12PWK EVALUATION

To start with we drew some conceptual shapes for a speaker designs on scrap paper to see what options we could come up with to flex our creative genius minds. After deciding on making the speakers from fire extinguishers we had to make a full scale faceplate mock up of 4 ml MDF, this was where we encountered our first problem for the amount of MDF we hade was to small to make a faceplate of the fire extinguishers we had. This was over come simply by making it half scale and writing that clearly so it could be seen in the photo taken of it to be posted on our blogs.

Now that the conceptual drawings and MDF faceplate where complete we had to make a half scale (or for us quarter scale) 3D model of the speakers out of old political campaigning boards this was all fairly easy except for deciding how to fit in the actual speakers, at the time we decided to build a small rectangular box outside the main cylinder of the fire extinguisher, later on we changed that to a cutting in to save time and materials.

With those three steps out of the way we started to remove the paint from the bottom of out fire extinguishers using a small dremel for welding which we later decided to avoid to allow access to the interior of the speaker for maintenance on the crossover and wires.

With our new design we needed to plasma cut out a side of the extinguisher, so we drew out the lines that needed to be cut and then removed the paint to make it easier to be seen through the dark glasses and cut. With that cut out we used a file and the angle grinder to flatten the edges.

We then used tin snips to cut out the semi circle of galvanised steel required to fit into the top undercut section of the extinguisher. The next piece we needed was the front plate which we cut from the same galvo as the last piece. The front plate did cause some trouble though. For starters it didn’t fit my box because the grinding cutting and filing of the box had made the sides on an angle making a wedge gap at the top of the plate between it and the semi circle plate. With the aid of Mr Mac and his knowledge of such metal things we came up with the solution to use fibre bog to fill in it and any other holes and dents in the work. The second problem we had was that we didn’t have a metal hole cutter the right size for any of the holes needed for the woofer, port and tweeter this posed a big problem until we decided to mark out the holes with a centre punch then drill the marks with a drill bit big enough to fit the end of a pair of tin snips in, cut out the circles with the tin snips and then file it back to fit the speakers in it.

Then we got out port tubes and started to make front covers for them. This started with making small brackets to hold the red acrylic ring on the pipe. We then had a lot of difficulty cutting the acrylic the right size, accountable for this was our misjudgement of the width of the drill bit in the engraver, it took about 5 tries to get it right. So we drew up the plates on 2d design and put it through the cam machine EGX 300. We bent the brackets at a 45 degree angle and drilled holes in them, we riveted them to the port tube and used 3.3 ml bolts with nuts to attach it to the acrylic ring.

Braising was next on the to do list so after some trouble getting hold of Mr Ben Warmouth we braised the two plates we cut earlier onto the main box and spent a few periods filing them down to size.

We then used fibre bog to fill in all the holes and dents in the speakers, Ryan had to do a lot more bogging than me because of the dents in his front plate. After bogging and sanding down the box I gave it a layer of primer and began sanding it with wet and dry sandpaper, once that had been done I gave it another layer of primer and a quick sand to get off the drips and lumps before leaving it and starting on the bottom.

The first thing needed for the bottom was small aluminium brackets to put on the sides of the bottom plate. Making the brackets was no problem so we then used the plasma cutter to cut out the bottom plate out of the same galvo used on the other pieces earlier. We then used tin snips to cut them down to the right size and drilled the necessary holes for the brackets to fit. So we riveted the brackets onto the bottom plate and made all the brackets fit in the main box.

With it primed and the bottom cut out we began to cut out the carpet for the inside acoustics of the speaker and we used a spray on adhesive to glue in the carpet to the inside of the box it was hard to make it stick to the galvo but with enough of the glue we made it stick.

To make the crossover we first had to draw it up on Circuit Wizard by getting all the components from a side bar on the program and dragging them onto the working area then connecting them in the correct manner with the wire laying tool. We then converted it to a PCB layout which we copied as a black template into macromedia fireworks. We then traced around it in red making sure there were no gaps. We dragged the red outline to away from the old template and copied it into 2d design to be cut out on PCB board. Once cut out we drilled holes in all the places that we were to put components and cut stripped then tinned our wires and cut the board into the two separate crossovers. After that we got our components and soldered them in along with the wires, we then ran them through a small amp, woofer and tweeter, one of them worked fine but one didn’t because the solder had got over the line stopping it from functioning properly. We fixed it by melting the solder and pushing it back on the main circuit and using a scribe to scrape the rest of the solder off the tracks, after doing this it worked well.

With the crossovers done I began to paint the overcoat onto the primed and carpeted box. The only red we could get was a thick darkish red which lucky for us worked perfectly with the fire extinguisher feel of the speakers, I painted both speakers with one layer then I painted the bottom plate then I painted the speakers with another layer. The gun jammed up half way through the 2^nd coat of paint so I had to pull it apart which I am grateful for because it allowed me to learn a lot more about the mechanism of the paint gun.

I then carpeted the bottom plate and drilled a hole through the crossover and bottom plate to bolt the crossover to the bottom plate allowing easy access for maintenance.

All that remained now was to solder the wires to the speakers screw all of them in, fit and tune the port and bolt the bottom plate with the crossover attached to in and onto the main box.

To finish off we completed the solid works engineering drawing and printed and posted on our blogs.