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Colored 2way Bookshelf Cheapies

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  • Colored 2way Bookshelf Cheapies

    Click image for larger version  Name:	 Views:	0 Size:	648.7 KB ID:	1434984

    This was my first build which let me try a few different things that I was curious about.
    Using the PC105-4 and TD20 Dayton drivers made it hard to justify spending a lot on crossover parts. Using a series crossover instead of parallel allowed a single 0.5mH inductor to somewhat fill the job of two (saving at least $3-$5 per box), while a couple capacitors and a single 4ohm resister are all that's left. The end result still leaves the woofer's ~10k spike more present than ideal (not a full 20db-30db down) and it lets the tweeter play a bit lower than specs want, but I haven't noticed either of them shouting or distorting when playing at uncomfortably high volume levels sitting 3meters away. I'm betting a good portion of that may be my inexperienced ear, but at least these problems must not be super obvious.

    I really tried to skip the resistor on the tweeter to squeeze the crossover down to three parts, but they definitely need it for any longer music listening and for general accuracy. Besides the overly present sibilance, the extra treble made trumpets (listening to the Jarassic Park theme) sound a bit thin and zingy while adding the resister to tame the rising highs flatter let the trumpets sound more brassy and bold.

    The boxes' exterior dimensions are 10"x10"x6", about ~7liters (almost 0.25ft cu) internal volume and a front slot port tuned around 55hz (about 1/2inch tall by 5.5inches wide). These seem to produce a healthy amount of low end reach for a lot of music though they do fall short for some electronic music. I was initially afraid of what would happen to the drivers with lower frequencies below tuning at high volume, but these little 4inchers appear to be nearly invincible against over-excursion inside their rated wattage.
    Another thing I was curious about was cabinet resonance and other possible problems from using a thinner material. The boxes were made using 1/2" plywood for the front and back and 1/4" plywood for the top/bottom/sides. This gave the screws holding the drivers and terminals something thicker to grab onto while also providing more surface-area for gluing the top/bottom/sides. These things feel like gingerbread houses for their size and weight, but they haven't broke despite moving them around (indoors and outdoors) for the last year, and resonance hasn't been nearly the issue I'd expected except when cranking them with sine waves.
    I thinned some acrylic paint with a lot of water and rubbed it on with a few paper towels (cheaper/rougher paper towels tend to drop less lint), first testing on some of the cut-off scraps.
    I encourage anyone else thinking of building with 1/4" plywood to use some internal bracing..because I didn't...and that was probably a dumb choice on my part. But this whole experience has been ridiculously forgiving.


    I've been using the free program VituixCAD for crossover design after seeing a video from KirbyMeetsAudio a little over a year ago. It also has a pretty nice box/woofer sim but I never found a port/air-speed modeller so I still used WinISD a little although WinISD seems generally less flexible and a lot more glitchy so I normally stick to VituixCAD.

    I like how these sound, but I'm curious how much better things can get and curious where my own ear's point of diminishing returns lurks.
    Last edited by LOUT; Yesterday, 11:50 AM.

  • #2
    Crossover, because I didn't write it super clearly, is like this:
    Click image for larger version  Name:	Series Crossover.jpg Views:	0 Size:	583.8 KB ID:	1435106

    At the time PE sold 0.5mH ironcore inductors which saved a couple dollars for each speaker (they were around $2-$3 each instead of the $4-$5 for inexpensive aircore). I'm pretty sure the wood, parts, drivers and everything altogether for these totalled around $60-$70/pair.

    I think they should be able to reach about 97-100db/1m peaks from 40watts with some BSC. Music with really deep lows can make them run out of steam earlier; for example Lorn 555-5555 sounds happier about 6db down closer to 10watts while cranking it up starts to make the ends of bass notes sound extra fat and "boomfy". The ridiculous pc105's still refuse to bottom-out or do anything super ugly even when pushed with far worse, so I can't help but love them.
    Last edited by LOUT; Yesterday, 11:16 AM.

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