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If you need the correct types of timber or fittings for one-off instrument construction in the UK, try touchstonetonewods.co.uk. I have no connection other than having been a very satisfied customer for many decades
For many years I used an airing cupboard heater (about 4 inches dia perforated steel) to bend ribs for lutes (the ribs were soaked in water overnight before bending
My sugestion referred to buying a cheap 12 string guitar to convert for such a project.As a 12 string guitar the Epiphone gives much what you would expect for the price -tp reduce the de-tuning, try tuning the whole instrument down by a tone or two. Back in the 60s the first "cheap" acoustic 12 strings (eg Eko Ranger 12) were recommended to be tuned down by a tone - that is how they were designed. I always played mine tuned down with a capo to restore the "open" tuning to the normal guitar tuning
as an experienced luthier, I suggest it would have been a lot easier to buy a cheap 12-string guitar and use what you needed.
An 8 ohm speaker compared to a 4 ohm speaker (both with the same efficiency, etc) will sound quieter with the volume control at the same level as the power output is directly proportional to the impedance. Thus, if the original speaker is rated 4 ohms 8watt, replacement 8 ohm speakers need only be rated at 4 watt (although to be safe I would tend towards something with a similar or higher rating. As a rough rule of thumb, the higher the power rating of a speaker, the less efficient (ie relatively quieter) it will be at lower output levels.
When connecting two wires, you should make a mechanically sound connection before soldering (eg by hooking both wires around each other), laying the two wires side by side increases the possibility of a dry joint. Another possibility is to make a coil of tinned copper wire which can be slid over the two wires (laying parallel) before soldering the whole assembly.
Laser Cutting Class