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  • Question regarding crossovers

    I've been experimenting with my car's tweeter output. Tweeters are 1 inch silk domes, 4 ohm nominal. I measured 3.7 ohms DC, so I believe the 4 ohms to be correct. SPL Approx 94dB.

    I had a 6.8uf cap in series, for a crossover of about 6 kHz @ -6dB/octave, according to most crossover calculators. Treble seemed strained, regardless of HU settings. Some sibilance. Some harshness. Trying to fix via EQ not that effective. Added padding resistors (both series, parallel and L-pad config), also not the improvement I wanted.

    I now switched to 2.2uf caps I had onhand. Def improvement. I believe the larger cap was causing the tweeters to reach too low.

    My question regards the 2.2uf crossover. According to calculators, the crossover should be about 18kHz @ -6dB/octave. To my understanding, my tweeters should now be down 3dB at 18kHz. Down 9dB at 9kHz. Down 15dB at 4.5kHz.

    I def notice attenuation of lower treble freqs. However, I was worried the tweeter would hardly output at all with a crossover beginning near the top of the audible spectrum. Yet, the tweeter still plays quite a bit of treble and actually still pretty loud? Why?

    What am I not understanding?
    Is the tweeter's impedance higher than 4 ohms at higher freqs, causing the crossover to actually be much lower than the predicted 18kHz? That's the only explanation which makes any sense to me.

    I mean, with an expected 18kHz crossover point, I was afraid the tweeters would output virtually nothing except maybe some hiss


  • #2
    So ...
    you've got a 1st order high-pass filter (2.2uF) on a tweeter w/an L-pad?
    What tweeter?
    What values for your "L" resistors.

    Crossover "calculators" don't work - don'cha know?

    Comment


    • Stash
      Stash commented
      Editing a comment
      No. No L-pad, currently. Only 2.2uf cap.

      I did experiment with some resistors, in various configurations. Did not like the results.

  • #3
    Originally posted by Stash View Post

    What am I not understanding?
    Is the tweeter's impedance higher than 4 ohms at higher freqs, causing the crossover to actually be much lower than the predicted 18kHz? That's the only explanation which makes any sense to me.

    I mean, with an expected 18kHz crossover point, I was afraid the tweeters would output virtually nothing except maybe some hiss
    That "4 ohm" rating is at some single frequency. The impedance of any driver usually varies all over the place with frequency, and each driver has its own unique curve. And that's why crossover calculators are a joke.

    Francis

    Comment


    • Stash
      Stash commented
      Editing a comment
      Ok. Thank you. That is what I assumed.

      I'm guessing, in order to design an actual functioning crossover, I will have to measure the DC impedance of the driver as it reproduces a specific crossover frequency?

    • fpitas
      fpitas commented
      Editing a comment
      No, the DC impedance (which is called resistance normally) really doesn't help anything, either. You need the AC impedance vs frequency. That includes the reactive (i.e., varying with frequency) terms.

  • #4
    Once one understands the dynamics of a speaker system they either run away from the hobby or slowly get more consumed by it - If I were smarter than I am I would probably run like hell . . .



    Comment


    • #5
      Originally posted by Stash View Post
      What am I not understanding?
      That a first order filter is next to useless.

      www.billfitzmaurice.com
      www.billfitzmaurice.info/forum

      Comment


      • #6
        Originally posted by Steve Lee View Post
        Once one understands the dynamics of a speaker system they either run away from the hobby or slowly get more consumed by it - If I were smarter than I am I would probably run like hell . . .


        It's a tough hobby to master. People spend their lives learning about this stuff. Which makes it a rewarding hobby for me at least, but I can see that it would be daunting for a noob, especially a non-engineer.
        Francis

        Comment


        • #7
          No-one masters this as a hobby - they just get more experience.

          That is the stuff that hobbyists share with others - experience.

          At the end of the day you have to make your ears happy and we all have different ears.

          Keep plugging away at it and thanks to all you experienced hobbyists here who share your knowledge - you are the reason this hobby exists.


          Comment


          • #8
            There's a decent chance your tweeter's response looks something like this ... with just a 2.2uF capacitor.
            Click image for larger version  Name:	VituixCAD_SPL.png Views:	0 Size:	17.1 KB ID:	1471876

            This is just a SIMed response of a 2.2uF capacitor and the NHP25F-4 tweeter which happens to be a ~1inch fabric dome tweeter with similarly high sensitivity, so it might be similar or it might be VERY different. But it kind of gives a rough idea how different a frequency plot can be compared to a perfectly flat thing with a gentle slope like the online calculator might lead you to expect.
            My first 2way build

            Comment


            • #9
              Ok. I learned something today. This will help me re-evaluate my car tweeters and design a proper 2nd order crossover, which I would prefer. I will try sending various treble freqs from 1kHz and above, through the tweeter and measure its impedance at each point. Try to get a better feel of the tweeter.

              BTW, the tweeters seem like decent silk fabric domes, but they are a cheap low-end brand. Their response may be more ragged then that of the tweeter graph posted by LOUT.

              When I built my retro MACH ONES, I made the mistake of designing my crossovers solely based on crossover calculators and assuming each drivers' stated nominal impedance rating. I wanted to match the specs of the original speakers, which were 800/8,000Hz 2nd order.

              I've measured my MACH ONES several times, only to find the crossover points are not where I wanted. The woofer/mid point is around 500Hz. The mid/tweeter point is around 5kHz.

              They sound good as-is. But, I may open up one, and test all the driver's impedances at the desired crossover points and modify my crossovers. That's a future project, anyway.

              Because I was unsure of what to do with my car's tweeters, and my funds are very limited, I tried a different approach, in the interim. I bought a pair of cheap 1.5 inch full-range drivers. 4 ohms, 3w, claimed response of 350Hz-20kHz, 83dB SPL +/-3dB. Spent $7.
              My thought was, being that my Mirage is so small, and I am basically sitting on top of my speakers, the close proximity is causing all sorts of chaos. Most car tweeters have SPLs of well over 90dB, which only seems to worsen the problem, by being overly bright and too close to my ears.

              I installed the full-ranges in place of the 1 inch soft domes, using the mounting pods of the tweeters (see pics). I added a small cotton ball amount of fiberfil to each pod. I left the original 6.8uf caps as the crossover. The results aren't bad at all. The full-ranges seem to mesh much better with the 6.5 woofers. I made some small adjustments via my EQ. I will listen to them for several days and decide if I need to try the dome tweeters again. I figured these small cones will deliver performance similar to a tweeter, but at lower efficiency and with less stress at lower frequencies, since its resonant frequency is much lower (350 Hz).

              Comment


              • #10
                Originally posted by Stash View Post
                Ok. I learned something today. This will help me re-evaluate my car tweeters and design a proper 2nd order crossover, which I would prefer.
                Make it a 3rd order highpass, along with a 2nd order lowpass for the midbasses.

                www.billfitzmaurice.com
                www.billfitzmaurice.info/forum

                Comment


                • #11
                  A 3rd order might work. Never constructed a 3rd order before. Would be interesting.

                  The problem here, is, do I spend money building an elaborate crossover, or, put that money towards a better pair of tweeters?
                  Preferably, smoother tweeters with SPLs of 90dB or less, as one might find in home-component tweeters.

                  It's easy to fall in that trap of trying to make a weak driver sound better. Been there more than once. You can't really fix a bad design or poor quality lol

                  Comment


                  • #12
                    I'll see what PE has on sale/clearance, for coils and caps. That may make my decision for me

                    Comment


                    • #13
                      Btw, I'd also like to mention, I have an identical pair of the 1 inch dome tweeters installed in a pair of speakers I threw together for my home office. They are powered by a small Kinter amp (5w/ch). All tone controls set flat except for a -3dB cut at 250Hz via my connected TV monitor.

                      These same tweeters sound much smoother in my home office set up. The woofers are also dual 6.5 inch.

                      The only difference in my home office set-up is the crossovers are the originals which came with the dome tweeters (-12dB @ 3,500Hz, tweeter only).

                      I honestly don't know why these same tweeters are more musical and listenable in my home office set-up?

                      Is it the crossovers?
                      Could the Kinter amp be rolling off the high-end?
                      Is it the distance from my listening position to the speakers?

                      I sit approx 6 ft or more in front of those speakers, as opposed to practically right in front of the same tweeters in my car. So, I keep coming back to thinking it's the car's interior and proximity more than anything else, causing the frustration. Just putting it out there.

                      Comment


                      • #14
                        Originally posted by Stash View Post
                        A 3rd order might work. Never constructed a 3rd order before. Would be interesting.
                        I haven't used a 2nd order high pass since I was in college. I graduated in 1971.

                        do I spend money building an elaborate crossover,
                        The 2nd order LP/3rd order HP crossovers I made for my car cost about $18 each. I don't see that as a deal breaker.
                        www.billfitzmaurice.com
                        www.billfitzmaurice.info/forum

                        Comment


                        • #15
                          I'll look into crossover components later this evening.
                          Money ia tight, but I'll see what I can put together.

                          Do not ever use a mini full-range as a tweeter. Wow! Even more terrible than what I had previously lol. What a horrible mistake.

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