I was talking on the phone with a friend and we got on the subject of how I handle the driver cutouts -- he asked, "do you veneer the cabinet before you route the driver cutouts and recess flanges and, if not, how do you trim the veneer?" Since my friend is a very experience speaker designer and builder, I'm guessing that there are a few more of you out there who might avoid using veneers because you don't know some of the tricks... and others of you are applying the veneer before cutting the driver holes.
I don't like the idea of applying veneer and then routing the holes and flanges for the drivers. Worse yet, not flush mounting the drivers can make an otherwise good speaker design sound bad. I like cutting the holes for my drivers and rabbetting the holes for flush mounting before I cut any other part of the cabinet. Why? The sound baffle is the most important piece of the enclosure. If the driver to driver space is not perfect or the width does work well or isn't dead-on, then I cut a new one. Also, veneer is expensive, while MDF if cheap. If I had to veneer before I cut the driver holes and the sound of the enclosure was right, I'd have wasted alot of veneer or I'd have to build cabinets JUST for testing and then have to rebuild them if I wanted to finish them.
So, here's how to cut first and veneer later. It's so much easier than you might think that you're going to kick yourself for not thinking of it already...
Figure 1 -- a driver cutout (a Dayton Silk Dome tweeter in this case) in which the mounting hole and flush-mounting recession, also called a Rabbet or Flange, were cut prior to applying veneer to the enclosure.
Ok. the first step is to apply your veneer to your cabinet (ignoring the driver cutouts initially). Once the veneer is applied, cut a small hole with a utility knife in the center of each driver cutout and using a flush trim bit, trim the veneer around the driver hole. This will leave the veneer overhanging the flange.
Figure 2 -- an enclosure after applying the veneer and flush trimming the interior of the driver cutouts.
Figure 3 -- a closeup of the tweeter mounting hole after flush trimming the veneer around the interior of the hole. Notice that the veneer overhangs the flange you cut for flush mounting the driver when you built the cabinet.
The next step is the "trick". Change the bit on your router from the flush trimming bit to the exact same rabbetting bit you used to cut the flange (or rabbett) for the driver (see fig. 4). In the case of the Dayton 275-070 tweeter, I set the rabbetting depth to 1/8" to flush mount it, so the rabbet under the veneer in figure 3 is 1/8" deep.
Figure 4 -- my base router with a 3/8" radius rabbetting bit inserted (I use 3/8" radius for the 295-305 woofers and 1/2" for the 275-070 tweeter). Also notice that these are good quality Magna solid carbide steel bits with bearings. If you plan to do much speaker building you should invest in some.
Now, set the depth on the router to about 1/2 the depth of the rabbett you cut for flush mounting the driver. In the case of the tweeter, as I mentioned, the rabbett is 1/8" deep, so I will set the router depth for trimming the veneer to 1/16". For the 295-305 woofer, I use a 3/8" rabbetting depth to flush mount (1/4" for the driver and 1/8" for gasket material behind the driver) and a 1/4" depth for the rabbetting bit when I trim the veneer. Now go ahead and insert the router into the driver cutout hole and follow the circle around the hole to trim the veneer -- if done properly, none of the previously cut MDF will be affected at all. With a little sanding, you should get an excellent, smooth flush trimmed veneer around the hole.
Figure 5 a closeup of the woofer mounting hole after using a rabbetting bit to trim the veneer around the flange.
That's it! Good luck and have fun!
