Introduction: Acoustic Amplifier
Acoustic Amplifiers have been well documented on Intructables. These most closely resemble the one posted by WildmanProject, but does not require a router.
This is a good project for students because it requires more design, planning and creativity than a project where they just replicate an example (like my Bandsaw Boxes with Lids).
For me, this is a good project to clean up the shop and use up scrap wood. I pre cut pieces of wood that are 3.5 by 6 inches and a variety of thicknesses. I cut up a variety of woods including plywood, hard woods, exotic woods, and old cutting board projects that were never finished.
Step 1: Design
Students take about 1 week to design their amplifiers with SketchUp. It is a good spatial/conceptual challenge for students to design a solid object in layers. I give them paper and pieces of wood to help them visualize each layer. Students use calipers and rulers to measure their own phones. This is a good opportunity to talk about how to measure accurately, and the importance of tolerance.
If students are designing for somebody else phone, they can typically find all important dimensions on the internet.
For phones with a speaker on the bottom (like an iPhone) student will have three layers: 1) a back, 2) a slot for the phone and a 'passage' to the hole, 3) a front with a hole.
For phones with a speaker on the back students will have to be more creative with their designs and may need a fourth layer.
Once their design has been improved, students print a template of their plans. They will use this template to easily transfer their plans to their pieces of wood.
Step 2: Scroll Saw and Drill Press
The order in which students drill, cut and glue some of the pieces can vary. The goal is to have the hole in the front align with the hole in the back as closely as possible. Generally, our process is to:
Use a hole saw or forstner bit to drill a hole in the first two pieces. Drill these together to ensure that the holes line up correctly. I have outfitted out drill presses with clamping jigs to allow for easier clamping of work pieces.
Scroll Saw or Bandsaw
Cut out the slot for the phone and the 'passage' to the hole.
Step 3: Assembly
Students will glue up all layers in this step. They will need to be advised how to apply glue strategically. For example, if they spread glue all over the back layer their will be dried glue visible in the back of the sound hole.
Edge Clean Up
Once dry, students will clean up the edges of their amplifiers. For students that lined up their pieces carefully, the belt sander is sufficient for smoothing out the sides. For students who have a lot of of offset, we use a sled/jig to run each side of their amplifier through the table saw.
Students then get to work sanding their speakers by hand, progressing through the grades to 220.
Students have the choice to decorate with acrylic paint, and finish with either a wipe on oil finish, or a water based urethan clear coat.