ZYGI
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Damien,
I would not suggest particle board for the ZOB's as there are a lot of edges that would take way longer to fill and smooth with particle board than it would with MDF.
Jon,4krow,
Yes wood does expand and contract with the seasonal changes, and different woods do this more or less by species. But there are also different cuts that in the same species will also expand and contract more or less. Quarter sawn the least and flat sawn the greatest. Quartered is also less likely to warp than flat sawn. Rift sawn is in the middle with the best looking grain, and is easier to find than quarter sawn, and is less expensive than quarter sawn.
As far as using solid wood for the baffle, the ZOB's can easily use solids for the front baffle, just do as 4krow suggests and slot the mounting holes. The only place you are going to have to be careful with is the driver mounting. I've seen a 5-1/4 driver mounting split the front of a solid would baffle right up the center of the screw holes. The baffle was fine until I moved from Virginia to Arizona which was quiet obvious why the problem arose. If you are using a driver with 4 mounting holes mount it square so the distance is the least in width. If you use a 6 hole mount, place 2 of the screw centered and this will give you the least width of driver mounting screws. With the ZOB being accessible to the driver, both front and back, you could used machine screws with nuts and washers on the back side, this would allow you to drill a larger hole, and allow some seasonal movement. You may also want to enlarge the driver mounting hole just a bit, so that didn't cause any problems. How much will depend on what time of year you build your speakers and if the wood has been in an environment long enough to acclimate to the room which the speakers will stay. If you build in the winter months you can usually build a little tighter as the wood will expand in the summer months. The opposite would apply if building in the summer. Just make sure you apply the same amount of finish to all surfaces.
MDF on the other hand doesn't really expand/contract in width or length but instead with its thickness. This was why when we build the ZOB's, on the sides panels the depth at the bottom from front to back and the height from the bottom to the port plate is made 1/4" bigger than the plans, keeping all other dimensions the same and rounding over both inside and outside edges with a 3/16" round over bit. This is more for aesthetics, but it also doesn't allow the joint to get ugly over time, it always looks the same. We had to Lock miter the corners of the ERR's for this very reason, as we were having a lot of people wanting piano black and the joint would telescope the finish over time.
Unlike the plans, when we build the open baffles we use cleats around the interior bottom to screw the bottom in after the front has been mounted, this allows us to finish everything, then mount the baffle and seal up the bottom of the cabinet, its the least obtrusive look, as you don't see any screws on the back of the speaker.
Hope this helps, ZYGI
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