Tuesday, December 18, 2018

Even More on that Speaker Box

This speaker box has become quite the project. I swear, if I look back on the number of hours I've spent on this thing, it will rival the hours spent rebuilding the front end of the MGB. Anyway, more progress to update.

testing only-angled idea
In my last post about the speaker box, I mentioned adding in some extra support along the edges. I'm sure it was helpful, but when I thought about how much air would be moving around the inside of the box, I got concerned about how the sub-woofer speaker would have air-influence over the 6x9's and vice-versa unless I created some kind of barrier between them. I had initially planned to do that, but this project has lingered on for months now, so I had almost abandoned it. I had some time and some left over materials, so I constructed a couple interior walls to isolate the 3 speakers from each other.

wiring cup
I initially thought about something simple: one wall per side that ran at an angle from the rear wall to the front wall. There's a dark picture to the right that shows what that would have looked like. This would have been easier, but consumed a lot of air space that probably should be available to the sub-woofer. To maximize the air space available to the sub-woofer, I changed to an an angled wall from the front face back parallel to the 6x9 speaker angle until it was clear of the rear of the 6x9 speaker magnet (this was about 3-1/2" long by just over 9-1/2" tall). I connected a wall from that point parallel to the rear/front walls to the side. This left little excess air-space for the 6x9, but the sub needs all the air volume I could bring it in this small box. As it is now, I am at the low-end of the air volume recommended by the manufacturer.

Cutting and Fitting
baffle glue drying
With the walls cut with an old-skool hand saw (I make crap-cuts with power tools), I shifted to test-fitting. The extra supports in the corners required cut-outs in the baffles. You can sort of see the square-ish cut outs in the corners in the picture on the right. The left-side baffle wall fit perfectly though the right side did not. From this, I discovered that some of my early work was not 100% square/perfect. So, some additional trimming was needed on the right side. Still, things looked good so I drilled one hole per baffle to hold the 2 pieces together and glued them.

To support the inner wall baffles, I took a couple small pieces of cut-off left-overs and placed a support along each of the inside of outer walls. I was able to rest the parallel-to-rear-wall baffle against this support to hold it straight as well as for an extra surface for glue.

I had planned for 3 wire cups on the right side of the box. I bought these cups from Crutchfield, and used a hole-saw to mount them. The orientation of these cups becomes interesting when we consider the interior baffles I'd just built. I had 2 cups set side-by-side for the left and right 6x9 speakers and one below it for the sub. You can just make out the left-side hole in the picture below. This speaker cup orientation seemed intuitive. Once the baffle was set in place, wiring into the cups will be compromised. So, I had to pull out the Dremel again, and shave down a gentle curve behind 2 of the cups so there would not be any pressure on the wiring once all the various pieces were together.
smoothing the edges

With the baffles shaped, I glued them into the box. Once the glue had dried overnight, I assessed the gaps, and plugged them with wooden kabob skewers... and more glue. Basically, I determined the length of the gap, and cut a thin skewer to length. I then squeezed the skewer with pliers until it was thin enough to fit into the gap. With a thin slotted screwdriver, I pushed the filler material into the seam, and repeated until the gap was completely filled with wood and then slathered it with glue. I then ran a thin bead of glue along every seam to make sure the 5 sides and the baffles were sealed.

At this point, I decided to fix the misaligned outer edges with the Dremel and a hand planer. Ideally, it would have lined up perfectly. If I build another box, I'll take much more care to align just one hole per side for the screw, so the sides fit much better. I did that with the inner baffles, and they aligned far better. Anyway, after a bunch of hours with the Dremel and hand planer, the wall mate-points are smooth enough where I think it will be hard to see how out-of-alignment they are once covered with carpet. That's what I'll do for next time... as well as get some wiring in, and the 6th side of the box attached... and then the edges planed.... yeah, this project got a little out of hand. But it keeps me distracted without pulling a car off the road.

Thanks, as always, for following along.

Tuesday, December 4, 2018

More on that Speaker Box

I've continued to tinker on the box I started over the Summer (see MGB Gets Sound). Today's post covers some of the headway.

Sub Hole
I had about 2 hours of forecasted rain-break on a Saturday that also coincided with a reasonably good game of college football. So, I was torn, but I figured that I could do something on the box on the back patio and sort of keep track of the game through the sliding glass door. Yes, this sounds like a set up that ends with a board sticking out of said glass door, but actually, it all went relatively well. I started with measurements to find the exact center of the rear of the box. Centering on that with a compass, I drew a 9-inch diameter circle to cut. First, I set the panel on the box with the drawing side facing in, so I could check my spacing, and sure enough, that would have been a miss. Because of the bump in the center of the rear frame of the MGB, I have a corresponding bump in the box. To account for that, I need to slide the 9 inch hole towards the top by a half-inch or so. Another quick turn with the pencil, another upside-down check and I'm ready to cut.

way too many pilot holes around the
edge: don't do that
I drilled a pilot hole with a drill bit that was just larger than the saw blade. Then, I made the mistake of thinking that cutting the hole on a bias rather than at 90* was a good idea. Big picture, I may have retained a little more meat of the MDF, but it created a lot more fit challenges. Anyway, I cut the circle and test fit the subwoofer (still in the plastic bag to protect it from the dust). Yeah.. it fit through the top fine, but hung-up on the inner part of the circle because of that bias. To remedy, I attacked the inner lip with various tools: a file, the Dremel, sandpaper.. Eventually, the inner edge widened out and the sub fit. Word to the reader: don't cut on a bias; follow the directions from the sub-woofer manufacturer and trust that when they say the hole needs to be x in diameter, they mean both the top and bottom edges unless otherwise stated. With the sub capable of fitting in the box, I switched back over to the 6x9's.

The sub-woofer sites stress re-enforcing the edges of your box because of the force the speaker will exert upon it. I used some of the scrap MDF from the box construction to brace the corners. I've toyed with more bracing in the middle of the box. I may hold off and see how it performs before gluing the rear panel, and sealing my fate.

6x9 Fiddling
I had 2 things I needed to resolve with the 6x9's. First, the box needed threaded studs on the outside so the 6x9 could be attached and replaced from the outside. For this, I found some 1" long bolts that came with some kitchen drawer knobs. These are thin enough to easily fit through the mounting holes on the speakers, but don't protrude too far past the MDF edge to present fitting issues later. Best of all, I have 8 of them. So, I pulled one of the 6x9's from the rear firewall, test fit in the box holes, marking where the mount holes are and set it aside. A few quick runs with the drill, and I was threading the bolts through from the inside. I test mounted the speakers, and they will work great. I will need to be careful about carpeting, though, as the bolts really don't stick out very far. I may need to trim the carpet at the speaker edge rather than wrap through the hole. We'll see.

I then pulled the 6x9's out of the box and started test fitting the box into the trunk of the MGB. Post-assembly, the box is a smidgen taller than space would allow. Enter the Dremel again. I shaved down the front corners to fit under the fuel tank vent lines, and, after a couple hours of fiddling, I was able to get the box flush against the rear firewall. Once I had the box exactly where I liked it (dead center), I reached through with a Sharpie and marked where the 6x9's would need new cut-outs in the rear firewall. Recall that this firewall had been cut up pretty badly by the PO and I slapped together something to make it less crappy. Now, with these new holes, it is PO-level of crappy again. I'll need to do something eventually to make it nicer. Anyway, I cut along the Sharpie lines with my jig-saw. With the speakers back in the box, I set the box into the trunk against the firewall, wired up the speakers with the version 2 wires and tested the system.

We have sounds again. I spent most of a Saturday getting this far. I'll post next time on getting the rest ... or maybe just a little more headway... done. Thanks, as always, for following along-