( ( ( ( s h o c k w a v e ) ) ) )
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objectives
inexpensive 3-way with a coaxial driver and 7" woofer
meant for desktop nearfield listening
aiming for f10 of 35Hz
very close to sealed, overdamped impulse response
group delay x frequency under 400 rule being followed
mdf - silicone - tile constrained layer sides, top and bottom
linear phase crossover
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drivers
rockford fosgate r1675x2 6.75" coaxial driver
vifa/tymphany pl18wo-09-08 woofer
parts express #299-018 buyout passive radiator
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plan of attack
concept
design
c.a.d.
sawdust
glue
cut holes
finishing touches
measurements
crossover design
buttoning up
finished
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concept
so i've been helping out my parents build a house lately mainly because they're letting me live in it rent free while i'm in school. new room for grey means new battlestation since i'm a total computer gaming nerd. one thing i've never had is some really nice looking speakers on my desk and i need to remedy that.
i bought the vifa woofers from mr. scott quick a while back and needed to put them to purpose. i really love the aesthetic of coaxial drivers, having two in one really cleans up the baffle and allows for a more compact design, which is great because i over-engineer everything and like to try new concepts for each build.
a few months ago i stumbled upon this rockford fosgate driver while looking at car audio stuff. wow, they're only $40 on amazon prime and would you know it, i got a $25 gift card from the parents for xmas.
modeling the woofer hundreds of times and slowly working out a shape and various alignments. sealed is great quality bass, but i've done 3-4 builds now with sealed. ported is too "floppy" - if i may - and balancing the port volume and enclosure volume is tricky, not to mention i need a 2.5" port in a .5cf box which is silly huge, and in turn, ventures into peter north territory.
so i opened up parts express' website and looked for a passive radiator, size doesn't change, so it's more simple than a port. first one i picked, i get a similar response to sealed, but with more booty, and my anaconda don't, so that was the way to go. group delay, what's that? did a little research, and read about the 400 rule (frequency x delay in ms <= 400) and tweaked my box size a little to attain that quality. gotcha. unibox (sorry bagby, i just prefer unibox still) says the impulse response is nearly identical to the sealed, over-damped impulse response, which i used in my last build and i loved those speakers, didn't want to give them away, but they're being enjoyed by a real vinyl lover, my bff.
so the new things i'm trying out this build are: coaxial driver, passive radiator, constrained layer, (possibly) hardwood baffle, and distortion measurements. This will also be my second ever passive crossover.
finally the name, in case you were wondering is my favorite transformer, he's only got one eye (coax driver looks like an eye).
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design
with this being a desktop speaker, they need to be compact, but not too compact because i have a pair of 27" monitors that i use.
after tweaking the design a bit i experimented with a piece of birch, silicone and tile, to see if it compresses and after a couple weeks, it's still sitting pretty at 29mm thick. 19mm for the wood, 3mm of silicone and 7mm thick ceramic tile. so i fired up boxycad and 1.1412" thick top, bottom, and sides. the front and rear baffles are different monsters, they'll be 1.5" thick on the backside, and a total of 2.25" on the front with a normal 3/4" baffle and recessed drivers and a "facade" 1.5" thick with some fancy (to me) router work.
the mid/tweet coaxial driver will have it's own compartment, which i sized to make the woofer compartment the correct volume. which leaves a small amount of room for the crossover between the woofer and passive radiator, or in the tiny compartment in the back of the box.
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c.a.d.
i have been using eMachineShop forever now, so that's what i use to draw stuff up and do simple 3D like the baffle, etc. the massive 1.5" roundovers and 1.375" chamfers are only meant to be aesthetic, but will probably just introduce some wiggles into the frequency response due to their size, no doubt. here's what i've got so far:
this is as far as i have gotten, and i'm hoping to be able to cut some wood tomorrow, stay tuned for updates!
Comments
i finally got some wood cut! everything is on the money except the tops, bottoms, and braces are only 1mm off! also did a mockup to see how fracking huge they're going to be and they're going to be fracking huge. finally I will definitely need to do the crossovers externally because there will be little to no room inside the cabs for crossovers. i will move on to the router work over the weekend possibly, we're still very busy with moving and getting settled into the new house.
girlfriend's sister came to visit, so i ended up working on these all day long! first i had to go find my handheld router, and it had gotten wet, so it's all oxidized and rusted up, unfortunately, but still works like a charm. when i finally got the bit installed and tightened down, i rounded over the cutouts on the braces, when ended up looking like a kinda nice turd. I thought to myself, "never mind them, they'll be inside the box, nobody will see them." and proceeded to begin gluing up the first box...
... at which point i realized that the holes in the braces, which were supposed to create extra airspace for the woofer, were cut on the side of the brace instead of the rear ughhhhhhhhhh. so i had to create new braces, but had limited scraps, so i cut pieces big enough to replace the holes wrongly cut in my original braces. Well, the new braces turned out much nicer, and aren't quite turds.
so now i can start gluing up panels... no. i actually decided it would be easier to attach the ceramic tiles to the inside of the enclosure while it's open. so then i setup the tile saw and marked all the tile to be cut. this was probably the easiest thing i've ever cut in my life, especially having never used it before.
so now i finally started gluing up panels. my plan is to glue up the brace (which was the first one I glued up), top and bottom. then onto the side panel tiles, then top and bottom tiles, finally onto the front and rear baffles. I'll get started on those in the morning.
thanks for tuning in!
silicone & tile
i spent the entire day yesterday working on these again, feels great. anyway, i started with the silicone and tile, pretty messy endeavor. so what i did was lay down a bunch of silicone (the one speaker carcass used 3 whole bottles of silicone caulking!) and used some little pieces of 1/8" aluminum rod for spacers, dropped the tile in place and weighed it down with some bricks we had left over from the house. This took pretty much all day because i did two side pieces, left it to dry for 30 minutes, other side pieces, top, then bottom. 10 minutes of work, and 30-40 minutes of drying time. then i went back and filled in between all the tiles with silicone, so they will never touch one another and aren't touching the wood either.
Also, forgot the knuckle wrap test
Yeah I did a little bit of reading up on constrained layers before I tested out this combo. Then I bought a small piece of 3/4" birch and siliconed a tile to it. Measured the thickness and compared "knocks" and decided it would work well enough to try. I'm headed to the "gittin' place" for some more silicone and other doo-dads to get started on attaching the tile to the second carcass today.
What do you think?
ps - black silicone is $4/tube and clear is $6/tube...
Got some more work done on the second cab yesterday before work, bought some more silicone, too, I'm about to get started on attaching more tile today, should have the cabs finished up this week!
When I did this in the first box, I was having phone problems and couldn't take any pictures. This is how I aligned and siliconed in the mid-wall, the wall that separates the coax and woofer enclosures. I measured and trimmed the mid wall to be 1/4" smaller than the opening and taped the 1/8" aluminum rods into the area where the wall goes, then I squirted some silicone into the areas around the sides of the panel. Pretty simple, and works. In an hour or so I'll go back and do the backside, then lay the enclosure down and do the vertical sections, I just don't want the silicone running (it probably won't but I don't like leaving things up to chance like that)
I have heard some pretty good sounding car speakers and that is in an environment that sucks for speakers.
I *SHOULD* be getting some router work done this week and then mounting the speakers in the box for measurements. It's been a loooooong time since I've done measurements and I'd like to do some THD measurements this time because I never had and that has quite a bit more to do with sounding good than FR does, IMO. It would be badass if I could actually have these buttoned up enough to take to Iowa DIY (and if I'm able to go in the first place).
Your tiled boxes remind me of these btw. Tiles really do deaden a box. http://techtalk.parts-express.com/forum/tech-talk-forum/52993-killa-continuum-build-thread