to learn. My latest project is a 3.5 way tower speaker design for my HT room. I have picked out and already received the drivers, and have already started building the enclosures for this MTMWW design. The drivers I am using are as follows:

    http://www.parts-express.com/pe/psho...number=277-010
    http://www.parts-express.com/pe/psho...number=264-873
    http://www.parts-express.com/pe/psho...number=299-245

    With two mids and two woofers per tower (one tweeter of course).


    I planned on using the prefabbed 3-way crossover for this system:

    http://www.parts-express.com/pe/psho...number=260-210

    While using additional components to make the second woofer the .5 woofer to compensate for baffle loss. I don't so much have questions regarding this added low pass filter, but rather about Zobel networks and how important they are. I am assuming I can have Zobel networks for the tweeter and mids even though I have a prefabricated Xover? I also have looked at some websites that have Zobel Network calculators, and I have looked at other projects on the PE project showcase to try to understand them. I have not been able to follow along with any of the PE project showcase crossovers and how they match with the so called "Zobel network calculators" found. Can someone please tell me why this is? I am assuming it has something to do with the added resistance of the crossover itself. So does this mean I need to measure the resistance of the crossover as well and add this to the resistance of the driver?

    Any help would be appreciated. Am I going about this the wrong way?

    Thanks,
    Jesse

  • #2
    Re: 3.5 Way project.....need crossover help

    Originally posted by jcrane82 View Post

    Any help would be appreciated. Am I going about this the wrong way?

    Thanks,
    Jesse
    I fear you may be over your head with this one.

    Try reading over this article.
    http://undefinition.googlepages.com/diy-gettingstarted

    Comment


    • #3
      Re: 3.5 Way project.....need crossover help

      Originally posted by brianpowers27 View Post
      I fear you may be over your head with this one.

      Try reading over this article.
      http://undefinition.googlepages.com/diy-gettingstarted
      I obviously need to be clearer on my questions......

      Can someone please explain to me why Impedance Equalization calculators from this site (for example) http://www.diyaudioandvideo.com/Calculator/ImpedEqual/
      give the following values for the RS28AS-4 aluminum Dayton Tweeter of C=2.84 uF and R=3.75 Ohms where the crossover network for the "Syphon" speakers in the showcase show these values: C=4 uF and R=4 Ohms?

      This is just ONE example of more than 5 projects I looked at that I cannot "calculate" the same values that were used. Like I said above, I am assuming that I need to take into account the impedance change of the crossover itself......Is this assumption correct?

      Thanks,
      Jesse

      Comment


      • #4
        Re: 3.5 Way project.....need crossover help

        The goal of the crossover is to create a more or less flat frequency response, while at the same time having the phase of each driver working together so that the same frequency from different drivers is not canceled.

        Generally, one must decide which target crossover slope will likely achieve that and then choose crossover components and design to match those target slopes.

        The problem is that textbook calculations never approximate the desired slopes. That is because the textbook calculations make assumptions about the characteristics of drivers that are not met.

        You will probably not ever find textbook calculation results that match the results of designs done using actual driver characteristics.

        Comment


        • #5
          Re: 3.5 Way project.....need crossover help

          Please click on the "Specifications" for your mid range driver. Note that the speakers impedance is a function of frequency, i.e., after the resonance 'hump" the impedance rises with increasing frequency. You cannot input the "listed" impedance value into the textbook equations. At a minimum would have to use the actual impedance at the XO frequency. But there is more!

          The impedance on that spec sheet is not the speakers impedance in your enclosure. To get it "right" you have to model (design) a box based on the manufacturers T/S, values build it and measure the T/S parameters yourself to obtain the actual impedance to be used in the XO calculation. This is a simplistic statement of the XO design process.

          In addition when you change any component of a XO, it not only shifts the XO frequency of that section (say the mid range driver) but also affects the other sections (woofer and tweeter) to some degree. Modeling with Jeff Bagby's programs (and others) is the only way to get it right. You may get lucky (less than 1 in 1000) but not likely.

          As each XO is unique for the speakers used, no two Zobels will be identical for the same speaker when it is used if different XO's. This is the reason for the difference you see
          in the two designs; they happen to be close in value but are not exactly the same.

          As previously stated please read Paul's FAQ; it is very informative.

          There are many proven designs that will give you what you desire. You wish to "roll your own" but once you dig into the design process (my discussion is simplified) you will understand the magnitude of designing a 3 way.

          To date I have build 7 designs by others [from a simple single speaker full range (Roman's Bandit) to a 3.5 MMTMMW for my main listening system, i.e., the Cinderella's]. Still have not designed a speaker yet but a 2 way may be in the near future.

          Good luck, the hobby is an addiction. :D

          George
          "In order to really enjoy a dog, one doesn't merely try to train him to be semi-human. The point of it is to open oneself to the possibility of becoming partly a dog." - Edward Hoagland

          Comment


          • #6
            Re: 3.5 Way project.....need crossover help

            Originally posted by jcrane82 View Post
            I obviously need to be clearer on my questions......

            Can someone please explain to me why Impedance Equalization calculators from this site (for example) http://www.diyaudioandvideo.com/Calculator/ImpedEqual/
            give the following values for the RS28AS-4 aluminum Dayton Tweeter of C=2.84 uF and R=3.75 Ohms where the crossover network for the "Syphon" speakers in the showcase show these values: C=4 uF and R=4 Ohms?

            This is just ONE example of more than 5 projects I looked at that I cannot "calculate" the same values that were used. Like I said above, I am assuming that I need to take into account the impedance change of the crossover itself......Is this assumption correct?

            Thanks,
            Jesse
            Those zobels you mention are hand-tweaked to dump different amounts of current based on need. Each and every one of them optimized to the task at hand. Luckily, since you're already working with an off-the-shelf crossover, getting ballpark will do as much for you as being exact. Just use the textbook values.

            I gotta ask, why are you putting a Zobel a the tweeter and NOT putting one on the woofer? One doesn't put a Zobel on a tweeter without a really good reason.
            nothing can stop me now

            Comment


            • #7
              Re: 3.5 Way project.....need crossover help

              That's going to be a massive speaker--and a massive project in general.

              First off, don't do a 3.5-way, but instead just run the woofers in parallel. The .5 baffle-step loss thing is really more intended for the range where that occurs (say, between 200-800 Hz). The woofers are gonna take care of that range automatically.

              Second, the purpose of a Zobel is to flatten the impedance of a driver, and thus make it cooperate better with a textbook filter. See, the textbook filter is looking for a "textbook" driver, which there is no such thing. So a Zobel is calculated to make the driver look a little more "textbook."

              While I don't recommend the pre-built XO (especially for a 3-way with drivers that nice), I'd say it's a good idea to use a Zobel on the woofer and mid. If you're DYING to do the thing, then just go ahead. However, when you get a chance, get a copy of Passive Crossover Designer or Speaker Workshop (both free), and try modeling the speaker. The difference between a textbook crossover and a custom-designed one is basically the difference between "oh what nice-looking speakers I made" versus "These speakers sound amazing, and I cannot stop listening to them!"
              Isn't it about time we started answering rhetorical questions?

              Paul Carmody's DIY Audio Projects
              Twitter: @undefinition1

              Comment


              • #8
                Re: 3.5 Way project.....need crossover help

                Despite all the posts of caution here, your driver choices ARE intriguing in their potential. The tweeter's faceplate is too big for a 5khz XO point, though. Especially if used in an MTM. You'll have all sorts of vertical off-axis issues. This won't be a speaker to audition unless you're sitting with your ears perpendicular to the tweeter. You'll probably also need to L-pad the mids a bit.
                nothing can stop me now

                Comment


                • #9
                  Re: 3.5 Way project.....need crossover help

                  Originally posted by Paul Carmody View Post
                  First off, don't do a 3.5-way, but instead just run the woofers in parallel. The .5 baffle-step loss thing is really more intended for the range where that occurs (say, between 200-800 Hz). The woofers are gonna take care of that range automatically.
                  If he does the two in parallel, it will screw up his impedance with regard to the stock XO, won't it?

                  I do think parallel would have been ideal, though. His 10" woofers would probably require a box that's 12-14" wide, and that dovetails nicely with the 500hz Fc. As he needs the extra sensitivity, the dual woofers would be coming on like gangbusters.

                  See, Jesse? This is what happens when you take the red pill. :D
                  Last edited by Dirk; 10-06-2009, 03:55 PM. Reason: stoopid nazi politeness filters
                  nothing can stop me now

                  Comment


                  • #10
                    Re: 3.5 Way project.....need crossover help

                    Completely unrelated, Jesse, there's a DIY gathering next weekend down in Grinnell. You should come on down. When you're designing your own speakers, hearing what others are doing is a HUGE help.
                    nothing can stop me now

                    Comment


                    • #11
                      Re: 3.5 Way project.....need crossover help

                      Originally posted by Dirk View Post
                      I gotta ask, why are you putting a Zobel a the tweeter and NOT putting one on the woofer? One doesn't put a Zobel on a tweeter without a really good reason.
                      This is a great question as I assumed the Zobel on the tweeter was more important than one on the woofer. I know the Zobel network flattens the impedance throughout the frequency range, but when the woofers are crossed at 800 hz, the impedance can't have changed that much at that frequency. While where the tweeter plays high frequencies and therefore I would assume the impedance flattening characteristics of the Zobel would be more important on the high frequency drivers. Is this assumption wrong?

                      As for the question by Dirk about the driver choices.......I tried to do as much research as I could about off axis lobing effects caused by resonating frequency effects. This was a refresher course for me as I remember this from the "Double-Slit Experiment" in my physics classes. My HT room is large, and I will be at least 15 feet from these speakers, so that equates to less than +/- 5 degrees off axis assuming a +/- 1 foot change in vertical listening position. Only reason I chose the prefabbed 3 way crossover was for cost and because it was easier. I have considered returning them and designing specific crossovers for these towers since I am putting quite a bit of money into the drivers.


                      As for what Paul said,

                      Quote, "First off, don't do a 3.5-way, but instead just run the woofers in parallel. The .5 baffle-step loss thing is really more intended for the range where that occurs (say, between 200-800 Hz). The woofers are gonna take care of that range automatically."

                      Baffle loss is more important in the low frequencies since the compression waves reflect less times compared to higher frequencies (difference between 2pi and 4pi space). For example, for a 100 hz signal to be in 2 pi space, the baffle width would need to be the size of the wavelength, or 3.3 meters. I did some basic Bass Box Pro simulations for these Peerless woofers and saw a +2 dB rise at 120 hz, so I figured if I had both playing full frequencies, they would be too boomy sounding since it would be over +4 dB at 120 hz.

                      Comment


                      • #12
                        Re: 3.5 Way project.....need crossover help

                        Originally posted by jcrane82 View Post
                        This is a great question as I assumed the Zobel on the tweeter was more important than one on the woofer. I know the Zobel network flattens the impedance throughout the frequency range, but when the woofers are crossed at 800 hz, the impedance can't have changed that much at that frequency.
                        Hell, that woofer has an inductance of 2.1mH. It's going to probably be 16ohms by 800hz. :eek: That's definitely worth compensating for.

                        While where the tweeter plays high frequencies and therefore I would assume the impedance flattening characteristics of the Zobel would be more important on the high frequency drivers. Is this assumption wrong?
                        If you look at the response graphs of any driver, its natural inductance is already figured into the frequency response you see. Besides, the inductance of a tweeter is a VERY small thing and is not likely to have a significant effect on audio frequencies.

                        As for the question by Dirk about the driver choices.......I tried to do as much research as I could about off axis lobing effects caused by resonating frequency effects. This was a refresher course for me as I remember this from the "Double-Slit Experiment" in my physics classes. My HT room is large, and I will be at least 15 feet from these speakers, so that equates to less than +/- 5 degrees off axis assuming a +/- 1 foot change in vertical listening position.
                        Vertical response, not horizontal. When you place two drivers on the same baffle and feed them the same source (as per the mids), the sound waves coming from each driver will interact with each other destructively when you are closer to one driver than the other. This is what happens when you stand up. It makes an oblique triangle, with the upper driver being the "adjacent" and the lower driver being the "hypotenuse". Now, for low frequencies, this can never create enough of a phase shift to matter. But for high frequencies, where wavelengths are a matter of a few inches, it DOES matter. To minimize the effects of this phase cancellation (since you can never really negate them), the two woofers in an MTM should be kept no more than 2 wavelengths apart. Thus:

                        5000hz wave = 2.712"
                        2.712 * 2 = 5.424"

                        So the center of the upper Tang Band should be NO MORE THAN 5.424" away from the center of the lower Tang Band.

                        Only reason I chose the prefabbed 3 way crossover was for cost and because it was easier. I have considered returning them and designing specific crossovers for these towers since I am putting quite a bit of money into the drivers.
                        In for a penny, in for a pound. Given your impending blood, sweat, & tears, you may want to go custom. OR, start with the stock XO, add zobels & L-pads and then see about an alternate XO later.
                        nothing can stop me now

                        Comment


                        • #13
                          Re: 3.5 Way project.....need crossover help

                          Originally posted by Dirk View Post
                          Hell, that woofer has an inductance of 2.1mH. It's going to probably be 16ohms by 800hz. :eek: That's definitely worth compensating for.
                          Very good point....I concur.


                          Originally posted by Dirk View Post
                          Vertical response, not horizontal. When you place two drivers on the same baffle and feed them the same source (as per the mids), the sound waves coming from each driver will interact with each other destructively when you are closer to one driver than the other. This is what happens when you stand up. It makes an oblique triangle, with the upper driver being the "adjacent" and the lower driver being the "hypotenuse". Now, for low frequencies, this can never create enough of a phase shift to matter. But for high frequencies, where wavelengths are a matter of a few inches, it DOES matter. To minimize the effects of this phase cancellation (since you can never really negate them), the two woofers in an MTM should be kept no more than 2 wavelengths apart. Thus:

                          5000hz wave = 2.712"
                          2.712 * 2 = 5.424"

                          So the center of the upper Tang Band should be NO MORE THAN 5.424" away from the center of the lower Tang Band.
                          Isn't it the delta distance of the listener to Driver1 compared to Driver2? Not the distances between the drivers? Either way I think I am going to go custom with the crossovers. I am going to download some of those crossover programs to see what I am in for. Hopefully these crossovers won't be over $100 to make.....otherwise the wife is gonna flip.

                          Comment


                          • #14
                            Re: 3.5 Way project.....need crossover help

                            Originally posted by jcrane82 View Post
                            I did some basic Bass Box Pro simulations for these Peerless woofers and saw a +2 dB rise at 120 hz, so I figured if I had both playing full frequencies, they would be too boomy sounding since it would be over +4 dB at 120 hz.
                            You fix that in the box tuning. You owe it to yourself to try Unibox or WinISD. They're excellent, and again, free.
                            Isn't it about time we started answering rhetorical questions?

                            Paul Carmody's DIY Audio Projects
                            Twitter: @undefinition1

                            Comment


                            • #15
                              Re: 3.5 Way project.....need crossover help

                              First off, baffle diffraction for the woofers mounted closer to the floor is a bit more complicated. The woofers will get some boundary reinforcement from the floor due to the long wavelengths of the frequencies they're reproducing. So doing a 3.5 way with those woofers is a mistake. They're not going to be going high enough in frequency to approach it that way.

                              Also, since you're getting significant boundary reinforcement for the woofers, baffle step loss below 200Hz will be almost zero. The sensitivity of the woofers run in parallel may be too much for the mids to keep up. However, if you run the woofers in series, and the mids in parallel, you'd be right on track to keep the levels well matched when baffle diffraction loss for the mids is factored in.
                              R = h/(2*pi*m*c) and don't you forget it! || Periodic Table as redrawn by Marshall Freerks and Ignatius Schumacher || King Crimson Radio
                              Byzantium Project & Build Thread || MiniByzy Build Thread || 3 x Peerless 850439 HDS 3-way || 8" 2-way - RS28A/B&C8BG51

                              95% of Climate Models Agree: The Observations Must be Wrong
                              "Gravitational systems are the ashes of prior electrical systems.". - Hannes Alfven, Nobel Laureate, Plasma physicist.

                              Comment

                              Working...
                              X