Home Forums DIY Speakers and Subwoofers Help with first two way crossover/system design

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    Good evening!  I’m looking for suggestions about how to proceed with this project.  I’ve chosen drivers, but haven’t bought anything, so am open to alternate suggestions (esp the tweeter).  My goals/constraints for the speaker are:

    1) high level of detail/good imaging. reference is Zaph ZD5, (5.5″ SS revelator/Vifa XT25)

    2) reasonable low end extension (doesn’t NEED a sub)

    3) bookshelf form factor.  these will most likely end up on top of a cabinet in my basement, maybe 6″ from the wall

    4) 8 ohm nominal impedance, so they can be driven by any cheap receiver

    Here’s what i’ve come up with so far. hopefully these images are viewable:

    Woofer: Dayton RS150P-8A, Tweeter: Vifa DQ25SC16-4 (started with Dayton ND28F, but had trouble with response bump in the crossover)



    So, in terms of designing the crossover, I took a lot of cues from Zaph’s site.  I set my target to 2kHz LR4 for the woofer and tweeter sections.  Ended up with second order electrical on the woofer and 3rd order on the tweeter, plus an L-Pad.  I cranked up the size of the inductor on the woofer for BSC (that’s what you do, right?), but didn’t attempt to get it totally flat on the low end, as it will be close to a wall.  Otherwise, the SPL looks reasonably flat to me.

    Where I need help:

    1) I’m pretty sure i have a very bad impedance problem.  it’s down to about 2.2 ohms on the high end.  How do you adjust this?  Different tweeter?

    2) Phase?  I know that generally you want “phase alignment” in “the crossover region”, but not sure what that actually looks like on a graph.  Should the driver phase plots be right on top of each other?  How close is close enough?  And how do you get there?

    3) I haven’t accounted for z-offset.  Is there a rule of thumb to apply without actual measurements?

    4) I should probably be looking at off-axis/power response.  How do you go about looking at/evaluating those in PCD?

    Grateful for any pointers!

    –Pat

  • Help with first two way crossover/system design

  • polyrhythmic81

    Member
    February 4, 2021 at 2:30 pm

    I realize now that I posted this in the wrong section.  My bad

  • polyrhythmic81

    Member
    February 7, 2021 at 6:51 pm

    I approximated Z offset at 22mm and phase alignment looks….better?

  • 123toid

    Administrator
    February 7, 2021 at 7:14 pm

    I’m going to try to look more into this on Monday.  I am working on editing a video right now. My initial thoughts though, is the response looks good.  I am concerned about two areas.  I would work a little more on the response between 1-4Khz, unless you like a bright sounding speaker.  It isn’t up much, but might be up enough that you may find it fatiguing. Of course, this is coming from someone very sensitive in that area. 

    Second your impedance is too low from 2Khz on.  What impedance do you want this speaker?  If 4 ohms, keep it closer to 3.6 and up. One easy fix is to add a resistor in front of the  tweeter network.


    Help with first two way crossover/system design

  • polyrhythmic81

    Member
    February 8, 2021 at 4:01 am

    @123toid Awesome, thanks for the look!  I ditched the L-pad and just used a 6 ohm resistor ahead of the crossover for attenuation, which fixed the impedance problem.  I’m going for 8 ohm nominal.  Also played with the tweeter high pass values some more to bring that 1-4kHz region down.  PCD not playing nice with my version of Excel, so you can’t see the second capacitor’s value is 100uf.  The auto-calc set it at around 45uf, but phase alignment looks slightly better to me with a bigger value.  Cost difference is minimal for NPE caps.  Updated responses and impedances attached.


  • 123toid

    Administrator
    February 10, 2021 at 5:30 am

    @polyrhythmic81

    The impedance looks much better.  You could probably still use a little bigger inductor on the woofer, to smooth out that top end, but that is just preference more than anything else. Another way to check phase alignment is to hit the +/- tweeter button to reverse phase.  You should see a pretty pronounced dip when in perfect phase alignment. 


  • polyrhythmic81

    Member
    February 11, 2021 at 3:05 am

    @123toid

    cool. i think i’m convinced i can make these drivers work together enough to buy them.  then i’ll try to measure them in box and see if i can learn anything from that.  do you have a recommendation for a good practical/beginners guide on setting up for measurements?  You haven’t done a video on your measurement technique, have you?  from what i’ve read i’m thinking i should probably just pick the biggest room in my house and then figure out how to gate to cut out reflections.  outdoor measurement would be pretty miserable this time of year.

    next question: I know Soundeasy has a crossover simulator that lets you audition different iterations without actually buying the parts and building them.  Do you have any experience with this or anything similar?  I’ve though about MiniDSP for the same thing, but that might be a little harder to convert to a passive filter after you find something you like the sound of.

    I think as a noob it would be really instructive to hear both e.g., a 3.0 and a 3.5mH inductor on the woofer, but it doesn’t take too many of those to equal the price of a miniDSP 2×4 or even the $250 for SoundEasy…

    thanks for nudging me in the right direction!  I enjoy your videos and the Sound Advice podcast.

  • 123toid

    Administrator
    February 11, 2021 at 7:22 pm

    @polyrhythmic81

    Here is the method I use which has never failed me: https://youtu.be/zW5ZjN-gp_Q

    I have switched over to doing it all in Xsim now.  This is how to take those measurements and use them in Xsim: https://youtu.be/xoJjeK4rKNM

    What measurement equipment do you plan on using?

    I have never used Sound Easy, so I can’t say.  I would rather just have the Omnimic, dats and Xsim.  The omnimic is invaluable in my opinion.  It makes taking accurate measurements very easy.  It offers a blended mode which gives you much more accurate in room measurements. Does a great job with phase.  In fact so much so, that I never have to worry about figuring out minimum phase anymore. Finally it selects all the right tracks for you based off what you are measuring (distortion, response, etc). So for me, I would rather have the Omnimic over either the mini dsp or soundeasy (Although, once again, never used sound easy, but also haven’t had the need). All in all, all I use is the omnimic and dats and have had great success with them. 

    As far as telling the difference between a 3.5 and a 3.0 inductor, typically that is best just to have a few on hand to really listen to the differences.  

     

     


  • polyrhythmic81

    Member
    February 14, 2021 at 12:26 am

    @123toid  Thanks.  I re-watched these, and will definitely give xsim a try for crossover design.  PCD is cool, but it’s a bit long in the tooth/finicky with excel and won’t be supported anymore for obvious reasons. =/  

    I did buy a DATS and looked at the omnimic, but went with umik-1 to start.  I have been reading the REW help text over the last couple days, so hopefully i can get up and running with that.  will post progress after i get the things built and running with the v1.0 crossover. =)

  • 123toid

    Administrator
    February 15, 2021 at 7:57 am

    @polyrhythmic81

     

    Let me know if you need help with the umik.  I used it for years before switching.