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First TMWW - VituixCAD / Crossover advice and critique

Working on my first TMWW. Trying to follow the VituixCAD instructions very closely but going back over things I think I made a mistake during measurement. Once I get this figured out, I'll likely have other xo related questions.

For the two woofers:

  • Impedance: I measured impedance in the box with both drivers wired in parallel, just as they will be in the final speaker.
  • Far field: I measured SPL at 1m, on axis of the top woofer, with a pillow covering the bottom woofer. Both drivers connected in parallel.
  • Near field: I measured SPL at 0.25" from cone of top woofer, with a pillow covering the bottom woofer. Both drivers connected in parallel.

Doing some more research on forums (not the manual), while the nearfield should be measured this way, Kimmo recommends the far field be measured by disconnecting the bottom woofer rather than using the pillow. He suggest the effect of the disconnected woofer acting like a passive radiator will be irrelevant once merged since its effect is only around tuning like a port.

I think...IF I would have measured with the 2nd woofer disconnected I would have an accurate SPL measurement for the single driver and would need to scale the impedance by 2, since my measured impedance was with both drivers connected in parallel. I would add both drivers to my crossover and would get +3db for doubling drivers and +3db for the lower impedance.

In my case...I have SPL of only one driver, but because it was still wired in parallel I still have +3db due to the lower impedance. So when I add my driver, I need to scale impedance by 2, and scale SPL by -3db.

Does that sound right??

Is the image below the right way to enter two drivers in parallel, setting each's y-offset correctly?

Comments

  • edited July 26

    @a4eaudio said:

    I think...IF I would have measured with the 2nd woofer disconnected I would have an accurate SPL measurement for the single driver and would need to scale the impedance by 2, since my measured impedance was with both drivers connected in parallel. I would add both drivers to my crossover and would get +3db for doubling drivers and +3db for the lower impedance.

    In my case...I have SPL of only one driver, but because it was still wired in parallel I still have +3db due to the lower impedance. So when I add my driver, I need to scale impedance by 2, and scale SPL by -3db.

    Does that sound right??

    In both cases you have measured the response of a single driver, the SPL does not need to be adjusted. The driver is provided the same voltage whether 1 or two are connected in parallel, SPL out of a single driver will remain the same whether one is covered by a pillow or physically disconnected.

    Scale impedance accordingly for the driver physical wiring, that is , scale the impedance by 2 for a pair of drivers measured in parallel, and scale by 0.5 for a pair of drivers measured in series.

    Is the image below the right way to enter two drivers in parallel, setting each's y-offset correctly?

    Yes, those are 2 drivers in parallel. Enter physical x and y axis coordinates accordingly.

    I'm not deaf, I'm just not listening.
  • Is the upper woofer really 1 mm to the right (or left) of the other drivers? That typo probably makes no difference in the real world.

  • I have no doubt that 1mm is crucial to the design of this speaker. ;)

    I'm not deaf, I'm just not listening.
  • Ha, nice catch. I'll claim that it was a typo and not the fact that my measuring and routing of driver recesses is off by 1 mm.

  • Just messing with you David ;)

  • Okay, next question. I understand how baffle step loss works and that I would pad down my tweeter and midrange to the level of my woofer if I wanted full baffle step compensation. But I often see people only partially compensate for baffle step loss, say 4.5db. In xo software, would the SPL curve just look about 1.5db low and gradually rising to the baffle step frequency, relative to a flat line? Below is a simplified illustration I've worked out for my own thinking. (By the way, other than perfectly flat SPL curves, these are my actual drivers - 93db tweeter, 90db midrange and dual 87db woofers.)

  • How does it sound currently with the actual measurements in room ? Im looking at the mid in your measurement and wonder if you couldnt recess the mids a bit?

  • excuse me if I missed something

  • edited July 27

    @a4eaudio said:
    Okay, next question. I understand how baffle step loss works and that I would pad down my tweeter and midrange to the level of my woofer if I wanted full baffle step compensation. But I often see people only partially compensate for baffle step loss, say 4.5db. In xo software, would the SPL curve just look about 1.5db low and gradually rising to the baffle step frequency, relative to a flat line?

    All of my speakers ended up with BSC in the 5-6dB range, none I feel are boomy or unbalanced sounding. Most of that I believe will come from poor room placement, or poor measurement and response processing that leads to inconsistent results. For room placement issues such as jamming a speaker in a corner in too small of a room, I would still prefer to design the speaker for "every room" and fix the room placement issue with EQ after the fact. This will allow the speaker to be used anywhere with predictable results. The only exception would be a woofer right at floor level, where completely reflection free measurements may be a bit skewed as the floor can be considered a constant here and provides bass reinforcement that probably should be included in the design process.

    To answer your question, yes the full BSC implementation will be "flat on-axis", 4.5dB implementation would simply mean that >1kHz response will be 1.5dB lifted vs the 100Hz response, so you can expect a slight uphill slope from 100Hz to about 1kHz.

    Since you are using VituixCAD, I suggest turning your focus to the in-room response in the power & DI chart. This is a spacial average that approximates that "every room" as a typical in-room response. I find that setting up the optimizer using listening window at -0.2dB/oct from 100Hz to 10kHz and in-room response at -0.8 to -0.9dB/oct from 100Hz to 10kHz provides excellent results. You can dive into the preference rating tool for optimization as well, which balances many factors and not at a specific constant slope like I've described.

    I'm not deaf, I'm just not listening.
  • @Nicholas_23 said:
    excuse me if I missed something

    Hi Nick. The graphs were just lines and curves in Excel to illustrate what I "think" the intuition is. I have what I hope are good measurements and now the speaker is disassembled while I paint and veneer it this week. I'm trying to work on the xo and this is where I start questioning my understanding and ability to take accurate measurements.

  • @dcibel said:

    Since you are using VituixCAD, I suggest turning your focus to the in-room response in the power & DI chart.

    Yes, I am working on that. I had worked up what I thought might be a good xo to then realize that I had only put in ONE of the woofers. I realize that if my measurements are wrong OR I process and get them into VituixCAD wrong then a great looking xo in the program isn't going to reflect anything in reality. I do think my measurements are good, so hopefully will make progress soon. I will then post here for more feedback on the crossover as well as in-room response, directivity, etc.

  • Here's something that might help provide some context to the charts and graphs and make sure the first crossover you build is a good one. I wrote up this document a while back on how to use VituixCAD along with APO EQ to simulate any crossover designed in VituixCAD digitally. It can be active blocks or passive components, the result can be exported to APO EQ and simulated as a digital crossover using your PC as the DSP. You just need enough audio channels and amplifiers available for the speaker you have in mind. Many desktop PCs these days have 5.1 or 7.1 audio built in which is enough for a pair of 3-way speakers.

    https://diy.midwestaudio.club/discussion/1832/simulating-crossover-filters-with-vituixcad-and-eq-apo#latest

    Steve_Lee
    I'm not deaf, I'm just not listening.
  • Looking at other screenshots on the internet, the SPL curve of dual woofers is represented by a single line showing the combined effect. The way I have them, VituixCAD shows two separate SPL curves. (I have exaggerated the y-offset just to make it obvious.) Do I have them hooked up wrong or do I need to change some option to have it shown a single combined line??

  • edited July 27

    You will only see a single line for drivers where the x,y dimensions are the same (incorrect configuration) or in an MTM configuration where distance from speaker to listener and angle are the same.

    You have a pair of drivers with significant difference in the y dimension, so the response from each should be different. Each driver has a different distance and angle to the listener. so what you are seeing in VituixCAD is correct.

    I'm not deaf, I'm just not listening.
  • But the two drivers combined are 6db higher than the individual drivers. This does show in my reference angle and listening window curves...but when I am trying to match for example an LR2 on the midrange and an LR2 on the combined woofers, the crossover "appears" to be about 12db down on the individual drivers but really is only 6db down (as it is supposed to be) on the dual woofers. Is that just normal and you just mentally take it into account when trying to fit the target curves?

    (I appreciate everyone's patience, as I get that a lot if this is obvious to those who already know what they are doing.)

  • With such a distance between drivers, you can expect some phase interaction as you approach 1kHz. Design your speaker for the resulting sum of the two drivers together.


    I'm not deaf, I'm just not listening.
  • The large distance between drivers was added to specifically make the lines diverge. The actual offsets are -286mm and -508mm. What was confusing me was having two lines (even if right on top of each other) vs a single line 6db higher.

    I'm pretty sure I made a mistake measuring the woofer and can't re-measure until Saturday so I'm stuck on hold for a few days.

  • 2 drivers, 2 traces, sorry but I’m not understanding the confusion. Turn on reference trace and you will see that it’s roughly 6dB higher as the two individual drivers add together.

    I'm not deaf, I'm just not listening.
  • There was something "off" on my measurement of the woofer so I redid my measurements. Measured outdoors, tweeter 77" from the ground, nothing other than the ground within about 12 feet of the speaker and mic setup. I should be able to put components together and actually listen tomorrow. Speaker is 40" H x 9.5" W x 15.5" D

    Below are two starting points - does anyone see any obvious issues/problems or have general recommendations? I get the basics - different orders of xo, L-pad, zobel, and notch filters and that is about it. 2nd crossover notches out the peak 1.5khz which I'm quite sure is baffle step induced.

  • The images got squished down when you posted so it's a bit hard to read. Considering overall response, the second would be much preferred by myself. First one needs the mid padded down a bit more. Second crossover has a impedance dip around 1.5kHz, not a big deal but something to be wary of.

    I would consider a series notch around 7kHz for the midrange breakup peak. The tweeter as well has a fairly wonky response, I would consider lifting its response a bit if you find it a bit dull as-is.

    I would also consider turning on in-room response (orange trace) on Power & DI and using that as the optimizer target.

    I'm not deaf, I'm just not listening.
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