for Speaker Builder Magazine
We all know the importance of flush mounting drivers in our DIY speakers, right? Well a while ago I started on a Focal based home theater speaker system. I was all ready to go until I got the drivers. What’s this, a round woofer with square sides and square tweeter with rounded corners? How am I going to flush mount these? I scratched my head for a while and came up with this method. It is quick, easy and makes perfect fit flush mounts for drivers of any shape or size. I am by no means a master cabinet maker so if you see anything that might make it easier I, as well as the rest of the SB family, would love to hear comments and suggestions!
Now first off, safety is a big concern. Always wear safety glasses, and follow tool manufacturer’s instructions. Most importantly wear hearing protection!! No use building speakers if you are going to be deaf!
Tools and Parts needed:
- Handful of ¾” screws
- 8 1/16” thick washers
- 1/8” thick foam gasket tape
- ½” MDF size dependant of driver size
- Plunge router
- Router table (if you have one)
- Circle jig (again if you have)
- Jig saw or table saw
- 1/4” straight cut router bit
- 3/8” flush trim router bit
- Router base attachment with 3/8” guide
First off, cut 5 pieces of the ½” MDF to a size approximately 2” larger, on all sides, than the driver to be flush mounted. (Photo 1) This should give plenty of room for your fingers, I like to keep mine the length they are. Now mark the center of them and drill a pilot hole through two of the pieces of MDF. Here is were a circle jig comes in handy. This is an indispensable tool for the DIY speaker builder yielding perfect circles every time. If you are countersinking tweeters, most of them have removable faceplates. I recommend removing this to prevent tweeter damage. Cut a hole in one of the pieces of wood to the outside diameter of the surround of the driver. (Photo 2) Do not throw this piece away yet!
Next, mount the driver inverted to this piece of wood using screws and 2 washers per screw to space the woofer off the wood. (Photo 3) Here is where another “make it yourself tool” comes in handy, a router table. Mine is an old worktable. I cut a 2” hole close to the end of it and made a bracket to hold my plunge router in it. This with a flush trim bit works wonders for cutting many identical shaped pieces. Router off all the excess wood leaving a piece the exact shape you want.
Remove the driver, blow of the dust and put it away. Using the pilot holes as guides attach the circular piece you cut out of the first piece to the second piece of MDF. Take a strip of the gasket tape and cut it into 9 1” long pieces. Stick them three high at equal distance around the circular piece. You can now mount the shaped piece together with a fresh piece and remove the centerpiece. Drill a 3/8” hole on through the fresh piece of MDF on the very edge of the shaped piece. (Photo 4) Next, carefully trim the shape of the piece into the new MDF, leaving a hole in the MDF exactly 3/8” larger than the driver. (Photo 6) This piece is the pattern for your template so it must be perfect! Square any corners with a chisel if necessary. If it is not quite right do it again until it is. I cannot stress this enough, better to do it right now than to mess up a baffle!!!
Now that you have a perfect pattern it is time to shrink it down to size! Two options go to your local electronic supply store and buy the parts necessary to build a DIY MDF shrinker or use a router. Attach the pattern to a fresh piece of MDF. Using a plunge router with a 1/4” straight cutting bit and a 3/8” bushing guide cut out the middle section. This will leave the original pattern and the new one, which is 1/8” smaller than the original. (Photo 7) Repeat this step once more. Once it has been repeated you are looking at your template. It should be 1/8” larger than the driver all the way around.
To countersink your drivers now it is as easy as can be. Cut the hole in the baffle for the driver and mount the driver. Using the 1/8” foam tape, line the inside of the template. This acts as a spacer to guide the template so the driver is exactly centered. Attach the template using air nails or wood clamps or two sided foam tape, and remove the driver and foam tape. Using the plunge router with 3/8” bushing and 1/4” straight bit, set the depth you want the driver countersunk remembering to account for veneer and gasket thickness. You can now remove all the excess wood inside the template. (Photo 9) Once complete remove the template and square out any corners if necessary and you have a perfect countersunk hole! (Photo 10)
It is that easy! I hope that this will aid people in the construction of speaker cabinets and add to the enjoyment of speaker building!!!
About the author:
Rodney Buike is employed as an auto sound and security installer in Winnipeg, MB. He runs a small DIY supply on the Internet at www.hifiaudiolabs.com servicing the Canadian DIY’er. He is currently enrolled in an Electronics Technician course.