MA Audio MA80XE 8" Dual Opposed

After my recent 5 channel build i was is sore need of a little low end filler. This system is not for hard core listening, but the mid drivers don't do much under 200hz so you definitely notice that something's missing.

I had a 10" JL sub that i was considering adapting for the job. But it's currently sitting in a custom fiberglass box i made for my wrx and i'm thinking of maybe selling the car soon... target audience for that car would probably appreciate it if i threw that in with the sale, so i figured i might try something else. Before i had much of a chance to research my options, PI stepped in with an incredibly generous offer to donate a few 8"s he wasn't using. Very much appreciated sir

My goal is to make something visually appealing and matching in looks to the 5 channels it will compliment. I've never built a dual-opposed design, and i'm not sure this qualifies (there is no shared chamber), but attached are some Sketchup renders of what i have in mind. It will be two separate ported chambers, one for each sub, with the drivers facing eachother and the ports facing eachother.

The subs in question are car-audio models and are very showy, with big writing on the front... This is not a showy system so i would like to minimize their display somewhat. Bottom firing is also an option, but i thought this idea seemed unique and kind of cool. I plan to make some cloth grilles to cover the subs as well.

Each ported enclosure will be about 0.4cuft... i knocked a little off for driver displacement and came up with the attached WinISD model, tuned around 50hz. Note that ports will actually be external to the chamber, hidden in the curved 'legs' on the sides of the enclosure. I tried larger chambers tuned lower, but they didn't model well in my opinion.

Kind of curious to hear feedback... the open space between the subs will be a relatively large cavity, but still, the fact that they fire into a somewhat confined space is the biggest question mark in my head. I might give it a shot regardless of feedback but i'd still like to hear what the drawbacks might be.

Thanks,
Joe

Thanks for the feedback guys.

Agreed about the HT potential of this setup. That tune is startlingly high. I would not have expected super low extention from car audio 8's so it is what it is. Large sealed boxes result in falloff starting very high up... i couldn't find an acceptable configuration. Initially the Bravox-TangBand setup was going to be 2 channels and was intended for music only. I ended up building 5 channels because PI donated enough of the Bravox mids to create a full HT setup and i didn't want to see them go to waste. I'm glad i did it because now i have flexibility in their use.

HOWEVER - I'm somewhat embarassed by the fact that i can't remember where i got the T/S params for these 8's from. I did a search last week, popped some numbers into WinISD, and started fiddling. Before posting those numbers in this thread i was going to look for the source - but now i cannot for the life of me find them online.

I thought i had gotten them from sonicelectronix, but now when i go there i don't see them listed anywhere. It says "discontinued" on that page now - i don't remember it saying that the first time i visited . After a bunch of searching, i'm out of ideas. Cannot find those damn params anywhere Looking at my browser history i see a few relavent sites from the previous week, but none list the params. Truly don't know where i got them.

The values i had are listed below, but now i'm not sure how much weight to give them at this point

Qts : 0.31
Vas : 0.753 cuft
Fs: 38.31 hz
Re: 1.5 ohm (dual 4ohm in parallel?)
Le: 0.71mH
Xmax: 10mm
Z: 2Ohm (dual 4ohm in parallel)
Qms: 4.23
Qes: 0.34
SPL 87.28
Pe: 250.


Not sure how to proceed now. I've never measured params before but maybe i'll look into it. Going forward with theses unvalidated params... i don't know... if they are correct and i just get a high-tuned music-only sub, that's fine, if they're not correct and i end up with complete garbage, that would be frustrating.

Zora - that might indeed be the safe way to go. I'm thinking now that i'll turn this into a sealed build with the current ported volume. Then i can build a little MDF block to take up some volume and see if it helps. I'm also considering making a little removable 'window' leading from the main chamber into each 'leg' of the build.... if i replace the subs down the road with something that does well in an even larger sealed box, i can remove the window and give it a little more space. Are 8" sub cut-out holes and screw holes fairly consistent across brands? i fear not.... or rather, i fear they are not consistent.


First the materials. These are the 8's and here is the Prima Vera veneer i'll be using to try to match the sub to my Bravox build.

I chose the radius of curvature based on how much space i thought i needed for the ports i planned on using... they were originally supposed to pass out of the top and bottom chambers, through the hollow 'legs', then exit in the center void of the design where the woofers were mounted.

There won't be any ports now, but i kept the same radius... something like 6.5". I routed out some ~13" circles. Then i built my first tablesaw sled by making a little guide out of a thin piece of MDF and glueing that to the bottom of an MDF panel. For furture reference, don't use MDF for the guide... it was too fragile and part of it ended up splitting. I got some use out of it, but next time i guess i would try to cut it from a 2x4" or something... anyone care to comment on what is the correct material to make that guide piece from?

I secured a circle to the sled and sliced off the arcs i needed to form the skeleton of my curved legs. After i had made a couple, i just used the router table to duplicate them with a flush-cut bit.

I can't stop thinking about building lately I'm already thinking about what to build next... it's like i have woodworker's attention deficit disorder.

Didn't occur to me to wax up the runner - great tip, thanks!

I treated my tablesaw to a nice new Diablo blade recently. Helps a lot. Now i have to figure out how to square up the movable fence... lately when i lock it in place it seems to angle itself such that the wood gets closer to the blade near the back of the table. Hope i can find some adjustment screws or something.

I went with the kerf-bending approach for the curved panels. Making all those cuts in a 24"x17" piece of MDF made tons of dust. Don't think i'll be doing kerf bending on anything this big again... the new blade helped tho.

I did a less than stellar job of filling the kerfs with PL... the legs were not designed to be pressurized anyway.

My initial idea for bending the panels to the desired curvature was to create a skeleton and strap-clamp the kerf'ed board in place. it seemed like a good idea at the time, but as you can see in the pic, it didn't work out very well.

I left a little overlap so i could cut it flush against the panel it is supposed to match up with. This extra piece bent over the edge of the form and turned into a big mess - splitting and cracking.

I ended up with a formed panel, but it's not pretty. I'm hoping i can force it into place, patch it up with some bondo, and still get to use it.

Alternative approach to making the second formed panel - i used the cutouts from the circles in a previous step as negative-side-reinforcement. It worked out pretty well... better than the strap clamps

Because the design has a void in the middle, the boards that will show on the inside have to be veneered before assembly. This evening i decided to do the first panel. A few things made it more difficult than i hoped.

Firstly, the widest Prima Vera sheets i could find on Veneer Supplies that were long enough (24"+) to fit my build and matched the look of the Bravox build were only about 5" wide. That means a lot of seams. My hand-veneering skills are relatively limited and i still can't manage great seams. Tonight was a vivid reminder of that.

Secondly, i put he first seam together thinking the edges were square and clean... turns out they were less than perfect. For the second seam i tried the "overlap-then-cut" approach. It helped a bit, but i still couldn't get it nearly as tight as i'd like. Further complicating things was the fact that i ran out of one type of hide glue (192 gram strength i think it was?) and had to use some other stuff i had (251 gram strength) that is harder to work with. So i'm thinking i order some more 192 or try my hand at the heat-lock technique.



The next day i did a little more veneer work. The overlap-and-cut worked a little better for me when i ran some blue tape down the back of the seam and then cut through the front. I'm always using a piece of mdf as the straight edge. The thick edge helps keep the veneer saw perpendicular and limits the risk of running over my fingers. I also read a steel edge can discolor veneer (maybe only if there's moisture involved?)

I'm disgusted by my lack of planning for this build. Today was time to try to apply one of the curved panels. It wasn't pretty.

PI's two simultaneous curved builds are both very impressive and super informative - great stuff, as always. Any future curves i attempt will probably use custom jigs and laminate layers of 1/4" MDF. I noticed last week that my local Home Depot does carry it - limited to 2'x4' sheets but that's all i can fit in my car anyway

Thankfully i remembered to run speakerwire from the top chamber to the bottom through the leg before attaching the outer shell. I trimmed up one of my formed curved panels to fit in place, then tried various approaches to snug it up to the skeleton. I thought i might be able to do it with regular clamps at various angles, but it didn't work out. 3 strap clamps tightened within an inch of their life proved enough to get it into place.

I sort of planned for a bit of overlap so i could trim flush and then backfill the crack with bondo. It's ugly looking but it's too late to turn back now.

This seam is not part of the air-tight chambers, so it just has to look good, doesn't have to be sturdy. That raises the question - why didn't i use something easier to bend than 1/2" MDF? I really don't know. Part of me was worried it might rattle or something. Mostly, i guess i just wasn't thinking

The box design calls for creating two legs with the curved panels shown above. Then secure two independant enclosures between them. I did some work on the sealed chambers the last two days.

Because it will be difficult to veneer inside the void at the center of this design, i had to apply the Prima Vera to the baffles before assembly. The flat panel of the half-moon shapped legs will provide two of the six walls for each of the chambers. The top chamber only needs the bottom (baffle) applied because the entire top of the cabinet will be a single panel of MDF. The bottom chamber needs top and bottom applied because the 'feet' of the legs will stick out an inch or two past the bottom of the chamber and there will be no MDF panel holding everything together.

i did have a design from the start - there's a couple of reasons this build turned into a mess. part of the problem was the timeline.

1 - i got the heads up that some donated drivers were heading my way

2 - i came up with the idea for the dual-opposed facing design and designed the box in my first post using some T/S params i found online

3 - i cut most of the wood for the build and started some assembly

4 - a week later i couldn't figure out where i got those T/S params from and lost faith in the accuracy of the design... as zora suggested, i switched from a super high tuned ported to a large sealed design that i can later fill with blocks to tune as needed.

by this time i had a good amount of the box assembled and i really want to see what the design will look like. i decided to go forward with the build.

things are going epicly bad, but figuring out how to deal with problems during a build is a good learning experience.

no idea what this thing will sound like, but it will probably just do light duty as a music sub anyway. hope it looks halfway decent

made some progress today... at first good, then bad.

routed out the countersink and the woofer holes. fit nice and snug. dropped in one sub for a test fit. looked pretty good, till i realized the basket of the sub was taking up more space than i planned for. i grabbed the Bash plate to confirm the miscalculation. indeed, the depth of the plate amp was hitting the basket of the sub.

after a little jumping up and down and stamping my feet i decided i'd just have to bump the plate amp out a bit. it's gonna be an eyesore but in any placement, hopefully that side of the sub will face the wall anyway. i couldn't think of any better alternative.

i made a few frames that i'll slap on the side of the enclosure that will bump the plate amp out a few inches and give me the clearance i need. i tried to cut the frames out with a jigsaw but it was tedious and sloppy. I ended up cutting strips of MDF and glueing them together.... much cleaner and a lot easier

also took some time to cut out 1/2" mdf panels with large holes that i'll cover in grille cloth and use to cover these vulgar looking drivers.

finally, i trimmed some overhang on the first curved-leg i glued up the previous day, then slapped some bondo over the gap. looks hideous now, hope it will sand down nice and smooth

sanded down some bondo today.. still not pretty, but hopefully the veneer will hide it.

made some more extention panels today for the plate amp. somehow managed to make the last set off by 1/2"...

worked a bit on the grilles. rounded over everything then sprayed it matte black to make sure no mdf shows through grille cloth when i stretch it out later.

I routed the countersink for the first driver, measured it, and it looked good. I *though* i used the same depth-gauge setting for the second driver countersink, so i didn't measure it before cutting out the driver hole. I should know better by now. When i finally dropped in a driver to predrill the screw holes, the countersink was too shallow by a noticable amount. With the driver hole already cutout, i had to hack something together to get the same centerpoint back

Something similar happened to me once before, so i had a proven approach at hand. I used 4 shims to secure the driver cutout back in place... a bundle of shims from home depot range upwards of 1/4"+ thick and i used a 1/4" straight cut bit to route out the hole, so they fit nicely. After centering and leveling the cutout piece, i used a flush-cut saw to trim the top of the shims. The result was a semi-stable platform with the same centerpoint used for the original countersink passes. A few more runs with the correct depth and the driver fits a lot cleaner.

Working on the window that will house the Bash plate amp and the ugly wart that i'm going to have to retro-fit on top of it because i didn't properly account for the mounting depth of both the woofer and the amp.

New top-bearing flush trim router bit worked nicely... i'll do anything to avoid using my ghetto jigsaw. Guess i should break down and get a new one at some point.

Finally time to sandwhich the enclosures between the curved leg sections. Going to have to do one side at a time. Getting these clamps setup was a challenge because of the curve.

The enclosure that will be on the bottom is raised about an inch off the edge of the leg... it has its own bottom panel. THe bottom of the leg will get some feet eventually.

The enclosure that will be on the top is flush with the top of the leg and a single mdf panel will cover everythiing. Hoping that will ensure i get a flat smooth surface to veneer so the enclosure can be used as a little end-table or plant stand or something.

Still having a lot of problems at pretty much every step. Definitely bit off more than i can chew with this build. No idea how it's going to work out.

a little more assembly....

Thanks. Can't wait for this build to end... partly because i want to see how it looks and sounds, moreso just because i'm tired of dealing with all issues popping up due to poor planning.

I need to make some right-angle clamp braces in the future. I tried using a square to keep everything aligned during clamping but several gaps have arisen due to things not being glued up just right.

The mystery bike in the background is the back end of 2 bikes hanging from hooks right next to eachother. Those little hooks were another great purchase from Harbor Freight.

There's an electric-assist bike hiding in the garage too. My wife loves that thing. Nothing like cruising home on battery power when your legs are shot.

Got the top panel glued up and trimmed it down. Then i hit the whole enclosure with the sander in preparation for veneering.

I planned on hand-veneering so i needed to build something to hold the enclosure in place while i worked on it. Quick and dirty little rig worked out pretty well. The piece slides in and stands on it's curved edge so i can work on the other curved side.

I tried my best to joint the pieces of veneer via the overlap-and-cut approach before starting application. Still, i cannot get a decent seam. Things are complicated when working on the curve so i figured that would happen. In the end, i overlapped the edges of the applied veneer so i can go back and sand them flush. I've done that before with pretty good success but consider it a hack - bums me out .

I used the random orbital in the past to sand away the overlap, but i can't remember what grit... maybe 100?. Anyone have recommendations? Needs to be aggressive grit to take off some material, but sanding through the non-overlapping section would really suck at this point. I already veneered part of this enclosure and ripped it off once.. i don't have enough spare veneer to do that again.