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  • Simple Crossover Question

    Okay I can install and wire blindfolded...I can build custom cabs with one arm literally! I CANNOT DESIGN A CROSSOVER...

    I have purchased these Celestion 5" Buyouts for "sound" in my card room

    http://www.parts-express.com/pe/show...number=299-414

    with this cheap Goldwood Piezo just to have some sound

    http://www.parts-express.com/pe/psho...80-062&scqty=2

    and the crossover I came up with is a very simple crossover just to help protect the drivers. I know by nature the Piezo's are in a sense high pass tweeters without the need of a crossover but I wanted to help protect them with a resistor as well. Please review my idea and just say yay or nay. THANKS A BUNCH

    Click image for larger version

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  • #2
    Re: Simple Crossover Question

    Having just asked a very similar question, i was directed to online calculators that can give you very basic crossover designs in seconds. I used the Erse calculator and it gave me exactly what i wanted. Basically a cap on the tweeter and a small coil on the woofer.

    Might give it a shot.

    Comment


    • #3
      Re: Simple Crossover Question

      Originally posted by nextbestthing View Post
      Okay I can install and wire blindfolded...I can build custom cabs with one arm literally! I CANNOT DESIGN A CROSSOVER...

      I have purchased these Celestion 5" Buyouts for "sound" in my card room

      http://www.parts-express.com/pe/show...number=299-414

      with this cheap Goldwood Piezo just to have some sound

      http://www.parts-express.com/pe/psho...80-062&scqty=2

      and the crossover I came up with is a very simple crossover just to help protect the drivers. I know by nature the Piezo's are in a sense high pass tweeters without the need of a crossover but I wanted to help protect them with a resistor as well. Please review my idea and just say yay or nay. THANKS A BUNCH

      [ATTACH=CONFIG]37859[/ATTACH]

      The piezo element is capacitive, so it can run without a crossover and your amp will remain stable due to its rising impedance at low frequencies. When you place the resistor in parallel with the element as shown you will remove that rising capacitive impedance and hold it at 20 ohms max. If you do this, then you can use a series capacitor to adjsut the crossover point if you want. Your 100uf cap on the Celestions will still keep the impedance from dropping too low at low frequencies, so you should be OK.
      Click here for Jeff Bagby's Loudspeaker Design Software

      Comment


      • #4
        Re: Simple Crossover Question

        Originally posted by Jeff B. View Post
        The piezo element is capacitive, so it can run without a crossover and your amp will remain stable due to its rising impedance at low frequencies. When you place the resistor in parallel with the element as shown you will remove that rising capacitive impedance and hold it at 20 ohms max. If you do this, then you can use a series capacitor to adjsut the crossover point if you want. Your 100uf cap on the Celestions will still keep the impedance from dropping too low at low frequencies, so you should be OK.
        Jeff,

        THANKS ALOT

        So in a sense leaving the resistor would stop the peaking capacitive impedance which in turn "as stated by others" help smooth out the harshness of piezo tweeters. Now, I can wire lets say a 3-5 Uf capacitor in series to pretty much start the piezo at 4-5k. What impedance should I use for the crossover point? FYI only asked for knowledge as I am content with what I am doing thus far. As a piezo does not have a nominal impedance and with the 20ohm resistor in parallel which ohm's rating should I use a reference point to determine the cap?

        Comment


        • #5
          Re: Simple Crossover Question

          Hey Dustin,

          Thanks for your reply and yes I actually attached a photo of a simple first order crossover design...but again thanks for taking the time to at least reply...much appreciated

          Comment


          • #6
            Re: Simple Crossover Question

            Using those online calcs for a single coil to roll off a woofer are basically useless, UNLESS you put a Zobel on the woofer to deal with its impedance rise. If you don't, save your money and just let the woofer run WOT, you basically are anyway.

            AFATTG, a single cap CAN generally roll off the bottom end of a tweeter, SOMEwhat (esp. if it's got ferrofluid), but an inline resistor should also be added to protect it even more, and to balance its output down to the level of the (BSC'd) woofer.

            This is weird, me giving advice to a bagby.

            Comment


            • #7
              Re: Simple Crossover Question

              This is weird, me giving advice to a bagby.

              Its not Jeff...LOL...im not by any means a common visiter to the tech site but when I do I read alot of Jeff's replies to learn as much as I can. Its not easy getting answers to the simple questions we all have...

              Comment


              • #8
                Re: Simple Crossover Question

                Originally posted by nextbestthing View Post
                Okay I can install and wire blindfolded...I can build custom cabs with one arm literally! I CANNOT DESIGN A CROSSOVER...

                I have purchased these Celestion 5" Buyouts for "sound" in my card room

                http://www.parts-express.com/pe/show...number=299-414

                with this cheap Goldwood Piezo just to have some sound

                http://www.parts-express.com/pe/psho...80-062&scqty=2

                and the crossover I came up with is a very simple crossover just to help protect the drivers. I know by nature the Piezo's are in a sense high pass tweeters without the need of a crossover but I wanted to help protect them with a resistor as well. Please review my idea and just say yay or nay. THANKS A BUNCH

                [ATTACH=CONFIG]37859[/ATTACH]
                Place the resistor in series with the piezo tweeter, not across it.
                Attached Files

                Comment


                • #9
                  Re: Simple Crossover Question

                  Originally posted by nextbestthing View Post
                  Jeff,

                  THANKS ALOT

                  So in a sense leaving the resistor would stop the peaking capacitive impedance which in turn "as stated by others" help smooth out the harshness of piezo tweeters. Now, I can wire lets say a 3-5 Uf capacitor in series to pretty much start the piezo at 4-5k. What impedance should I use for the crossover point? FYI only asked for knowledge as I am content with what I am doing thus far. As a piezo does not have a nominal impedance and with the 20ohm resistor in parallel which ohm's rating should I use a reference point to determine the cap?
                  Since piezo tweeters are basically capacitors, a series resistor of 20 to 30 ohms is often used for amplifier stability. Most amplifiers cannot drive a capacitive load.

                  Comment


                  • #10
                    Re: Simple Crossover Question

                    Originally posted by Chris Roemer View Post
                    Using those online calcs for a single coil to roll off a woofer are basically useless, UNLESS you put a Zobel on the woofer to deal with its impedance rise. If you don't, save your money and just let the woofer run WOT, you basically are anyway.

                    AFATTG, a single cap CAN generally roll off the bottom end of a tweeter, SOMEwhat (esp. if it's got ferrofluid), but an inline resistor should also be added to protect it even more, and to balance its output down to the level of the (BSC'd) woofer.

                    This is weird, me giving advice to a bagby.
                    What you and Alan have said is correct. I probably should have told him to move the resistor to a series position. However, once it is applied in parallel it will do as I described and limit the capacitive reactance. Once this is done he would be better off adding a series capacitor and treating it like a normal speaker. This is the way to use a piezo and change its crossover point if you need to. Now, if his piezo is purely capacitive then we would need to be concerned with ultrasonic oscillation, so a series cap should be used. I neglected to say that, thanks for bringing it up. Don't most piezo's have a resistor wired internally? I think the only Motorolas did, but I must admit it's been a long time since I used one.

                    Jeff
                    Click here for Jeff Bagby's Loudspeaker Design Software

                    Comment


                    • #11
                      Re: Simple Crossover Question

                      Originally posted by Chris Roemer View Post
                      Using those online calcs for a single coil to roll off a woofer are basically useless, UNLESS you put a Zobel on the woofer to deal with its impedance rise. If you don't, save your money and just let the woofer run WOT, you basically are anyway.

                      AFATTG, a single cap CAN generally roll off the bottom end of a tweeter, SOMEwhat (esp. if it's got ferrofluid), but an inline resistor should also be added to protect it even more, and to balance its output down to the level of the (BSC'd) woofer.

                      This is weird, me giving advice to a bagby.
                      You've got to remember, of the 3 Bagby's on here, only one of them really knows anything. The other 2 are still in pre-school.

                      Comment


                      • #12
                        Re: Simple Crossover Question

                        Originally posted by nextbestthing View Post
                        Jeff,

                        THANKS ALOT

                        So in a sense leaving the resistor would stop the peaking capacitive impedance which in turn "as stated by others" help smooth out the harshness of piezo tweeters. Now, I can wire lets say a 3-5 Uf capacitor in series to pretty much start the piezo at 4-5k. What impedance should I use for the crossover point? FYI only asked for knowledge as I am content with what I am doing thus far. As a piezo does not have a nominal impedance and with the 20ohm resistor in parallel which ohm's rating should I use a reference point to determine the cap?
                        Adding a parallel resistor as already pointed out swamps the rising impedance that is inherent wit a peizo. So now you can add a capacitor that will get you a roll off as desired. You can also calculate the value of the capacitor based on the value of the resistor . People typically use a larger value resistor like 20 ohm as it results in a smallish cap value for a reasonable crossover freuqency.

                        As far as the harshness yes it will improve it but it is not the resistor that reduces the harshness. It is the series capacitor that creates a high pass network. The resistor only facilitates a fixed impedance that you can use to get an idea of where the high pass will fall.

                        If you were to use 3 or 5 uf in conjunction with a 20 ohm parallel resistor your will net 2500Hz or a 1500Hz crossover frequency. Will this curtail the harshness maybe it really depends on the peizo and what is the lowest frequency it can be crossed at and not have high distortion. For a lot of popular peizos that is more like 3500Hz and up.

                        A 10 watt resistor is usually more than adequate for hifi applications but if you are going pro audio you may need to consider a higher wattage resistor if the amps you are using are very high power and will be used at very high output.
                        Dave

                        If you can read this, thank a teacher.
                        If you are reading it in English thank a Veteran
                        .

                        Comment


                        • #13
                          Re: Simple Crossover Question

                          Originally posted by Jeff B. View Post
                          Don't most piezo's have a resistor wired internally? I think the only Motorolas did, but I must admit it's been a long time since I used one.

                          Jeff
                          No internal resistors on any of those $2 piezos made in China. Yes, Motorola often did, but that was decades ago.

                          Comment


                          • #14
                            Re: Simple Crossover Question

                            Re: your schematic - AS IS (showing basically a "band-pass": 100uF high pass filter, a 0.26mH low pass) with TWO of these Celestions in series.

                            The cap has almost no effect until you get below the impedance "spike" near Fs: -3dB down at 60Hz, -6dB @ 45. I'd forego it.

                            The coil has BASICALLY no effect, only attenuating the "junk" near 8kHz by -6dB (which still leaves it roughly 5dB louder than mid-band output).

                            However; by adding a couple dollars worth of extra parts, you can force it to roll off about -3dB @ 6k, and -6dB @ 7k.
                            Put a Zobel across the woofers using an 8 ohm resistor and a 10uF cap (npe would be fine).
                            Add a very small ( 1.0 uF ) cap across the 0.26mH coil. This will act like a notch, effectively pushing down the garbage up at 8-10kHz.

                            Comment


                            • #15
                              Re: Simple Crossover Question

                              In a Piezo driver, the resistor value actually can set it's xover frequency due to the capacitance of the element itself. It's very similar to BW1 order types.

                              Later,
                              Wolf
                              "Wolf, you shall now be known as "King of the Zip ties." -Pete00t
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