1. Would it affect the sound if i built them in solid 26mm (aprox 1") oak? I would naturally keep the internal dimensions the same.
As long as the internal dimensions are the same as in the plans, it does not matter how thick the materials are. In the USA ¾" (19mm) thick medium density fiberboard (MDF) is commonly available. Two layers are used where the drivers are mounted on the front, but ¾" thick MDF for the rest of the cabinet is good enough. You will find that these cabinets are very heavy, and using thicker MDF will be much heavier. Internal cross braces are more effective at minimizing cabinet resonance, than using thicker layers of wood.
Solid oak or other hardwood should not be used for two different reasons. Hardwoods when stimulated by speakers have frequencies at which they naturally resonate. These vibrations color the sound. This may be desired in a musical instrument, but not in loudspeakers. MDF or good quality plywood, such as Baltic Birch, are much less resonant. The other reason is that hardwoods all absorb water vapor. They will shrink in the dry winter and expand in the more humid summer weather. A well constructed speaker cabinet, with 6 sides, cannot adapt to these changes in dimensions. As the hardwood expands and shrinks, the wood will crack and eventually split open. MDF or plywood do not change dimensions as the weather changes.
If you want an oak finish, I suggest you use oak veneer. MDF is flat and smooth and provides a good surface for veneer, and it doesn't expand and shrink as the weather changes. In the USA, good quality plywood with an oak outer layer is also available. I don't know what is available in Norway.
2. Would it make sense to use 4 binding posts for each speaker for bi-amping, connecting tweeter and woofers seperate?
Yes, you could use 4 binding posts. You would wire the woofer and tweeter networks separately to each pair of posts. Although this is commonly advocated in audio, there is no real advantage for this. However, if you build these speakers, you are free to build it as you like.
These speakers do not require powerful amplifiers – any amp that delivers an honest 50 watts will easily drive these speakers. And there are many home theater receivers available with about 100 watts per channel. The ER18 MTM speakers can easily handle much greater power, but they do not require it. I personally don't think bi-amping would provide any audible benefit.
3. The plans say unflared port, would it be better with a flared, if so flared in one or both ends?
Yes, you can use a flared port. The plans do describe that somewhere. According to the predicted bass response, it should not make an audible difference, but if you wish to use a flared port it will not cost much more.
- Ports tubes are 3" (76mm) diameter
- If not flared, the tube is 2¾" (70mm) long.
- If flared on one end, the tube is 3¼" (83mm) long.
- If flared on both ends, the tube is 3¾" (92mm) long.
