I wanted an extension speaker I could use with my phone, laptop or MP3. I didn’t need Bluetooth connectivity, which made the project simpler. Most of the cheap speakers have really poor sound and I wanted a bit more sound quality whilst adding something a bit more interesting to our kitchen worktop. I found this old fuel tank in a local scrap yard still attached to the remains of the ATCO petrol lawnmower it once provided the go-go juice to. I haggled the tank for £3.
The speakers came from a local IT recycler http://www.refurbit.uk.com/ who has contracts with local government, schools and businesses and always is a good source of good quality parts that can be bought very cheap. The speakers are really good quality and came as part of an interactive whiteboard used in school classrooms. I bought what I needed for £5.
Step 1: Clean Up and Cut Out
The inside of the tank was smelly and tarred with very old residual fuel. I left the tank for about a week, ¼ full of Gunk Engine Degreaser www.gunk.com and a load of old nuts and bolts. Every day or so I’d vigorously shake the tank and turn it slightly before putting it down for another day. I then drained it and began cutting. I used a well worn cutting disc in a grinder as the smaller circumference of the disc made it easier to cut out the circles from the ends.
I finished up cleaning the innards with a strong mix of washing up liquid and a brush, then cleaned up the rough edges of the cut out with a sanding drum in a drill. I then cleaned the inside with a wire brush on a drill.
Step 2: Stand
I pondered how to make a stand for a few days and on one of my searches for inspiration I found these parts in my stash of cycle bits. They’re the parts to an old accessory that allowed you to fit a bottle carrier to the seatpost of your bike. They never really took off or were really that necessary, but they are really well made, perhaps even a little over engineered. I combined the stand with a couple of short lengths of brass tubing to add to vintage/industrial look I was trying to achieve.
Step 3: More Holes
I cut three holes with a hole saw, the two top ones are for the tweeter speakers and the big one is to access the device for the final wiring. The tweeter holes are towards the back of the tank so that when it’s on a shelf you don’t really notice them. In hindsight, I wish I hadn’t cut the access hole as I could have made the unit a lot neater at the back for just a little bit more hassle when it came to wiring.
I copied the wiring from the original speaker donor unit. However I omitted one big speaker from each side, and then lined the inside of the tank with some foam sheeting about 2-3mm thick. This I glued in using spray adhesive. This avoids too much resonation through the metal which would lead to a tinny sound.
I cut out a piece of a spare toilet waste pipe I had to make a cover for the access hole and to fit the speaker cable connectors. I used this as it’s roughly the same diameter as the fuel tank and then added a bit of paint effect as well as an old peseta coin which has no relevance except to cover the hole made by the hole saw!
Step 4: Wiring and Finishing
I bought these 4x 4mm Gold Plated Speaker Binding Post Terminal Socket Cable Connectors off Ebay for £6.50. My original plan was incorporate the amplifier inside the tank, but space was very limited and as already mentioned I wanted the sound to be good. I bought this Gemtune SMSL SA-36A (PRO) Class T Amp Stereo Amplifier + Power Adapter off Amazon and it was reduced from £99 to £36. When I first got it I tested it with a pair JPW mini monitors I have and the sound was awesome from such a little amp. It works really well with the speaker box too.