Boombox, part 4

Status update..

6″ compartments are shaping up neat. Two layers of paint have been applied, so what little remains to be done is mainly the wiring chores. I’ll wait with this until I have the treble compartment ready to be wired up too. As a neat little extra detail for cabling through-holes, I now have some rubber grommets. These were sourced from the Panasonic speaker enclosures, where they were used to attach the decorative fabric in front of the speaker.

Rubber grommets, just loaded with high re-use value!

Painting with the hammer-finish paint proved a tricky task. Based on my current experiences, it seems to lump up so fast (for that “hammer” finish) that you should just quickly apply one thick layer and never touch that surface again while its still wet. Touching on such leaves visible brush marks that will not cure to a smooth looking hammer surface. On the other hand, applying a thick layer you’re under a constant risk of having paint runs. Not sure how a paint roller would work with Hammerite, but I’ll leave testing that for some other project.

The 6″ compartment volumes changed a bit too, with the sheets assembled they now measure 5,4 and 4,3 liters (front and rear speakers respectively). Judging from the final volume of the rear compartment, I must’ve had some calculation error. The dimensions didn’t change that much, after all. The rear compartment does seem like it could fit the reflex tube with a bit of modding, so if the compartment turns out “no bass” I’ll just add a installation hole for the tube and see if that helps. The volume is pretty close to the original speaker box at least.

Jennifer never had enough of flare :)

Some of the “waiting to arrive” parts in as well! Namely, a couple of these sound-activated frequency spectrum t-shirt transfers. Priced a little less than 5€ a piece, these were pretty much a fun last minute addition on my (miniscule) shopping list :).. Surely this project could also use a bit of “flare” and with a price like this, it doesn’t really matter if the transfers prove out to be a complete waste of money. If the transfers work anything like I’d imagine them to, they should turn out a nice little detail.

As you probably knew to expect for the price, these transfers are not real spectrum analyzers: They simply have hardwired spectrum-ish patterns that are brightness-controlled according to what the internal mic picks up. The sensitivity is adjustable, of course. These patterns then create an illusion of sound spectrum being “analyzed”.

The spectrum analyzer, shopping clues included!

As you can see from the picture above, the transfer connects to a separate battery (2* AAA) / electronics box with a flat cable. Silly little extra detail here is that you can connect the cable either way around. This simply reverses the direction of the spectrum analyzer. You know, if you’d for some reason would like to have your analyzer working upside down ;).

I briefly tested running the electronics with a +5VDC feed, this increased the overall graphic brightness to some extent. Since I have +5V available from the USB port of the amplifier, being able to run the analyzer electronics with this voltage would free me from adding a separate DC/DC stage just for the analyzers. I have no idea whether they can take the increased voltage in the long run, so if +5V proves out ‘the way to go’ I’ll just have to accept the risk of damaging the electronics. Just to mention currents, I got the analyzer to draw around 180mA tops on a +3V feed whereas with +5V this went up to a little below 300mA. These were measured with most of the graphic lit, idle current is of course far more lower.

As for attaching to a surface, these analyzer transfers have strips of double-sided tape on the back side. The strips do not run perfectly on the edges, so I’ll probably end up adding a bit more tape just not to have the edges peeling off (or collecting dust) at some point.

In order to get the transfers installed (flatcables require neat pass-through holes), I ended up drawing CAD models for the side panels. Doing so, I could’ve just as well milled the entire side panels according to this freshly drawn CAD and saved quite a bit of build time.. d’oh!! While sketching the panels, I decided to add some holes to the battery compartment in order to trim down the overall weight a bit.

Battery compartment hole milling in progress.

After milling, I (of course) had to quickly test attaching one analyzer to the side panel. Just checking for appearance ;)

Here, the electronics box is pretty far away from the speaker, so the analyzer mostly reacts loudest transients (in this case, the kick and snare drums). Anyway, if you spend a while looking at the spectrum, the hardwired patterns become rather apparent. But whatever, I reckon these analyzers will turn out a bit more than just a “nice little detail” all in all. :).

Paint paint paint..

Side panels ready to receive paint <3 <3

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4 responses to “Boombox, part 4”

  1. Brian says :

    I would like to know exactly those rubber grommets at the top of the page are called…………..

    • arto says :

      Not sure if they have any exact name. Like said, they were recycled from the same Panasonic loudspeakers as the speaker drivers of this project.

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