Saturday, October 31, 2009


The recycled materials used in my design are both effective and cheap. The MDF is a very good wood for speaker cabinets as its density greatly adds to the overall sound quality. It is also a convenient material for use in school projects as it is easy to use and very cheap. If I had used a native wood in my cabinet such as rimu the cost would have been much higher and therefore impractical. For example; the amount of MDF I used cost around $10 – the same amount of rimu would have cost $100. The wood does the same job and since I planned to paint the cabinet, a nice looking native wood would be wasted.
The carpet underlay was extremely good value as it does exactly the same job as acoustic foam but cost nothing. Enough acoustic foam to cover the inside of my speakers would have cost around $100. Because I used these recycled materials I paid only 5% of what it would have cost, and the speakers ended up being worth much more than the cheap products they are made from.


Both the recycled materials I used – MDF and carpet underlay - can be prone to decomposing. To avoid decomposition limiting the efficiency of my speakers both materials are exposed to only minimal air. The three layers of both primer and top coat I sprayed onto my cabinet effectively seal the MDF and ply from the elements. This greatly increases the lifespan of my speaker cabinets.
The carpet underlay is also sealed in a mostly airless environment. The cabinet is airtight aside from the ports, which cannot be avoided. It is unlikely that the small amount of air drawn in though the ports when the speakers are playing will cause a lot of decomposition. So the carpet underlay is relatively protected too.


When I started to design my speakers the only thing I was thinking of was that I wanted it to be curved so that they would sound better and would be more challenging to make. I also wanted it to look a little different from all the others so I decided not to have it sitting flat on the ground, I would have a curved raised bit in the middle of the base. From there I sketched until I found a shape that I liked – the whale tail. In my first few designs the shape was taller, fatter and pointier. But that developed so that there is a flatter base for better balance and a rounder top for a more.

I got through the rest of my design process on Freehand and Solidworks without any problems. I made my mock up out of cardboard and it does look almost exactly like my final product, except for the pointed edges. After I finished my designs, the engineering drawing and my mock up I started the construction. The first thing I did was cut out the front and back plates of my cabinets. I cut out the holes ( 70mm for the tweeter, 110 for the woofer and 55mm for the ports) on the drill press with the circle cutter.

After the front and back plates were ready I cut out the frames for the inside. The frames give added structure to attach the bendy ply to, and also to secure the circuit inside the cabinet. I recycled the cut out insides of the frames to be used as supports. I cut out 42 identical pieces of MDF. In the end I couldn’t use these as, because it is made of thin layers of cardboard and wood, the nail just broke the MDF down. When I tried the put a nail into them they split. I cut out another set of supports from … and these were strong enough to be used.

To attach the supports to the other side of the frame I had to put the nails into the frame first and hammer the supports down on top of them. This was difficult as the nails bent and sometimes went through the frame on the underside, but after a lot of patience they were all put in place. Once the inside structure was built I had four rectangles of bendy ply cut out on the table saw and soaked them in water over night. The water softened the wood so that it could be wrapped around my speaker without cracking. I attached them to the cabinet with nails on the front plate, back plate and frame. I then soaked another four sheets and attached these with glue, held to dry by all the clamps at WHS and a few ratchets. By using glue I gave the visible sides of my cabinets a smooth finish.

Once the glue was dry I had the unwanted overhang cut off on the table saw, and I sanded them almost flush on the belt sander. The whale tail was starting to take shape, but was still full of gaps and cracks, so I spent the next couple of weeks bogging and sanding to achieve a smooth finish. Once this was done I had my first coat of primer applied and bogged some more cracks that showed up. I repeated this after my second layer. After the third layer of primer I was satisfied. By then I had chosen my paint - a blue green colour. By the end we had sprayed around two and a half layers of this, because of hardening blobs of paint in the gun causing me to have to sand and spray again and eventually just stop. The finish is good but maybe it could have been better.

Before I started spraying the cabinet I had spent a few hours in the electronics lab creating my crossovers. I designed the circuit, cut out the PCB board on the CAM machine, drilled the holes and soldered the components and wires in place. A test showed that they worked fine. Now that my cabinets were ready I could attach these to the inside. I tied each one to a support with a cable tie.
I soldered the woofers, tweeters and input terminals to their corresponding wires and screwed them into place. We tested the speakers at this point and they worked but weren’t perfect. After the ports were tuned and screwed into place they sounded much better and I could finally take them home.


Along with the supports cracking and the paint setting in the gun, there were a few other problems. While I was cutting out the holes for the ports I set the circle cutter just slightly bigger than the 55mm it was supposed to be. I realised this after three holes and changed it. So I had three slightly too big holes and one right sized. I solved this by buying four bigger ports and rasping out the holes to fit them.
Because of the rather complex curved design I had trouble with the wood splitting. It completely snapped at the top of one of my cabinets so that I had put another small piece of ply in the gap and bog it until it look smooth again. This means that while one of my speakers is perfectly rounded, the other is slightly pointed.
On my PCB board there was a piece of my tracking with a very small gap which may not have made the connection. This problem was solved by soldering a piece of wire between the two points affected by the piece of tracking.


The two recycled materials I used in the construction of my speakers were MDF and carpet underlay.
MDF is made by combining wood fibres with a resin and formed into sheets at a very high pressure. The wood fibres used in this would otherwise be wasted and in that way it is a recycled material. It is very dense and easy to use, and is perfect for making speaker cabinets because of this. The density is very important because a dense wood prevents waveforms from flexing the wood of the cabinet, which makes for a more accurate bass response.
I used the carpet underlay to line the inside of my speakers in the place of acoustic foam. In a speaker cabinet acoustic foam absorbs frequencies. Without it the lower frequencies would bounce of the sides of the box and hit other frequencies, canceling them out and making the speaker sound tinny. Carpet underlay does this job perfectly, improving the sound quality in a much cheaper way.

Thursday, October 15, 2009

- Speaker 2 just about to be sprayed

(this is the better speaker, the top is smoother and rounder.)

- Speaker 1 with its first coat of primer