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Theorized and proven: "Zingers", an InDIYana 2019 8" 2-way design...

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  • Wolf
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    I happened to have a pair of Peerless DA25BG08-06 tweeters on hand, and thought these would be a good tweeter to pair the SD215A-88 with. They have a low enough Fs, low cost, and a really nice sound I'd heard in a few others' builds before. They are touted as being able to xover fairly low in their spec sheet as well. Their sensitivity was also high enough that they should have enough output to keep up with an 8" DVC woofer wired in parallel. I also wanted to be different and not use a waveguide or the newer RST tweeters since those seem to be the latest hot-ticket items.

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    Woofers in box:

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    Tuning verified! On-tweeter-axis and 20* H off-axis measurements for both units were then taken as you see here:

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    Did I mention that the ply I found had a really nice figured veneer already applied? A bit of Watco Danish oil and a couple wipe-on polyurethane coats are all this took.
    Measurements up next...
    Wolf

    Leave a comment:


  • Theorized and proven: "Zingers", an InDIYana 2019 8" 2-way design...

    I built these for the Bare Minimum challenge for InDIYana 2019. I've long wanted to build a 2-way with the SD215A-88, even when the older model, SD215-88, was around. The theme just gave me the excuse to do so. Yeah- I know what you're thinking... "An 8" subwoofer in a 2-way? That won't work!" However- it works rather well! The name comes from the toys and built up 1/32 scale models from the '70s, as well as those related to Rat Fink, et al. Basically, a large performance motor crammed into a chassis that had nowhere near enough volume for it to occupy the destination without some major changes. This wasn't that drastic of a shoehorn, but the namesake still applies hearkening to the larger woofer 2-ways of old, as well as the bigger motor in a small box mantra. The following will lay out the pertinent information.

    I'm going to start off by saying these should have been characterized as a build that was done all wrong. I didn't round the baffle edges to reduce diffraction. I didn't round the port exit to reduce turbulence, even though the inner end is angled for a utilized flare. I didn't flush-mount the woofer, as it had to mount atop of the tweeter for a closer CTC distance. I used an 8" in a 2-way, which is seldom done well, and even more often unsuccessfully. Then I was limited to use 5 parts per the challenge- which was listenable- but I preferred the addition of a 6th part to make it as good as I felt it could be without much more complexity. I had 2 weeks to assemble, measure, listen, and verify results. And lastly- I finished the baffle first before I cut the drivers' locations so the tear-out would be minimized. Suffice to say the odds were stacked against me.

    I've been a fan of these woofers since 2007 when I heard them in Paul Carmody's 'Aethers' design at Iowa DIY. The bass was solid, deeply extended, and pretty well defined for a driver of that price. It was utilized in a 1.5ft^3 vented box for an F3 of 29Hz at that time. While it would likely still apply to this design by elongating the cabinet a bit, I shrunk the volume to 1ft^3 and lost 5Hz off the bottom end in extension. Using real T/S as follows:

    As in the Aethers:

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    As used here in the Zingers:

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    Next step was a logical look and layout to make them buildable:

    Click image for larger version  Name:	Zingers.png Views:	1 Size:	404.0 KB ID:	1412018

    I was able to get these constructed with bracing from a 2' x 4' MDF Handipanel and another plywood panel of the same. I only used half the ply for the 2 baffles, and required minimal scrap MDF to complete the boxes. All panels are tied into the bracing scheme, even the baffles between the W/T and just below the woofer. I used a side-exit port this time around just to be different and to the fact these might end up against a wall. The cabs had a barrier of rolled on RedGard applied to the inside walls. Ed Froste always swore by this elastomeric shower moisture barrier product inside his boxes. I finally clicked this method on my building bucket-list. It is messy, but it does damp the walls a bit, as well as seal the inside rather nicely.

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    The terminals were from a large bag of binding posts that did not have the jam nut, solder-ring, isolation washers, or the outer free-wheeling nut to clamp down on the wire/spade. I had to devise a solution to use these, and it turns out they will thread into a 9/16" hole, half-inch thick, rather nicely from the inside. I soldered leads, shrunk some heatshrink around them, and installed them by hand. I laid some E6000 adhesive over the collars and all was done. Note to self- make tool to install posts this way to avoid massive blisters and bloody knuckles. I have the hand strength to get them threaded in, but my fingers weren't happy, and my knuckles kept getting scraped on the RedGard stuff. In the end, this leaves a nice pair of 'Nanner-Only' connections:

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    More in the next post...
    Wolf

    EDIT: The 5.325" dimension in the baffle and size layout is incorrect. The tweeter to top, and CTC is accurate, so please use those for dimensional agreement, and allow the woofer to bottom to be the variable unknown. Drawing is not to scale.
    Last edited by Wolf; 05-03-2019, 04:26 AM.
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