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  • rpb
    replied
    Originally posted by Jicafold View Post
    I had considered that in my first graph as Kirby from KMA had said, some people like a smiley face response. That's how you ended up setting the Sansui EQ back in college anyway. However, I realized that this is going to be a center channel and I may need more midrange for peoples voices.

    It looks like I finally ended up with a 0.45 inductor on the woofer.

    Thank you.
    One thing to consider is the location of the center. I made a xo for a center once with lots of BSC. I listened to it with a good selection of dialog, and music with the speaker on a stand well away from any walls. It seemed very neutral. I then placed the speaker on my 46" RPTV. The tonal balance changed drastically, and was now way off. The screen caused the balance to be dark, and murky. It had too much BSC. These drivers will tend to have a full BSC response. That's not necessarily a good situation. I would suggest attempting to flatten out the response. I'm not sure if it can be fixed easily. You might want to use different drivers if you can't make the bass and mid-range level with each other. The tone control may remedy the imbalance if it's in need of correction.

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  • Jicafold
    replied
    I had considered that in my first graph as Kirby from KMA had said, some people like a smiley face response. That's how you ended up setting the Sansui EQ back in college anyway. However, I realized that this is going to be a center channel and I may need more midrange for peoples voices.

    It looks like I finally ended up with a 0.45 inductor on the woofer.

    Thank you.

    Leave a comment:


  • Billet
    replied
    Originally posted by Jicafold View Post
    So after watching online instruction with Vituix on designed a crossover with it. This is my first attempt at this. It is an MTM with a Dayton NDFA20-6 and two Dayton TCP115-8 in series. This is what i got after 6 parts. It looks reasonably flat from a distance. Opinions and advice? Thank you.
    I would say that your original crossover actually looked pretty good to me. The phase response is smooth and a midrange dip often sounds nice, especially with budget drivers.

    I like to start with a simulated design to check basic compatibility, then build something and listen for a while before making changes.

    You are getting a lot of great advice here, but sometimes it is best to start off as simple as possible and go from there.

    I would probably use a larger inductor for the woofer low pass, 0.18 is pretty small. And I would also have an assortment of resistors or an L-pad on hand to level match the tweeter.

    Most important of all, have fun while you learn!

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  • LOUT
    commented on 's reply
    Will a capacitor running parallel with the woofers' inductor basically always want a resistor in series with that cap to avoid dropping impedance too low way up in the high-frequencies, or does that become unimportant as long as the tweeter's HP has enough added resistance of its own?

  • LOUT
    commented on 's reply
    That NAD can push somewhere between 110-230watts into 8ohms and more into 4ohm, so it can exceed maximum headroom of the speakers whether you go 8ohm or 4ohm. In other words, your current amp will be equally loud either way.
    It does look like a really nice and robust reciever so you'll probably be fine for a long time.

    Changing these to 8ohm (4+4 in series) will make them more versatile if you ever use them with a different amp AND will only lose ~3db of output (which you'll only lose if you end up needing to pair them with a 4ohm amp that outputs ~80watts or less @4ohms...a more powerful 4ohm amp will only lose 0-2db). But you ARE right about that NAD being 4ohm stable, and it does look like it could potentially outlive us all, lol.

  • Chris Roemer
    replied
    Per rpb, a TINY - 0.47uF cap across the coil will push the 10k resonance down from -15dB (below 84dB reference) to -27dB.




    in answer to LOUT's ?
    TTBOMK, in THIS instance the "tank" cap doesn't need any series resistance - because the following shunt (to gnd) is a "Zobel" (-like thingy) - with resistance.

    If it were merely a 2nd order (shunt cap to ground w/NO inline resistor), THEN I'd use a 4ohm resistor in series w/the TINY cap. We're just trying to avoid a direct short to ground for any freqs. high enough to pass.
    Last edited by Chris Roemer; 06-11-2021, 12:11 PM.

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  • rpb
    replied
    I'm not running any sims, I'm just looking at your posted results, and making hunches. Try adding a cap across the coil to hammer the spike at 10k like I suggested a few posts back. You might like what it does.

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  • Jicafold
    replied
    AH yes. Z - offset. Thank you. I had forgotten about that. SO much to digest. Fooling with the program does drop those values.

    I have an NAD T773 which I assume should be stable with a 4 ohm load. I chose to go to 4 ohms for gain sensitivity.

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  • LOUT
    replied
    Are you too far along to suggest switching to a pair of TCP115-4 in series (for a total 8ohm load) instead of your current 8/8, 4ohm parallel configuration?
    Some surround recievers can handle a 4ohm load, but most (particularly the more affordable ones) want 8ohm speakers.
    I might be a little sensitive about this because I built a set of 4ohm surrounds for an older reciever which broke shortly afterward...then I realized how difficult (or expensive) it can be to find a decent 4ohm reciever when most are 6-8ohm.

    You can usually get close results to your current crossover by doubling the mH-values of your woofers' inductors and halving the uF-values of the woofers' capacitors and doubling the woofers' resistor ohm value....and also taming the tweeter's overall response -3db.
    Probably not exact, but usually a good starting place.

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  • a4eaudio
    replied
    Originally posted by Jicafold View Post
    Additionally, I put these identical values in Passive Crossover Designer and came up with a similar sum response other than a dip at 4000 Hz. Now why would that be?
    Chris touched on this, but to expand a little:

    1) You need at least decent estimates of x, y, and z offsets to get accurate sim. Chris may have input some different assumptions than you. x and y are easy, because you can decide how you want to place the drivers on a baffle. For simulating, just estimate a z offset. If you build the cabinets and have the real drivers in them, you can determine x-offset with measurements. (Disclaimer: there are some who don't think this is worth the effort but no point in debating that here.)

    2) You need to have minimum phase files. I'm assuming you have just traced the mfg specs, but you need to extract minimum phase for accurate sim. If you haven't done this, and Chris has, you will get different results. Not sure how many options there are to do this, but Jeff Bagby wrote a program for DIYers that extracts minimum phase.

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  • Jicafold
    replied
    Originally posted by Chris Roemer View Post
    Another aspect of the tweeter's power handling is how much its attenuated. In this case, its about -9dB down (at ALL freqs. - so its not being asked to handle rated power - or anything close to it). That puts it at about -20dB down at its Fs (resonant freq. - based off Dayton's .zma files). I think it'll be happy there, in this instance. .

    I understand about the tweeter.

    I substituted the numbers that you had said, unless I am missing something, it should be the same thing. So the dip is a mystery. I could try it in Vituix, or erase my data and start from scratch. At any rate, I’ll play around with this more so I can duplicate your graph. Thank you for your time.

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  • Chris Roemer
    replied
    Another aspect of the tweeter's power handling is how much its attenuated. In this case, its about -9dB down (at ALL freqs. - so its not being asked to handle rated power - or anything close to it). That puts it at about -20dB down at its Fs (resonant freq. - based off Dayton's .zma files). I think it'll be happy there, in this instance.

    As far as your "dip" goes, when using mfr. data files, you really need to plug XYZ coordinates into your XO sim model. Also, I told you about DCR. If you showed me your latest XO schematic (where you tried to copy my suggestions) it might tell me more. I'm pretty sure you've got 0.1 ohms (now) for a 0.40mH coil, whereas its more like 0.4ohms. That added DCR (in series w/your woofer) will pull it down (at all freqs.) a bit. MY "phase" (model) is summing about +5dB (above where the 2 drivers cross). Your model is only half that. I'm not saying that MY phase (model) is right, but most likely yours isn't either. If it IS, one way to get better (higher) summing is to flip the tweeter polarity, OR add another order to the filter(s).

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  • Jicafold
    replied
    Thank you Chris. I see how your graph solves the problem of the baffle step. However, the resultant crossover is now at 3000 Hz. The spec sheet for that tweeter says there is a usable frequency response only down to 3500 Hz.

    But I could use a different tweeter.

    Additionally, I put these identical values in Passive Crossover Designer and came up with a similar sum response other than a dip at 4000 Hz. Now why would that be?


    I see that book is on Amazon. I will have to order that.

    Click image for larger version  Name:	BSC Example.jpg Views:	0 Size:	84.7 KB ID:	1471094
    Last edited by Jicafold; 06-09-2021, 11:55 AM.

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  • Jicafold
    replied
    Originally posted by rpb View Post

    When you actually measure the response in a box, the bass frequencies will drop by 6dB. This is due to what we call baffle step. When someone uses baffle step compensation, ie BSC, they are correcting for this bass drop. In a sim like yours, it might be desirable for the bass to show 5dB louder than the mid-range.
    Oh.... So not just of prominence in the bass frequencies but a prominence that is higher than the midrange and treble. Thank you.

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  • rpb
    replied
    Try this. Put a cap in parallel with the .18mH coil, and see what it does to the woofer response at 10k. Adjust the cap value till it eliminates the response spike. Start with around 5uf, and adjust from there. a smaller cap raises the notch frequency. ( 5uf is a WAG, and might make a notch much lower than needed, but you should easily see where it is. )

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