Boombox, part 2

Plenty of movement with this project, namely in the form of enclosure materials and quite a bit of design changes!

Looking for what to make the enclosure with, I soon came across this damaged shelve in the dumpster. Made out of particle board and torn to sheets for the bin, most of the parts were slightly broken from the edges. Then again, with the bad parts cut off you still had plenty of usable material. Biggest downside immediately apparent: With these sheets being 19mm thick, whatever you build with them is not going to be exactly lightweight. But sure, I’ll accept free “raw materials”, at least for testing something. Once installed in the trolley, the weight becomes less of an issue anyway.  For outdoor use, the sheets will also need a layer of paint applied, something I was planning to do anyway.

Getting down to measuring enclosure dimensions for the 11″ element with these sheets shortly proved out a difficult task. For vertical installation, you’d have the battery at the bottom of the trolley. The speaker would then face forward with the magnet slightly above it. A fairly OK solution for the trolley, but this wouldn’t leave much room for any additional speaker compartments.. and I’d sure like something a bit more than a plain subwoofer!

On the other hand, mounting the speaker facing down at the bottom of the trolley would make use of the dimensions better. As bass frequencies are omnidirectional, the speaker doesn’t have to be targetted towards the listener. However, this approach would also require installing the car battery further up in the overall structure, in turn making the weight base shift higher and the trolley becoming easier to tilt over. Also, a base sheet larger than what the particle board sheets are, would be called for.

Some of the MDF sheets and some other leftovers, 11" measurements in progress.

Not that the bigger sheet would’ve been a problem, since I even had a suitable leftover piece (lower left in the picture above) from my rack trolley project. Enclosure-wise either approach is about as complex to implement, as many small pieces are required to make a solid speaker compartment.. at least the way I had them thought out ;). But yeah, maybe about time to accept the fact that the sheets (as well as the trolley) are simply too small for the 11″, and move on!

A worthy solution “appeared” shortly after, namely in the form of these Panasonic SB-AK45 (part no. SGTPAK45) speakers I had found in the dumpster a few years earlier. What I mean with “appeared” is that I kind of forgot about having these! Made for a compact stereo set, these speakers sounded mostly like epic HORROR if connected to any other amp. Or well, at least the ones I had to test them with :).. No idea what the original set might sound like, but judging from the above there must’ve been quite a bit of DSP on-board to make it sound decent.

For me, the weirdest part about the design of these speakers is, that the main box houses a 6″ (reflex port) bass driver whereas the triple mid/treble tweeters (4″, 2″ and 1″) are housed in a plastic piece partially in front of the 6″ speaker. Both the 6″ and the tweeters have their own cable pair for connecting to the amp. According to the spec label behind the speakerbox, these speakers are 6ohm and able to deliver 80W RMS. Well enough for my use, so fuck yeah, let’s strip them for parts. They’re no good as-is anyway.

Lolwtfbbq, the Panasonic SB-AK45 speakers. I took a picture of the ones I have, but since I seem to have misplaced them here's an alternate picture stolen from the internets.

Unfortunately, the original speakerboxes seemed to resonate a bit along the lower frequencies. Although I would’ve liked to use at least the 6″ speakerboxes as-is, the  rattle caused by the resonation made them completely unusable. Wonder if this is why they were binned?

But yeah whatever, with the speakerboxes available my design instantly became a whole lot easier.. at least on paper! Despite the original boxes being shit, I could still measure them for cubic volume and (experimentally) go for “whatever fits my raw materials” around the same amount. According to my measurements, the original boxes were somewhat about 4,6 liters each (speaker and reflex tube excluded). On to design then!

Enclosure design in progress, 6" compartments laid out.

Laying out something similar on the particle board sheets, I ended up with 5,20 and 5,36 liter compartments. The latter can be fitted with the reflex tube whereas the former can’t, so it remains to be seen how this solution turns out. I’m definitely going to test doing both compartments sealed-box first. And so, after about four hours into sketching..:

Somewhat completed layout for various sheets..

..and preliminary dimensions for all the sheets to be installed between the side panels.

The dimensions above still need some adjustments. F.ex. the possible reflex port placement on part ‘A’ equals “whatever out of the way” whereas part ‘G’ is missing proper angle dimensions. Figured I’ll just handle these on-the-fly, so it’s cutting time coming up!


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