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VituixCAD nearfield merger question

DanWDanW
in DIY

Tossing this out to (hopefully) gain consensus on my approach to the current build. Question is about the 'count' of nearfield sources in the Merger tool.

Background, I'm building the scan-speak/eminence kit that Madisound currently has on special for a friend's shop: https://www.madisoundspeakerstore.com/mtm-speaker-kits/scan-speak-eminence-alpha-95-mtm-speaker-kit-pair/

I built a quick prototype enclosure to make measurements and get his go-ahead before spending time and money on a proper pair of enclosures. Using parts on hand I built a box tuned to 90 Hz using four 1.5" diameter ports 1.25" long. Box is not braced (quick and cheap prototype) but is lightly stuffed with pillowcase fibers, and I cleared the area around the ports of stuffing.

Following the REW measurement guidelines from VituixCAD documentation I measure:
1. One meter far field measurements with a single woofer of the MTM pair driven. I only show on-axis, but I did 10 degree off-axis steps too.
2. 5mm measurement of woofer cone with enclosure laying on hard surface floor, both mid-woofers driven but measured cone isolated with pillow wall
3. Port measurement with mic slightly inserted into one of the four ports, both mid-woofers driven

REW measurements below.

In the VituixCAD Merger tool, I think I should enter 1 cone source and 2 port sources for the nearfield as shown in this screenshot:

I am merging the far field response of a single woofer. I have isolated a single near field cone for the measurement. I have measured near field from one port (but can't really isolate without effecting port dynamics) driven by woofers in parallel. Even though there are 4 ports, should I only use 2 for the Merger tool calculation??? A single woofer is only contributing half of the port volume velocity, and the other two components are for a single woofer...

Screenshot of Merger response with 1 cone and 4 ports certainly looks better, but I don't think it is correct.

Here is the Vituix 6-pack with crossover from Madisound modeled with the 1 cone and 2 port merger:

Thoughts? Should I try to crossover away that 200-400 Hz hump? Missing info I need to provide? Thanks in advance!

Comments

  • DanWDanW

    The speaker in question

  • WolfWolf

    I've had to EQ that kind of bump out of a system once by way of xover.
    Here is what I did. This can be placed before the xover for the system, or used in the woofer leg. Use a 3mH steel laminate coil. Place a 1.5 ohm in series with a 600uF NPE across the coil. Adjustments may be needed, but this will bring down the bump.

    DanW

    InDIYana Event Website

  • DanWDanW

    Thanks Wolf, I’ll give that a go tomorrow and also do some mono channel listening. I don’t have golden ears but I would hope my damaged pair will help validate the vituix merger approach I described.

  • Ron_ERon_E

    I use SoundEasy and merged FR measurements include simulated baffle step. Does VituixCAD have anything similar?

  • DanWDanW

    @Ron_E said:
    I use SoundEasy and merged FR measurements include simulated baffle step. Does VituixCAD have anything similar?

    Yeah, there is a diffraction/baffle step correction process. I followed the documentation steps for that.

    Always possible I've fudged something in the measurement chain, but I’m fairly confident in my process right now. Compiling results now, but I added a notch as Wolf described to some success this morning.

  • DanWDanW

    So I first took the previously measured and merged response in Vituix and simulated the notch filter Wolf described. Before and after simulations below. After exploring the design space I ended up with a 3 mH inductor (spot on call Wolf), with a 250 uF npe cap and 1.25 ohms in parallel with the inductor. Placing this segment in front of the whole crossover tilts the HF response down 1 dB at 4 kHz and 2 dB by 10 kHz. So I placed it only in front of the woofers.
    Before:

    After, 'best' modeled response:

    I then measured and performed the near field merge with the whole crossover in place, there was some difference in the 200-400 Hz region, but not as much as modeled. After addition:

    Gameplan has always included a subwoofer, so I added a 2nd order 80 Hz highpass (with a peaking response in the 80-200 Hz region) and measured something I'm happier with. Below is the merged response with 80 Hz highpass and the notch:

    And the 'final' Vituix 6-pack. (with woofer xover shorted because the merged response had the full xover in place).

    And for completeness, the REW nearfield cone/port measurements with only notch, and with notch + highpass. Can't say that I'm happy with the parts count.

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