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new project > Push-Pull Bass +Coaxial

Twin box, bi-amped active btwn bass and coax, passive Xover for the coax (hoping for a modified 1st order series). Quasi M&K style push-pull / aperiodic vented & eq'd, targeting ~ 80% Qtc .707 Vb (per my shrinking box experiment I took it down to 70%, so backing off that minimum size a bit). This nets a bass unit 10.25W x 17H x 12.5D. Top unit will be ~open backed 10.25W x 7.5H x 6.5D (plus grills). Initial goal is to run the coax full above 300, so 1st order HP ~145 to 150Hz (depending on what it can do dB-wise in my room).

Started making sawdust- got the bass box mostly cut (was getting tired, so thought best to leave the mistakes for another day…).

jr@macSteve_Lee6thplanet4thtry
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Comments

  • I’m thinking about placing some small round indents (+/- 1/4 in deep) into the top of the bass unit to set and line up with small rubber feet on the bottom of the top box. Can I just run a ball router bit in my drill press or will it not spin fast enough? Thoughts / ideas ? Thx

  • I've used a router bit in my drill press, kinda depends on the RPMs options it has. That's actually how I cut the recess in the aluminum top of my Monument speaker for the little spike.

  • edited August 7

    Of all the many lines I can cut with a jig saw, straight and/or accurate are not in my toolbox repertoire.

    So, I’ve been fretting cutting the rounded-cornered rectangle at the bottom of my baffle (3/4 in ply) design.
    I'm thinking using a drill press to cut out the corners is a first step- and only getting close (maybe ⅛ to ¼) to the straight lines, and using some sort of guide and a flush trim bit - somehow ???

    Help w suggestions - thx

  • @6thplanet said:
    I've used a router bit in my drill press, kinda depends on the RPMs options it has. That's actually how I cut the recess in the aluminum top of my Monument speaker for the little spike.

    I thought the Pickelhaube on those cabinets was a nice 18th century aesthetic.

  • @tajanes said:
    Of all the many lines I can cut with a jig saw, straight and/or accurate are not in my toolbox repertoire.

    So, I’ve been fretting cutting the rounded-cornered rectangle at the bottom of my baffle (3/4 in ply) design.
    I'm thinking using a drill press to cut out the corners is a first step- and only getting close (maybe ⅛ to ¼) to the straight lines, and using some sort of guide and a flush trim bit - somehow ???

    Help w suggestions - thx

    You could use a round wood rasp with some backer board behind it and sneak-up on the corners after drilling some starter holes near the corners . . . you'll need to run that drill press spindle as fast as possible with a router bit in it and will be prone to grabbing the work piece but you could test it with some scrap to practice ahead of the actual work.

  • I would cut close to the line with a jig saw, make a template the correct size, double side tape it to the baffle, and finish with a router / flush trim bit.

  • @Steve_Lee said:

    @6thplanet said:
    I've used a router bit in my drill press, kinda depends on the RPMs options it has. That's actually how I cut the recess in the aluminum top of my Monument speaker for the little spike.

    I thought the Pickelhaube on those cabinets was a nice 18th century aesthetic.

    So that's what that's called...🤔
    I call it "shit! I drilled to far through....now what"

  • At least you are as creative as you are talented, dude - they look great.

    6thplanet
  • edited August 9

    To cut a straight line with a jigsaw I found I need 3 things: 1) patience - go slow / let the saw do its thing
    2) a thick(er) / solid blade, and 3) to quote George Michael ‘Gotta Have Faith’

    …and knowing I’ll be finishing the baffle in textured matte black didn’t hurt.

    6thplanet
  • Well, if it's what you got, it's what you got. Good job.

  • Duratex baffle, top & back to be matched with espresso stained / matte finished side panels.

    Steve_Leeugly_woofer4thtry
  • edited August 13

    This may be my first build w/o the need for a flush trim bit - ha

    6thplanetSteve_Lee4thtry
  • edited August 14

    While I designed the width of the speaker for dropping the bottom woofer in via the removable back, I hadn't thought about the size constraint presented by the 'frame' support for the removable back. Ooops.

    So, I improvised and cut in a little wedge to put in after the lower woofer gets placed. The wedge will get compressed (with blue painters tape as a gasket) as the back is screwed in place (with thin speaker gasket material). There will be a mirrored frame support on the other side (the other side is not yet attached in the photo).

    Also, what looks to be the making of a slot port > will actually be a tightly stuffed aperiodic vent.

    Steve_Lee4thtry
  • edited August 14

    Guess it would not fit in diagonally? Possibly not due to big magnet.

  • edited August 15

    There is another internal piece that is yet to get added to the A-Vent, and it’s limited by needing 5 inches for the depth of the driver. It’s seen lying flat in the previously posted pic - will line up approximately 45 degrees to the vent that is in place (you can see the penciled line).

    Now in place, with back temp placed.

    Steve_Lee6thplanet4thtry
  • edited August 17

    A little progress: bracing for the top panel, and fortunately I was able to re-purpose from the Celestion’s previous build (non-round driver face). The table saw cut through the previous box and felt w/o issue - so I can build the new box around it.

    Updated with start of coax top box build.

    4thtrySteve_Lee6thplanet
  • Separate grills for each unit, or one?
    (None when I’m listening by my lonesome, but these will be in the main room)

  • Separate would look better, imo.

    hifisideSteve_LeeBillet6thplanet
  • edited August 19

    The further I get, the slower the progress seems to be > impatiently waiting for pieces to glue-up before next steps. Right up there with waiting for water to boil. Anyway, now waiting for UPS delivery with a few internal pieces (connectors for between bass and top box - I’m going with 3.5mm couplers) and some additional damping material.

    My wife came in from the garage and said I see those cute little speakers you are making (with some hope for the main room yet). I had to break it to her those were just the top boxes…. In any event, these will be the same height (30 inches) as the current speakers - but on 5 inch stands vs the current ones on 10 inch stands (approx 4 degree tilt). But THEY ARE ¾ inch narrower and ½ inch less deep. I tried. Current ones 11W x 20H x 13 ½ deep. The new ones look to be coming in at 10 ¼W x 24 ⅞H x 13 deep. The second pic shows top unit with two rubber front feet, the back third (middle placed as its easier to level a 3 legged stool) will be a ¼ in piece of felt.

    kenrhodes6thplanet4thtrySteve_Lee
  • Very nicely done.
    Have you tried any automotive triaxials in those sort of open backed boxes?
    I'll bet a 6X9 JBL could sound great with a little EQ in a small box of this sort . . . and then they could become "cute little speakers" with punch, depth and imaging.

  • edited August 21

    Years ago I took a week’s + vacation to learn from a woodworker (he actually at one point worked for a small speaker company, had a couple of big dynaco mono tube amps). Anyway, the top was a 5x7 polk coax (sorry guys) and the bottom was a folded horn with a 9in morel. I didn’t bi-amp back then- but guess I’m coming back to my twin box roots.

    And, fyi the top box was a sock covering stapled along the bottom - mad sewing skills ! Ha

    Steve_Lee4thtry6thplanet
  • edited August 25

    separate grills it will be… the smaller grills for the coax box will have felt along the inside of the frame- fw its worth.

    & now time for a little elbow grease…

    hifisideSteve_Lee6thplanet4thtry
  • Spent what little time I had today smoothing out the edges of the grill frames, and set the magnets in the grills and the boxes.

    Also cut to fit metal grill coverings / slightly recessed into the bottom of the bass unit. The bottom reversed woofer will be open through the front baffle, but also to the bottom (and open stands) so thought it best to provide some protection from the woofer from underneath.

    6thplanet
  • I like the look of wood / stained baffle with flat dark painted sides but I need to go with grills so I opt for the other way around.

    Baltic birch does pretty well with darker espresso stain - just need to use a pre-stain.

    Steve_Lee6thplanet
  • edited August 30

    Some initial fitting of the grills and stands,
    a bit more finishing (flat top coat and add’l roll of black on top, baffle, and stands) and then onto internal dampening/ felt and poly etc. and _finally_loading the drivers for measurements.

    I’m looking to compare the 2x 8in push-pull woofers vs my previous 8in W (same driver) + 10in PR for both roll-off low extension and distortion. Thinking while the 8+10 in PR hits lower at -3db biz surface advantage, I’m actually more interested in targeting a much less severe rolloff and looking at -6 and -10dB levels. Additionally will look at distortion / impact of a PR (similar to ports) being both a bit behind the 8 ball (the 8 in woofer), as it as with a port, are reactive. Being reactive- distortion levels - that of the signal vs the PR may be telling.

    Steve_LeeDrewsBrews6thplanet
  • edited August 31

    Wow, the grittiness of the grain after stain gives an interesting visual texture in contrast to the chunkiness of the enclosures. Enough so the eye doesn't get bored with all that real-estate. The stubby chunky feet are fitting too. Looks like something I'd want to walk around and experience from all angles rather than just sit in front of. Nice!

  • edited August 31

    Thx, I used to just clear coat- which I liked, but tends to look a bit IKEA / Scandinavian, which doesn’t fit into our more rustic place.

  • edited August 31

    I see what you are saying, for me that comes from geometric nature of the different size enclosures. It actually gave me a Japanese vibe initially. Though the colors I think would still not look too out of place in a rustic environment.

  • edited August 31

    While not a fan of making grills, especially glueing and getting the corners somewhat tight, I’ve found a couple of things that help. 1) pass on the PE grill kits (unless you are doing a subwoofer) as the lip design is IMO very poor- think an inward directed L beam. Make your own > I use quality ply, and triangle corners - support and a place to set magnets. 2) I found a contact cement in a tube (ACE hardware)- so you can just run it along the frame and give it a minute or two and it holds enough to do the opposite side, and then repeat for the top/bottom. I’ve tried the glue gun, but I’d rather get a little contact cement on my fingers… and the stuff (glue gun plastic) hardens up too quickly. With contact cement you can pull it and reset if necessary. And 3) the only way I’ve found to get the corners right is by using a compressed air staple gun with ¼ in staples. If you are a bit messy (like me) and have a little extra contact cement from the sides get to the corner- all the better! Pull it tight and press the stapler down hard to get a tight staple. Then just go around with the better half’s best scissors and trim off the balance of the cloth. And, mineral spirits to clean off the scissors before soap and water and get ‘em back into the drawer…. I’ve attached a couple of pics of the grills and a comparison of my new build vs my previous for size comps. I’m debating (even before the drivers are in) just making the top box all black, and a bit less deep - but that’s for another day. Final black coat not on as of yet. And, don’t they look smaller than the current ones ? Ha

    4thtryRon_ESteve_LeeColonel7
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