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  • Series 2-way crossover help

    Hey all, as most of us probably have, I have several spare parts from over the years of speaker building. I decided to throw some stuff laying around and make a random portable speaker system out of it. I decided on making a 3-way system. I have a subwoofer, 3” full range that I want to cross off and use as a mid, and a tweeter. All 4 ohm speakers. A 50x2 watt @4 ohm Bluetooth amp. The sub I was gonna have a simple low pass filter for channel 1. Channel two would have to be the mid and tweeter in series to see 8ohm because the amp isn’t stable at 2ohm. My problem is the crossover design for the series wired mid/high. From what I’ve researched, series wired crossovers are far more complicated than parallel. I really really need to at least cut off the full ranges high ends to make this design work. I’m not sure how to go about designing this. Any diagrams, online calculators, programs, advice for series specific crossovers would be MUCH appreciated. Also if there’s another creative way to make my design work with the speakers and amp I already have!

  • #2
    Parallel xovers do not parallel loads across the xover point. A 2-way with 4 ohm drivers will be nominal 4 ohms above and below the xover unless series/parallel padding of the tweeter is required and changes that. The xover attenuates heavily in the stop-band by increasing impedance. They are not directly in parallel.
    You do not need a series xover. In a series xover, the driver that operates under its stop-band is shorted out so that the nominal impedance of the other driver is that of the load. The drivers are wired in series, but don't see each other as you'd think.

    Later,
    Wolf
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    • #3
      Originally posted by Wolf View Post
      Parallel xovers do not parallel loads across the xover point. A 2-way with 4 ohm drivers will be nominal 4 ohms above and below the xover unless series/parallel padding of the tweeter is required and changes that. The xover attenuates heavily in the stop-band by increasing impedance. They are not directly in parallel.
      You do not need a series xover. In a series xover, the driver that operates under its stop-band is shorted out so that the nominal impedance of the other driver is that of the load. The drivers are wired in series, but don't see each other as you'd think.

      Later,
      Wolf
      Is there anything I could do to just simply prevent the full range from playing higher than I’d like with out impacting something else?

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      • #4
        It would be a good idea for you to read up on crossovers. Not only don't you know how they work, but you don't understand Wolf's (brief) explanation of how they work.

        You can't wire your mid and tweeter in "series" (meaning they should be in parallel).
        The only way to keep the load "up" (near 4 ohms) is to have a low-pass filter on the mid, and a high-pass on the tweeter. Running EITHER of them "full range" WILL potentially drop your load into the 2 ohm range over some of the frequencies. Not only that, but MOST tweeters NEED a high-pass filter on them (probably at LEAST a cap - for protection, and a resistor - for level balancing) or you'll get bad distortion, OR burn up the tweeter.

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        • #5
          Ok so since I apparently don’t know what series, parallel or a crossover is or how it works... I do know I want both a low pass and a high pass for the woofer and tweeter. How would I be able to wire the high and low filters onto the tweeter and woofer while keeping the ohm at 4 or higher? The channel is only able to give out 50rms and the tweeter is rated for like 100-125 rms so between 2 speakers sharing the wattage, I’m not worried about the tweeter being played loudly but for nicer listening experience I’d like a high pass on it. I’m not looking to build anything complicated, just want to repurpose some speakers and make them blend together

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          • #6
            Originally posted by Chris Roemer View Post
            It would be a good idea for you to read up on crossovers. Not only don't you know how they work, but you don't understand Wolf's (brief) explanation of how they work.

            You can't wire your mid and tweeter in "series" (meaning they should be in parallel).
            The only way to keep the load "up" (near 4 ohms) is to have a low-pass filter on the mid, and a high-pass on the tweeter. Running EITHER of them "full range" WILL potentially drop your load into the 2 ohm range over some of the frequencies. Not only that, but MOST tweeters NEED a high-pass filter on them (probably at LEAST a cap - for protection, and a resistor - for level balancing) or you'll get bad distortion, OR burn up the tweeter.
            So basically you’re saying to just wire them in parallel with their high pass and low pass filters on the respected speaker and hope the ohm stays high enough for the amp?

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            • #7
              Each section of the crossover is designed to feed the appropriate limited signals to the respective drivers. In your case you want to use the full ranger as a mid, and you also have a woofer and a tweeter. The Mid crossover should filter the lows out (so the mid will not do the woofer's job), and limit the highs it receives, because those are the tweeters job. This portion of the crossover will be a separate section from that of the tweeter and woofer. The tweeter's filter will block all of the lows and mids, allowing just the high frequencies through to the tweeter. Conversely the woofer's section of the XO will block the mids and highs from being routed to the woofer. In most crossovers, the sections are in parallel, but the drivers are not wired to each other in parallel. Look at the diagrams of the XO's that are submitted on TT and you will see what I mean.
              In series crossovers, it is different.
              Hope this clarifies a little.

              Steve

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              • #8
                If the crossover is done properly the impedance will be just fine. As the low pass goes into effect, the woofer is attenuated (impedance on the filter increases) until it is effectively inaudible. And the same for the tweeter with a high pass.

                In addition, the tweeter will probably be of a higher sensitivity than the woofer and need added resistance to level it to the woofer. This added resistance will also help.

                You also seem to assume that the drivers are a flat resistance, 8 ohm. Actually, they are not. Impedance varies wiwi frequency. This again is taken into account in the crossover.

                For an example; A crossover I am currently working on uses an 8ohm nominal woofer and 4 ohm nominal tweeter. Together these would have a 2.67 ohm load. But with the crossover, the impedance does not drop below 4 ohm at any point and then that is only a dip. The remainder of the crossover remains at least 6ohms throughout.
                https://www.facebook.com/Mosaic-Audi...7373763888294/

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                • #9
                  Can you tell us ANYthing about your drivers? Who made them? Model numbers? Sensitivity?
                  Your question is kinda like asking what plugs you should buy for your car, w/out telling us what it is.

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                  • #10
                    Originally posted by Chris Roemer View Post
                    Can you tell us ANYthing about your drivers? Who made them? Model numbers? Sensitivity?
                    Your question is kinda like asking what plugs you should buy for your car, w/out telling us what it is.
                    Tweeter: peerless by tymphany BC25SC08-04, 98.8 dB 2.83V/1m

                    Full range to be mid: faitalPRO 3” 3FE25, 91db 1w1m

                    Sub: peerless by tymphany SDS-135F25CP02-04, 86.1db 2.83v/1m

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                    • #11

                      A second order will shift the phase of each speaker 90 degrees, so that both speakers are 180 degrees out of phase. This means that at the frequency, the two drivers will be moving in opposite directions at the same time. Sarkari Result Pnr Status 192.168.l.l
                      Last edited by qnnqxh; 09-15-2019, 05:23 PM.

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                      • #12
                        Well why didn'cha say so !

                        Low pass (for the woofer), parts from left (amp side) to right (speaker):
                        2nd order: use a low DCR (iron core) 3.0mH series coil and a 100uF (npe) shunt cap (to ground).
                        On the 3" we'll go 2nd order w/an L-pad (next to the mid):
                        Use a 0.70mH series coil (modeled w/a DCR of 0.6n(ohms)) and a 100uF (npe) series cap, then a 12uF shunt cap (to gnd) and a 4.0mH shunt coil (DCR not critical). On the "L" use a 2n SR (series resistor) and a 5n PR (parallel resistor). Try negative polarity on the mid.
                        For the tweeter, 2nd order w/an "L": use an 8uF series cap, then a 0.30mH shunt coil. For the L-pad use SR=3n / PR= 0.5 ohms. Normal polarity.

                        Since you're bi-amping (sorta), the L-pads COULD use less attenuation, but I'd try them this way, they can be adjusted later (just by swapping resistors).
                        As it is, these filters COULD all be used on a single 3-way delivering appropriate baffle-step.
                        Runs around 81dB w/Fcs near 400Hz and 3kHz. Full BSC. 4ohm nominal as a 3-way, or bi-amped.

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                        • #13
                          I'm going to guess, drawing it out will be good for him.
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