Bravox-TangBand Bookshelf Build - AVS Forum
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post #1 of 55 Old 02-02-2012, 08:11 PM - Thread Starter
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I was looking to build some small bookshelf speakers for a mini cd receiver my wife just bought. PassingInterest happened to have a set of components he wasn't using and I was lucky enough to be the recipient of his good will. Many thanks PI. The origin of these components was GarciaB - to whom I also would like to extend a hearty thanks. You guys are both promoting a great sense of sharing in the DIY community.

This build is based on this design:
http://www.partsexpress.com/tech/269-680.html

The mids are no longer available so i guess i can't hope to inspire any duplicate builds, but i thought i'd share my first experience trying to build a curved box.

I did some reading on kerf-bending MDF and decided to give it a shot. The mids only want 0.05cuft each, which lead to a pretty small box design.
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post #2 of 55 Old 02-02-2012, 08:28 PM - Thread Starter
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I decided on a 10" tall by 5" wide baffle... with that i calculated about a 10" depth. That was actually incorrect. I accidentally calculated for a box volume 2x bigger than i needed. I remembered the wrong cu-ft figure when doing the math in my garage and didn't realize till all the wood was cut - i modified my design later to account for this.

I figured i'd use one long piece of mdf to create the flat front baffle and then curve around for the bowed-out sides... then i'd attach the rear panel afterwards. I was playing it by ear. I ran deep kerf cuts every 1/2 along the part of the mdf strip that i planned on bending. Then i wet down the kerf'ed area and try to get a feel for how much i could bend it.

Well.. as you can see, the result was 2 pieces of mdf.
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post #3 of 55 Old 02-02-2012, 08:38 PM - Thread Starter
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Plan B - i would independantly bend the kerfed pieces of mdf into a reasonable curve and then attach the flat front and rear panels. I sort of eye-balled how much curve i thought i could safely get from my kerfed panels. Then i made a form to wrap them around.

I followed some directions i had read about - i covered the panels with PL adhesive then forced it into the kerfs with a drywall knife. I wet the boards then wrapped them around my ~11" diameter forms and strap-clamped them in place overnight.
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post #4 of 55 Old 02-02-2012, 08:47 PM - Thread Starter
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The following day, the curve seems to have held pretty well with the PL. I tried wood-glue as well as PL, but that did not go as well. The wood glue dripped down the kerfs before it dried and left a gloppy mess on my tabletop.

My table saw's blade was on the way out and now it's completely finished from the kerf cuts. Waiting for a new Freud Diablo from Amazon - hope it's good.

Another important note: wearing a mask when making this many cuts in MDF is probably a good idea. I don't want this stuff in my lungs.
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post #5 of 55 Old 02-02-2012, 08:53 PM - Thread Starter
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About this time i realized i built for 2x the volume by accident. I decided to just cut the sides in half to get about a 5" depth instead of 10". I recut the front and rear panel miters at about 45 degs and everything matched up pretty well after some fiddling. I strapped everything together and let it dry over night.
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post #6 of 55 Old 02-02-2012, 09:04 PM - Thread Starter
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After gluing up the first cabinet i realized it might have been a better idea to cut the speaker holes before assembly. Before assembling the second box i cut the holes. Then i cut the holes on the first cabinet. To my surprise, i think it was actually easier to work with the assembly cabinet. Both came out pretty well but I cut it VERY close... not much meat left around the midrange driver cutouts.

The curve is *very* subtle. One might say - not worth all that work - - but it was a good learning process. I would probably try the kerf bend technique again, but probably cut the top and bottom panels first, then try to create a single kerf'ed strip that wraps all the way around. That might be harder than it sounds but i'm worried that the miter joints won't clean up so nice and will be difficult to veneer cleanly on this project. A single 360deg wrap won't need any mitered edges
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post #7 of 55 Old 02-03-2012, 07:14 AM
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Looking good, Joe.
You got the curve just right for the cabinet size and definitely worth the trouble.
And for the record, our AVS friend GarciaB deserves the credit for the parts used in this build.
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post #8 of 55 Old 02-03-2012, 07:41 AM - Thread Starter
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Thanks PI.

Late last night i remembered you had credited GarciaB in your original post and i forgot to include him in the start of my thread. My bad.

Thanks GarciaB!
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post #9 of 55 Old 02-03-2012, 08:55 AM - Thread Starter
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When i walked through my garage this morning to head out to work i remembered why i had wanted to route the holes in the baffle before assembly - not just because i thought it would be easier, but because i wanted to able to chamfer the back of the baffle for the mids.

Can't do that now that is unless there's a reverse-chamfer router bit out there. Something with a bearing on the opposite end so i could route the back of the cutout by placing the the router on the front of the baffle. Wonder if that animal exists?


AWESOME - found it for a mere $101. lol

http://www.amazon.com/Festool-492704...8288834&sr=1-2
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post #10 of 55 Old 02-03-2012, 09:10 AM
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Cool stuff. Thanks for sharing.

You could maybe use a dovetail bit carefully. No bearing, but most router bit kits contain one, and you could just free hand it carefully. I've done it. Works like a charm.
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post #11 of 55 Old 02-03-2012, 10:14 AM
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You could just grind the backside with a small drum sander in a drill.
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post #12 of 55 Old 02-03-2012, 10:33 AM
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Those look like they'll turn out great. Thanks for sharing! And you too PI!

I peeked in to see if this was 'that' project, and was pleasantly surprised to see that it's actually my contribution being put to good use. Good times!

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post #13 of 55 Old 02-03-2012, 10:36 AM - Thread Starter
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Good suggestions guys. I have a dovetail bit and a drill and dremel with small drum sanders. Could definitely try both approaches.

How are those router spacer/guide things used? For pattern cutting or something? Don't they take the place of a bearing? Ive never used them and don't know exactly how they work - could they be used with the dovetail bit to help keep me from destroying the hole? Do they attach to the router or the router table? I'll have to do some research
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post #14 of 55 Old 02-03-2012, 10:40 AM - Thread Starter
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Quote:
Originally Posted by garciab View Post

Those look like they'll turn out great. Thanks for sharing! And you too PI!

I peeked in to see if this was 'that' project, and was pleasantly surprised to see that it's actually my contribution being put to good use. Good times!

Hey! Thanks for stopping by and thanks for helping make this project possible
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post #15 of 55 Old 02-03-2012, 11:08 AM
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Quote:
Originally Posted by lowpolyjoe View Post

Good suggestions guys. I have a dovetail bit and a drill and dremel with small drum sanders. Could definitely try both approaches.

How are those router spacer/guide things used? For pattern cutting or something? Don't they take the place of a bearing? Ive never used them and don't know exactly how they work - could they be used with the dovetail bit to help keep me from destroying the hole? Do they attach to the router or the router table? I'll have to do some research

Guide bushings attach to the router's base plate.

I'm glad to see you found this build thread GB! I meant to send you a PM, to make sure you didn't miss it, but it slipped my mind.
Joe will put these to good use.
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post #16 of 55 Old 02-03-2012, 09:00 PM
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Quote:
Originally Posted by lowpolyjoe View Post


The curve is *very* subtle. One might say - not worth all that work - - but it was a good learning process.

I think the curve looks great.
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post #17 of 55 Old 02-04-2012, 04:56 PM - Thread Starter
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Thanks for the encouragement Erich.

Today i decided i might as well use all the drivers PI/GarciaB sent my way, so i bent a few more panels. In addition to the two cabinets i'm working on already, i will be making a 3rd very similar cabinet for (possible use as a center channel) and then two smaller cabinets that will be 1-mid and 1-tweet.

If all goes well i will end up with everything for a 5.1 ht setup except the sub. For the time being i plan on using these for my wife's cd/ipod player but it would be cool to have the option to put them to work as a secondary tv-room ht system at some point in the future.
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post #18 of 55 Old 02-04-2012, 05:08 PM - Thread Starter
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I'm planning on veneering these little guys, so i figured I would do a little prepwork. I was getting splits and cracks in the last few projects i veneered, so i thought i should try using some veneer softener to help reduce those issues. I have a box of random species from veneersupplies.com. It includes some crotch mahogany that is *very* difficult to work with (by my standards). It also included a light colored species with a nice figure to it which i plan to use for these cabinets.

I tried the softener on the mahogany and the other species just to see how both reacted. I sprayed them pretty wet on both sides and slapped them between absorbent paper and two sheets of mdf with weights on them. I changed the paper a few times until the veneers were dry.

I wasn't overly impressed with the results. Not as pliable as i hoped, so i repeated the process. Still didn't quite meet my expectations, but definitely an improvement over non-treated. Perhaps i applied the stuff wrong or there is an issue with the fact that it's pretty cold in my garage?
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post #19 of 55 Old 02-04-2012, 05:21 PM - Thread Starter
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One shot here shows the third cabinet i started on today. It is intended to be a horizontal center channel. Who knows how that will work out since it deviates from the original design. I had to make one of the curved sides flat since that will be the side it lays on, other than that, it's the same as the other two.

One thing i'm getting a little worried about with these *tiny* cabinets is how/where am i going to fit the crossovers. Ill probably try to assembly one today or tomorrow to see how tough it's going to be.

The tweeter in this build does not fit in a simple round cutout. Today i took on the task of trying to mod the cutouts to get everything fitting nicely.

I put the tweeter in as far as it would go, then traced the outline as best i could. Then i took a file and went to work making space where needed. After a while i finally got the tweeter to fit but it seemed like a slow process so next i tried using the router table.

I put a straight cutting bit in the router and again marked roughly were i needed to make some space. That was much quicker but that sort of free-hand work is (apparently) not my strong suit. One of the two cabinets i used the router on resulted in a sloppy oversized tweeter cutout. I think it will still work out, but it's pretty close to being too-big. I think the file is a better approach since it's harder to screw it up. Anyone have a better way to do this sort of thing?
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post #20 of 55 Old 02-04-2012, 05:25 PM - Thread Starter
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It was at this point in the afternoon that i did something so foolish that i have not yet decided if i'll share the details with you. I was REALLY just not thinking and did something that put a big divot in the front of one of the cabinets. I'm attempting a repair overnight but i may have to ditch that enclosure

I must have been distracted by thoughts of Diaz-Condit tonight
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post #21 of 55 Old 02-04-2012, 05:28 PM
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Added this to "Master Index of DIY Speaker Projects" which is still not stickied for some reason...
http://www.avsforum.com/avs-vb/showthread.php?t=1334432
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post #22 of 55 Old 02-04-2012, 05:32 PM - Thread Starter
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Quote:
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Added this to "Master Index of DIY Speaker Projects" which is still not stickied for some reason...
http://www.avsforum.com/avs-vb/showthread.php?t=1334432

+1 to sticky that thread. it's a very valuable resource when looking for walkthroughs of proven designs or random inspiration.
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post #23 of 55 Old 02-04-2012, 05:56 PM
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I'm attempting a repair overnight but i may have to ditch that enclosure

If it is too much for Bondo to fix, use an epoxy putty. Hardware stores sell it and automotive stores sell it. It's really easy to use. You slice off a piece and knead it like bread dough. Then apply it to the damaged area and wait an hour for it to cure as hard as a rock.
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post #24 of 55 Old 02-05-2012, 05:08 PM - Thread Starter
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Thanks for the advice. I was hoping to have exposed MDF for consistency in the hopes that veneering would go smoothly over the patch. I filled in my monster divot with thin slice of kerfed MDF that i bent and glued into place.

After drying overnight and then some cleanup work with the sander and a file, it seems like it could work out OK. I don't have a pic after hitting it with the file - the final product looks a bit better than this "after" pic suggests. we'll see if any other issues crop up due to this...
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post #25 of 55 Old 02-05-2012, 05:46 PM - Thread Starter
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Overnight i had glued top and bottom panels on one of the cabinets. Today i was ready to put my new 1/2" flush cut router bit to work and cut down the overhang.

Anyone who has performed this operation before (i have not) may see the problem straight away in the first two pictures. The bearing does not have a brain... it follows the workpiece. If there's a big hole in the workpiece... say a 3 1/2" speaker cutout, the bearing dives headlong into the hole and you get a big fat chunk out of your front baffle. The moral of the story is to make sure the bearing will ride on solid wood as close to the edge as possible. After adjusting the height of the bit, i finished removing the excess.

This was very disheartening after i had just finished working on my repair from a previous screwup. This time i decided to try wood glue + MDF dust... mostly because there is about an inch deep river of MDF dust on my floor and i figured i might as well use some of it. Tomorrow i'll see how it sands out. Fingers crossed.
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post #26 of 55 Old 02-05-2012, 05:56 PM - Thread Starter
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I started assembling the rear-channel 2 driver cabinets today. This time i was able to add the rear-chamfer to the driver cutouts prior to assembly as i should have done with the original cabinets. These smaller speakers will be about 6" high instead of 10" and only have one midrange. The crossover network is slightly different. Otherwise they are pretty much the same.

I also picked up some more MDF so i could glue top and bottom panels to the other 2 full height enclosures.
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post #27 of 55 Old 02-05-2012, 06:06 PM - Thread Starter
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I figured i had done enough damage in the woodworking department today, so i started working on the crossover assembly. To be honest, I'm pretty nervous about fitting the crossovers in the cabinets - especially the half-height ones. I had to split the woofer and tweeter networks up into two boards in hopes of getting them to fit.

I have some electronics experience but i admit i've never wired up a crossover myself. I used some thin plywood and traced out a circuit that would most efficiently fit the components to conserve space. I started some soldering - i'm seriously out of practice in that department. I picked up some industrial velcro that i plan to use to stick the xover boards to the sides of the enclosures. The one large(ish) inductor on the woofer network was not held in place by its leads so i zip-tied it in place (not shown in this picture). Do i need to hold other components in place with zip-ties or hot glue?

I'd appreciate it if anyone could comment if there are any problems with how i'm going about this.

I'm almost out of lead-free solder but i have some old rosin-core stuff (60/40). Is there a preferred solder for this application?
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post #28 of 55 Old 02-07-2012, 07:21 AM
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I remember reading a Tom Swift novel when I was a kid. His plane crashed and wrecked his radio. He rebuilt it using a slab of wood for a "mother board", using conductive pencil lines in place of copper traces. Pretty fanciful? yes

Wood is a good enough insulator (when dry) but I wonder if what you used to draw the component outlines and connections is conductive.

I'd also make sure you have a good air gap between the power resistors and the board.
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post #29 of 55 Old 02-07-2012, 07:44 AM - Thread Starter
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Quote:
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I remember reading a Tom Swift novel when I was a kid. His plane crashed and wrecked his radio. He rebuilt it using a slab of wood for a "mother board", using conductive pencil lines in place of copper traces. Pretty fanciful? yes

Wood is a good enough insulator (when dry) but I wonder if what you used to draw the component outlines and connections is conductive.

I'd also make sure you have a good air gap between the power resistors and the board.

That is an excellent (tho slightly tragic) point. I did use a pencil to sketch out the circuit path on the top side of the plywood without thinking of that. A little research online suggests that you are correct. The graphite does have conductive properties. Thanks for pointing that out. Hope i can find my desoldering iron...
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post #30 of 55 Old 02-07-2012, 08:29 AM
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Joe--the solder type won't make a difference for your application (leaded or lead-free). Also, the graphite paths probably won't make any difference at the frequencies involved, but if there's any doubt, you can just use an eraser to "break" the paths without de-soldering. In other words, you don't need to remove every pencil mark, just break any point-to-point paths.
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