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How do you know how low you can cross over a tweeter without damaging it?

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  • #16
    Not to be a smarta$$ but why not look at the spec sheet. The spec sheet should have a frequency range listed, which is a good place to start. Some manufacturers will even specifically spell out a minimum crossover frequency along with what the minimum slope crossover is. That said Wogg's advice is a good place to start, 2x the Fs. Some commercial speaker manufacturers have had internal guidelines that say 3x the Fs just to cut down on the number of warranty repairs.

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    • #17
      If a resistor and tweeter are parallel wired both receive the same voltage swing from the amp, therefore the tweeter isn't attenuated. Both the tweeter and resistor will draw current, so the power output of the amp will increase, with no benefit being realized from it. There's simply no reason to do it.
      www.billfitzmaurice.com
      www.billfitzmaurice.info/forum

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      • #18
        But... as part of an L-pad, the parallel resistor (alone) DOES change the impedance load (curve), flattening out (somewhat, at least) the Z-peak at Fs. Using a series resistor (alone) does not flatten the Z-peak. Attenuating by L-pad (as opposed to just series resistance) usually helps to get more of an "expected" HP rolloff from the pass filter (due to the parallel component of the L-pad).

        Take tweeter #264-1478, for instance. You want to attenuate it -2dB, AND you want a 1st order (elec.) HP on it at 3kHz.
        You can achieve this by using 1.5n(ohms) of series resistance and a 9uF cap, BUT, even though the filter's rolloff starts out normally (being -3dB down near 3k), it basically flattens out from 1.5k down to 500Hz before the curve turns downward once again. At the tweeter's Fs (400Hz) the entire filter only has the output down -11dB.

        OTOH, an L-pad: SR=1n / PR=7n, ALSO attenuates it -2dB, with a 1st order elec. HP achievable using a 13uF cap. W/the "L" for attenuation (which helps flatten the Fs Z-peak) the tweeter's now down -17dB at Fs, with a rolloff curve that looks a lot more "normal".
        Last edited by Chris Roemer; 01-15-2019, 02:32 PM.

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        • #19
          The more that I read threads like this one (which is a very good one), the more I want to just totally dismiss passive crossovers.

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          • #20
            AEIOU no reason this thread should scare you. In fact, it's a good learning lesson in electronics and also helps in designing active crossovers. I personally find passive XO more attractive. As far as the L-pad Chris Roemer summarizes the situation very well.

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            • #21
              Originally posted by billfitzmaurice View Post
              If a resistor and tweeter are parallel wired both receive the same voltage swing from the amp, therefore the tweeter isn't attenuated. Both the tweeter and resistor will draw current, so the power output of the amp will increase, with no benefit being realized from it. There's simply no reason to do it.
              I don't get that, if you wire a 4 ohm resistor in parallel with a 4ohm tweeter it with cut the tweeters output in half.
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              • #22
                That's only correct IF the tweeter had constant impedance, which is NOT true. The nominal impedance might be 4 ohms, but this is just an `average` number.

                Remember a tweeter's impedance is NOT constant, but changes with frequency.

                Think about it this way:

                The resistance of the tweeter changes as a function of the frequency. This dependence is plotted and provided by manufacturers in an impedance plot.

                This is why an L-pad can be useful. At certain frequencies the impedance of the tweeter shoots up (at resonance), which is where the L-pad would have its strongest impact to lower the impedance seen by the tweeter.




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                • #23
                  Originally posted by 6thplanet View Post
                  I don't get that, if you wire a 4 ohm resistor in parallel with a 4ohm tweeter it with cut the tweeters output in half.
                  Not when wired parallel. The tweeter will receive the same voltage in both cases, so its output will be the same in both cases. If the resistor is in series then the drive voltage would be split between the resistor and the tweeter.
                  www.billfitzmaurice.com
                  www.billfitzmaurice.info/forum

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                  • #24
                    "Originally posted by billfitzmaurice View Post
                    If a resistor and tweeter are parallel wired both receive the same voltage swing from the amp, therefore the tweeter isn't attenuated. Both the tweeter and resistor will draw current, so the power output of the amp will increase, with no benefit being realized from it. There's simply no reason to do it."

                    "I don't get that, if you wire a 4 ohm resistor in parallel with a 4ohm tweeter it with cut the tweeters output in half."

                    Bill is correct. remember that the voltage across the tweeter and resistor doesn't split, both will see what ever input voltage is present. what does split in the circuit is the amperage. so all this means is your amplifier will make up the difference in amperage to keep the voltage constant.
                    craigk

                    " Voicing is often the term used for band aids to cover for initial design/planning errors " - Pallas

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                    • #25
                      Right, not thinking there's a series resistor there and the parallel resistor would be the other part of the voltage divider. Brain fart...
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                      • #26
                        There is a way around everything. I am currently working on a design with a nd28 in a 10” waveguide - May or May not be the middle of an rs270 with no phase plug ;) ,crossed 200hz above fs, second order electric, sixth Bessel acoustic, with the fs notched with a parallel rlc filter.

                        I played it for an extended period at 100-103db/1m (music, not sine) for over a half hour as a torture test with no issues whatsoever. Distortion measures -40db at its highest at 1000hz at 95db. This combo breaks a lot of rules it seems, but no signs of thermal issues whatsoever. Of course the 15 or so dB of boost from the guide helps, but I think the fs damping and Bessel filter help a fair amount.
                        Projects:

                        Breezy Monitors: http://techtalk.parts-express.com/fo...reezy-monitors
                        transcenD: http://techtalk.parts-express.com/fo...5035-transcend
                        Summits: http://techtalk.parts-express.com/sh...75-The-Summits
                        References: http://techtalk.parts-express.com/sh...-My-References
                        Vintage Style 2-way: http://techtalk.parts-express.com/sh...-vintage-2-way

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